I Want My Skyline To Rev

[rev210]

scathing,

You have the worst experience with a light flywheel I have ever heard of bar people who have been silly and lightened the factory cast flywheel and had it explode on them (hard to top that for a bad experience after all).

regardless of low or high rpm a good lightweight flywheel results in faster acceleration times. This includes under load situations like going up a hill. There is enough good data to back this up so we don't get stuck on stopwatch inaccuracy and bad theory.

I notice you have a 350Z? perhaps there are some other issues at play with your car? How are the spacings between the gears? Did you alter the wheels and tyres so as to effect ratio at all etc? did anything else get altered when changing the flywheel? It seems odd as the VQ35 doesn't lack torque when compared to the RB's it would be even more capable with flywheel weights around 4.8kg. Having a fair bit of experience in this space I am really interested in your situation and a little suspicious that there is something else going on.

Could be a good thing for the old Z if we can work out what it might be on another thread.

[rev210]

oh and for the record the flywheel weight doesn't effect torque negatively when actually measured. On some types of dynos torque and power will come up a tad higher actually.

For those who haven't seen something to indicate this I can put a dyno or two up if people think it helps to get over the myth?

[scathing]

The flywheel was the only thing I changed.

All the documentation I've ever seen says that lightweight flywheels will lose engine "inertia". I probably phrased it wrong in parts above. Acceleration is meant to be better everywhere (I get the feeling I just had my reaction times off with the stopwatch), but when you're trying to hold a specific speed a heavier flywheel will do a better job of it.

Since its performing as advertised, I'm fine with it.

[Roy]

Whats the radius of the flywheel? Cut the weight in half and i can understand why the engine spins easier. What is the radius of a tailshaft...again, im not saying it wont make a difference. But have you seriously been in a car with a 2530? They are more responsive then std nd make way better power. i cant see how you can want the thing to rev any quicker then this.

I agree about the flywheel, when your clutch is dead do the flywheel at the same time. And the turbo setup will be more expensive but a 2530 equipped RB25 would be quicker and more reliable then a stocker with a tailshaft (all other things beign equal)

Thats about 14c worth from me now

[rev210]

Roy,

Taking 8-10kg or so out of the rotational mass on the tailshaft will get you very close to the acceleration difference the 2530 provides over stock. Assuming it's around 35rwkw that the 2530 gains over stock.

In another 2530 space there are plenty of GTRs running the very responsive twin 2530's however the Mine's car seems to stand out in terms of aceleration. Shin at prospec in the UK built his car around the Mines catalogue and understandably he raves about the carbon fibre shaft and the difference it makes to his own car, if you have that UK made GTR DVD Shin's car is used for the 'ring'.

You can always have both you know.

Edited November 20, 2006 by rev210

[Roy]

Yeh, sure you can always have both. But i would hate to be the owner of an R34 GTT who has just spent the bank on the clutch, flywheel, tailshaft, ecu, suspension, tyres etc and first day out the turbo shags itself and im broke because of the recent shopping spree.

The only thing wimpier then an R33 turbo appears to be the R34 turbo. They seem to fail pretty often with a hint of boost and they are the newest of them all.

And the Mines car...lol, i suppose i look at cars worth a lot less money. Compare the Mines R34 to the HKS 34 on the same track and there has to be something to the fact that the HKS car is just getting into 5th gear yet the Mines car is almost limiting 6th...so sure the tailshaft has to make a difference, but the diff ratios the thing has would be a big contributer.

So, i just have trouble spending that sort of money on a tailshaft before other things.

Also your comment on acceleration, one thing to consider is that a turbo like the 2530 will give the car heaps more torque. So on winding roads the extra torque is going to help...and whilst the tailshaft helps get what the engien is producing to the rear wheels, its not actually increasing the torque.

I suppose id rather get rid of the weak points rather then mask them with clever mods elsewhere.

[Abo Bob]

Roy, I think most of us are reading/contributing to this thread because we are interested in this concept in addition to aftermarket turbos etc.

I know we had a big thread about tailshafts but by the time I got around to asking questions everyone was sick of the thread.

I want to know how much diff a tailshaft can make when it has such a small diameter compared to wheels and flywheel?

I mean is it a given that I should go wheels, flywheel, tailshaft in that order?

