newbrian

I have an 1st gen small block that is 12.1:1 compression that I run on pump gas. I Run conservative timing and have run 11.89 @ 118 in the quarter with it. It has 49 cc chambers with steal shim head gasket and flat top pistons. I know it will do better times in the quarter but i have traction problems off of the line. My 60 ft time was in the high 1.70s. This leads me to my current build a lq4 402 stroker. I was planning on trying for 11.7:1. Does this seem impossible on pump gas with fuel injection. I will use a cam that will get my dynamic compression below that of the sbc in the camaro. I want keep the compression up to mitigate the low rpm torque losses due to the cam. I am currently on the fence on the compression. I may play it safe and go with flat tops and 11.1:1. What do you guys think?

Pro Stock John

iTrader: (34)

I had a 422 cid iron block stroker in 2000 and it was 12.2:1. But I ran conservative timing and the cam profile will help/hurt as well.

newbrian

I am planning on running the comp cams xr275hr-12. From what I have read so far it looks like torque will be higher every where on the curve vs stock cam. As long as torque is higher I should be able to maintain gas mileage. It may even pick up some since the torque is higher, in theory it would mean the engine is more efficient. I guess I will find out. I should also be ok with stock converter as the recommended range on the cam is 2000 rpm on the bottom end. I have found the truck doesn't run under 2000 very often with 4:11 gears. I am not to concerned about around town mileage anyway. What I can't afford is 10 mpg on a long trip. I am usually over 2000 at highway speed. If I do have to change the converter it shouldn't affect mpg on highway due to lockup.

The1N_only

iTrader: (7)

For whats its worth im sitting at 12 to 1 and I run 26 degrees of timing around peak hp and 20 at peak tq. 12.5 to 1 seems to be the limit on 93 octane and be able to run a decent about of timing. Your cam does play a decent roll as it affects your dynamic compression.

Where the converter will come into play is keeping you from pushing through the brakes when you are stopped.

newbrian

Thanks for the info. I decided to go .030 over so I had to go flat top. The domes would have put me near 12.4. I would be willing to risk it on a toy, but can't afford it on a daily driver.

03EBZ06

I have 11.7:1 RaceTech pistons in my 416. I have run the 247/255-113 cam and a 204/218-117 cam in this motor. With the larger cam, 22 BTDC. With the smaller cam, 21 BTDC. It wasn't "that" much of a diff in spark control, except midrange needed about a 2 deg reduction. The real trick is the right plug heat range. My engine uses 91 octane Kalif gas and on race day a splash of 110.

sman

iTrader: (4)

6.0 running 12.1 here, timing around 26 IIRC. Run anywhere from 91 to 94, I buy the highest available at whatever gas station I stop at happens to be. Was given specific instructions from the tune NOT to get anything less than 91 though.

1972chevyls1

How is you fuel mileage with the higher compression?

newschool72

iTrader: (12)

Higher compression "generally" gives better fuel economy because the engine is more efficient . Notice I said generally, because there are many things that contribute to good fuel mileage .

1972chevyls1

I'm trying to get max HP and keep it street able with some what good milage.

427zm

iTrader: (9)

I'm in the process of an ERL 434 LS7 build that'll be 11.8-12.1 static and I plan on running pump. Sure hope I'm safe when's she's together! I don't want to be forced to run E85.

N20zuki

Comparing a LS to a Gen I is kinda not going to be the same, chamber design and head material have a lot to do with detonation in a GENI as well as cam profile. With a GENI you need to watch what your dynamic compression is almost more important then static compression. Honestly I have never heard anyone ever talk about dynamic compression when it comes to cam selection on this site with a LS series lol.

I have seen people with 12.5-13.1 with a LS motor on pump gas... I would shoot 12.1-12.5 to be safe.