Supercharging

[geordie]

This topic was brought up in a topic about turbo conversions and i was real keen on the idea but wasn't totaly shure of the problems that may arise as a result. All i wanted to do was to put a very small low boost set up(6-7psi) to give the car that extra go that we all crave. The idea for a cheap setup was put forward buy FUNKYMONKEY, to use a supercharger of one of the old toyota engines that utilised them in the late 80's-early 90's, these go relatively cheap and can be picked up for as little as 2-250 at a wrecker or over ebay. Then aparently you would need a custom manifold ( was wondering if you could plum the return of the intercooler to the existing manifold, which would eliminate some costs).

Now this all sounds great, and the results would be quite good value for money, but some questions need to be answered. So if there is any technicly minded people out there that may have a fair idea of what the results would be, please enlighten me.

Problem #1 - Computer - I get the feeling that a fully programable aftermarket computer would be required and if this is so..then well it start to take the shine of what could be a realy cheap power up, considering some of the computers are going for $2000 plus, the microtech mt8 would be the cheapest option coming in at 1100.

Problem #2 - Fuel system - Is the standard system up to the job??, is it different to that of a GTS-t, if so, the gts-t injectors would be able to cope with low boost aplication with the supercharger having similar stains on the engine as the stock turbo.

Problem #3 - Compresion - Would the standard compression be to much for even a mild boost application, if not would a thick metal head gasket lower the compression enough to support the SC, and would this result in a loss of top end power which is pretty sweet at 5000rpm on the rb25.

Well sorry for the essay, but these are my thoughts and it would be a very different sort of power up and could have alot of potential for those on a budget. Any thoughts????

[Guest RedLineGTR]

Sounds like a good idea, i have a turbo myself. But would like a good read on what ideas people have had..

[slip]

With a skyline, all the turbo parts are readily and cheaply avaliable, youre probably better off just using standard stuff. Ive been in a 32 and 33 that have had this done, they were both good. the 33 was using non turbo injectors and a link ecu, and a maximum of 6psi boost. The RB25DE have a 10.5:1 compression ratio which is not too boost friendly. If you had a front mount intercooler you might be able to go higher. Very smooth power delivery, nice midrange, gave it that 'pull' that it needed.

A crappy old toyota supercharger = meh.

Go for a centrifugal style, its like the front half of a turbo thats run off the pulley, and you set the rest up like a turbo setup. It would cost more than doing a turbo conversion if you do it right with ecu etc, because of the purchase price of centrifugal supercharger and mounting hardware/labour.

[geordie]

"Ive been in a 32 and 33 that have had this done, they were both good. the 33 was using non turbo injectors and a link ecu, and a maximum of 6psi boost. The RB25DE have a 10.5:1 compression ratio which is not too boost friendly. If you had a front mount intercooler you might be able to go higher. " - is this for a turbo set up or supercharger??

The aim of this investigation is to get some cheap horsepower, thus why using an old toyota charger just coz its cheap as chips, if you could run 6psi through the toyota charger and a front mount (something small and cheap, ie:supra intercooler=370mm x 280mm x 75mm) and and spend the most money on a good computer to get the right tuning............if an extra 50-60rwhp is possible then it would be good. Also some extractors to help out with the extra exhaust gasses

[slip]

ok, so youre going to do all the same mods, but use an old pd type supercharger instead of putting a turbo and manifold on? Turbos and 2nd hand manifolds are cheap.

Youve gotta mount the supercharger too so thats going to cost.

[geordie]

So you believe that it would be just as cheap to run a turbo setup, i have considered this but have been told that the engine is too highly compressed for this (thus one of the problems for all forced induction), i have also been told that the holes required to attach the turbo exhaust manifold and such dont exsist on the N/A block. I think the compression is the greatest problem for this investigation, and the need for a the ecu to be upgraded.

If the turbo setup was to be put on and running very low boost (6psi) with a front mount intercooler. Would this be possible, because there seems to be problems with both ideas, turbo and supercharger, in the mounting of either charger. Which is most feasable/possible/affordable and give the greatest gain.