[rev210]

Abo Bob,

the guys at ACPT are very helpful if you are serious they could give you some numbers. Afterall they are an areospace company.

http://www.acpt.com/

[J_Red33]

So you're saying that a front mount, with its greater restriction due to the larger core size (for the purpose of this comparison we'll say that a unit length of core between the OEM 'cooler and the aftermarket one is just as restrictive to airflow), and its increased plumbing length, is more responsive than the OEM side mount?

Interesting......

This seems to be a common misconception. A larger core is not more restrictive, it is in fact less restrictive. If you have a core that is wider & has more rows to flow air through this is a reduction of restriction meaning more air can flow through for more power, this is why a standard R33 intercooler is only good for roughly 200kw as it simply can not flow enough air let alone the fact that that air is really hot due to the core size.

To keep power down on world rally cars they install a mandatory restrictor (of set diameter) which allows only a certain level of power. If you can't get the air flow you won't make the KW as more power requires more oxygen to burn more fuel. It's also why there's less pressure drop across a deacent front mount as a greater difference in pressure equals a greater restriction.

Hope that makes it a bit clearer

I don't think a lighter flywheel gives you better economy. Its worse, if anything.

I'm running a flywheel that's have the weight of OEM. Because I now have to drop down a gear to go up hills I could ignore the shifter in previously, and I'm having to rev the engine harder from a standstill to stay on-torque, my economy has suffered.

It sounds like you live somewhere very hilly for the economy to drop noticeably.

This all works on Newtons law of Inertia which is roughly quoted as 'a mass or object that is travelling at a given velocity, will tend to stay at that velocity'

The larger that the mass is the more inertia it has regardless of whether or not it is moving. Because the car with the heavier flywheel has more intertia it is harder for it to slow down than the car with the lightened flywheel & the same also applys for acceleration.

Take note that the same will apply with a carbon driveshaft, so the car is more susceptable to speed loss between shifts due to the driveshaft not resisting reduction in speed due to air resistance & friction on the road.

The main thing that would be hurting you is that you are having to put the foot in more up hill to maintain you speed, while when going down hill you don't gain it back due to the fact that you have to maintain your speed down hill braking rather than being able to go faster due to gravity. If you were able to go flat out up & down a set of hills you would still use the same amount of petrol, but practically this almost never happens.

Yes from a shaky start it's done well. (the thread that is)

I have to take a point with:

"everyone I know that has put a front mount on their car has noticed a massive increase in response."

You can't be serious. Response is the one thing you lose with a front mount upgrade. I'm not talking about lag here.

Also, the R34 sidemount is significantly bigger than the R33 one and until you've experienced it you wont understand. Plenty of things between R33 and R34 are practically the same but this is not one of them.

As response is the subject of the thread I would strongly recommend keeping the stock cooler but would of course add the usual warnings about heat soak. You might find it worth while to have a temp probe, gauge and maybe a warning light for after cooler temp so that you can see when it has stopped being effective.

Interesting to hear about the economy Scathing.

Rather than just saying you loose response, could you please clarify how you could loose response from something that allows higher air flow? I'm totally confused, what kind of response are you referring to if it's not a reduction in lag?

Just for the record too, one of my friends that made such a comment about the response improvement with his front mount drives an R34.

Edited November 20, 2006 by JazzaR33

[rev210]

Hi JazzaR33,

The response intercooler thing becomes one of those he said she said things. Although it's not really, there is a scant amount of real data sitting around for us to have a squiz at.

For the most part you will have a very small number of people with a little knowledge in race car prep telling you that the R34 intercooler has some benifits over a much bigger core on a GTST from the perspective of a shorter air path and lower total volume. Air gets to where it's going quick enough at the same time as recieving a nice efficient cool down. If you keep going bigger on a core size you eventually hit a point where getting bigger and bigger doesn't drop the temp any more, adds weight and so on.

Rather than talk about 'what ifs' ,Sydneykid kindly added some info on the R34 intercooler some time ago it went along these lines comparing the very good core found in the GTR intercoolers;

He found the R34GTT intercooler was around 68% efficient for cooling (thats very good) at ~200 rwkw. That compares pretty favourably with a standard R32GTR intercooler on the same engine which was 72% efficient at similar power levels. At 200 rwkw and 7,250 rpm, the R34GTT intercooler (and pipework) had 1.5 psi restriction at 1.3 bar. The R32GTR intercooler, with larger pipework and similar power, was 0.75 psi. So even the airflow wasn't too bad.

