Trick For More Horses. Need Clarification

[rmahnovetsky]

Hey Guys

The other day I had a drag against my friend v8 supercharged VT runing at 8psi. To put it bluntly I was flogged. Off the mark up to 130klms/hr I was about 1.5 secs behind him. Well thats how long it took me to get to where he was. 80klms/hr launch to 130 klm/hr he would have beaten me buy a good 3-4 car lengths. At this stage I was not really worried as I haven't spent much in mods. But later that night he raced a vl with an rb25det. This is the work it had done to it

Hybid 600x300x76 cooler with custom piping 2.5"

3 inch exhaust

plumb back screamer pipe

13 psi

I think bigger fuel pump

ah cant think of the name moly something. It adjusts the fuel pressure it goes in the return line.

So basically nothing really done to it. Pretty much the same as what I have done to my car except for the screamer the moly thing, fuel pump and I was running 10 psi.

The end result was the V8 just beat him. From 80k to 130k the v8 was only a 1/4 car ahead.

It turned out that I know the mechanic who tuned the car for the VL. So I asked how the hell can the vl basically flog my car. this is what he told me.

With a plumb back screamer they found that it held boost really well with a t piece.

Gota watch the rb25det flat spot. To over come this you need higher fuel pressure so use the moly thing. Advance the CAS to full timming, apparently this over rides the knock sensor and it wont ping because you have increased the fuel pressure. Thats it.

Now I just need some clarification on this. How far are we talking here 25-30 deg advance on full CAS! is this good? Does it override the knock sensor so it won't play silly buggers with the computer and pull out the timming?

This tunning technic sounds like gold!!! nearly keeping up with a v8 that has had a good 10G on the motor ...

I have a SAFC so I wont mind trying this out. But need to see other options first.

[paulr33]

ok this makes no sense, a plumb back screamer??? the purpose of a screamer is to vent the exahust wastegate gases out to the atmosphere instead of going through the cat. surely you dont mean plumb back into the intake? how on earth could that work? exhaust gases going back into the intake and being reused? anyway the v8 supercharged has stacks more capacity than your car, what did u expect

[rmahnovetsky]

no it doesn't go back into the intake it plumbs in just before the cat at the bottom of the dump pipe. Apparently it controls the waste gate a little better to hole boost..

V8s there made for towing not racing

[paulr33]

well then its not a screamer pipe. its a split dump. where the stocker int gate and exhaust outlet are split and then rejoined just before the cat. this helps prevent backpressure as they met up further down the pipe and don't push out pressure against each other like in the stock dump/front pipe setup

[paulr33]

http://www.skylinesaustralia.com/forums/in...showtopic=74022

[rmahnovetsky]

OK split dump pipe it is... The results from the link are amazing... I really didn't think the split dump could make that much of a difference compared to a normal 3" dump pipe. But it is logical in your explaination. Mod noted!

What about the other mod he has that I don't. "Gota watch the rb25det flat spot. To over come this you need higher fuel pressure so use the moly thing. Advance the CAS to full timming, apparently this over rides the knock sensor to stop it from retarding and it wont ping because you have increased the fuel pressure." .. This is what gave him the most gains on the dyno..

[paulr33]

if your talking about with the stock ecu and piggyback you have to juggle the load points of the piggyback and avoid the stock ecu protection which makes it hard to tune. so you get some flat spots through the rev range.

with an aftermarket ecu you can fully tune it and have no flat spots like this http://members.dodo.com.au/paul/pics/paulr33-193rwkw.jpg

im running stock fuel reg and fuel pressure just an upgraded fuel pump

[Cubes]

I think what he's done is raised the fuel pressure then used a fuel computer such as a SAFC to lean it out again. This would make the ecu think its seeing much less airflow, as a result missing the ecu's protection (rich retard).

Doing this you WOULD NOT want to advance the timing, rather retard it slightly as these lesser load points (lesser airflow) cells have a much higher ignition timing.

Hope that makes sense.

Its bodgy, but works I guess. By the time the tuner stuffs around with the cost of an fpr and settings it up, ignition timing, safc cost and safc tuning you could grab a pfc for 1k, plug it in and grab a cheap 1hr WOT tune for $100.