[slip]

My friend bolted the stock turbo hardware to his 33 GTS with a link ecu and STANDARD shitbox intercooler. Went well (refer to my first post). I drove the car and it was very smooth. Non turbo injectors. 6psi max. Use a decompression plate if you want to get the compression ratio down a bit, but Matt's car was very driveable and smooth.

Whoever told you that bolting the turbo manifold to the head would be a problem is a goose, because they are the same head basically.

Its relatively cheap and easy, if you think about it.

[geordie]

Well a pretty respectable tuning shop told me that and they know there skylines pretty good, they pretty much said it would be easier just to buy a half cut and do the lot.........

[WazR32GTSt]

geordie,

there has to be a supercharging-specialist shop somewhere near you. ask them for a ball-park figure... this should give u an idea of what to go for: turbo vs. supercharger

personally i rekon if they cost the same, the supercharger would kick-sh1t all over an identical turbo setup with HEAPS of low down torque and max boost very early

but then again that's just my 2c and what do i really know? i'm a biomedical scientist not a mechanic

[geordie]

I think that is the best thing to do, is just ask. And if the pricing is similar, i think i will go for the supercharger just coz well, its original, how many SC skylines do you see??, and yeah the low down torque would be insane, it would be alot of fun and possibly a little scary in the wet.....WazR32GTSt - i like your 2c

[Pva_Glue]

pppfffff.... Good luck.

its too much hassel going super charger, dotn get me wrong its some what unique but why? if there is chceap turbo parts are avaliable...

love to see them on the road but!

besides we want to hear blow off sound in skylines SSSHHhhhhhh!!!!

[slip]

Waz - there are different types of superchargers, PD blowers act in the way you describe. To get a storming bottom end you may have to trade off your top end. Can be a hassle to fit.

Probably easier to go a half cut, gotta try and sell your engine though, not a big market for them.

[geordie]

yeah there are cheap turbo parts available but there are also cheap SC's available to.........i dont have the BOV sound now...cant say i want it either, i like the full descreet not let anyone know whats happening under the bonnet, dont draw attention etc......let em guess, the SC whine would be evident though, keep em realy guessing......i going to ask around the performance workshops and get there thoughts. How much are r33 half cuts these days any way??

[Warpspeed]

Supercharging CAN theoretically be far better, but it is not necessarily going to be better if is all done on the cheap.

For example, you could buy a $300 turbo that came off a smokey old 2.0 litre 150Kw engine that has already seen a million miles and is a bit loose. Just bolt it onto your Skyline with no other changes. should make an easy 400 Kw at the back wheels, right ?

Must be true, all turbos are the same and make big power, right ?

Or you could buy a $300 supercharger that came off a 2.0 litre 150Kw engine that has also done a million miles and just bolt it on. You will get massive torque and horsepower.

All superchargers do this, right ?

Sorry about the sarcasm.............

But you would be surprised how many people think a very small $300 blower is going to make absolutely huge power numbers when fitted onto just any engine.

If you size and fit a decent blower, and tune it properly you can make a far more drivable and powerful package than any turbo. But it is not going to be cheap. The secret is to have the correct size and type blower that works efficiently over the pressure and airflow range you need, just as with a turbo.

If you want cheap, and easy, stick with a turbo.

With a big turbo you will make big numbers, but it can be a pig to drive every day.

I have built, owned, and driven, supercharged cars, turbocharged cars , and a car with both supercharger AND turbo fitted, at different times over the last thirty five years.

You only get what you pay for.

[Pva_Glue]

well said... but at the end of the day the RB engine can not (without major engine modification) support the SC belts...

I say picture of one SC skyline... runs on boot full of batteries.. only manage to score 6~9 psi...

is it really worth it? eh?

[Warpspeed]

As far as supporting the front drive-belt goes, there are three cardinal rules.

The first is to have the supercharger drive pulley mounted as far onto the crank snout as it will go, not cantilevered right out on the end of all the other assorted stock pulleys. It must get pride of place next to the timing cover.