So does the R34 intercooler drop the temp enough and provide an acceptable pressure drop at 220rwkw to make it a good little option?

Yep.

Here's the big BUT;

BUT you need to ensure there is good ducting to the intercooler to make the most of its efficiency. On the stock intercooler/R34 that means making a hole in the dust cover inside the wheel arch behind the intercooler for the air to get out nicely (for the low pressure effect) and if you want to be really tricky making a flared duct.The sidemount has a great advantage in this respect. And ensuring the duct at the front is well made and is catching lots of good clean air and forcing it to go through the core.

The same goes for any intercooler setup. It works so much better that way, so does your radiator if it's a front mount.

Edited November 20, 2006 by rev210

[Abo Bob]

Abo Bob,

the guys at ACPT are very helpful if you are serious they could give you some numbers. Afterall they are an areospace company.

http://www.acpt.com/

I'll get there but I was hoping that you guys could help me confirm the order of mods I posted above. I used to be auto so there was no point in lightening my tailshaft but I'm manual now so there's no reason why I shouldn't do it. Maybe I should do a Bass Junky and do them in opposite order just to test the effect...

It sounds like you live somewhere very hilly for the economy to drop noticeably.

This all works on Newtons law of Inertia which is roughly quoted as 'a mass or object that is travelling at a given velocity, will tend to stay at that velocity'

The larger that the mass is the more inertia it has regardless of whether or not it is moving. Because the car with the heavier flywheel has more intertia it is harder for it to slow down than the car with the lightened flywheel & the same also applys for acceleration.

Take note that the same will apply with a carbon driveshaft, so the car is more susceptable to speed loss between shifts due to the driveshaft not resisting reduction in speed due to air resistance & friction on the road.

The main thing that would be hurting you is that you are having to put the foot in more up hill to maintain you speed, while when going down hill you don't gain it back due to the fact that you have to maintain your speed down hill braking rather than being able to go faster due to gravity. If you were able to go flat out up & down a set of hills you would still use the same amount of petrol, but practically this almost never happens.

Ahh I get it now. Your inertia helps you up the first bit of the hill - or the whole thing if it's small enough - which saves fuel, but without this inertia you need to be straight onto the gas.

Rather than just saying you loose response, could you please clarify how you could loose response from something that allows higher air flow? I'm totally confused, what kind of response are you referring to if it's not a reduction in lag?

Just for the record too, one of my friends that made such a comment about the response improvement with his front mount drives an R34.

The response I'm talking about is the transition between off the throttle and back on. Ie; coasting along then plant your right foot. How long does it take to get up on boost? I can tell you from my experience that in this one area, a smaller intercooler is better.

Hi JazzaR33,

The response intercooler thing becomes one of those he said she said things. Although it's not really, there is a scant amount of real data sitting around for us to have a squiz at.

For the most part you will have a very small number of people with a little knowledge in race car prep telling you that the R34 intercooler has some benifits over a much bigger core on a GTST from the perspective of a shorter air path and lower total volume.

I think the total volume is the important part here.

So does the R34 intercooler drop the temp enough and provide an acceptable pressure drop at 220rwkw to make it a good little option?

Yep.

Here's the big BUT;

BUT you need to ensure there is good ducting to the intercooler to make the most of its efficiency. On the stock intercooler/R34 that means making a hole in the dust cover inside the wheel arch behind the intercooler for the air to get out nicely (for the low pressure effect) and if you want to be really tricky making a flared duct.The sidemount has a great advantage in this respect. And ensuring the duct at the front is well made and is catching lots of good clean air and forcing it to go through the core.

The same goes for any intercooler setup. It works so much better that way, so does your radiator if it's a front mount.

On the stock R34 there are already holes in the inner guard lining behind the cooler for this reason. When I put an oil cooler in the opposite guard I cut the same holes in that lining. Some ducting that lets no air escape the cooler would be great too.

The only other thing to consider is the heat sink aspect. How long are you going to be on boost? Will it be long enough to completely saturate the cooler with heat? I don't know but it's worth considering. If this was a drag racing thread then no way would it be good enough, and probably not on the circuit either, but street - probably.

