8:5:1 or 9:0:1?? Searched.......

[SHIEF]

I'm going to start my KAET engine build up soon. I'm stuck inbetween these 2 compression setups. I'm shooting for 400-450hp in the end (I think ) on a car I'll drive a few days out of the week and to the 1/4. Currently I'll be running a T3/T04e 50 trim because I already bought it before I decided to build the engine, so I'm gonna see what numbers I can get out of it. So which one should I go with? I'm kind of leaning toward the 9:0:1, but I'm not 100% on that. Any info is appriciated.

[:: orion ::]

It makes very little difference...maybe 10-12rwhp at that HP level.

It's about 4% per point increase...but the benefits of the higher compression is better off boost driveability and response, and spool.

But you're talking about half a point...I'd bet you could build 2 identical motors, but one at 8.5 and one at 9:1 and not know the difference.

That being said, I'd do 8.5:1...b/c the pistons are readily available, and the margin of tuning error is that tiny bit larger as compared to 9:1.

- Brian

[SHIEF]

I plan to bore the cylinders 10-20 over so readibility isn't really a concern on the pistons. As far as the spool time, how much of a difference are we talking based on that turbo do you think? If nothing huge then I could see your point on having the extra space for tuning with the 8.5 pistons, and maybe some extra space for boost as well.

[Nismoguy]

Hey buddy I have some crower rods and cp 9:1 pistons .020 over if your interested.... thanks

Nick

[SHIEF]

I'll keep that in mind Nick if I go 9:1, but I think I'm now leaning toward 8:5 or 8:6.Other opinions?

[Projex240]

9:1 is more than the power increase over 8.5 to one that just 10-12--it also helps spool time immensely and will make the car more responsive on the street. kind of like the difference is lowering the comp on a stock motor--youll lose not just power--but response, which will make the car more fun to drive as well as giving it a faster feeling due to response. Your timing could probably be left the same as it would for 8.5 to one if you are going witha plug and play like JWT. The increase in comression isnt enough to where you will be at a detonating point unless you try to push the boost to high without race fuel.

Good luck--BTW--im going 9:1 --its more important to me to have awesome response along with good power than just having the good power--but dont worry--8.5:1 is still just as torquey and drives just fine.

-Josh

[SHIEF]

Hey Josh, how much of a spool up difference are we talking in rpm say using that turbo? I mean can I get to that 400-450hp mark using those 9:1 pistons and no race gas, but possibly some water/alcohol injection if needed?

[Projex240]

About the spool, it may see an increase of about 200-300 rpms. It will depend heavily on what cams you have. I suggest crower cams. They have a custom set of cams the\at they will grind for you out of bare cores(no regrinds) for only 400, and they will make good off boost power as well as on boost power. Jwt would be my second choice--though i have seen a few people that may be losing power due to the overlap. Use the sprockets of you get JWT cams. It doesnt seem like much, but the biggest difference youll see is off boost driveability(talking about spool up). The lag wont seem so laggy if you know what I mean. Picture an all moter ka with no boost---its alright--and the driveability is ok as its not sluggish due to its 9.6 :1 comp ratio--now picture the same car with no boost and 8.5 :1. Thats the difference. But its all about preference. The big power guys--the ones you dont see on forums much--they run higher then 8.5:1 for the comp gains and power and off boost response. More response = faster car almost every time.The alky question--alky and/or water injection make pump gas as resistant to detonation as race fuel is. Itll be like having race fuel in all the time(and its a HELL of alot cheaper). Alky injection is another one of my projects. I plan to have an alky kit on the car when the built motor is in. The one I am looking at is a real steal, and has safety features such as low alky warning light, cut off, and vaccum/boost controlled spray volume. Ill have programed or setup to come on at 12 lbs on the street..BTW--this aint easy---450 to the wheels is no joke. Alky, race fuel or both--youll still have a tough time with it. Ask klatter--hes had a few stumbles here and there--but he got them worked out. He makes the power your looking to make.good luck,

Josh

[SHIEF]

Hey Josh remember this will be a KAET (sohc) and not a dohc. So does that 9:1 compression still sound good? I mean being that the sohc is 8:6 if it's a earlier. The engine I'm going to build is out of a 90 so it should be the 9:6. I haven't really looked for a sohc cam but PDM seems to have a decent/not radical street cam. Yeah let me/us know how that alky kit turns out. I know 400-450hp is no joke, people come on here all the time saying that they are looking to make 1000hp and such. When people have no idea how to get there, and more or less keep it streetable. 400 consistant hp is near the edge as it is.