Edited September 24, 2005 by Cubes

[Sydneykid]

Hey Guys

The other day I had a drag against my friend v8 supercharged VT runing at 8psi. To put it bluntly I was flogged. Off the mark up to 130klms/hr I was about 1.5 secs behind him. Well thats how long it took me to get to where he was. 80klms/hr launch to 130 klm/hr he would have beaten me buy a good 3-4 car lengths. At this stage I was not really worried as I haven't spent much in mods. But later that night he raced a vl with an rb25det. This is the work it had done to it

Hybid 600x300x76 cooler with custom piping 2.5"

3 inch exhaust

plumb back screamer pipe

13 psi

I think bigger fuel pump

ah cant think of the name moly something. It adjusts the fuel pressure it goes in the return line.

So basically nothing really done to it. Pretty much the same as what I have done to my car except for the screamer the moly thing, fuel pump and I was running 10 psi.

The end result was the V8 just beat him. From 80k to 130k the v8 was only a 1/4 car ahead.

It turned out that I know the mechanic who tuned the car for the VL. So I asked how the hell can the vl basically flog my car. this is what he told me.

With a plumb back screamer they found that it held boost really well with a t piece.

Gota watch the rb25det flat spot. To over come this you need higher fuel pressure so use the moly thing. Advance the CAS to full timming, apparently this over rides the knock sensor and it wont ping because you have increased the fuel pressure. Thats it.

Now I just need some clarification on this. How far are we talking here 25-30 deg advance on full CAS! is this good? Does it override the knock sensor so it won't play silly buggers with the computer and pull out the timming?

This tunning technic sounds like gold!!! nearly keeping up with a v8 that has had a good 10G on the motor ...

I have a SAFC so I wont mind trying this out. But need to see other options first.

<{POST_SNAPBACK}>

The engine mods are probably only half of the reason, the VL weighs ~150 kgs les than your Skyline, that's why is accelerates faster. The VT is ~150 kgs heavier again, same result.

cheers

[rmahnovetsky]

thanks guys for you input..

After a little research on the split dump pipe I found the split works well to spool up the turbo but for top end nothing really noticable. I found this on the MRT site. http://www.mrtrally.com.au/performance/doc...20Middleton.pdf

Sydneykid is right the VL is lighter found that somewhere too. I forgot to mention he has a rollcage in there too. I doubt it would be 150 kg to compare apples with apples.

Yeah he did raise the fuel pressure but using a device that sits on the return fuel line and it is adjustable. The original valve that is connected on the return line is replaced which lies on the side on the engine bay next to the fuel filter. Thats how he adjusted it.

I think what he's done is raised the fuel pressure then used a fuel computer such as a SAFC to lean it out again. This would make the ecu think its seeing much less airflow, as a result missing the ecu's protection (rich retard).

Yeah thats probably his little trick to bypass the ecu protection!!! Nice little trick.

I also remember him telling me the VL has 250 horses at the wheels.

Also what I forgot to mention is he said he turned the CAS all the way to the right. I he was facing the car when he said that. I believe that is advancing as far as it would go? somehow this overrides the computer to stop it from pulling back the timming. There was no computer to adjust it it was all adjusted by the device he added in the return line.

I has seen some guys on the furums running 25, 30 deg advance. I would like to know how much difference this makes compared to stock timing. They would have had to increase the full pressure alot to stop the car from pinging.

[paulr33]

your understanding of the split dump seems backwards. it wont help spool up at all, neither will the stock one, when the int gate (during spool up) is closed all exhaust gas goes out the exhaust wheel spinning it faster and faster. once target pressure is achieved at the manifold the pressure pushes the actuator spring open, which moves the rod and opens the int gate flap. when this happens (aka say 7psi in manifold) exhaust gas comes out the int gate flap and the exhaust wheel outlet at the same time. when on full load and as you flow more and more gas theres lots of backpressure. the stocker dump has the outlet for each in the same area so you basically have gases hitting each other, thus slowing it down and making a pretty big restriction. when its split the int gate gas goes down its own pipe and the ehxast wheel gas goes down another pipe. they join up further down the pipe where pressure isnt as much. the purpose of the split dump is to prevent excess back presurre and keep top end flowing as much as possible. in the stocker dump / front pipe combo the top end suffers a little on full load and lost of boost as theres a big backpressure build up at the turbine outlet / dump pipe connection area