[illusiVe]

i have a intercooler spray if that counts

Anyway we shall see how the car goes, ive got some suspension work which needs to be done 1st, but the car should be back on the road march/april with some nicer parts

Edited November 20, 2006 by illusiVe

[J_Red33]

Hi JazzaR33,

The response intercooler thing becomes one of those he said she said things. Although it's not really, there is a scant amount of real data sitting around for us to have a squiz at.

For the most part you will have a very small number of people with a little knowledge in race car prep telling you that the R34 intercooler has some benifits over a much bigger core on a GTST from the perspective of a shorter air path and lower total volume. Air gets to where it's going quick enough at the same time as recieving a nice efficient cool down. If you keep going bigger on a core size you eventually hit a point where getting bigger and bigger doesn't drop the temp any more, adds weight and so on.

Rather than talk about 'what ifs' ,Sydneykid kindly added some info on the R34 intercooler some time ago it went along these lines comparing the very good core found in the GTR intercoolers;

He found the R34GTT intercooler was around 68% efficient for cooling (thats very good) at ~200 rwkw. That compares pretty favourably with a standard R32GTR intercooler on the same engine which was 72% efficient at similar power levels. At 200 rwkw and 7,250 rpm, the R34GTT intercooler (and pipework) had 1.5 psi restriction at 1.3 bar. The R32GTR intercooler, with larger pipework and similar power, was 0.75 psi. So even the airflow wasn't too bad.

So does the R34 intercooler drop the temp enough and provide an acceptable pressure drop at 220rwkw to make it a good little option?

Yep.

Here's the big BUT;

BUT you need to ensure there is good ducting to the intercooler to make the most of its efficiency. On the stock intercooler/R34 that means making a hole in the dust cover inside the wheel arch behind the intercooler for the air to get out nicely (for the low pressure effect) and if you want to be really tricky making a flared duct.The sidemount has a great advantage in this respect. And ensuring the duct at the front is well made and is catching lots of good clean air and forcing it to go through the core.

The same goes for any intercooler setup. It works so much better that way, so does your radiator if it's a front mount.

Yes this is totally true that the air flow for the sidemount R34 cooler is not as efficient as it could be, & something I didn't take into account. Even with the venting on the mud guard it will not flow air anywhere near as well as if it had just a hole for the air to flow out. All just a matter of if you want to hack up/remove your guard. The biggest draw back with this set up is that the cooler is then exposed to any crap that your wheel flings up & over like stones etc. 1.5 PSI drop at 1.3 bar isn't too bad, though I think you'll find that the pressure drop with a deacent & not overly large aftermarket front mount to be even less than the GT-R one too. Also were both the R34 GT-T & R32 GT-R running the same boost for the same power figures? I'll see if I can find the thread, sounds like an interesting read.

The other alternative to help reduce the air volume with a front mount is to reduce the piping length by going to a front facing plenum, which probably saves something like 3/4 of a metre of piping & therefore reduced volume. With piping like the PlazmaMan setup on the stock plenum however, it would be less than 3/4 of a metre difference, very nice kit.

I should also point out that the guy's I know that have put front mounts on their cars have all generally used more premium level high quality set ups (no I'm not rich & neither are they) which may be a sign that they are better designed for the job & more efficient. This is one reason I certainly won't be skimping with a cheap kit.

I'll get there but I was hoping that you guys could help me confirm the order of mods I posted above. I used to be auto so there was no point in lightening my tailshaft but I'm manual now so there's no reason why I shouldn't do it. Maybe I should do a Bass Junky and do them in opposite order just to test the effect...

Ahh I get it now. Your inertia helps you up the first bit of the hill - or the whole thing if it's small enough - which saves fuel, but without this inertia you need to be straight onto the gas.

The response I'm talking about is the transition between off the throttle and back on. Ie; coasting along then plant your right foot. How long does it take to get up on boost? I can tell you from my experience that in this one area, a smaller intercooler is better.

I think the total volume is the important part here.

On the stock R34 there are already holes in the inner guard lining behind the cooler for this reason. When I put an oil cooler in the opposite guard I cut the same holes in that lining. Some ducting that lets no air escape the cooler would be great too.

The only other thing to consider is the heat sink aspect. How long are you going to be on boost? Will it be long enough to completely saturate the cooler with heat? I don't know but it's worth considering. If this was a drag racing thread then no way would it be good enough, and probably not on the circuit either, but street - probably.

