Impco 425 boosted CFM rating

[LPG383]

Hi Franz, I contacted you a while ago about modifying an Impco 600 mixer with an idle circuit for street use on my turbo 454 malibu still back on the old Impco message board. I'm really glad I found this new forum where everyone is now after the Impco forum was terminated. Anyway, I never got around to purchasing and modifying an Impco 600 for the shear sake of cost for that particular mixer so I just ended up using a single 425 and am quite surprised at the results that I'm getting. With my current set up on a bone stock Chevy 454 I am able to push 10 PSI boost on a blow through set up using two OHG X-1 vaporizers and twin Vff-30s. I couldn't believe it at the time that I was able to get that much boost out of a single 425 mixer and have it feed a boosted big block to almost 5000RPM. My best ET at the track on radials so far has been a 13.07 with a trap speed of 106MPH all weighing in at 4100lbs. Currently I am building a healthier big block at this time with twin 425s and hopefully around the same amount of boost. Now this leads me to the question about the Impco 425 CFM rating in a blow through set up. From what I am achieving with a single mixer in a blow through set up on my combination it is obvious that this little 425 is delivering more than its rated CFM. Does the Impco 425 provide significantly more fuel delivery and airflow in a blow through set up rather than in a draw through set up?

[franz]

The short answer is yes. When the system is boosted, the air-fuel density is increased. Not considering the temperature differential, if an engine is pulling 15 psi boost, it is running APPROXIMATELY twice the CFM as a normally aspirated engine.

I would guess that your engine is pushing about 60% more air at 10 psi than NA. With that said, we have to consider the law of compressibility, the gas law, and Thermo 101. When a gas is compressed, heat is generated. The heat causes an expansion of the gas-fluid which in some cases can negate the effects of the boosted pressure. This is why an intercooler can provide some great power gains and helps explain how using a CO2 spray can increase power, by cooling the inlet charge after boost.

Glad you found your way to this forum, there are some great resources here. Take a look at the memberlist at the top of the page plus you can PM anyone for a personal chat. You will find some familiar names.

Franz

[sleepybu]

LPG383, bout time you found this site... haven't seen you in years. Tryed getting your e-mail off of maliburacing.com but no dice.

[LPG383]

That makes sense Franz, in that the air density is increased at the mixer while the turbocharger draws the extra CFM. We'll see how well it will work with the two 425s on a dual quad intake in the same configuration. I'm using a single Turbonetics T66 turbo rated to about 750hp not to mention that the CID will be significantly greater as well.

Hey sleepybu, I haven't been around much I know, been busy with school and work for the last couple of years so I had to let my projects sit for a while. Finally back in the game and it's good to hear from all you guys.

Are you still running your bu on LPG? I wish we could have got in touch earlier when you still had the turbo on it, I would have helped you with your tuning. My dad has a lot of propane stuff seeing as he has been converting vehicles since 1981. How's the nitrous set up working out on LPG? I've got a kit lying around too and been thinking about tossing it on my 383 stroker car.

As soon as I get my computer running better here I'll post some pics of my stuff.

[sleepybu]

Hey sleepybu, I haven't been around much I know, been busy with school and work for the last couple of years so I had to let my projects sit for a while. Finally back in the game and it's good to hear from all you guys.

Are you still running your bu on LPG? I wish we could have got in touch earlier when you still had the turbo on it, I would have helped you with your tuning. My dad has a lot of propane stuff seeing as he has been converting vehicles since 1981. How's the nitrous set up working out on LPG? I've got a kit lying around too and been thinking about tossing it on my 383 stroker car.

As soon as I get my computer running better here I'll post some pics of my stuff.

I haven't had my car out in the last year I'm still on LPG. I think the problem with my turbo system was the reg was leaking fuel under boost cuzzing a lean backfire. As for the nitrous it works good. I'm using gas for the fuel enrichment. This big thing i don't like about the nitrous is it's hard to maintain good bottle presser.

Good to see you on here

[michael]

I gave you the enrichment jetting for LPG/n2o.
why are you still using dino juice?

[LPG383]

What enrichment jetting for LPG/n2o do you have? I've got a proper ratio as well from the guys at NOS but still haven't done any testing.

[sleepybu]

I gave you the enrichment jetting for LPG/n2o.
why are you still using dino juice?

Time...

[Harmon3]

im looking to build a propane small block (probably 383 chevrolet or 355 chevrolet) and run it with a turbo.
will a impco 425 support a healthy small block with a turbo at 12-15 psi? or would i have to run two of them?
i want to use a blow through set up with intercooler.

is there a single vaporizer that can support this? ive tried reading the IMPCO website but its not that great.

thanks in advance

Harmon