11.0:1 306 vs. 9.0:1 306

[Nitrous Al]

I asked a similiar question a few weeks ago, but I still wonder about an engine's compression ratio. It's taken me a while, but I almost have all the parts ready for my engine rebuild. I try to learn as much about automobile engines as possible. Now I just learned the 200 hp Acura RSX engine (K20C) made 170 whp with 11.0:1 compression inline four. If I bump my 306's compression ratio to 11.0:1 instead of 9.0:1, how much more power will is see going to the rear wheels?

[Stang Runner]

Not sure on how much more it will do but it will help you out But if you wnat to do a Blower 11:1 is a bit high for Boost. Or if you do you will need Race gas all the time with it.

[302 LX Eric]

Great question! Where's PKRWUD when you need him?

BTW - if you are planning on boosting the motor, I think 11:1 is way too much. 9.0:1 or lower would be more ideal.

E

[red82gt]

It would depend a lot on the airflow requirements, combustion chamber shape, camshaft, etc. If you put in a cam with a lot of overlap, the extra compression would help to restore the low end torque and would allow the motor to get into the powerband for the camshaft. I think it would be worth about 20 ft/lbs of torque at the low end but I'm not sure how much up top.

I think 11:1 would be a bit much for a street motor, even with aluminum heads. You'd have to run probably at least 93 octane gas and hope you don't run into a bad tank. If you have emissions testing, it may be difficult for an 11:1 306 to pass.
My car has just over 10:1 with iron heads and if you use less than 91 octane it knocks and pings like a pig.

I'd go with about 10.5:1 or even 10:1 and make the power with more airflow.

[PKRWUD]

red82gt's advice is very good. 11:1 pistons would very noticably increase your power, but you have to have the fuel to run them. 93 octane wouldn't do it. Also, as mentioned, if you ever plan on adding forced induction, forget 11:1's. If a blower isn't in your future, 10.5:1 is the highest you can expect 93/94 octane to handle, and would provide alot more torque (acceleration) than 9:1 pistons. You should only do so if you have a cam (and intake) that is designed to run with compression that high.

Take care,
-Chris

[PKRWUD]

Originally posted by 302 LX Eric
Great question! Where's PKRWUD when you need him?


Hehe, it's racing season, man. :D I'm not going to be around as much as I used to. I'm working up to 14 hours a day, 6 days a week until November. I try to check in every chance I get, though!

Take care,
-Chris

[Nitrous Al]

Originally posted by PKRWUD
red82gt's advice is very good. 11:1 pistons would very noticably increase your power, but you have to have the fuel to run them. 93 octane wouldn't do it. Also, as mentioned, if you ever plan on adding forced induction, forget 11:1's. If a blower isn't in your future, 10.5:1 is the highest you can expect 93/94 octane to handle, and would provide alot more torque (acceleration) than 9:1 pistons. You should only do so if you have a cam (and intake) that is designed to run with compression that high.

Take care,
-Chris

Thank you for the answer, Chris. I understand what you're saying, but how is Acura and other import makers building "everyday cars" with 200 hp, 11.0:1 compression 2.0 L inline fours? Don't these cars run on 89 octane, get 25 mpg and their smog legal? How do I build my 5.0 306 motor to totally blow away their numbers?

[PKRWUD]

I'm not aware of any car that has a 200 hp engine with 11:1 pistons, that get's 25 mpg and runs on 89 octane, smog legal or not. Keep in mind, though, that an engine with aluminum head(s) can handle higher compression than one with iron head(s) (usually .5:1 higher compression). Still, 11:1 pistons and 89 octane gas isn't going to work, unless you live in Denver (or some other town with an elevation of 6000' or more).

How do I build my 5.0 306 motor to totally blow away their number

Screw numbers. Numbers are for accountants. Just worry about blowing them away, period.

If you want to really piss off some know-it-all ricer, go buy yourself a '78-'79 Ford Fairmont Futura w/ a straight 6 cylinder in it, and swap in a bone stock 302. Their actual weight is close to 2300 pounds. You will eat them for lunch.

Take care,
-Chris

[Nitrous Al]

Originally posted by PKRWUD
...an engine with aluminum head(s) can handle higher compression than one with iron head(s) (usually .5:1 higher compression)...

Chris, I hope I'm not bothering you. You know exactly what you're talking about. I have a pair of Edelbrock 6037's with stage 2 port work. I think I might sell them and get Victor Jr's. (I have a machined OEM 5.0 block and boxes of speed parts.) But back to my questions, what #'s can I expect with 93-94 octane in a 11.0:1 compression, naturally aspirated 306 5.0 motor with a custom "Ed Curtis" cam, Edelbrock heads, a Performer RPM intake, 70mm TB, etc. Nitrous oxide will be run ocassionally. I'll "pay" for my emission stickers and run a H-pipe with cats, but I want an 11 second street car. Will a 11.0:1 306 make 400 hp or more?

Thanks again, Chris!

[PKRWUD]

Al-
I'll let you know if you become a PITA. ;)

The one thing I really hate doing is estimating numbers for someone. Especially 1/4 times. There are so many factors involved, it's just more of a headache than it's worth. BUT, with a good driver on a cold day, with the appropriate gears and suspension modifications, and an engine that is quality built and tuned, and includes the parts you mentioned, and with 94 octane gas AND an octane booster, sub 12's are not impossible.

My personal opinion? Get a blower, and build up the bottom end. The easiest, most cost effective way to build an 11 second street car is with forced induction. It will be much more streetable, as well as dependable. The old saying ("there's no replacement for displacement") is true. That's all a blower is doing; increasing your displacement. What's more streetable than a 306 that becomes a 510 when you get on it, but returns to being a 306 after the race? Not much.

Take care,
-Chris

[Nitrous Al]

Chris, I'm going to be a PITA. The '02 Import cars are making about 200 hp with a naturally aspirated 2.0 inline four. That's about 100 hp per liter. So if I build my 5.0 306 motor with the same "tricks" I should see about 450hp to 500hp, right? I talked to a friend with a 10 second Mustang and he said to "Mill my heads to a get a higher compression ratio, install a larger cam and I could see another 50 hp." Is this correct? Any tips on making power NA? How are those Import cars making so much power?

[Killercanary]

Nitrous Al- hopefully soon, my dad will have an answer to your question. Currently Ed Curtis is milling, porting, and flowing my dad's entire Holley Systemax II kit, and is custom grinding a cam for it. These parts will make their way onto a new production 302block with stud girdle, and SRP (probe) high compression pistons, stock rods and crank. Out back he's ditching the 3.73's for a set of 4.30's, and he just installed an 8 point cage. Last year with a box stock holley kit, it went 12.7 at 107 on ET streets. This is in his 91GT. We're hoping for mid to high 11's with the above work. The pistons supposedly shipped from Ed this week, so the short block will be assembled shortly, and Ed is finishing up the heads hopefully this weekend.

I was told on a 325FWHP engine, a bump of 1 full compression point is worth in the neighborhood of 12FWHP, but you know how that goes, there's a lot of variables as was mentioned above.

[Nitrous Al]

Thanks Killer!