Carb advice please

gonzothegreat · Dec 28, 2007

I currently have a BIGS Holley 650 stage 3 double pumper.
I will be installing the Paxton supercharger very soon, and I need a blow thru carb.
Now, I could send my existing carb back to Jesse at BIGS, but the cost involved is too high. It makes more sense to buy a new carb... at least at will have a spare one (just in case).

Now here's my combo:
342 stroker
Weiand X-CELerator manifold
Dart PRO1 heads
full MAC headers
Compcam 280RH
T5 and 3.55 gears

I'm undecided between the 750 stage 5 and the 950 stage 5
Looking at BIGS's website
http://www.bigsperformance.com/productpage.htm
They are the same price, now is it a typo.... who knows... so I checked on his eBay store and they are the same price.

What would be the pros and cons between the 2 carbs for my engine please?

D.Hearne · Dec 28, 2007

A 950 is WAY too big for even a blown 347. When it comes to carbs, bigger isn't always better. The 750 will flow all it needs, especially with a blower, huffing thru it. And looking at your sig, I hope you've done some suspension and brake upgrades to that car

Jimmys66 · Dec 28, 2007

I'm thinking the 750's plenty also.......

What's Jesse think?

iskwezm · Dec 28, 2007

send a pm to 10secgoal, he modified his carb and a few others to a blow through

gonzothegreat · Dec 29, 2007

D.Hearne said:
A 950 is WAY too big for even a blown 347. When it comes to carbs, bigger isn't always better. The 750 will flow all it needs, especially with a blower, huffing thru it. And looking at your sig, I hope you've done some suspension and brake upgrades to that car

I'm getting the TCP G-bar for the rear suspension and the front is a full Global West system (Which will be upgraded with the Ron Morris coil over shocks )

gonzothegreat · Dec 29, 2007

Jimmys66 said:
I'm thinking the 750's plenty also.......

What's Jesse think?

Jesse quoted me for a 750.

D.Hearne · Dec 29, 2007

Just your questioning whether a 750 or a 950cfm carb, tells me you're not real versed in carb basics. If a 950 wasn't too big for your motor, the only place in the rpm band it would show an improvement over a smaller carb would be at the very top of the rpm band. Carbs do not operate like a fuel injection system, the only thing pulling the fuel into the air stream is the pressure differential in the venturis, and with a too big carb, there will be no differential to do that. There has to be a restriction in the carb throat to create a pressure differential. It's a little less critical with a blower, but the basics are still the same.

10secgoal · Dec 29, 2007

A 650 PLENTY for your combo. The t-5 will expire long before the 650 becomes too small. Save the money and convert yours to a blo thru yourself. Or if you really wanted to spend money on a carb, send yours to a company that knows how to do it, rather than a carb tricked out for N/A. They are different carbs.

gonzothegreat · Dec 30, 2007

10secgoal said:
A 650 PLENTY for your combo. The t-5 will expire long before the 650 becomes too small. Save the money and convert yours to a blo thru yourself. Or if you really wanted to spend money on a carb, send yours to a company that knows how to do it, rather than a carb tricked out for N/A. They are different carbs.

Thanks for the advice 10secgoal, much appreciated.
I've found this link
http://www.hangar18fabrication.com/blowthru.html
Is this a good HowTo to go blow thru?

Edster · Dec 30, 2007

Seems to me the mod for a Holley is a lot of trouble. I would thing an Edelbrock or Carter would be easier. Aside from air horn mods all you would have to do is juggle around w/ metering rods, jets, and springs vice drilling out PVCRs. Also backfires would not be a worry. Also the carb body and throttle plates are all one assembly. Less stuff to leak. All you have is the air horn to body gasket. Just my 2cents

mrmustangman357 · Dec 30, 2007

you lose alot of tuneability with the afb/edelbrock carb. stick with holley

10secgoal · Dec 30, 2007

gonzothegreat said:
Thanks for the advice 10secgoal, much appreciated.
I've found this link
http://www.hangar18fabrication.com/blowthru.html
Is this a good HowTo to go blow thru?

This is pretty much the article you need right there. The only thing I wouldn't recommend yet is drilling the PVCR's. All that will do is richen the front of the motor unequally unless you also go up in the rear in jets also. You probably won't even need to ever go up in size anyway. Rich is up 477rwhp, stock PVCR's. Each car is different, but total fuel requirements don't really change to much for the same power levels.Only the timing of the fuel delivery really.