What you've said about reponse has always been what I understood to be lag, the delay between when you plant your foot to when the turbo is on the maximum possible boost for a given rpm as lag literally means to go slow. What you've also said about it taking longer to boost up under the scenario you described is also the complete opposite to what I've previously heard, which for me is surprising.

What kind of kit do you have on your own ride out of curiousity?

Edited November 21, 2006 by JazzaR33

[Abo Bob]

What you've said about reponse has always been what I understood to be lag, the delay between when you plant your foot to when the turbo is on the maximum possible boost for a given rpm as lag literally means to go slow. What you've also said about it taking longer to boost up under the scenario you described is also the complete opposite to what I've previously heard, which for me is surprising.

What kind of kit do you have on your own ride out of curiousity?

You're right - about response and lag - it's just that 95% of the people on this forum use lag when they mean boost threshold and if I follow suit I don't have lag left in my dictionary to use where it should be used.

You mean when I said I have more lag* with a bigger intercooler? Well suppose I have a pump (the turbo) that is going to pump an exact amount of air no matter what it is pumping into. Now say I want to pressurise a 2 litre coke bottle. This will take X amount of time.

But what if I increase the size of the bottle to about 6 litres? Obviously it's going to take longer to pressurise, the pump is pumping the same amount of air.

If nothing else changes (and in the real world it usually does), how can a larger intercooler not increase lag*?

* Using the word properly here.

I used the stock cooler up to 190rwkw then put on a Blitz LM kit. I have not measured the pressure drop but I've always made very good power for quite low boost so it must be good.

[rev210]

JazzaR33,

Fitting any kind of intercooler requires good ducting, if you want it to be most effective and efficient. Nismo make a duct for the GTR's intercooler, but ensuring the air continues into the radiator core by sealing the gaps between intercooler core edges and radiator is also part of the deal.

You are quite right , reducing pipe volume and to some extent keeping pipe diameter to an optimum size and no bigger certainly does help.

With the factory intercooler and removing a section at the front of the wheel well can be done very neatly, alternatively you can take it out all together. I did so on my old R33 and drove it many kms, some unsealed roads too and I can assure you there is no crap flung into the back of factory intercooler, so no worries about that which is good.

[Roy]

LOL...std intercooler is poo

Has anyone ran a thermocouple on inlet temps and kept an eye on it as they drive the car hard? Whats the rule of thumb again?For every 3deg C increase you lose 1 hp???

Also, if your car is on a dyno, how do inlet temps hurt the tune? How do they impact on the tune? Does it mean more fuel and not as much ignition?

...i dont know the answers, but these are the sorts of things that impact on why i would bin the std cooler.

[J_Red33]

You're right - about response and lag - it's just that 95% of the people on this forum use lag when they mean boost threshold and if I follow suit I don't have lag left in my dictionary to use where it should be used.

You mean when I said I have more lag* with a bigger intercooler? Well suppose I have a pump (the turbo) that is going to pump an exact amount of air no matter what it is pumping into. Now say I want to pressurise a 2 litre coke bottle. This will take X amount of time.

But what if I increase the size of the bottle to about 6 litres? Obviously it's going to take longer to pressurise, the pump is pumping the same amount of air.

If nothing else changes (and in the real world it usually does), how can a larger intercooler not increase lag*?

* Using the word properly here.

I used the stock cooler up to 190rwkw then put on a Blitz LM kit. I have not measured the pressure drop but I've always made very good power for quite low boost so it must be good.

Ok good to see we're talking on the same plane here .

Now this is where it starts to get really complicated, this is my understanding of higher flowing frontmount can improve response/reduce lag:

Lets look at the intake side of things first, with a front mount in comparison to the standard side mount you will have cooler intake tempuratures, better flow & less pressure drop but more air volume to pressurise. Now when you first put your foot down, the charge of air that is in the intake gets sucked into the engine. The cooler the air that gets sucked in, the more of it there is, the more fuel the engine management will feed it to create a bigger bang & therefore more power. So straight away from here the car with the better cooling frontmount is off to a good start.