[Projex240]

even as sohc--youll still notice the difference if offboost driveability. I wasnt aware about it being soch though--gues i missed that--the dam grinds are upto you of course. If pdm has a good cam, then give them a call and talk to don(hes a prick though) and see what his results are.The only reason i havent bought much from pdm is that they are 1) into all motor cars as of right now, and 2) they are too expensive on everything.If you want a cam--call up bria crower and crower cams and have him make you a custom turbo cam--itll be better than what pdm offers. Plus--you can talk to him(the same guy who make the cam) and not just a sales person. The odhc cams are 400, so the sohc cam would probably be cheaper.

_josh

[SHIEF]

Ok so you'd recommend going with the 9:1 even with the sohc based on what we talked about right?

[Projex240]

Yep--it doesnt really matter whether thats sohc or dohc. The compression of the motor is independant of the head design.As long as you order the correct pistons for the soch motor to be 9:1 then your fine.

[illspace]

I didn't read the whole post, but to clear something up, higher compression does not equal quicker spool up. The higher compression just gives the illusion of a quicker spool, because of the better off boost throttle response. I have heard this from quite a few experts.

[Projex240]

Higher compression DOES give you less spool time. On a stock compression motor, youll see about a 300-500 rpm spool up difference. When you lower the compression, you lower the air flow amount. I have seen people gain power by building the motors, but get worse spool due to the comp being dropped. ANd yes--that was actually my point, even if the spool is only minimally affected, the off boost driveability will be better anyway, thus making it a faster responding car.

[TrunkMonkey]

Higher compression DOES give you less spool time. On a stock compression motor, youll see about a 300-500 rpm spool up difference. When you lower the compression, you lower the air flow amount. I have seen people gain power by building the motors, but get worse spool due to the comp being dropped.

actually, a higher compression ratio will not increase spool. in fact, high compression engines produce less exhaust gases than their lower compression counterparts

-demetrius

[SHIEF]

actually, a higher compression ratio will not increase spool. in fact, high compression engines produce less exhaust gases than their lower compression counterparts

-demetrius

That is true, but only because there is less space inside the cylinder.So BOTTOM LINE.....9:1 is probably the best choice for around 400hp...

[TrunkMonkey]

That is true, but only because there is less space inside the cylinder.

to be more specific, since the combustion chamber is smaller, the intake charge and fuel is compressed tighter resulting in a more complete burn when it is ignited. the more air/fuel that's burned in the combustion process, the less exhaust that's left.

-demetrius

[SHIEF]

to be more specific, since the combustion chamber is smaller, the intake charge and fuel is compressed tighter resulting in a more complete burn when it is ignited. the more air/fuel that's burned in the combustion process, the less exhaust that's left.

-demetrius

I didn't want to get all technical...for people like myself, I'd say that then confuse myself with what I just said

Demetrius....would you go with the 9:1's as well??

[TrunkMonkey]

Demetrius....would you go with the 9:1's as well??

yup.

-demetrius

[Projex240]

shief--look at the post where ivan at sp racing made like 400 to the wheels on a tock block 240--thats 9.6:1--and get this--on only 16 psi.Higher compression with boost yields more power just as reliably with proper tuning.

That doesnt mean to go build a 11:1 motor though--heh.

[topsecret76]

Hey nismo guy I may be interested in your crower rods and cp 9:1 pistons. please email me.

[email protected]