LS1 max compression for 91 octane and 8lbs of boost?
LS1 max compression for 91 octane and 8lbs of boost? Just day dreaming, and I am curious. What would be the lowest, safe, compression ratio on a 75,000 mile LS1 to be able to run 91 octane (in a pinch) and 8lbs of boost for a daily driven car?
317 heads would be about 9.3:1
243 heads from AI with 69cc chambers would be about 9,7:1
243 heads just shaved for flatness would be about 10.6:1
I am sure that 10.6:1 is too much, but what about 9.7:1?
317 heads would be about 9.3:1
243 heads from AI with 69cc chambers would be about 9,7:1
243 heads just shaved for flatness would be about 10.6:1
I am sure that 10.6:1 is too much, but what about 9.7:1?
Last edited by FCar2000TA; Sep 22, 2019 at 04:56 PM.
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So your gonna gain .9 points of compression with just a shave. Seems off but no 10.6 to one doesnt seem to high for 8 pounds of boost. Just sneak up on your timing instead of just wacking a guess in there.
Then a agian you ask waht was the lowest safe compression. So i dont know if im answering the right question. What is your power adder. A positive displacment blower requires a different set up then a centri or a turbo but i believe they would all be safe with 10.6 and 8 pounds.
Then a agian you ask waht was the lowest safe compression. So i dont know if im answering the right question. What is your power adder. A positive displacment blower requires a different set up then a centri or a turbo but i believe they would all be safe with 10.6 and 8 pounds.
Edit: 10PSI not 12.
Gonna bring this back from the dead since I have ditched my LS1 plans and am planning a resleeved 4.155" bore, hopefully in the next 18 months. Since my endgame (we are talking many years down the road) is a resleeved 12571048 4.155" bore and 4" stroke, LS7 style heads, and a Magnuson 2300 blower, I want to set this motor up for the future (as Tony Mamo once said, do it right the first time…. It is less expensive than doing it twice).
With all of that in mind, what would be the maximum safe static compression (I know the cam specs can help some, but for now, just going off of static) that could be run on a 4.155" bore x 4" stroke with up to 12PSI (I think I read that 12 is the max before dimensioning returns for the 2300)? I would be running flex fuel (E54) the vast majority of the time, but might have to run 91 in a pinch.
The reason I am interested in this is because the motor will be NA right now, so I want to get pistons that will be good now, but will not have too much compression when paired with 70cc heads (assuming 70cc is what aftermarket LS7 style heads max out at) down the road.
Gonna bring this back from the dead since I have ditched my LS1 plans and am planning a resleeved 4.155" bore, hopefully in the next 18 months. Since my endgame (we are talking many years down the road) is a resleeved 12571048 4.155" bore and 4" stroke, LS7 style heads, and a Magnuson 2300 blower, I want to set this motor up for the future (as Tony Mamo once said, do it right the first time…. It is less expensive than doing it twice).
With all of that in mind, what would be the maximum safe static compression (I know the cam specs can help some, but for now, just going off of static) that could be run on a 4.155" bore x 4" stroke with up to 12PSI (I think I read that 12 is the max before dimensioning returns for the 2300)? I would be running flex fuel (E54) the vast majority of the time, but might have to run 91 in a pinch.
The reason I am interested in this is because the motor will be NA right now, so I want to get pistons that will be good now, but will not have too much compression when paired with 70cc heads (assuming 70cc is what aftermarket LS7 style heads max out at) down the road.
Last edited by FCar2000TA; Nov 8, 2020 at 12:04 PM.
With that type blower and alot of cubes, your boost/power is pretty instant. So running on the low side compression wise isn't a big deal IMO. It sill be a snappy tire fryer with that large of a motor anyway. How much boost you can run without detonation isn't something we can answer. Alot will depend on the tune and load. You can detune higher compression to help it live (run way under MBT timing.) Or you can run less compression and optimal timing. I can't imagine that motor being a slouch even at 8.5:1. Since you have E available, I'd run around 9:1 personally. Use a flex fuel settings to drop timing when it senses less than 50% ethanol. Should be fine.
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If you're really going to run straight 91 on a regular basis then I agree, go 9:1. If you're going to run flex and mostly run E, you could just have the timing in the dirt on 91 and reap the benefits of a higher compression and E.
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Verdad Gallardo What would you say would be safe with 91 and timing in the dirt?
Last edited by FCar2000TA; Nov 6, 2020 at 09:46 PM.
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And are you sure all that will work with a 4" stroke ?
I have the LS9 type squirters, and not a hope in hell would they work with a 4", I'm on 3.825" and even then I had clearance issues. I had to machine the bolt heads down to clear the crank counterweights ( LS2 block machined for squirters...so maybe height difference there ? )
And also had to machine the pistons to clear the little squirter tube itself. And also bend the tube a little to clear the rods.
And even then, there really is minimal clearance, like 20-40thou although it seems to be ok last time it was apart. Well...one little squirter tube was ready to fall off lol as it had been making some contact and fatigued where it was soldered into the base. Although I broke it off when checking integrity, it had not already fallen off.
I know Katech do offer new squirters seemingly made for strokers though now.
As for CR, with crappy fuel, a tiny blower, lots of heat....keep it safe. I'd usually say 9.5:1 would be safe, but as you'll be ringing the life out of that tiny blower, 9.0:1 seems the safer go anywhere, fuel anywhere option.
http://www.csgnetwork.com/compcalc.html
I have the LS9 type squirters, and not a hope in hell would they work with a 4", I'm on 3.825" and even then I had clearance issues. I had to machine the bolt heads down to clear the crank counterweights ( LS2 block machined for squirters...so maybe height difference there ? )
And also had to machine the pistons to clear the little squirter tube itself. And also bend the tube a little to clear the rods.
And even then, there really is minimal clearance, like 20-40thou although it seems to be ok last time it was apart. Well...one little squirter tube was ready to fall off lol as it had been making some contact and fatigued where it was soldered into the base. Although I broke it off when checking integrity, it had not already fallen off.
I know Katech do offer new squirters seemingly made for strokers though now.
As for CR, with crappy fuel, a tiny blower, lots of heat....keep it safe. I'd usually say 9.5:1 would be safe, but as you'll be ringing the life out of that tiny blower, 9.0:1 seems the safer go anywhere, fuel anywhere option.
http://www.csgnetwork.com/compcalc.html
Id start at 10 degrees and read the plugs.
Kaytech says that their stroker squirters will clear 4" stroke but the piston bottom might need clearancing. I will be having the short block assembled at a shop, so they will clearance the pistons as needed before balancing the assembly.
EDIT: I didn't consider that PSI of boost is inversely proportionate to CID. So, you are correct. 12PSI will be spinning the 2300 a lot. I think 10PSI is probably what I would run.
Last edited by FCar2000TA; Nov 8, 2020 at 12:02 PM.