13:1 c/r on pump gas?
07-23-2010, 05:23 AM
#1
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13:1 c/r on pump gas? ok let me lay out my situation, just picked up an ls2 block, stroker 402 with 10cc domed diamond pistons. with the 66cc combustion chambers on the afr's the compression is appx. 13:1. now the previous owner of the short block claims to have run on pump gas with some kind of tune and a special cam. my plan is to mill the pistons down to 5cc and run a 12:1 ratio on pump gas. the question is what would be required and what are the effects of running either one of these ratios on a street driven car. The cam I plan on using is an ms4, 239/242, .649"/.609".
07-23-2010, 08:54 AM
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its not the 12 to 1 ratio i am so much worried about, im confident a modern fuel injected engine could handle a ratio like this, I just want to know how you could run a 13 to 1 on any engine with pump gas, at least not without taking all the timing out and loading up on fuel.
07-23-2010, 02:55 PM
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The cam should be specifically designed for the compression and head. I don't know that an off the shelf cam that small will work without moving it around a great deal. Then you might end up with less than optimal valve events. We have a 12.5:1 427 with ET LS6 heads that will run on pump gas...
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07-24-2010, 10:02 AM
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the cam was actually bought for my stock bottom end and afr heads, the short block was an after thought that just kind of presented itself. So I guess my next question would be has anyone had any experience with this ms4 cam on higher compression engines?
08-06-2010, 03:34 PM
#11
Heres thing, theirs what works in theory and what actually happens.
418ci flat top pistons, AFR heads, .045" quench, 251/259 camshaft, TR6 plugs, timing @ 20º
SCR: 12.4:1
DCR: 8.5:1
pinging its nuts off at 4000 rpm in 3rd with a load on it
93 octane BP, in Chicago we're supposed to get best quality 93 octane, BP fuel is pipelined from BP's Whiting, IN refinery directly.
100 octane unleaded, fine, made 520rwhp though auto.
I know a few 13:1 LS builds even SBC street cars running 100 unleaded, in Chicago we have 100 octane available
in most suburbs on the pump. If you consider that pump fuel you're fine.
418ci flat top pistons, AFR heads, .045" quench, 251/259 camshaft, TR6 plugs, timing @ 20º
SCR: 12.4:1
DCR: 8.5:1
pinging its nuts off at 4000 rpm in 3rd with a load on it
93 octane BP, in Chicago we're supposed to get best quality 93 octane, BP fuel is pipelined from BP's Whiting, IN refinery directly.
100 octane unleaded, fine, made 520rwhp though auto.
I know a few 13:1 LS builds even SBC street cars running 100 unleaded, in Chicago we have 100 octane available
in most suburbs on the pump. If you consider that pump fuel you're fine.
Last edited by AES Racing; 08-06-2010 at 11:39 PM.
08-06-2010, 08:56 PM
#13
Heres thing, theirs what works in theory and what actually happens.
418ci flat top pistons, AFR heads, .045" quench, 251/259 camshaft, TR6 plugs, timing @ 20º
SCR: 12.4:1
DCR: 8.5:1
93 octane BP, in Chicago we're supposed to get best quality 93 octane, BP fuel comes from Whiting, IN BP refinery directly.
pinging its nuts off at 4000 rpm in 3rd with a load on it
100 octane unleaded, fine, made 520rwhp though auto.
I knew a few 13:1 LS builds even SBC street cars running 100 unleaded, in Chicago we have 100 octane available
in most suburbs on the pump. If you consider that pump fuel you're fine.
418ci flat top pistons, AFR heads, .045" quench, 251/259 camshaft, TR6 plugs, timing @ 20º
SCR: 12.4:1
DCR: 8.5:1
93 octane BP, in Chicago we're supposed to get best quality 93 octane, BP fuel comes from Whiting, IN BP refinery directly.
pinging its nuts off at 4000 rpm in 3rd with a load on it
100 octane unleaded, fine, made 520rwhp though auto.
I knew a few 13:1 LS builds even SBC street cars running 100 unleaded, in Chicago we have 100 octane available
in most suburbs on the pump. If you consider that pump fuel you're fine.
08-07-2010, 07:44 AM
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ok so back to the original question, with the 111 lsa and specs posted above for the ms4 cam im assuming its a higher valve overlap camshaft, what would this do to the engine with 13:1 compression pistons, if it lowers the static compression would it still have problems on the top end?
08-07-2010, 12:17 PM
#17
ok so back to the original question, with the 111 lsa and specs posted above for the ms4 cam im assuming its a higher valve overlap camshaft, what would this do to the engine with 13:1 compression pistons, if it lowers the static compression would it still have problems on the top end?
We've also run a 418ci engine with 12:1 SCR 9:1 DCR and had no problems on 93 pump fuel.
08-07-2010, 09:22 PM
#18
If it helps at all I ran a 388cid sbc with world products iron heads and a mild sollid roller with a static compression of 13 to 1 and it ran and drove fine at 32 degrees of timing but definately ran it's absolute best when id mix 2 gals. of vp c16 fuel and about 20 bucks of 93 pump gas.
08-09-2010, 10:21 AM
#19
FormerVendor
If your engine has very poor VE you can run more compression. This is the opposite of what you want. You want great VE which is what makes Tq and power and the right amount of compression to go alonmg with it and your fuel.
If it's a solid dome have it lathed off. Call Diamond if you are unsure about the piston. If it's a hollow dome you are probably screwed. I wouldn't screw up the engine to try and run higher compression than what your local fuel can handle.
If it's a solid dome have it lathed off. Call Diamond if you are unsure about the piston. If it's a hollow dome you are probably screwed. I wouldn't screw up the engine to try and run higher compression than what your local fuel can handle.
