im building a all motor now. and i ordered the 12.8 to 13.2 pistons is that okay for pump gas or should i go lower

 

i'm right at 12.8~13.0 on pump gas.. doing well for the last 8 months.

 

No that's not okay....That's too high for pump gas bro.......I suggest 11-12:1 compression on pump gas....If i'm correct the maximum compression for pump gas is below 11.5 compression, but I've seen 12:1 on 93 and does okay....

But IMOP i wouldn't go above 12:5 compression on 93 pump gas......

 

there's a lot of controversy about this subject. lots of people run 13:1 or even more on pump gas, but it's possible that they have to pull so much ignition timing that with all else equal, they'd be making more power with 12:1 compression...

 

13.0+ compression can be done on pump gas, but in most cases you have to pull timing which in turn equals less power! you can make more power with less compression in a sense:p but throw race gas in the mix and that's a different story! I like 13:1 compression street motors, the few setups that I have seen and rode in pull like crazy and the throttle response is just plain stupid. nicest setup yet was my boy's
82mm ls/vtec with wiseco 8cc pistons, pro 2's, egay 4-1 it only put out like 201whp on a dynojet with pump gas, but it was really fast for what it was. It barely ran even on pump gas, if you put race gas in it the idle would change and it was like a whole different car! I say do it if you don't care about having a tempermental street car, but my friend rarely drove his, and you could really tell when you got a bad tank of gas. have fun with spark knock!

 

12:1 is the highest i would say go and if it was my car i wouldnt go that high lol for my personal car 11:5.1 is the highest i would go im at 11:1 right now

 

I agree with that completely. All it takes is one bad tank a gas, and you'll be getting back to the drawing board.

 

Compression ratio is directly related to the RPM at which peak torque is made. It has nothing to do with detonation or whether you can run pump gas.

You could have a 20:1 static compression ratio and still run pump gas.

BUT only if your intake valves close late enough, which means a cam with a lot of duration.

The compression ratio that is important is the effective compression ratio. This is the compression ratio measured from the point the intake valves close. Your engine does not start compressing the air/fuel mixture until the intake valves are closed.

If someone has high compression and their engine is detonating it is because they don't have enough duration on their intake cam (assuming its tuned correctly).

With that ~13:1 static compression ratio you are going to need to rev it to at least 9000 rpm to get any power out of it.

 

This is a really long-winded way of saying "yes, in the real world, 13.2:1 is too high for pump gas".

 

lol well its 12 to 13 is what there rated at. my tuner says it will be fine just get good gas like bp or shel

 

running over 13:1 cr on 93 octane here, made 202hp on 93.

https://honda-tech.com/forums/all-motor-naturally-aspirated-44/my-81-5mm-build-2661474/

 

Looks like they were launching the car on the dyno..??

 

13 points is ok, as long as your not running stock cams

 

13:1 engines making as much power as 12:1 engines.

EDIT: just read that you used 110, which isn't pump gas.

 

just run it at 11:1. if you are on honda-tech asking if you can do it, then you shouldnt do it.

 

I made 202hp on 93 octane and 214hp on 110 octane, I just didnt post the 202 graph and info.

 

8-10 years ago, I was building all my street B series motors at 13:1 - 13.5:1 compression but I later realized I could make the same power (and sometimes more) at 12.5:1 compression. And its safer, with more room for error.

 

yes

 

I love these threads, Just run Pro 3's and 11:1 thats what all the guys making 200 whp are doing.

And the whole thread is based on the pistons saying they are 12.8-13.2:1. If it is CC'd it won't be that high. Trust me.

 

You cannot run 13:1 on stock cams, if you can't run it at 13:1, your not using the right parts. ALL of these are at least 13:1 cc'd........running on 93 octane.

84.5 x 89

85 x 95

84.5 x 92

81.25 x 89-This is my car, and it has 76,000 miles on it........It makes as much torque as a lot 2 liter motors, compression is your friend :-)

81.25 x 77.4- 12:1 tuned on 89 octane.......

 

you actually only get 2-4% more power by raising compression by 1 point(10-11 or 12-13) so on a 200hp engine at 12:1.......13:1 would only get you 4-8hp............consider the lower piston-valve clearance, the higher risk of detonation, and the fact that on pump gas......13:1 has no real advantage over 12:1..........id say its a waste of money and too much risk. AND you can still run 12:1 tune it on pump gas, and have a tune for race gas and youll see gains too.

just for some comparrison information........the porsche GT3 RS comes from the factory with 12.2:1 compression last year it had 12:1.............the difference between the years is the engine is larger(3.6l vs 3.8l) and last year had port fuel injection vs this years direct injection.

port injection injects the fuel into the intake air before the valve, the valve closes and the air/fuel mixture is compressed.
direct injection injects the fuel directly into the cylinder precisely before the plug fires.........which means the fuel isnt compressed with the air(and as things are compressed they get hot).......which is what causes detonation.

direct injection also runs at VERY high pressures which improves the fuel atomization when its injected...........further decreasing the risk of detonation.

direct injection is also what allows recent turbocharged engines to run high static compression(gti 10.5:1 and 15psi on 93, mini cooper S 10.5:1 with similar boost)

none of this really applies to the OP......but its good information anyways.

 

run lower compression if u gonna be dd it alot.

 

I do not understand this philosophy. My car gets 30mpg and has been doing so for 75,000 miles. Its all in proper parts selection and TUNING. Why do people waste their money "building" a motor with no compression? When you spend money on a build don't you want to get your money's worth. But yet these same people complain when their setup doesn't make the power they think it should.

 

well like i said, 1 point of compression is good for 2-4%......the gain is not worth the risk IMO.

and id hardly say 11 or 12:1 is "no compression"

 

The ONLY risk is getting bad gas. 12:1 works great with T/R cams. The gains are larger than that. Not being a dick, just stating facts based on my personal experience.