Next, keep both the drive pulleys as large a diameter as is reasonable, this reduces belt tension both static and dynamic, and also the extra belt wrap reduces the chance of slippage. With less belt tension there is less strain on everything. Modern thin multi rib belts can run at fantastic belt speeds without flying apart.

Third, run a forged steel crank, no problem on a Skyline, because that is all there is.

As to if it is worth it, consider a stock GTR with about 350BHP at stock boost level, and stuff all torque below 4,000 RPM. It will rev cleanly to 8,000 RPM though.

Chuck the turbos and fit a sufficiently large screw blower where the airconditioner usually sits, and a good tubular minimum back pressure exhaust manifold. Stock cams, stock intercooler, stock everything else.

The power you lose driving the blower will be picked up by the increase you gain by not having any turbine back pressure. this usually works out at about 10% engine power, equal to about 10psi back pressure across the turbines (roughly).

It will still make similar power at similar boost, and similar maximum torque as well. The difference will be though that the torque curve will be totally flat from about 2,000 RPM to around 5,000 RPM with zero lag.

Standing quarter times probably would be no different, but as an everyday street car it would be far more grunty and easy to drive. It would be consistently quicker from a standing start as well, without having to thrash it.

To beat it with a turbo, you would need to do rev limiter launches, and even then it would probably sometimes bog down on you. Only a complete moron drives like that every day on the street.

If you fit bigger cams and turbos it gets even worse. With a blower you can increase the boost without losing any drivability at all, and that is its best feature. There is not the same compromise of drivability versus power that a turbo has.

People claim turbos give higher power, and its true. You can set up your 1,000+ BHP turbo engine that has a 500 RPM wide power band, and yes it will be more powerful. So what ?

You could probably build a similar centrifugally supercharged engine with similar power and minimal power-band, and it will be just as equally useless.

[pstanbis]

warpspeed has a good point... most turbo cars are cops on the street, not just the driveablility, but stop/start as well. But im also interested in the compression side of things... how much do they have stock? 9.5-10 : 1 im lead to believe, and if so, is well above that of even a mild turbo (EXA Stock, case in point) putting out 5/7psi, and the compression on those is back at 7.5-8 : 1 ! so is it really worth trying to get it back and allow the higher boost, or would you get a simmilar result from lower boost/higher compression?

like WarR32 said, just my 2c...

[Warpspeed]

All the RB26DETTs have 8.5 : 1 stock factory compression ratio.

There is no simple single answer, it depends on so many factors including fuel octane, induction temperature, boost level, inlet valve timing, and combustion chamber anti detonation characteristics, and even exhaust back pressure believe it or not.

You can juggle so many factors around and get a good result, there is really no fixed rule on what works best.

For instance the V6 miller engine that Mazda make has a 10.5 : 1 compression ratio, and runs a supercharger with 15 psi boost, and very inefficient inter-cooling. This is a stock factory engine as well, and detonation is certainly never a problem either.

You could probably do something pretty similar with a stock compression RB25DE if you really wanted to, by fitting a different inlet cam and a decent supercharger (not a Toyota blower !).

[geordie]

So a decent blower were talkn some of the more populr brands such as eaton and such......and i wasnt really thinking 400kw at the wheels at all.......i was thinking maybe 50hp and slab of torque......lol.....heres what i been thinking as aparts list tell me how i would go with this:

*microtech mt8 for the management.....

*some extractors (such as those in the grup buy)

*a charger That is not a toyota one......due to advisement against them.

*a hks thick copper head gasket to lower compresion

*a stock supra intercooler (decent size, cheap price)

Hows the parts recipe looking now...what other things should be considered, how much would average cost to get all this work done????, this topic is really getting rolling now, keep it coming.

REMEMBER: This is an investigation into a feasable alternative power up for the n/a skyline, and pending on what people think would depend on wether i will attempt it in the future.

I have heard that the stock pistons dont like forced induction very much......any thoughts

[Warpspeed]

Sounds like a good plan.

An Eaton M90 is almost exactly the same size as an SC14, (90 cid = 1475cc) but it is a far better blower though, and should work very well. You should be able to pick one up secondhand at a reasonable cost.