[paulr33]

that doco is a bit one sided but anyway the split dumps BATMBL's sells if you look at the pics have a vane in the inner side of the wastegate / exhaust outlet to split them properly. so the gases are forced down seperate pipes, they dont have a chance to collide. the pipes BATMBL sells are fabricated on the stocker turbo so it meets up perfectly and ensure they are truely split, not the like pic in the pdf where they've just welded another pipe on and hope for the best then when the gate opens. also that pipe rejoines a short way down the pipe, it should be 30cms odd before the wastegate pipe rejoins for best flow

[paulr33]

""If I wanted just grunt I'd put a good air intake

system on and a rear muffler - and that'd be your

$1000. You'd have money left over, but not

enough to do anything else - maybe a water spray

or something."

what a strange comment. cold air intake and a muffler costing $1000 ? theres stacks of good cheap upgrades you could do for under a $1000

[rmahnovetsky]

your understanding of the split dump seems backwards. it wont help spool up at all, neither will the stock one, when the int gate (during spool up) is closed all exhaust gas goes out the exhaust wheel spinning it faster and faster. once target pressure is achieved at the manifold the pressure pushes the actuator spring open, which moves the rod and opens the int gate flap. when this happens (aka say 7psi in manifold) exhaust gas comes out the int gate flap and the exhaust wheel outlet at the same time. when on full load and as you flow more and more gas theres lots of backpressure. the stocker dump has the outlet for each in the same area so you basically have gases hitting each other, thus slowing it down and making a pretty big restriction. when its split the int gate gas goes down its own pipe and the ehxast wheel gas goes down another pipe. they join up further down the pipe where pressure isnt as much. the purpose of the split dump is to prevent excess back presurre and keep top end flowing as much as possible. in the stocker dump / front pipe combo the top end suffers a little on full load and lost of boost as theres a big backpressure build up at the turbine outlet / dump pipe connection area

<{POST_SNAPBACK}>

OK can see you point of view two gases colliding into each other right at the back of the turbo causing back pressure. At your set psi some will go through the turbine, some wil go through the wastegate then meet up at the end on the turbo to cause turbulence and create back pressure. So the back presssure from the turbulence will restrict the turbo from flowing as well as it could. ON a stock setup I guess this will increase the psi slightly. IF you had a digital boost controller then the twin pipe will not really benefit? mmm but I guess the more back pressure there is the hotter the turbo gets and more the more chance of the motor detenating thus reducing timming / increase fuel and less kw?

this is what you mean the pics on the home page of this website. To ensure they dont collide

http://www.cesracing.com.au/

[Cubes]

Also what I forgot to mention is he said he turned the CAS all the way to the right. I he was facing the car when he said that. I believe that is advancing as far as it would go? somehow this overrides the computer to stop it from pulling back the timming. There was no computer to adjust it it was all adjusted by the device he added in the return line.

<{POST_SNAPBACK}>

All the way to the right as in turning the cas clockwise? That would be retarding.

Anti clockwise is advancing.

To help visualise it i've attached a picture.

The above pic had ignition timing sitting 6degree's.

Edited December 3, 2008 by Cubes

[rmahnovetsky]

All the way to the right as in turning the cas clockwise? That would be retarding.

Anti clockwise is advancing.

To help visualise it i've attached a picture.

cool retard it is... So he would retard it for the purpose to trick the ECU.

Doing this you WOULD NOT want to advance the timing, rather retard it slightly as these lesser load points (lesser airflow) cells have a much higher ignition timing.

I dot really get this. If my R33 pings I increase the amount of fuel on my SAFC. det is a ratio of heat, octane, timing. So if I now have more fuel pressure I have more fuel thus I can advance the timming. Now in the R33 we are trying to bypass the boost cut. I understand by increasing the fuel pressure we can decrease the air fuel ratio to trick the ecu as it thinks it is running from a stock fuel pump. But now the ignition should be retarded, wont that decrease performance - maybe this has to be retarded to match the ecu, ah I'm confused with this bit.

