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11:77:1 Compression on pump gas

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Old Jul 4, 2006 | 10:35 AM
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Default 11:77:1 Compression on pump gas

Yes, this is an opinionated question. So, whats you opinion. Is 11.77:1 to high for pump gas (93) octane?

Thanks in advance

Also, can you double check my math

Bore 4.060
Stroke 3.82
Deck height .007
-2cc dish piston
gasket .060
cylinders 8
head CC 59.45
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Old Jul 4, 2006 | 10:39 AM
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That's a lot of compression. What is your DCR?
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Old Jul 4, 2006 | 11:28 AM
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Isnt the LS7 a 11.5:1 pump gas motor?
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Old Jul 4, 2006 | 11:37 AM
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Totally depends on dynamic compression. You could be running a lazy cam with big duration (like a 240/248 115LSA) and only have 7.8:1 dynamic compression. This would be OK on pump gas. Or if you were running a 220/220 110LSA +4 cam, this might put your dynamic compression above 9.0:1 and the motor would rattle its *** off on pump gas. Again, depends on cam timing. As a general rule of thumb, you can run up to between 8.3-8.5:1 on 91 octane and 8.5-8.8:1 DCR on 93 octane. FWIW, the DCR with the stock '98-00 cam is 6.9:1.
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2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
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2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
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Old Jul 4, 2006 | 11:47 AM
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Pick a cam with a IVC that will put you in the 8:3-8:5 range and you'll be fine.
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Old Jul 4, 2006 | 12:22 PM
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I'm running my 370 cid with ~11.7x SCR and 8.6x DCR on 94 octane (US rating), 98 (RON rating), no issues at 26* timing.
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Old Jul 4, 2006 | 08:03 PM
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what DCR does Pat G's cam put a Stock 00 ls1 at , can I mill my 241's
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Old Jul 4, 2006 | 09:48 PM
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Originally Posted by cws T/A
what DCR does Pat G's cam put a Stock 00 ls1 at , can I mill my 241's
It brings the stock DCR of 7.0 up to 7.9:1. If you mill your heads, that could bring your DCR up to the magic 8.5:1 level.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.

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Old Jul 4, 2006 | 10:14 PM
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Think this combo would pull 400rwhp my stock 241s , milled for 8.5 DCR + your highlift torque cam + fast 90/90
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Old Jul 4, 2006 | 11:10 PM
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Nope your screwed 11.75:1 is all you can do on pump gas.

Bret
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Old Jul 5, 2006 | 09:14 AM
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Originally Posted by cws T/A
Think this combo would pull 400rwhp my stock 241s , milled for 8.5 DCR + your highlift torque cam + fast 90/90
Good question.
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Old Jul 5, 2006 | 09:17 AM
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Originally Posted by cws T/A
Think this combo would pull 400rwhp my stock 241s , milled for 8.5 DCR + your highlift torque cam + fast 90/90
If your car is a 6 speed with all the bolt-ons and a good tune, it should hit 400+rwhp with ease.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.

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Old Jul 5, 2006 | 09:31 AM
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Remember, it's not just dcr that comes into play either. It all depends on the cylinder pressure your motor generates. The lsx manifolds are probably more sensitive to compression considering they work much better in the midrange then the single plain/sheet metal intakes and more time for detonation will be present in the midrange then in the higher rpms. So basically if you have a high rpms type setup (via intake tuning) you can get away with a little higher dcr i'd think. Also, your heads combustion chamber, heat range on the plug, yadda yadda all in the combination will make or break your tolerance for pump gas.

Hell, if you didn't ever go wide open throttle you could probably get away with 13 to 1 on pump gas but as soon as you go wide open, unless your cam is silly silly late on IVC then you're going to have a pop corn machine
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Old Jul 5, 2006 | 11:07 AM
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If I remember correctly on my current set up cylinder pressure is 200.
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Old Jul 5, 2006 | 11:53 AM
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I went 11.8 to 1 on my new build, not concerned with it being too high one bit. It will be fine.
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Old Jul 5, 2006 | 12:31 PM
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Originally Posted by Taphee6
If I remember correctly on my current set up cylinder pressure is 200.
Yeah, but that's during a compression test though. Now think about all the effects that intake tuning and exhaust tuning cause at different rpms on cylinderfilling resulting in more or less pressure in the chamber, which can't be measure with a compression test
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