There are two ways of getting around the compression problem without stripping and rebuilding the whole motor with low comp pistons. But if you do plan to go that way, a secondhand low mileage set of GTR pistons and pins can be had for about $200.

Ask around some of the "name"engine builders, they often throw a set of forgies into a GTR rebuild, and the stock pistons are often in as new condition and unwanted.

I am not a great fan of decompression plates because it removes the squish area where the piston crown comes very close to the flat area on the head. It can effect combustion characteristics as well as make the engine more prone to detonation than it otherwise would be at the same reduced compression.

So you are really making two changes that work against each other. The lowered compression helps, and less squish hinders the detonation resistance of the engine.

A lesser known, but excellent way to tackle the compression problem is to fit a long duration inlet cam, effectively turning the engine into a Miller Cycle engine. To find out more about this type "Mazda Miller Cycle" into Google, and do a bit of research.

This has the advantage that you do not have to remove the engine or even the cylinder head to do it. Also you are not going to lose any fuel mileage as you certainly will if you lower the compression ratio in the normal way. The only slight disadvantage is about 10% less low end torque, (under boost) but no midrange loss, and probably a very slight top end power gain.

As far as the exhaust goes, I would stay with the stock manifold and fit a slightly larger cat back system. It will save you money and lose hardly any power over a set of extractors.

Extractors can cause problems with supercharged engines, and offer none of the benefits that they have with n/a motors.

The first problem is that the extractors are going to be restrictive, believe it or not. On an n/a motor the pipe branches are sized to give a pretty high velocity of gas down the pipe, and this DOES have a significant pressure drop. The benefit is that the negative return pressure wave during valve overlap helps scavenge the exhaust from the combustion chamber, and draw in fresh charge from the n/a induction system. So you lose from the initial pressure drop, and gain from the negative reflected pulse. So extractors are able to give more power, because the gain is greater than the loss.

Now if you supercharge the engine, there will be a far greater volume of exhaust gas going down the pipe every exhaust pop. The rather long, small diameter extractor branches are really too small, and the back pressure rises to a very high level. You could make yourself a set of big bore extractors, but you cannot buy them, because they would be far too large for any n/a application.

So you pay with high pressure drop. The negative reflected pulse is now of no value, because boost pressure is going to sweep out all the exhaust anyway during valve overlap. That is if boost is higher than exhaust back pressure, and it damned well should be. So tuned pipes are a complete waste of time unless you are building an extreme horsepower engine.

The other problem with extractors is noise. By concentrating every exhaust pop in the extractor tube, what emerges is a shock wave of frightening intensity. Only an angry rotary engine can do it better. It will destroy your cat, blow the fiberglass or steel wool out of your muffler, and be really objectionable.

Tuned pipes are a waste of time on a street blown engine, so what to do? To begin, keep the stock manifold, it will help reduce noise, then just make everything slightly bigger. But it might still be noisy though, noisier than a turbo with an identical exhaust system, and it will probably drone if too large.

Once everything else is sorted, there is another way to do it though. The trick is to keep both exhaust back pressure and noise low, without any "pipe tuning", which offers no advantage.

Now here is my little secret, that I have developed myself for solving all these problems on a street car.

What you need are short exhaust stubs welded onto the head flange, maybe only an inch long. Just enough to get a ring spanner in there. These go straight into an exhaust plenum which might be a length of four inch pipe running along the head, down, and then into a reducing cone just in front of the cat.

The secret here is that each exhaust pop empties into a very large plenum volume, maybe thirty times the volume of each exhaust pop. The peak and average exhaust back pressure will be extremely low, and the pulses and the shock waves beat themselves to death in the plenum. The cat (which must be there anyhow), offers some restriction, so the pulsing flow tends to even out. It is fantastic for noise reduction, and pressure drop. After the cat a slightly larger bore pipe and muffler works fine, and it can be as quiet as you want to make it.

That is the Warpspeed secret formula, of how to make a quiet low back pressure street blower exhaust system.