high compression turbo engines..

[:madaz:]

what are the pros and cons of doing a high compression turbo engine?
for example, i have a very efficient head( i state this because i am of the understanding that a better flowing head helps with avoiding detonation ) and was going to get an engine built with lower compression (8.2:1) and run more boost. but as im not aiming for huge power, more of a snappy, sharp engine, i thought it may be viable to run more compression (say 9:1 or more) and run less boost to get more response and crispness with the engine.

does tunability completely dissapear when your dealing with high compression turbo engines? I imagine it will be important to have a good ignition system to avoid detonation? how much is the amount of boost you can run hindered? is there any other factors to consider when aiming to build a high compression turbo engine? thanks in advance for any help or info!!

cheers

[Ako]

Higher compression of engine = Higher IQ required by tuner

In mega simple terms - you can pull more power and response out of it, but you'll have less leeway for "trial and error" on the tuners part.

Lower compression = safer proposition if you're not 100% confident in the person pushing the buttons.

Just as one example - evo 1-3. The 1 and 2 run 8.5:1 comp, and you can safely crank the boost to 20psi with a big pump and make good numbers. Evo 3 you have to play things safer as they run 9.0:1 comp, but you can pull marginally more power out of an identical setup than the 1 and 2 - but the monkeys who run them on 20psi wonder why it died.

[:madaz:]

haha yes i see...

i do trust the tuner whole heartedly, its bob homewood from hitech motorsport and he has very good feedback fom everyone ive asked.

with the example of the evo's, id have thought its not so much power thats concerned when raising compression, although it will be an advantage, its moreso the torque and response is it not?

so in conclusion, its possible to get good results from a high comp. setup as long as the tuner is switched on and good at what he does, and modifications are taken out to try and lower the detonation onset.

[slighty_sykotic]

If I was to rebuild my 4agte again, I would go for a 9:1 ratio, at least. (got a 8.1:1).

Having a higher compression motor makes for a nicer car to drive really, its not so much a "on and off" car, makes it smoother to drive.

And yeah, agreeing with above, can get more power out of a higher compression motor, but you just got to be more careful.

--Sykotic

[Mr Revhead]

but as im not aiming for huge power, more of a snappy, sharp engine

that says it all really... compression is your freind.

what kind of engine is it? and whats it for? ie road use? track only?

[:madaz:]

its a mazda bp8t (1.8l turbo) engine, il be using it for street and track use only, no dragging, and will be doing lots of long distance driving. i think these engines are pretty resistant to detonation as it is so with a bit of luck will perform well with higher compression!

[bluemaumau]

dont get serious without thinking bout your driveline

[Mr Revhead]

haha yeah the engine isnt your main problem!

[CAMB01]

I'm building my 4AGTE with 9.0:1 compression.

[Caveman]

Ive built a 4age turbo with 10.3:1 compression. Will see how it goes and how long till it pops

[Drifter4ag]

once you get over 9.5 you will run into issues with detonation at any decent boost ... ideal comp ratio is 8.5-9.5 for power and response ...

but at the end of the day .. only 3% actually hit the track be it drag or circuit so best is just go with 9.0 & a moderate boost level.

[Caveman]

once you get over 9.5 you will run into issues with detonation at any decent boost ... ideal comp ratio is 8.5-9.5 for power and response ...

but at the end of the day .. only 3% actually hit the track be it drag or circuit so best is just go with 9.0 & a moderate boost level.

What would you call a decent boost level? I was going to run 8psi on 10:1 comp and rebuild with forgies at 9:1 and run 14psi a bit later

[Drifter4ag]

Decent boost is 20+
10.0:1 8psi is probably ok with efficient turbo and cooler. just gotta watch the timing on the engine otherwise POP
on 9.0:1 you can run great amounts of boost ... 15-20-25 no worries as long as ecu good .. pistons good .. rings good ..bearings & rods good