[Busky2k]

He obviously has no f**king idea if he says just to wind the CAS as far as it'll go. Its a recipe for disaster.

Go see a real dyno tuner who can tuen your SAFC and timing to get you safe and real results...

[paulr33]

OK can see you point of view two gases colliding into each other right at the back of the turbo causing back pressure. At your set psi some will go through the turbine, some wil go through the wastegate then meet up at the end on the turbo to cause turbulence and create back pressure. So the back presssure from the turbulence will restrict the turbo from flowing as well as it could. ON a stock setup I guess this will increase the psi slightly. IF you had a digital boost controller then the twin pipe will not really benefit? mmm but I guess the more back pressure there is the hotter the turbo gets and more the more chance of the motor detenating thus reducing timming / increase fuel and less kw?

this is what you mean the pics on the home page of this website. To ensure they dont collide

http://www.cesracing.com.au/

<{POST_SNAPBACK}>

nah nah nah you wont see an increase in psi pressure with a split dump what you will (not) see however is on a dyno run (or any normal operation) a drop off in power in the top end as the gas is split and there is no where as much turbelance and backpressure on the exhaust outlet as each has its own pipe. the pipes batmbl sells are just like the ces racing pipes

ever seen dyno graphs where the cars power drops off after around 5500rpm ish? its cos theres too much back pressure on the exhaust

[Cubes]

cool retard it is... So he would retard it for the purpose to trick the ECU.

I dot really get this. If my R33 pings I increase the amount of fuel on my SAFC. det is a ratio of heat, octane, timing. So if I now have more fuel pressure I have more fuel thus I can advance the timming. Now in the R33 we are trying to bypass the boost cut. I understand by increasing the fuel pressure we can decrease the air fuel ratio to trick the ecu as it thinks it is running from a stock fuel pump. But now the ignition should be retarded, wont that decrease performance - maybe this has to be retarded to match the ecu, ah I'm confused with this bit.

<{POST_SNAPBACK}>

Changing the cas timing will do nothing to trick the ecu.

Thats the job of the safc and the fpr (increase fuel pressure).

When increasing fuel pressure and touching nothing else the car runs as rich as buggery, this is where you use the safc to lean the thing out and bring the afr's back in to something respectable.

Leaning it out via the safc tricks the ecu in to thinking the motor is using less air, as a result injector duty cycles are less and less fuel squirts in to the pots. This 'evens' out the effect of having a higher fuel pressure.

The ECU has a MAP. The map is a 16 x 16 grid of load and rpm.

Load is how much air the motor is swallowing.

Each cell contains a fuel and ignition timing value.

Lesser load cells contain lesser fuel values but higher ignition timing values. As fuel is less dense (less fuel pushed in) in the combustion chamber the charge burns slower, due to this the ignition timing has to be higher as to have peak combustion pressures roughly 10degree's after top dead center.

Full throttle generally runs ignition timing values of around 18-20degree's depending on setup. Cruise and light load runs a hell of a lot of ignition timing, high 20 something degrees right up to mid 40 degree's.

This is why you use the cas to reduce the igniton timing.

Using the SAFC to make the ecu think the motor is swallowing less air WILL use a lesser load point, as said previously using a lesser load point means that lesser load point will be running much more ignition timing. This is where you use the cas to bring the ignition timing back to what it should be and not so advanced. Running ignition too advanced doesn't gain power, it robs power and causes the motor to detonate.

If you have peak combustion pressures before ~10degree's after top dead center (crank movement) the flame will be trying to push the piston down as the crank is still trying to push it up.

Its got nothing to do with stock fuel pumps or what ever your line of thinking is. Its exactly as I said above, nothing more nothing less.

Edited September 25, 2005 by Cubes

[rmahnovetsky]

Top explaination!!! You deserve a purple heart for that one I didn't relise the ignition timing values where that high during the light loads... I alway thought the timing increases with the rpm.. Now I know why they retard the timing in this case.. cheers