What is the lowest cc/ highest compression that can run on pump gas?
08-10-2012, 09:45 AM
#1
Staging Lane
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What is the lowest cc/ highest compression that can run on pump gas? My question is how much can I mill my 243's that go on a stock bottom end ls1? I've heard 60cc at about 11 to 1 compression will still run on 93 octane pump gas. But I'm not exactly sure. Any info?
08-10-2012, 01:05 PM
#3
2) the tune and gas quality matter more than just a magical number
Heck, there are LS engines with just about that compression that run on 91 gas (LS2s for example), so an LS1 at 11.1:1 on 93 is no biggie.
Get the right cam, get the right tune and you can run upwards of high 11s compression on 93 octane.
08-10-2012, 01:27 PM
#4
Redtan beat me too it but it has nothing to do with static compression.
Dynamic compression will determine what fuel you can run.
What are the cam specs? Chamber size? Flat tops, dome or dish? Piston in the hole? Head gasket thickness, installed cam centerline? Bore, stroke and rod length?
Dynamic compression will determine what fuel you can run.
What are the cam specs? Chamber size? Flat tops, dome or dish? Piston in the hole? Head gasket thickness, installed cam centerline? Bore, stroke and rod length?
08-10-2012, 02:23 PM
#5
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Stock bottom end so stock ls1 pistons and bore. Cam is .598 .602 lsa112. Car was tuned by vengeance the first time so I'm sure they could get my timing and stuff right
08-10-2012, 03:45 PM
#7
Everything I posted above I need to find out your dynamic.
I already know the bore, stroke, rod length, head gasket thickness and that the piston is .006 out the hole, but we need intake duration and installed centerline of the cam and chamber volume.
I already know the bore, stroke, rod length, head gasket thickness and that the piston is .006 out the hole, but we need intake duration and installed centerline of the cam and chamber volume.
Last edited by Sales@Tick; 08-23-2012 at 04:34 PM.
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08-10-2012, 03:55 PM
#8
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228/234 .598 .602 lsa112. The cam was in the car when I bought it and that's what the guy said it was. And that's about all I know unfortunately.
08-10-2012, 06:13 PM
#9
Well with my calculations if that cam is installed straight up dot to dot and it's correct dot to dot at 112icl then it has 8:1 DCR as it sits with stock 241 heads.
If it were mine and it is truly installed dot to dot(you need to verify this as it is crucial and people overlook it all the time!) you could take the chamber down to 61cc and it would put you at 11.12:1 SCR and 8.43:1 DCR which is fine for pump gas.
If it is installed at 110icl it changes the DCR from 8.43:1 to 8.58:1 still fine for pump gas. If it's installed at 108icl it goes to 8.78:1 which is still ok, but it won't want more than 27-28* timing maximum I'd bet to make peak power. I usually don't recommend over 9:1 DCR for pump gas although it has been done before.
If it were mine and it is truly installed dot to dot(you need to verify this as it is crucial and people overlook it all the time!) you could take the chamber down to 61cc and it would put you at 11.12:1 SCR and 8.43:1 DCR which is fine for pump gas.
If it is installed at 110icl it changes the DCR from 8.43:1 to 8.58:1 still fine for pump gas. If it's installed at 108icl it goes to 8.78:1 which is still ok, but it won't want more than 27-28* timing maximum I'd bet to make peak power. I usually don't recommend over 9:1 DCR for pump gas although it has been done before.
08-21-2012, 12:30 PM
#11
Well with my calculations if that cam is installed straight up dot to dot and it's correct dot to dot at 112icl then it has 8:1 DCR as it sits with stock 241 heads.
If it were mine and it is truly installed dot to dot(you need to verify this as it is crucial and people overlook it all the time!) you could take the chamber down to 61cc and it would put you at 11.12:1 SCR and 8.43:1 DCR which is fine for pump gas.
