High Comp and Turbocharged

[curtis73]

As a very vague generalization, dropping compression one full point drops the hp and torque curves about 5% across the board, but the resulting boost you can successfully push can take you back up about 70%, for a net increase of 65% power on the same fuel.

Compression is not the free ride every one purports. Sure it gives a touch more VE, throttle response, and low end torque by about the same % as the HP, but I run 8.6:1 in a 400-hp 454. Of course, torque is not my weak point with this engine, but the ability to run 86 octane on the hottest day towing a 6000 lb trailer is a very nice thing. I could pick up 20 more horses by going to 9.6, but its just not my thing. I would much rather have a long-life reliable engine that is easier to tune without catastrophic failure if you don't do it quite right.

Another thing you could do to combat the detonation is to use a piggyback computer to stage a second bank of injectors that throw Methanol in under boost. There is a good writeup on that in an EFI tuning book... can't remember which one... but its on an NSX. The owner kept the factory assembly at 10.2 and was able to run 12 psi by staging alcohol under boost.

The problem with avoiding detonation by "easy" methods like excessively retarding ignition, dumping extra fuel, and things like that is that they are a crutch. Its not the "right" way to do it. Dumping extra gas in will cool the combustion, but at the expense of intensely rich conditions. Clogged cats, fouled plugs, wasted fuel, and reduced power will be the side effects. Retarding ignition timing will have the effect of increased HC emissions (it richens things artificially), and only does good to a point. There is a point where enough cylinder pressure will ignite itself without a spark at all like a diesel. Retarding timing will stave off knock for a while, but as cylinder pressures rise, there is a point at which no amount of retard will help.

I say do it right. Lower CR, use 114 octane, or inject a fuel with a much higher detonation tolerance like one of the alcohols.

[nissanfanatic]

Originally Posted by jupilerman

Do I read the graph correctly, by saying that 6psi on 10.5:1 C/R is safe?

On a correctly sized turbocharger with an efficient intercooler, 6psi with 93 octane fuel should be very safe. Could prolly even go to 8 if you are feeling frisky. But once again, using higher octane fuel or anti-knock would allow you to run much more. Say you go to 110 octane, you could run 8+17=25psi assuming your turbo and intercooler are efficient at that level. General rule of thumb is one octane point up=one more psi of boost you can run without pre-ignition/detonation.

[jupilerman]

thanks for the swift reply! That confirms what I was thinking. nice finally talk to people who know what they´re talking about.

A pitty my turbo suppliers don´t reveal their compressor/turbo efficiency maps. e.a. they cut back their Garrett GT25 compressor wheel vanes to get compressed air out temperature down.

Is there a anlogue relation between ignition retard (retarding the advance BTDC if you wish) and boost?
I´d like to map my piggy back so that my car is driveable. At least to the RR to do some proper mapping!

thanks,
david

I´m new here, but it seems I´m going to like it!

[nissanfanatic]

It depends a lot on the setup how much you retard timing. On KA24DEs with 9.5:1 compression ratio, we retard approx .5*-.75* per psi of boost.

No doubt the best way to tune timing is to get on a dyno and do trial and error while watching the torque curve. Start safe, advance up until torque begins to go back down.

Some guys also use MSD Boost Timing Master. Works well. I used to use one.

[jupilerman]

Thanks for the rule of thumb.
I use perfectpower´s smt6
wwW.perfectpower.com
you can tune e.a. MAP signal, 4 additional high impedance injectors, ingintion retard/advance. And all reasonably priced (about 400USD I believe) the smt7 can even tune more than that.
SplitSecond www.splitsec.com has some good stuff as well.

About my IC efficiency. In theory efficiency is pretty straightforward. In reality however I have no clue. I have a rear/mid engined car. So plumbing to the front would be deevious and producing too much head loss. I positioned the IC in the wheel arch. Unfortunately only parrallel to the wheel itself against the liner. No other options available. I hope turbulance will be enough to proof at least 60% efficiency.
I´d like to use LM-1 by Innovative motorsports and their rpm convertor which enables 5 more aux inputs, which I will be using to monitor pressure and temp diff. across the IC. What I like about innovative is that you can calibrate output for you sensor. 2V=70F nice!!!
cheers
david

[Reed]

well i dont know much (read as anything) about MGs but here is how we mr2 spyder owners intercool
http://hassproturbo.com/catalog/MRS-Tkit-dtls.html

i have seen this rear mount setup also with some ducting and also with fans attached directly to the IC like a fan on a radiator

[jupilerman]

Wow, nice setups they/you have there!

Low rear IC:
The IC at the low rear isn´t gonna work for me as that´s where my exhaust sits. And just above that my boot ;-)

Top mounted IC:
My car has about the same vent appeartures, but smaller.
Also, according to my workshop manual it seems air is drawn in through the side vents (cool dense air) and exits at the top of the engine compartiment (less dense warm air). Seems logical as warm air is less dense and rises up.
I believe the function with MR2 isn´t any different.
That would mean you get warm air coming into the IC from below.

Have you any measurements on engine bay temp or cooling efficiency (temp-in/temp-out?)

cheers,
david

[Reed]

you can check around spyderchat.com and do some searches for stuff about intercooling. an engine temps.

[jupilerman]

cheers for that !