How much boost before pump gas will not work?
How much boost before pump gas will not work? Looking into getting forged block and boosting the hell out of it with a S/C. But when is too much boost gonna make me run race fuel. Someone told me 15psi but was reading another thread and saw were the cobras were around 20psi. So that confused me. Can someone shed some light please. Thanks
TECH Fanatic
Joined: Jul 2002
Posts: 1,218
Likes: 1
From: MI
All depends on your compression ratio/timing/tune/heads/cam/and quality of gas. Too many variables to put an exact figure on it. But many members on this site have been using methyl/alky/water injection to run more hp on pump gas.
First i am gonna buy the d1sc kit and keep the car running. After that, start the build on LC 427. What would be the ideal compression to maximize the S/Cer. Just doing some home work before i dish out all the cash. Thanks
TECH Fanatic
Joined: Jul 2002
Posts: 1,218
Likes: 1
From: MI
Well since you are increasing the cubic inches of the motor, you can run more power on pump gas. A streetable F/I motor would be about 9.0:1. Some have gone 8.7 or 8.5:1 for higher power levels, but you will lose some streetablility.
I used to think compression ratio's in the low 8's would show up in the drivability, but honestly the cars still seem to run fine. The only difference you will notice is that the car will be a turd without the blower or turbo.
FWIW, we had a 99' Cobra owner come in and put down a rediculously low dyno number. (210 or something). I couldn't figure out what was wrong with his car so I started asking him about is blower motor that he just put in. I did a few calcs concerning his compression ratio and it came out to something like 7:1. The car still ran fine with no drivability problems, but was just a complete dud.
FWIW, we had a 99' Cobra owner come in and put down a rediculously low dyno number. (210 or something). I couldn't figure out what was wrong with his car so I started asking him about is blower motor that he just put in. I did a few calcs concerning his compression ratio and it came out to something like 7:1. The car still ran fine with no drivability problems, but was just a complete dud.
Just trying to figure out what my options are... Want a nice streetable Supercharged 427 to show off, drive around town as well as go to the track and blow some peoples doors off as well..... What kind of power you think that will put down? 
Originally Posted by waterbug1999
Just trying to figure out what my options are... Want a nice streetable Supercharged 427 to show off, drive around town as well as go to the track and blow some peoples doors off as well..... What kind of power you think that will put down?
Big power on pump gas.
8:1 Compression
Custom Front Mount Intercooler (very important)
Custom Tubing
Blower Heads
high 220 to low 230 'ish cam
Pin the crank
ATI SuperDamper with custom 7.25 SC crank drive
SDCE Drive System
ATI D1
RR Supercharger Pulley (3.2)
LT Headers
Stock Catback (or something else mildly restrictive)
All said and done you should have a streetable 700HP running 17 psi on pump gas.
Good Luck
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Originally Posted by NoGo
Big power on pump gas.
8:1 Compression
Custom Front Mount Intercooler (very important)
Custom Tubing
Blower Heads
high 220 to low 230 'ish cam
Pin the crank
ATI SuperDamper with custom 7.25 SC crank drive
SDCE Drive System
ATI D1
RR Supercharger Pulley (3.2)
LT Headers
Stock Catback (or something else mildly restrictive)
All said and done you should have a streetable 700HP running 17 psi on pump gas.
Good Luck
8:1 Compression
Custom Front Mount Intercooler (very important)
Custom Tubing
Blower Heads
high 220 to low 230 'ish cam
Pin the crank
ATI SuperDamper with custom 7.25 SC crank drive
SDCE Drive System
ATI D1
RR Supercharger Pulley (3.2)
LT Headers
Stock Catback (or something else mildly restrictive)
All said and done you should have a streetable 700HP running 17 psi on pump gas.
