lq4 whats the highest compression i can run on pump gas?
05-24-2012, 02:07 PM
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lq4 whats the highest compression i can run on pump gas? I have a LQ4 what's the most compression I can run on pump gas? I want it around 12.1 or 11.6.1 all naturally aspirated motor. Punched out 30 over 317 heads mast intake 1000 cfm carb, roller rockers, head ported and polished, race valve job I need some help I really want to run 12.1 I have access to 110 octane, but I'm worried on can I drive to street races and get groceries ???
05-24-2012, 02:33 PM
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The old rule of thumb is 10:1 with cast iron heads and 11:1 with aluminum heads on 91-93 Unleaded I'm sure with a good camshaft and some good tuning you can push that 11:1 number slightly. We are lucky to have access to 93 here in the Midwest and that helps things a bit. However I think 12:1 is a bit much without at least mixing some race fuel with pump gas.
05-25-2012, 01:05 PM
#3
The old rule of thumb is 10:1 with cast iron heads and 11:1 with aluminum heads
With today's technology, you can safely push 11.6-11.8 on pump gas and not have a problem with the right setup and tune.
Then there's always E85, which is also pump gas and you can increase the compression even more past the high 11s safely.
05-25-2012, 03:20 PM
#4
Clearly, we don't live in the 70s anymore. 11:1 and higher is what several production cars come with...not all of them are even required to run 93.
With today's technology, you can safely push 11.6-11.8 on pump gas and not have a problem with the right setup and tune.
Then there's always E85, which is also pump gas and you can increase the compression even more past the high 11s safely.
With today's technology, you can safely push 11.6-11.8 on pump gas and not have a problem with the right setup and tune.
Then there's always E85, which is also pump gas and you can increase the compression even more past the high 11s safely.
06-01-2012, 04:25 PM
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Timing and the air/fuel ratio plays a factor when it comes to running higher compression. Car manufacturers are getting away with more compression by turning the timing down a little which causes the piston to be driven down by the flame propogation a little bit later thus creating less cylinder head pressure which causes less chance of detonation. This is why race gas helps. You are able to add a few extra degrees of timing for the ignition event on the compression stroke which causes a much tighter explosion which will drive the piston down with more force and more pressure. Also having a richer air/fuel ratio will help because when its running a little lean it slows down the burn causing temperatures to rise which can cause preignition or uncontrolled explosion of the atomized mixture. You might be ok with 12:1 compression but on 93 it might detonate so you might have to turn your timing down until you're at the track running 110 (which isnt as easy as simply rotating a distributor clockwise anymore)