The next step, when the engine then pumps out the burnt mixture it now has more exhaust gas to drive the turbo which then in turn spins harder to increase flow to the intercooler & the rest of the intake & therefore pressurising the larger frontmount intercooler just as fast, if not faster than it would the standard side mount. The turbo will also not have to work as hard to get to the set intake pressure (this is provided the boost level has been adjusted to compensate for the lower pressure drop across the frontmount, otherwise it will boost higher) & can therefore also reach the same boost level earlier because of this.

That the theory as I understand it & what I believe is happening with the cars of others I know. Practcally these differances may be greater or less from once specific set up to another.

JazzaR33,

Fitting any kind of intercooler requires good ducting, if you want it to be most effective and efficient. Nismo make a duct for the GTR's intercooler, but ensuring the air continues into the radiator core by sealing the gaps between intercooler core edges and radiator is also part of the deal.

You are quite right , reducing pipe volume and to some extent keeping pipe diameter to an optimum size and no bigger certainly does help.

With the factory intercooler and removing a section at the front of the wheel well can be done very neatly, alternatively you can take it out all together. I did so on my old R33 and drove it many kms, some unsealed roads too and I can assure you there is no crap flung into the back of factory intercooler, so no worries about that which is good.

Yes I was quite aware of this.

The main point I was making was that you can improve the performance of the stock cooler greatly by doing this mod, probably more so than any frontmount due to the small surface area it has to be cooled & the fact the guard makes it a lot harder for the air to flow. Higher airflow = better cooling no arguement there.

Personally I'll just be waiting till I have the money for a good quality frontmount & saving my guard. I'm really fussy with the appearance of my baby

LOL...std intercooler is poo

Has anyone ran a thermocouple on inlet temps and kept an eye on it as they drive the car hard? Whats the rule of thumb again?For every 3deg C increase you lose 1 hp???

Also, if your car is on a dyno, how do inlet temps hurt the tune? How do they impact on the tune? Does it mean more fuel and not as much ignition?

...i dont know the answers, but these are the sorts of things that impact on why i would bin the std cooler.

No need for a thermocouple just do a couple runs on the dyno & watch that power drop like a bomb. Reacently went to a dyno day here in SA with my 33 a lot of other skylines. Other 33's that ran with less than a full 3-inch exhaust & stock cooler ran consistent, but much lower figures in about the low 150's. When mine was put on with the full 3-inch system & stock side mount it ran 177KW on the first & then 170KW on the second successive run. So after 1 run & only about 15 to 20 seconds of hard acceleration I'd dropped 7 kw, which going by the formula you gave is an intake temp increase of about 28 degrees! Every other 33 that went on there with a front mount ran much more consistent figures that barely dropped any more than 2KW & sometimes gained a little. All had higher power outputs too.

However this is a 33 side mount not a 34, but still I can't see it cooling working that much better for the increase in core thickness. It can still only suck in just as much cooling air, which means you need reasonable speed for it to start having a significantly improved cooling effect.

Edited November 22, 2006 by JazzaR33

[illusiVe]

you wont loose 7RWKW in 20 seconds unless the ambient room temp raised 17 degrees... literatly.

[mokompri]

Lets look at the intake side of things first, with a front mount in comparison to the standard side mount you will have cooler intake tempuratures, better flow & less pressure drop but more air volume to pressurise. Now when you first put your foot down, the charge of air that is in the intake gets sucked into the engine. The cooler the air that gets sucked in, the more of it there is, the more fuel the engine management will feed it to create a bigger bang & therefore more power. So straight away from here the car with the better cooling frontmount is off to a good start.

The next step, when the engine then pumps out the burnt mixture it now has more exhaust gas to drive the turbo which then in turn spins harder to increase flow to the intercooler & the rest of the intake & therefore pressurising the larger frontmount intercooler just as fast, if not faster than it would the standard side mount. The turbo will also not have to work as hard to get to the set intake pressure (this is provided the boost level has been adjusted to compensate for the lower pressure drop across the frontmount, otherwise it will boost higher) & can therefore also reach the same boost level earlier because of this.

what you say is true, but when put it into context theres other things to consider. the difference in temps between a front mount and a standarm IC will vary depending on the amount of airflow. the more airflow, the greater the difference, and for low amounts of airflow the difference is probably marginal at best. for example at 5psi, i dont think you will have any measurable difference in temps between a standard IC and a FMIC, they both have enough capacity to bring temps down to almost ambient.

so when we start talking about lag, where talking about going from vacuum, then going through boost build up stage, then peaking and staying at the max predetermined boost. and from the point of vacuum to relatively low amounts of boost, we are pumping low amounts airflow which probably wont show much difference between the 2 ic's, so you dont get that affect of cooler air>more exhaust flow>boost sooner, although it may shoot up from 'low' boost to your max boost a bit quicker, but we dont really consider that area when we talk about response/lag. ive seen a few dyno graphs of cars running stock boost, switching to fmic's and running that same stock boost without showing any real measurable difference.

although this doesnt take into account high amounts of heat soak in standard ic's.

