Quench vs Timing question
Quench vs Timing question I'm probably splitting hairs here, but I want some input. I've got a 430" build with PRC LS7 heads (70cc chamber), cam is a Cam Motion 243/259 113.5+4, I'm in California with 91 octane. Callies compstar stuff with Wiseco flats.
Option 1: LS7 gasket 4.150x.051.. compression of 11.66.. quench of .044
Option 2: Cometic gasket 4.140x.045.. compression 11.84.. quench of .038
Which one?
Option 1: LS7 gasket 4.150x.051.. compression of 11.66.. quench of .044
Option 2: Cometic gasket 4.140x.045.. compression 11.84.. quench of .038
Which one?
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I'm probably splitting hairs here, but I want some input. I've got a 430" build with PRC LS7 heads (70cc chamber), cam is a Cam Motion 243/259 113.5+4, I'm in California with 91 octane. Callies compstar stuff with Wiseco flats.
Option 1: LS7 gasket 4.150x.051.. compression of 11.66.. quench of .044
Option 2: Cometic gasket 4.140x.045.. compression 11.84.. quench of .038
Which one?
Option 1: LS7 gasket 4.150x.051.. compression of 11.66.. quench of .044
Option 2: Cometic gasket 4.140x.045.. compression 11.84.. quench of .038
Which one?
.038 is going to be a slight bit more detonation resistant, but you're not even too high on compression with that big of a cam anyways, plus the aluminum block will grow...Cometic would be preferred, but likely you'll never see a difference between those two options.
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Option 2 would be more detonation resistant, but more apt to detonate with the higher timing? Lol edged sword here... I just want it to be able to handle decent timing with the pump gas. If there's no real difference in either option I'll go LS7, since the gaskets are quite a bit less expensive.
Go for the LS7 if cost is an issue, it will be fine either way.
Option #2 for sure. I'm running 11.56:1 and about a 8.96 DCR(baby cam) with a .033" quench. That's the tightest I'd ever run. I measured rock of every piston to ensure clearance. Now granted I'm on much better gas. (93oct). It takes me about 31* of timing to get any knock...
If you look back at one of Pat G's thread he went to a thinner gasket and SCR was nearly 12:1. Absolutely no sign of knock. Think it was his SBE 500rwph thread.
If you look back at one of Pat G's thread he went to a thinner gasket and SCR was nearly 12:1. Absolutely no sign of knock. Think it was his SBE 500rwph thread.
How do you calculate DCR? what's considered safe with 91?
The guy who'll be tuning this said he wants me to go with the LS7's as he thinks 11.6 is already a tad high for 91.. ugh.
The guy who'll be tuning this said he wants me to go with the LS7's as he thinks 11.6 is already a tad high for 91.. ugh.
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There are a number of online calculators to figure out your dynamic compression based on your cam, static compression, and gasket/chamber volume. You need to know your cam's valve events to accurately calculate dynamic compression.
Usually, anything in the 8.5:1 range is safe, but there are a lot of factors, such as quench and quality of the tune, that will determine what is safe and optimal for your build.
Getting the quench in or around that .035" sweet spot will allow you to safely run both a higher static and higher dynamic compression... assuming your tune is decent.
That all being said, if you are set on the tuner who is giving you advice, then you might want to follow his advice. Not because it's the best advice, but because you don't want to build your engine outside of your tuner's ability to safely and properly tune it.
In a closer to perfect scenario, you would set your squish as close to optimal as possible, and let the static compression be whatever it ends up being. Then you would coordinate with your tuner and cam builder to set up your closest to perfect dynamic compression. And let your tuner do their magic.
If your tuner isn't comfortable tuning your engine with a higher static compression ratio, then it would behoove you to listen to him... or find a better tuner.
Usually, anything in the 8.5:1 range is safe, but there are a lot of factors, such as quench and quality of the tune, that will determine what is safe and optimal for your build.
Getting the quench in or around that .035" sweet spot will allow you to safely run both a higher static and higher dynamic compression... assuming your tune is decent.
That all being said, if you are set on the tuner who is giving you advice, then you might want to follow his advice. Not because it's the best advice, but because you don't want to build your engine outside of your tuner's ability to safely and properly tune it.
In a closer to perfect scenario, you would set your squish as close to optimal as possible, and let the static compression be whatever it ends up being. Then you would coordinate with your tuner and cam builder to set up your closest to perfect dynamic compression. And let your tuner do their magic.
If your tuner isn't comfortable tuning your engine with a higher static compression ratio, then it would behoove you to listen to him... or find a better tuner.
I agree with listening to the tuner. As far as his abilities, they aren't in question. He's most deffinatley one of the top tuners in California. I plugged some numbers into a calculator and it came up with 10.38 DCR... I assume that's incorrect with your figure of 8.5 being safe.
Ok so 51 was @.050... Kip said I needed 78.5.. plug that in to the calculator and I get ...
11.84:1...DCR 8.37
11.66:1...DCR 8.25
Is 8.37 low enough to get solid timing out of a street car with 91 octane?
11.84:1...DCR 8.37
11.66:1...DCR 8.25
Is 8.37 low enough to get solid timing out of a street car with 91 octane?
Ok, let me just get this out there to make sure I've got the right idea. Stock deck height of an LS(3) block is 9.240" with my rotating assembly and pistons that SHOULD put me at zero deck... ERL decked the block a tad in turn making it 9.231"... this tells me ill be .009" out. Right? If that's the case my figures have changed slightly.
Nevermind dudes. A quick email to Andres @ ERL got me sorted out.
With my rotating assembly I'm sitting at .004" out. That said, with the 4.140x.045 Cometic I'll be 11.75:1 with a DCR of 8.31:1 and a quench of .041"... this will be shifted at 7200 and I'm contemplating some spray, so I'm good with that quench.
Thanks guys.
With my rotating assembly I'm sitting at .004" out. That said, with the 4.140x.045 Cometic I'll be 11.75:1 with a DCR of 8.31:1 and a quench of .041"... this will be shifted at 7200 and I'm contemplating some spray, so I'm good with that quench.
Thanks guys.