carb. mods
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vw505
- Posts: 2151
- Joined: Mon Aug 27, 2001 12:01 am
carb. mods
what mods do you have to do to dells or webers to use them as blow through i will be useing an eaton blower from a ford.
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panel
- Posts: 4230
- Joined: Sun Sep 24, 2000 12:01 am
carb. mods
Email Moggy you can find his email and some pics here on one of the postings.Good luck.
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moggy
- Posts: 651
- Joined: Fri Mar 09, 2001 12:01 am
carb. mods
Don't go there.....
Here's why. I've recently discovered that a blow thru system using a supercharger is not good, especially for the blower. This is why I've scrapped the blow thru design on my motor and am at present rebuilding it to be a suck thru system using a single throttle body.
What happens is this. An Eaton is only rated to go up to about 14psi any more than that for prolonged periods and it overheats badly, which causes the end of the rotors to interfere with the blower housing due to heat expansion, not good. On wide open throttle (i.e. the butterflies fully open) the pressure below the carbs is the same as the pressure above them, no problem. And when you come off the throttle (i.e. butterflies fully closed) the pressure below the carbs turns into a vacuum cos the engines asking for more air than it's being given, however above the carbs the air is being pumped out in quantity by the blower, but cos the butterflies are shut it can't go anywhere, so the pressure goes skywards (BBBAAAAADDDD) thats where the by-pass valve comes in. This opens and vents air from above the carbs whenever it detects a vacuum below the butterflies, so the pressure above the carbs becomes aatmoshpheric i.e.0psi.
So far so good.
BUTTTT. How many times are you full throttle or totally off the throttle?? Most of the time you're part throttle. So what happens to the pressure difference above and below the carbs then, well thats where the problem arises. Cos at part throttle the pressure below the carbs may be at say 4psi but cos the butterflies are only part open there's still a restriction there so above the carbs the psi goes skyward again (mine read about 20psi above while below was about 4psi, at 2psi it was even more). Now the by-pass valve can't help you out cos it's not seeing a vacuum it's seeing 4psi so that pressure is aloud to build. The blower sees 20psi and overheats and within 500 miles you got a messed up blower badly scored.
This don't happen on a turbo motor cos of the wastegate, and most modern motors with blowers on are suck through FI systems, in fact so were the Judson and Shorrocks one from the sixties.
So learn from my mistakes and go suck thru. By the way anyone want to buy a pair of nearly new turbo spec DRLA48's?????
Here's why. I've recently discovered that a blow thru system using a supercharger is not good, especially for the blower. This is why I've scrapped the blow thru design on my motor and am at present rebuilding it to be a suck thru system using a single throttle body.
What happens is this. An Eaton is only rated to go up to about 14psi any more than that for prolonged periods and it overheats badly, which causes the end of the rotors to interfere with the blower housing due to heat expansion, not good. On wide open throttle (i.e. the butterflies fully open) the pressure below the carbs is the same as the pressure above them, no problem. And when you come off the throttle (i.e. butterflies fully closed) the pressure below the carbs turns into a vacuum cos the engines asking for more air than it's being given, however above the carbs the air is being pumped out in quantity by the blower, but cos the butterflies are shut it can't go anywhere, so the pressure goes skywards (BBBAAAAADDDD) thats where the by-pass valve comes in. This opens and vents air from above the carbs whenever it detects a vacuum below the butterflies, so the pressure above the carbs becomes aatmoshpheric i.e.0psi.
So far so good.
BUTTTT. How many times are you full throttle or totally off the throttle?? Most of the time you're part throttle. So what happens to the pressure difference above and below the carbs then, well thats where the problem arises. Cos at part throttle the pressure below the carbs may be at say 4psi but cos the butterflies are only part open there's still a restriction there so above the carbs the psi goes skyward again (mine read about 20psi above while below was about 4psi, at 2psi it was even more). Now the by-pass valve can't help you out cos it's not seeing a vacuum it's seeing 4psi so that pressure is aloud to build. The blower sees 20psi and overheats and within 500 miles you got a messed up blower badly scored.
This don't happen on a turbo motor cos of the wastegate, and most modern motors with blowers on are suck through FI systems, in fact so were the Judson and Shorrocks one from the sixties.
So learn from my mistakes and go suck thru. By the way anyone want to buy a pair of nearly new turbo spec DRLA48's?????