Hi all,

Im in SE London and having been checking this forum every other day for about 2 years so thought it was only right to post and say hi. I will put up a newbie post in the next few days with pics. I know you guys are going to love my car as any one in the US simply cant own one and I have about 280bhp\ton with a stock 20V BT. Any guesses!!!!???

Anyway, Im working on more power and thinking about supercharging my BT with an Eaton M45 supercharger that will push max boost 1 bar (14PSI). I am going to put in the latest large port rods and keep the pistons. Therefore I get the strength and keep the CR of 11:1. I have Omex 710 ECU (very advanced and aftermarket) high flow exhausts cold air feed and no major heat problems (due to the car its in).

What im asking is, with 11:1 CR and 1 bar boost with high (101) octance fuel do you think my engine will be able to get a usable map? In the UK we have some of the best engine mappers in the world so if its possible to avoid Knock (pre det) then it can be done here but Im scepticle. What I am asking from the 4age know alls (yoshimitsuspeed and others) is your thoughts on potential floors and things to plan for. I am hoping for 250hp+.

Its a budget build so no aftermarket stuff here. In the UK its hard to find spares for the 4age past AE86 so no AGZE stuff or ST bits. Im keeping the BT pistons but am thinking on getting them ceramic coated, P+P the head DIY if it looks like its needed. Fabricate everything else.

any thoughts or ideas welcome and keep an eye out for my pics and vids of my BT powered supercar beater!!

Bizz

Is it in a Caterham?

Cool project.
First thing to point out is the M45 isn't going to get you close to your goals you will want at least an M62.
Now the M62 should be able to do 250 hp at 14 PSI assuming you can get that out of the motor of course. You will be at about 58% adiabatic efficiency at that point so your outlet temps will be around 150 C with 38 degree inlet temps. Heat is definitely going to be one of your biggest issues so I highly recommend as much intercooling as you can possibly handle.

Something like methanol injection will give you cooler intake temps and also increases your octane giving you double benefits. Even just water injection would help lower intake temps a little.
Either will make your life much easier.

Now I think your power goals are possible but I'm not sure if your PSI goal will be. Fortunately the BT has a crazy low BSFC and as long as you keep those pistons you keep most of it even FI.
Due to superchargers natural disdain for high pressure ratios and the fact that heat will be your worst enemy your first goal should be to make power at the lowest pressure possible.
You didn't say CHP or WHP but for now I will assume CHP.
Unfortunately at just 10 PSI the M62 requires about 30 HP to spin it in the range you are talking about so now you need 280 HP just to hit 250 coming out the crank.

I don't understand why everyone thinks boosted motors need bigger rods. If you study the stresses that a rod endures you will see that the most likely point for failure is under tension on the exhaust stroke. The forces that the rod sees as the crank is trying to stop the piston and yank it back down are a far greater threat than compressive loads. In fact the compression stroke actually pads this tensile stress making the compression stroke much less stressful than the exhaust stroke. RPMs are what kill rods not boost. The one exception could be detonation but you will need to worry about youe OEM ring lands long before rods.

That actually gets me to my next point. If I can stress one thing it would be to take this as incrementally as possible. Those OEM ring lands are going to be your greatest concern and just a little detonation at this level could mean you popping the motor right out of the gate. Hopefully your engine management means you have done away with the AFM and rely on MAP. If this is the case then you could get the pulley ratio you want to run ultimately and use a popoff valve to regulate your boost for now. If you popoff to atmosphere you won't sacrifice anything significant.
If you had to recirculate like on an AFM motor then you would be putting heated air back before the supercharger and it would just heat up more and more as it recirculated.
I would try to start around 6 PSI, 8 PSI at the absolute most. Even then I would be very timid with the timing. I also can't stress enough how important a high end knock monitoring system will be for this build.
My first choice would probably be A J&S safeguard.
If that's not an option I would go with some sort of detcan. I would probably go with a professional one like AEM or Gizzmo. If those aren't options then look at DIY electronic detcan instructions online.
You will also want a pyrometer. If your timing gets too retarded your EGTs will get too high and you will start melting pistons or valves.
This build is going to be walking a tightrope between detonation and EGTs and without both you will be running a significantly higher risk.
It should go without saying that you will need a wideband gauge. If you are on aftermarket engine management I assume you already have one.
It's always hard to justify those things in the beginning but after you melt a motor and need to look at the cost of properly rebuilding it then the cost of the proper monitoring equipment is nothing. Plus after you melt your first motor you will probably decide you need to buy all that stuff anyway so start smart and save that first motor.
As far as the tuning goes.
I think as long as you work up in increments, play on the safe side of ignition timing and monitor AFRs, knock and EGTs you have a very good chance of catching small problems before they become catastrophic.

Can't wait to see the build.
If you need anything let me know.
I am currently modeling the 4AGE block and after that will be trying to work my way out to other parts of the motor. Once that is done making things like supercharger brackets and other parts becomes much easier.

+1

A little update.
I am now considering lowering the CR by using stock 4age large port rods and pistons. I found a CR calculator here.

http://www.streetracing.co.za/forum/vie ... =13&t=6211

CR is in high 9s if I do this. I will possibly run more boost then. Im thinking of buying a super charger turbo hybrid that uses a T04 compressor.

Any thoughts on this setup?
Aim is 250 chp

What do you mean hybrid supercharger turbo? You mean like a centrifugal compressor?
I assume you are talking about the NA pistons. In which case this is not a good idea. The pistons are cast and have a weak ring land that is known to fail in high stress motors.
I also don't like the idea of using 4 valve pistons in 5 valve heads. They were not designed for each other and are likely not optimal. This is especially true in domed pistons with topography that sticks into the head.
I'm not sure where you got your compression numbers. The LP pistons are 9.4:1 but the BT has a slightly bigger combustion chamber taking the CR down to about 9.1:1.

I would highly recommend running a custom piston or at the very least something like the CP shelf piston.
Of course I can get custom wiseco's made specifically to suit your build for barely over the cost of CPs and that should be a much better solution.

bi22le wrote:A little update.
I am now considering lowering the CR by using stock 4age large port rods and pistons. I found a CR calculator here.

http://www.streetracing.co.za/forum/vie ... =13&t=6211

CR is in high 9s if I do this. I will possibly run more boost then. Im thinking of buying a super charger turbo hybrid that uses a T04 compressor.

Any thoughts on this setup?
Aim is 250 chp