Inliners International Forums General Discussion Blown and Injected Carb sizing

Seems like in my searches, TLowe listed a link that helped choose a carb based off ci, rpm and boost.
Now when I search i can't find that thread. May have been on another board, not sure.
If it wan't TLowe, does anyone have a link to carb calculator for blowthru?
Lee

I think BDS has calculators for both draw-thru and blow-thru applications....

lee,
What size engine and rpm range do you have? How much boost?
I do remember throwing up a chart for picking a turbo. I have books and calculations for use with figuring the boosted flow.

Keep this in mind. If a 600 cfm Holley works good on a N/A motor, it will also work good in a boosted application for the same motor if it is blown thru. Of course the carb will need modifications to handle the boost, but that is a different story.

The boost makes the carb feel or flow bigger. So a 600 cfm will flow 750 cfm at the right boost. Tom

Doing a 250 not sure what to twist it to. It is stock bottom end.
Figure I may get 10 lbs out of it.
I have most of the turbo books also, but this was a link to an online site and you had to enter the boost you were whating to run.
Seems like the calculator was basically yellow on a white page?????
I noticed it didn't change the cfm required much (if any) for my application, may have for higher boost.

I will keep looking, but I believe a 390-500 cfm carb setup as a Blow thru will flex up in cfm with the added boost. For example the 500 cfm carb will actually flow 650-700 at 10 psi boost.

I have to find the proof though. tom

From BDS website: {(CID x RPM) ÷ 3456} x {Boost ÷ 14.7) + 1} = CFM required. This is for draw through for an engine that has lumps or better.

Okay, I understand most of this. I agree with TLowe that it doesn't need to change much from stock if you are not twisting it past stock. But seems like our 1 bbls were a limiter anyway.
I have a few carbs to try. One I was thinking of was the 2 bbl off a later integrated head. Also have a weber 32/36. Also a factory holley off a 300 f**d.
Any thoughts on which would be better to use/easier to mod for 8-10 lbs of boost.
I plan to go MS later, just needing to watch the bucks right now.
I am getting a JAW wideband for Christmas (woot, thanks Santa) so I'll be able to watch my afr.
Got the turbo pretty much mounted, need to brace it better. Going to mod the exhaust (3") off an old project, so getting closer. Have most of the basics done except the carb and hat.
Lee

a1953mdl

Holley or Holley type carbs have done everything from draw through to blow through,I would stick w/some sort of Holley,because there are books on how to modify or shops that know how to modify your carbs to your needs.

Holley sells plasitic floats that won't collaspe under boost.
My DCOE Webbers had brass floats & they collasped w/8 psi of boost pressure,so I bought there plastic ones that worked & did not collasped.

I remember a girl street racer here in Cali that had a early Nova ,ran a Weiand 164 IIRC, street blower,, all the books & calculaters from weiand & B&M & other sorces stated the 350 w/that blower & psi she made only needed a 750 CFM carb,,she ran that for a while then she decided to install an 850,,,quess what happened,she went slower,,,,just kidding,, she whet faster made a bit more boost & her 1/4 mile time dropped .5 seconds w/the carb change.

So, just saying some calculaters & charts don't always show what works best,sure they are pretty close for the most part.

Like my 48 MM DCOE Webers the books & charts said it was too big for my application.
But I got them so cheap $200 w/cannon manifold, I had to try them out anyways.
Those were the best running carbs set-up I have ever ran.

The thing I noticed mostly from them being too big was,@ 3/4 throttle to full throttle,really did not feel much difference.

I can only imagine how much better if would have run if I had more appropreatly sized 45 MM carbs on.

DCOE carbs have seals on the trhottle shafts,so no leak there,there are mods to do on the Holley throttle shafts so they dont leak.
You will see what I am talking about.
When you are blowing through a carb that was not designed to blow through,,you will find leaks that you would not have even thought about area could leak,but they are fixable.

Hope this helps some.

MBHD