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Either of those could work. Higher you go the smaller the tuning window becomes. Little bad gas here or there and you’ll be replacing parts. I always error on the lower side.
20lbs doesn’t give us much. 20lbs on a small motor with poor flowing heads isn’t much. 20lbs on a big motor with a nice flowing top end can be a ton of power. All comes down to cylinder pressure. How much you make and where you make it. Intercooling comes into play too.
The other thing that people don’t realize is E85 can vary a ton. I’m not talking about ethanol percentages. The base fuel used to blend it and additives used are the issue in most cases.
So if it’s a race car with a great tuner, great intercooler, and you have a known great consistent source of E85... Then I’d say go for the higher compression. No reason not to. If you’re an average guy wanting a toy. Stick to lower compression and watch out for bad gas.
Either of those could work. Higher you go the smaller the tuning window becomes. Little bad gas here or there and you’ll be replacing parts. I always error on the lower side.
20lbs doesn’t give us much. 20lbs on a small motor with poor flowing heads isn’t much. 20lbs on a big motor with a nice flowing top end can be a ton of power. All comes down to cylinder pressure. How much you make and where you make it. Intercooling comes into play too.
The other thing that people don’t realize is E85 can vary a ton. I’m not talking about ethanol percentages. The base fuel used to blend it and additives used are the issue in most cases.
So if it’s a race car with a great tuner, great intercooler, and you have a known great consistent source of E85... Then I’d say go for the higher compression. No reason not to. If you’re an average guy wanting a toy. Stick to lower compression and watch out for bad gas.
Thanks.
So, all else being equal except going 10.6:1 or 11.12.1...........what is the power difference going to be? Am I leaving a LOT of power on the table going klower compression, or are we just talking 30,40,50 HP on a 1,000 RWHP set up...?
What about the thickness of the gasket, are both just as good or is the more thick gasket going to be more prone to a blown gasket?
Not much power difference at all. Like 2% NA, if that. 1 point in the normalish range is usually worth around a 4% increase. But that’s NA. So if you make 400 NA, 2% is 8hp. Then for each 15lbs you run, add another 8hp or so.
Head sealing is more about the deck thicknesses of the block and head than the gasket thickness or fasteners used. .080 is fine. But factory blocks and heads only seal so well at higher CC pressures. They warp over time no matter what gasket or bolt you use.Alot of that is in the tune and staying away from peak TQ area of the tune.
Not much power difference at all. Like 2% NA, if that. 1 point in the normalish range is usually worth around a 4% increase. But that’s NA. So if you make 400 NA, 2% is 8hp. Then for each 15lbs you run, add another 8hp or so.
Head sealing is more about the deck thicknesses of the block and head than the gasket thickness or fasteners used. .080 is fine. But factory blocks and heads only seal so well at higher CC pressures. They warp over time no matter what gasket or bolt you use.Alot of that is in the tune and staying away from peak TQ area of the tune.
I need to upgrade my heads. I have flat top pistons so I cannot go LS3 top end or I would. What cathedral port heads can work with my flat top pistons? Thats the tough part. My current heads are ported 241's.....hardly even a fair head....LOL
Can you recommend a new head that will fit flat top pistons, thicker deck, cathedral port....and not be $4,000....?
I need to upgrade my heads. I have flat top pistons so I cannot go LS3 top end or I would. What cathedral port heads can work with my flat top pistons? Thats the tough part. My current heads are ported 241's.....hardly even a fair head....LOL
Can you recommend a new head that will fit flat top pistons, thicker deck, cathedral port....and not be $4,000....?
not sure about your engine setup, but mine is a l92 stock crank good rods and flat top pistons with -3cc valve reliefs. I use and really like my PRC ls3 as cast heads, theyre pretty affordable imo i believe the heads and cam kit were $2800. My compression is just over 10 to 1, I use the summit calculator and at first I was getting almost 12 to 1. But I figured out I was using the wrong figure some where, maybe deck clearance icr. I think the PRC heads are really good bang for the buck, but there's tons of options for cathedral or ls3 heads.
not sure about your engine setup, but mine is a l92 stock crank good rods and flat top pistons with -3cc valve reliefs. I use and really like my PRC ls3 as cast heads, theyre pretty affordable imo i believe the heads and cam kit were $2800. My compression is just over 10 to 1, I use the summit calculator and at first I was getting almost 12 to 1. But I figured out I was using the wrong figure some where, maybe deck clearance icr. I think the PRC heads are really good bang for the buck, but there's tons of options for cathedral or ls3 heads.
I thought I can't use LS3 style heads because I have flat top pistons.
If your goal is 1000whp you are on the edge with factory stuff IMO. They will hold awhile with a good tune depending on the loads and gearing. Lots of guys have gotten several seasons at 1000whp on factory stuff. Around 1200 flywheel is where the mains move around a bit, decks flex etc.