Good Luck
Yea, I am going with the ATI D1 kit. So i believe it has the 2 front intercoolers. Will bolt that up to my stock motor till i get the 427 built. Should get it in a few months. Just got a DUI so im paying 5K for that
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Verdad Gallardo Skit the two front mount intercoolers, they will end up holding you back with the 427. You need to build the boost to make the power. The intercoolers max at something like 900 CFM. You will need to flow close to 1300 CFM to make the proper boost.
-Kevin
-Kevin
Originally Posted by NoGo
Skit the two front mount intercoolers, they will end up holding you back with the 427. You need to build the boost to make the power. The intercoolers max at something like 900 CFM. You will need to flow close to 1300 CFM to make the proper boost.
-Kevin
-Kevin
For your goal and the 427 I would build the motor for 9.5-1 to 10.0-1 compression and a stage 3 head with 2.08/1.60 valves.Cam in the size of 238/250 on 115lsa and the D1 setup for 10psi (which will be near max on a D1/427 combo).Of course you'll need a good set of headers and the front mount intercooler would be very useful.
I could see this setup pushing over 700rwhp very easilly on pump gas.
I could see this setup pushing over 700rwhp very easilly on pump gas.
big displacement and low compression get pump gas numbers.... however it would be cheaper to get a methanol kit than to build a 427...but only by about 5 grand.
if you go big displacement like 427, that will give you good grunt.. enough to drop the CR to 8.5 or so and then i do think you could do 700rw.. thats what LPE does.
if you go big displacement like 427, that will give you good grunt.. enough to drop the CR to 8.5 or so and then i do think you could do 700rw.. thats what LPE does.
Originally Posted by NoGo
Get a big front mount. It isn't cheap, but it is the way to go as far as power is concerned.
Guess you are talking about the front mount in front of the radiator? Is there enough room for that, plus a tranny cooler you think?
Wasn't there a article in last months HOTROD about a competition for the fastest pump gas cars? I think the guy that all most won was running like a 9.08 with a twin turbo 406 small block. I think he would have won, but they averaged 3 passes and on his 3rd pass, he had a fuel system problem and only ran like a 10.50 or something. You might want to check it out.
Originally Posted by kbracing96
Wasn't there a article in last months HOTROD about a competition for the fastest pump gas cars? I think the guy that all most won was running like a 9.08 with a twin turbo 406 small block. I think he would have won, but they averaged 3 passes and on his 3rd pass, he had a fuel system problem and only ran like a 10.50 or something. You might want to check it out.
O.K.. Wll see what i can find.
TECH Enthusiast
Joined: Nov 2003
Posts: 689
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Originally Posted by Mike 01WS6
Well since you are increasing the cubic inches of the motor, you can run more power on pump gas. A streetable F/I motor would be about 9.0:1. Some have gone 8.7 or 8.5:1 for higher power levels, but you will lose some streetablility.
12 Second Truck Club
Joined: Feb 2002
Posts: 5,574
Likes: 0
From: Sacramento, CA
No fear os low CR here 
I ran 8.5:1 on my lil 306ci Mustang GT with only 9psi out of a Vortech S-Trim and there was no drivability issues or sluggishness at all. We are also talking about a car that had zero "tuning" besides what you could do with a distributor and a fuel pressure regulator LOL. I still maganed to run 11.82 in 105 deg temps on radial T/As and lifting before the end. Hahaha
I ran 8.5:1 on my lil 306ci Mustang GT with only 9psi out of a Vortech S-Trim and there was no drivability issues or sluggishness at all. We are also talking about a car that had zero "tuning" besides what you could do with a distributor and a fuel pressure regulator LOL. I still maganed to run 11.82 in 105 deg temps on radial T/As and lifting before the end. Hahaha
Maybe PSJ can chime in... 
Ive just heard that the lower the compression the less streetable (with pump gas) it becomes. Just trying to get the right combination (CR/PSI) for max potential..
Ive just heard that the lower the compression the less streetable (with pump gas) it becomes. Just trying to get the right combination (CR/PSI) for max potential..