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Old 03-07-12, 01:58AM   #1
conceptfab
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Default Who likes their blow through carb?

I have been calling around to have my carb modded for blow through and i get prices from $450-$1100. Thats a big difference and one thing i have learned is you get what you pay for. These are all big companies too. The one big difference is i hear that over 1000-1100 whp you need to go to dual needle and seat fuel bowls and thats what the double in price is for
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Old 03-07-12, 02:11AM   #2
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CSU is the way to go. Check over on Yellowbullet in the boosted section.
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Old 03-07-12, 02:13AM   #3
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CSU is actually the lowest!
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Old 03-07-12, 02:34PM   #4
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CSUTTFMF'r
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Old 03-07-12, 10:41PM   #5
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Oh NOOO!!!!! The MF'r's hit here too, LOL. I had an 830 converted by CSU and it was flawless. They built me a 750 which I have yet to run and I will be getting a second 750 built and probably both 750s converted to E85 at the same time. I'm sold on CSU. Mark L
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Old 03-08-12, 10:47AM   #6
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Yeah Mark Kevin is the man...couldn't ask to deal with a nicer guy!
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Old 03-08-12, 12:04PM   #7
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Hes doing an 850 for me for a boat project

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Old 03-08-12, 10:17PM   #8
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Quote:
Originally Posted by conceptfab View Post
I have been calling around to have my carb modded for blow through and i get prices from $450-$1100. Thats a big difference and one thing i have learned is you get what you pay for. These are all big companies too. The one big difference is i hear that over 1000-1100 whp you need to go to dual needle and seat fuel bowls and thats what the double in price is for
Yes fuel volume capacity is real important as you approach that power range especially if you run E85 or plan to in the future. IMO you could run two small Holley dual feed carbs to get enough needle area and probably improve on air/fuel distribution while your at it.

One of many reasons for not running a Qjet in blow-thru mode is the limited needle area and small bowl capacity.

Think about this... it takes @ 6000 lbs/hr air(@ 100 lbs/min) to make 1000 HP.

Turbo'd the fuel required would be @ 525 lbs/hr or 8.75 lbs/min.
Pump gas varies some but 6.01 lbs per gallon is typical.
So... 1000 hp will use @ 87.35 gal/hour or @ 1.46 gal/min fuel flow. Thats a bunch of fuel to move through a needle seat assembly.

That is primarily the reason for the dual needle bowls on the big HP blow thru carbs.


BTW I've heard no evil when it comes to CSU's blow thru carbs!
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Old 03-08-12, 10:25PM   #9
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I mised you mathmatical info !
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Old 03-08-12, 11:23PM   #10
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Pretty much like figuring minimum fuel injector size Jeff. I should have mentioned the carb(whole fuel system really) should be capable of moving more fuel than that thru it. Carb itself probably 15-20% more fuel capacity just to be safe.(Just like total injector flow.) Fuel pump even more due to G forces etc..

Also... too much carb(cfm) may not give enough pressure differential thru the venturis at modest boost levels making it harder to pull fuel as well as it should.
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Old 03-10-12, 01:53AM   #11
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I have built 2 blowthru's and they work great, cost about $300 ea. including the core. It takes time and a good wideband.
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Old 03-10-12, 09:25PM   #12
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Bruce, fuel bowel requirements is what's prompting me to run twin 750s. I could run a large single blow thru but I would have to spend the money for the big extra sized fuel bowls. I can do the same with twin 750's, and use the extra plenum of the tunnel ram AND the straight shot of the tunnel ram runners. Plus the wow factor. Maybe I'm off base but I like the added intercooling affect of the 8 smaller throttle bores versus the 4 large throttle bores of a big carb, especially a Dominator based big carb. I'm also thinking the 4 smaller primairy bores (even though you are using 4 versus two) of the twins may give better throttle responce off boost?? But that is an opinion, not a proven fact. Mark L
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Old 03-10-12, 10:34PM   #13
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Hello Guys!

CSU HP 1000 for me- Bolted ity on and ran perfect!
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Old 03-12-12, 01:25AM   #14
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Mark... two 750 AFBs we had on Debs car(406 NA) gave outstanding throttle response. In Tandem it was almost too responsive in traffic for my city drivin style. Deb wasnt too happy when I softened it up with progressive linkage! I had to change it back!

Yeah a pair of Holleys should work but I'd think a pair of 600 double pumpers would do quite well. Plus usually found cheap at swap meets etc.. A pair of 660 center squirt carbs (4224's iirc) would have all 8 working at once. No lack of response there. A little harder to find on the cheap though. I think Taff2 is using twin 600's on his modified Offy.

I've considered my big thermoquad (primary venturi's opened to same as the 1000 cfm version but booster ring still in place...about 950 cfm) but the large needle seat assemblies are hard to come by. Otherwise there are some features that would make for a decent blow-thru set up.

Hey Doc, hows your car doing?

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Old 03-12-12, 01:51AM   #15
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I already had the one 750 so it was easy to go with a second. I'm sending my first blow thru 750 to Kevin (CSU) for conversion to E85. Then later I'll send my second 750 for conversion to blow thru and E85. I've decided that race fuel on the streeet (E85) will run a little cooler and allow a full advance curve and some real boost. I'm also thinking the twin carbs will add a little more intercooling affect than a single larger carb. When I had the tunnel ram and twin 600s on my TA (before the turbo) I did feel a little loss of low end but the mid range (right where the converter came in) was much stronger than the single 830 and the top end was much stronger. The best ET with the single 830 (NA) on a torqer II was 11.6 @ 116 and that dropped to 11.2 @ 119 with the tunnel ram and 600s. So over all it ran well with the changeover.
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