Do the solid floats, drill out the PV protection, ( with 12psi you may even need to externally reference it), put about .018-.023 air bleeds in the high sides and take it to the dyno. That ought to be enough fuel for that thing. I'd try 80/90 jetting at first.

gonzothegreat · Dec 30, 2007

I'm about to secure a 750 double pumper Holley here in the UK for a really good price, that would be the ideal carb to get my hands on that conversion.

iskwezm · Dec 30, 2007

Edster said:
Also the carb body and throttle plates are all one assembly. Less stuff to leak. All you have is the air horn to body gasket. Just my 2cents

leaks are the least of your wories with a Edelbog..............that can work as a blow through,but are not known for it.

10secgoal · Dec 30, 2007

iskwezm said:
leaks are the least of your wories with a Edelbog..............that can work as a blow through,but are not known for it.

Edelbrock even says not to use them. You have to make you own solid floats, two springs instead of one diaphram means a chance for the enrichment timing to be off side to side. No adjustability in the air bleeds, and a pump shot that can't really be tuned. E carbs are pretty much last on the list for any performance mindset.

Edster · Jan 1, 2008

Ah I see. Now I understand why you wouldn't want to use an Edelbrock on a blow through set up. I remember years ago some one made Weber power plates foe Holleys. You just used a Weber jetting system. You can really fine tune if you understand Weber tuning. Seems to me a cheaper option than a new carb.

Fast63 · Jan 1, 2008

10secgoal said:
Edelbrock even says not to use them. You have to make you own solid floats, two springs instead of one diaphram means a chance for the enrichment timing to be off side to side. No adjustability in the air bleeds, and a pump shot that can't really be tuned. E carbs are pretty much last on the list for any performance mindset.

I'm not sure what you're talking about. Can you explain why you think they are last on the list for any performance mindset? After much tuning of both carbs, I had a 750 edlebrock running me down the track faster than a 650 holley DP on a 306.

Also interesting how at car shows, most people with roots blowers have edelbrocks on top. Are you saying they are just looking for the cheap route or the easier to tune route?

10secgoal · Jan 1, 2008

Fast63 said:
I'm not sure what you're talking about. Can you explain why you think they are last on the list for any performance mindset? After much tuning of both carbs, I had a 750 edlebrock running me down the track faster than a 650 holley DP on a 306.

Also interesting how at car shows, most people with roots blowers have edelbrocks on top. Are you saying they are just looking for the cheap route or the easier to tune route?

Search or go thru my old posts. I've got list of problems with them. It's just a less tuneable design, with huge flaws built in to boot. If you are running faster with a 750 E, then you probably didn't spend enough time with the holley.
Show cars and root blowers is why they use E carbs. How many E carbs have you ever seen in a winner circle ? Guys in car shows probably don't take their car down the 1/4 mi.Plus if it's a small blower, it's easier to install them than turning holleys sideways with linkage. Performance guys don't really use roots anymore. Unless it is a full blown car that runs on alc or as another cool burning fuel.

Fast63 · Jan 2, 2008

well I just have one thing to say then... the carbs you see in the winner circle don't have anything to do with the carbs themselves a lot of the time, you should know that. Sponsors sometimes. But you are also talking about really tricked out holleys or other holley type carbs. No, you can't trick out an edelbrock like you can some of the holley or other carbs, but when you're talking about a street machine, it's hard to beat an edlebrock. They are definitely more tuneable than you think.

10secgoal · Jan 2, 2008

Fast63 said:
well I just have one thing to say then... the carbs you see in the winner circle don't have anything to do with the carbs themselves a lot of the time, you should know that. Sponsors sometimes. But you are also talking about really tricked out holleys or other holley type carbs. No, you can't trick out an edelbrock like you can some of the holley or other carbs, but when you're talking about a street machine, it's hard to beat an edlebrock. They are definitely more tuneable than you think.

If Nascar could pick, do you think any of the crew chiefs would pick an E carb ? It's not because of sponsors. A out of the box Holley (tricked out or not) wins hands down every time. And I think if you knew alot about carbs and how they worked inside and out, and why, you would know that. If they were so tuneable, you wouldn't see a ton of threads floating around here with all the guys and a secondary lean hesitation that can't be tuned out.

Carb advice please

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