comp 2 high for 91 oct?

Posted By: cudaben1968

comp 2 high for 91 oct? - 11/19/09 01:57 AM

im rebuilding a little 4 cyl engine and was looking at using the stock style replacement pistons that will give me a compression rating of 10 to 1, but for a few bucks more i could get it up to 11.4 to 1. is this street-able with 91 octane? it will be a daily driver and gets lots of abuse / use. The engine has a knock sensor that will pull out timing till the knock goes away, but i don't want it to have to pull a ton of timing and kill performance. I know a thicker head gasket would help but then i lose some quench... so is 11.4 to 1 ok?

Posted By: BobR

Re: comp 2 high for 91 oct? - 11/19/09 03:01 AM

Quote:

im rebuilding a little 4 cyl engine and was looking at using the stock style replacement pistons that will give me a compression rating of 10 to 1, but for a few bucks more i could get it up to 11.4 to 1. is this street-able with 91 octane? it will be a daily driver and gets lots of abuse / use. The engine has a knock sensor that will pull out timing till the knock goes away, but i don't want it to have to pull a ton of timing and kill performance. I know a thicker head gasket would help but then i lose some quench... so is 11.4 to 1 ok?

Iron or aluminum block/heads?

Posted By: cudaben1968

Re: comp 2 high for 91 oct? - 11/19/09 03:06 AM

aluminum both, dohc

Posted By: ahy

Re: comp 2 high for 91 oct? - 11/19/09 03:15 AM

If everything is perfect and if the knock sensor works it may hold together at 11:1 but even then you could loose power and economy if the spark is retarded frequently. If everything isn't perfect including the gas it will fail early. I'd stay with the stock cr.

Posted By: HotRodDave

Re: comp 2 high for 91 oct? - 11/19/09 03:20 AM

What kind of motor?

Posted By: HotRodDave

Re: comp 2 high for 91 oct? - 11/19/09 03:26 AM

Probably a Honda since no mopar ever came with aluminum block and head and DOHC. No one hot rods a toyota. It could be a nissan but few people hot rod those either.

It depends on the cam timing and quench, also a Honda has a very efficent combustion chamber, kinda like a hemi. Many newer motors work wonders when it comes to compression, my dads geo-metro has very high compression and short cam timing and will blow 200 PSI on just about any compression tester but it runs fine on 87 octane.

Posted By: cudaben1968

Re: comp 2 high for 91 oct? - 11/19/09 03:59 AM

it is a honda, i have talked to a few engine builders in my area and they all say different things.... but none of them really speaclize in imports. mainly they do the super rare and powerful sbc...

the stock motor actually runs 10.2 to 1 and it ran just fine one 87, say about two 10ths lost in the quarter but nothing major. (when its running in the high 13's whats a few tenths???)
what about with adjustable cam gears?

Posted By: HotRodDave

Re: comp 2 high for 91 oct? - 11/19/09 04:47 AM

If your building a honda motor for a hot rod you are probably going to bigger cams, bigger cams are more forgiving of compression. You will be fine with that much compression.

Posted By: cudaben1968

Re: comp 2 high for 91 oct? - 11/19/09 05:50 AM

im actually sticking with the stock cams, the car ran high 13's in a close to 3000 lb car, it burned a bit of oil. so i figued i'd put new pistons and rings in yes overbore too... its now going in a car weighing close to 1000 lbs less at just over 2000 lbs. hoping for a bit more power would like to see 200 at the front wheels. o well, maybe ill just get a thicker head gasket.... thanks guys

Posted By: BobR

Re: comp 2 high for 91 oct? - 11/19/09 02:01 PM

Might be a bit dicey with the stock cam. You could build it then pour a little of this stuff in when you race it. I've used the unleaded version and it works well.

http://torcoracefuel.net/pro-accelerator.html