If it is installed at 110icl it changes the DCR from 8.43:1 to 8.58:1 still fine for pump gas. If it's installed at 108icl it goes to 8.78:1 which is still ok, but it won't want more than 27-28* timing maximum I'd bet to make peak power. I usually don't recommend over 9:1 DCR for pump gas although it has been done before.
If it were mine and it is truly installed dot to dot(you need to verify this as it is crucial and people overlook it all the time!) you could take the chamber down to 61cc and it would put you at 11.12:1 SCR and 8.43:1 DCR which is fine for pump gas.
If it is installed at 110icl it changes the DCR from 8.43:1 to 8.58:1 still fine for pump gas. If it's installed at 108icl it goes to 8.78:1 which is still ok, but it won't want more than 27-28* timing maximum I'd bet to make peak power. I usually don't recommend over 9:1 DCR for pump gas although it has been done before.
The ADVERTISED duration is the number that should be used, not the duration at 0.050" since compression doesn't begin until the valve is fully seated. Is this not true?
Or are you applying the 'guess rule' of "add 15°" to the 0.05 value?
Just curious, perhaps I calculated mine wrong... i used the duration at 0.06 values on the cam card. (e.g. 281/289 rather than 232/240 @0.05"
Last edited by vmapper; 08-21-2012 at 12:36 PM.
08-21-2012, 02:54 PM
#12
I always thought you require the Cam Spec Duration as advertised not @0.05" for calculating DCR?
The ADVERTISED duration is the number that should be used, not the duration at 0.050" since compression doesn't begin until the valve is fully seated. Is this not true?
Or are you applying the 'guess rule' of "add 15°" to the 0.05 value?
Just curious, perhaps I calculated mine wrong... i used the duration at 0.06 values on the cam card. (e.g. 281/289 rather than 232/240 @0.05"
The ADVERTISED duration is the number that should be used, not the duration at 0.050" since compression doesn't begin until the valve is fully seated. Is this not true?
Or are you applying the 'guess rule' of "add 15°" to the 0.05 value?
Just curious, perhaps I calculated mine wrong... i used the duration at 0.06 values on the cam card. (e.g. 281/289 rather than 232/240 @0.05"
You are correct though you use total duration to determine DCR. I looked the lobes up and found their total duration numbers and used a calculator I have saved in an excel file to find the rest.
08-21-2012, 03:18 PM
#13
I was just second guessing how I had calculated my setup after reading this thread.
Thanks Martin!
08-21-2012, 03:41 PM
#14
You did not (I had not meant to put words into your post), but the only numbers posted were "228/234 .598 .602 lsa112". Makes more sense that you had dug to get the proper numbers behind the scenes.
I was just second guessing how I had calculated my setup after reading this thread.
Thanks Martin!
I was just second guessing how I had calculated my setup after reading this thread.
Thanks Martin!
I don't have it on my work PC.
08-21-2012, 06:09 PM
#17
Martin is right on the money. 9:1 DCR is about the max for good 93. If you can find straight 93 not mixed with ethanol, you'll do better.
Place to find stations around you:
http://pure-gas.org/
Place to find stations around you:
http://pure-gas.org/
08-22-2012, 10:28 AM
#19
Martin is right on the money. 9:1 DCR is about the max for good 93. If you can find straight 93 not mixed with ethanol, you'll do better.
Place to find stations around you:
http://pure-gas.org/
Place to find stations around you:
http://pure-gas.org/
Also just a FYI the stoich of 93 with what they say "May contain up to 10% Ethanol" is not 14.67 it is 14.32. Just a FYI to all the self tuners out there.
08-23-2012, 12:20 PM
#20
Is that 14.32 at 10%E ? "May contain" to me means 1 tank fill at 8% the next at 2%. so stoich could be be anywhere between 14.68-14.32, its why I never use that fuel for use or tuning
Martin, does your Dynamic Calculator include the ability to add F.I. values?
I know the typical talk is ~8.5:1 Dynamic is 92 pump friendly. What if you add 12psi into the mix for example?
(sorry for the questions - OP )
