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[75evo]

DUk,

Sorry to interrupt your thread, but it's relavent to my question:

I'd really like Greg's future sprintex kit on on my 11:1 3.0 12V.

What is the difference between
a) high boost low CR engine
b) low boost high CR engine

?

I know the off boost performance on the low CR engine will not be as good, but this is not a centrifugal S/C, so torque should still be good, the "not be as good" is probably a very relative comparison thing.

But apart from that, is it the high discharge temp and high CR making the difference between the 2 engines I mentioned above?

Honda S2000 have super high CR and they S/C their engines all the time. If it's just about tuning then it's not a big deal, I will just dial down everything.

[Duk]

DUk,

Sorry to interrupt your thread, but it's relavent to my question:

I'd really like Greg's future sprintex kit on on my 11:1 3.0 12V.

What is the difference between
a) high boost low CR engine
b) low boost high CR engine

?

I know the off boost performance on the low CR engine will not be as good, but this is not a centrifugal S/C, so torque should still be good, the "not be as good" is probably a very relative comparison thing.

But apart from that, is it the high discharge temp and high CR making the difference between the 2 engines I mentioned above?

Honda S2000 have super high CR and they S/C their engines all the time. If it's just about tuning then it's not a big deal, I will just dial down everything.

This is 1 of those questions that can have a million answers, and I can only offer information on what I've seen and read about. I'm sure that Greg can offer much more input here.

With a high boost, low compression ratio engine, there will be the potential for plenty of full throttle power, that's pretty much a given.
The engine will be able to swallow more ignition advance to extract as much heat energy (to drive the pistons down) out of the air/fuel mixture, without being unduly retarded to avoid detonation.
Where the engines suffer is at part throttle (off boost) cruising, when the dynamic compression ratio (the real world compression ratio) suffers very badly. The end result is poorer throttle response and fuel economy.
Programmable ignition timing can only help so much with low compression ratio numbers. You will find that there will be a point in a vacuum based load cell (say cruising at street or even highway type speeds) that the ignition timing can be advanced past the point of peak torque (on a dyno) and can be advanced even further without suffering from detonation. All the while the ignition timing is advanced past the point of peak torque, the engine looses torque output.

High compression, low boost engines should give a good performance increase upto the knock limit of the fuel/engine/forced induction and intercooler (if fitted) combination. Typically high(ish) compression engines that have forced induction attached to them will reach a point where the ignition timing will be retarded to control detonation.
There will be a point of diminishing return, where the power gain of the extra flow of air and fuel isn't offset by the increase ignition retard (less advance). All the while adding to the thermal load on the engine.
If the detonation limit could be raised and the ignition timing advanced, the engine will make more torque and so, more power.
Obviously this knock limit will vary from engine to engine (combustion chamber design, bore size and the cooling systems ability to remove heat from the combustion chamber surface), efficiency of the compressor, the efficiency of the intercooler (if fitted) and the type of forced induction used.
As Greg has pointed out, mechanical supercharging has a distinct advantage over turbocharging here, in that there is no where near the back pressure built up in the exhaust, and so not as much heat retention in the exhaust ports, exhaust valves and combustion chambers. Hot combustion chambers and exhaust valves being the big promoter of detonation.
Detonation requires less advanced ignition timing. Less advanced ignition timing causes hotter combustion chambers, piston crowns, exhaust valves and ports. The point of diminishing return.
If the engine can run on higher octane fuel, then you will have a tuning advantage by being able to run more on boost ignition advance.
Water injection's primary roll of effectiveness is its ability to absorb heat during the combustion process. If the amount of heat absorbed allows the engine to take more on boost ignition timing and get a torque gain, then that's a win. If the water is just absorbing heat energy that would otherwise be used to push the piston down without any detonation limit, then torque could be reduced.

As for the Honda S2000, they would have a very efficient and effective combustion chamber design to allow them to get the factory performance that they do (while meeting emissions).
When they can swallow boost as well, says a lot about their basic design. Obviously they have to have the fuel and ignition timing to suit and it would be interesting to see the ignition map(s) from a force fed S2000's computer (what ever it may be).

I have seen the old Toyota 1UZFE (4 litre, quad cam, 32 valve V8) engine swallow a heap of boost and make some pretty massive power all on standard engine with standard compression ratio (10:1). Again, 4 valve per cylinder pentroof combustion chamber design that is very efficient and resistant to knock.
Another thing to consider with these engines is 'swirl'. Where the incoming air/fuel stream is directed to cause it to rotated. I know the earlier Toyota 4AGE big port heads had flow biased port(s) that point at a slight angle towards 1 side of the combustion chamber(s). Whether the S2000 and 1UZFE engines have such port characteristics, I don't know, but there has been suggestions that having the incoming air/fuel charge more 'active' makes the charge less prone to detonation.

[75evo]

I had a few laps on the track up against a Mazdaspeed3 with COBB exhaust and intake. On the straight we were about even, he couldnt pass me and I couldnt pass him. But the real killer was out of the slow turns, he had MASSIVE torque, luckily it was FF vs FR otherwise he could have put that torque to good use and blow by me.

So the plan is to hook up GG's new would-be sprintex kit to my 12v with about 5 psi of water injected and charge cooled air. That would give me TONs of low end torque. high compression and a posi disp. S/C. I would be in E46 territory.

[Duk]

Yeah the broad torque curves of turbo engines of the last few years is very impressive. Why they keep sticking them in front wheel drives, I'll never understand .
Powerful front wheel drives suck!

[MR2 Zig]

Why they keep sticking them in front wheel drives, I'll never understand .

Because they are "safer" ....

what a bunch of hooey.....learn how to drive. (I figgure the crowd reading this knows how to drive...comment aimed at the general public that doesn't and isn't willing to learn)

[Duk]

Why they keep sticking them in front wheel drives, I'll never understand .

Because they are "safer" ....

what a bunch of hooey.....learn how to drive. (I figgure the crowd reading this knows how to drive...comment aimed at the general public that doesn't and isn't willing to learn)

Pretty sure the general public aren't members of this forum .