[J_Red33]

you wont loose 7RWKW in 20 seconds unless the ambient room temp raised 17 degrees... literatly.

I think you underestimate how important good intercooling is & how hot a turbocharger can get. Consider this; if the exhaust housing gets to temperatures of several hundred degrees & the intake compressor is bolted right next to it, it's gonna have to get somewhat hotter. So by the time the second run begins with next to no opportunity to cool back down again the intake temps are much higher.

Torque was the biggest tell tale when looking at the dyno graph, as it dropped off slowly throughout the rev range due to the increase in heat. If you look at dyno graphs 33's with a front mount fitted the torque is almost dead flat until something like 5-6 thousand revs.

The R33 I think you will find is also a lot more prone to power loss after being loaded for even a short period, once an exhaust system is fitted while maintaining the stock intercooler. What proves this more than anything is the fact that before I had my exhaust system fitted, my intake plenum would be hot as buggery (at least 60 degrees, I know this because it hurt to touch it for much more than a few seconds), all the time whether or not I'd be driving it hard didn't matter. Once I had the exhaust fitted, the plenum was noticably a lot cooler, after steady driving (luke warm, about 25 -30 degrees roughly), but could be a fair bit hotter if I'd just been sinking the right foot a bit.

This meant that the new exhaust is more effective at sending the heat out the back rather than making it build up excessively at the turbo, & therefore bringing the intake temperature down more than just a few degrees.

However when put under heavy load, no exhaust system is going to get rid of all the heat, so the turbo then starts to heat right up again, bringing intake temps back up with it.

Apologies for highjacking this debate into another big intercooler arguement (although related to the issue). I hope you get some usefull information out of it all for what you are trying to achive.

what you say is true, but when put it into context theres other things to consider. the difference in temps between a front mount and a standarm IC will vary depending on the amount of airflow. the more airflow, the greater the difference, and for low amounts of airflow the difference is probably marginal at best. for example at 5psi, i dont think you will have any measurable difference in temps between a standard IC and a FMIC, they both have enough capacity to bring temps down to almost ambient.

so when we start talking about lag, where talking about going from vacuum, then going through boost build up stage, then peaking and staying at the max predetermined boost. and from the point of vacuum to relatively low amounts of boost, we are pumping low amounts airflow which probably wont show much difference between the 2 ic's, so you dont get that affect of cooler air>more exhaust flow>boost sooner, although it may shoot up from 'low' boost to your max boost a bit quicker, but we dont really consider that area when we talk about response/lag. ive seen a few dyno graphs of cars running stock boost, switching to fmic's and running that same stock boost without showing any real measurable difference.

although this doesnt take into account high amounts of heat soak in standard ic's.

Some very valid points here. However if you want to make the bottom end as responsive as possible relative to the top end, you want the same amount of boost throughout the rev range. To achieve the 200KW that illusive I believe would at least like, I would think that 10 psi would be the bare minimum requirement.

Personally I found that with a set boost of 10 psi the car doesn't really start to pull real hard until 2500 rpm where it can achieve maximum boost & the time it takes to spool up the turbo if you lift off the throttle at anything below about 3500 revs can be over a second still (Edit: tested this today, about a second at 2500 & half a second at 3500 from when I plant my foot). The time it takes to go from low to full boost is basically what lag is as the engine is not giving optimum performance until it hits max boost (unless the max is too high of course), it's just at lower rpm there is a lot more of it. Going from vacuum to atmospheric pressure takes barely any time.

For me it will be interesting to see what the response is like once I go to a much larger intercooler. Admittedly I had considered an R34 SMIC because it was a cheap & easy alternative stop gap, but it's not capable of the power I eventually want to achive & value for money was questionable.

Edited November 24, 2006 by JazzaR33