I wanna say the AFR’s 245's have 73cc chambers & .750" decks. Aren’t’ to crazy expensive. Could always give it a go with the 241’s for a season and get the “bugs” worked out.
Do you have an ET goal? Depending on weight 1000whp is more than enough for 8.50’s. that’s all the cage I was willing to put in my cars since I drive them too. Safety stuff gets crazy expensive quick after that. Might not even need 1000whp.
If your goal is 1000whp you are on the edge with factory stuff IMO. They will hold awhile with a good tune depending on the loads and gearing. Lots of guys have gotten several seasons at 1000whp on factory stuff. Around 1200 flywheel is where the mains move around a bit, decks flex etc.
I wanna say the AFR’s 245's have 73cc chambers & .750" decks. Aren’t’ to crazy expensive. Could always give it a go with the 241’s for a season and get the “bugs” worked out.
Do you have an ET goal? Depending on weight 1000whp is more than enough for 8.50’s. that’s all the cage I was willing to put in my cars since I drive them too. Safety stuff gets crazy expensive quick after that. Might not even need 1000whp.
I have all this from my old LQ9 we tore down last week.
Callies crank (fresh polish), Diamond pistons (in perfect condition), Compstar rods (perfect condition).
ARP head studs and main cap studs. (stand size, not 1/2" head studs)
CHE trunion upgrade (new upgrade going in)
Gaterman link bar lifters (new upgrade going in)
Level 4 - 4L80E / FTI triple disc 3200 stall
Strange 12 (new custom chromoly drive shaft just went in)
Every suspension upgrade possible for an Fbody.....(I think)
Just installed my offset LCA's
My new LY6 block is in transit from Bishop Engines in Texas. All of my parts of my LQ9 will go into it with a fresh 4.030" bore. The block is coming with 4.020" bore. The machine shop here will be further boring it exact fitment for my Diamond pistons which all measure in the 4.025-4.026 range. Diamond said .004-.005 PTW clerance is best. My LQ9 was a bit sloppy and had .007 PTW clearance.
I will (most likely) never go to a drag strip. Just a roll racer type/high power daily driver.
You say exactly what my builder said, stick with the 241's and get a feel for everything and work out the issues that will arise in the beginning. Then, upgrade the heads, intake and TB for some added power gains. So thats exactly what I'll do. Just ordered the cam, which we changed up last minute before they cut it last week, with Cam Motion. 234/234 .621/.604 115+4A, they're .660 dual springs with Ti retainers.
My builder told me today that he doesn;t quite remember the chamber size on my heads from 14 years ago when he refreshed them, but he thinks they are 68cc. He'll measure them later this week. So I can now figure out a compression ratio to go with.
Last edited by BigBoyWS6; May 25, 2023 at 11:46 AM.
I have all this from my old LQ9 we tore down last week.
Callies crank (fresh polish), Diamond pistons (in perfect condition), Compstar rods (perfect condition).
ARP head studs and main cap studs. (stand size, not 1/2" head studs)
CHE trunion upgrade (new upgrade going in)
Gaterman link bar lifters (new upgrade going in)
Level 4 - 4L80E / FTI triple disc 3200 stall
Strange 12 (new custom chromoly drive shaft just went in)
Every suspension upgrade possible for an Fbody.....(I think)
Just installed my offset LCA's
My new LY6 block is in transit from Bishop Engines in Texas. All of my parts of my LQ9 will go into it with a fresh 4.030" bore. The block is coming with 4.020" bore. The machine shop here will be further boring it exact fitment for my Diamond pistons which all measure in the 4.025-4.026 range. Diamond said .004-.005 PTW clerance is best. My LQ9 was a bit sloppy and had .007 PTW clearance.
I will (most likely) never go to a drag strip. Just a roll racer type/high power daily driver.
You say exactly what my builder said, stick with the 241's and get a feel for everything and work out the issues that will arise in the beginning. Then, upgrade the heads, intake and TB for some added power gains. So thats exactly what I'll do. Just ordered the cam, which we changed up last minute before they cut it last week, with Cam Motion. 234/234 .621/.604 115+4A, they're .660 dual springs with Ti retainers.
My builder told me today that he doesn;t quite remember the chamber size on my heads from 14 years ago when he refreshed them, but he thinks they are 68cc. He'll measure them later this week. So I can now figure out a compression ratio to go with.
Never heard you can't have ls3 heads with flat tops. I think they won't fit smaller than a 4" bore. My last engine was 4.005 and also had flat tops and ls3 heads.
I think he means because he doesn't have the valve reliefs in the pistons. Won't have the PTV clearance without reliefs. Block may have been decked etc?
I’ve got reliefs in my flat tops. Deck height with the old LQ9 that you see below was .020.
Not sure what deck height I’ll end up with after they bore, hone and deck (if needed) my new LY6 that actually got delivered here today.
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Which compression for full time E85..... 
