Ok to start the motor is a sbc 406, 6" rods, KB flat tops, 306/298 .499/.502 solid roller cam, Pro-Topline 200cc runner heads with 2.02/1.60 valves,RPM Perf. intake for now(going to single plane later). The question is on carburetor choice, i was looking at a 725cfm Demon, 750 Edelbrock and 750 Holley. The Demon is the cheapest but ive heard that the parts quality is great on them. I was wondering if i would see a noticeable amount of performance loss with it flowing 25cfm less than the other 2 carb's. Anyone that could help me with this i would greatly appreciate it. Thanks in advance.
Dale

 

It probably would help to know driveline and how car will be used.

IMO, 750 is too small.

I don't understand only .500 lift with a 300 deg (advertised) SR. That's only .333 lobe lift (with 1.5 RR) which seems lower than almost all SRs.

 

I don't really mean to use your thread as a plug for me, but if you do decide to go with a 750 I have a new double pumper I am trying to sell. It and one just like it was used on a tunnel ram on a 502. They were used for six months.

It's a 750 cfm double pumper (mechanical secondary) with the four-corner idle adjustment. It has been upgraded with a proform main-body. You can PM me if you are interested in it.

I certainly would not recommend the Edelbrock although I have no personal anecdotal experience, but every one I have talked to wishes they would have went with a Holley.

If you tell us what you're using it for we may be able to help you some. Check with places like

allcarbs.com and thecarbshop.com

If you need any help they may be albe to assist you in putting a custom carb together.

Ben T.

 

OldSStroker
It has a TH350 tranny with 2400 stall, 3.73 gears and detroit locker. I drive it pretty much every day and take it to the track on thursday nights (grudge night here). I wanted to keep it easy to drive on the street was the reason for the cam choice.

 

On a dual- plane intake you want a BIG carb. 750 CFM is probably about the smallest I would go. On a single plane a 750 is fine.

Old school reasoning: on a dual-plane any given cylinder only "sees" half the carb. On a single plane it sees all 4 barrels. My expereince has been that there's a bit of truth to this.

Even my mild 350 street motors just LOVE to have an 800 CFM Qjet sitting on top of their dual-plane intakes. On a single plane intake the motors seem to run nearly as well with a vac. sec Holley as small as 650 CFM (spread bore Holley carb) vs. the higher flowing QJet.

Go figure.

 

I still don't understand a 300* (advertised) cam for your application, but nevermind..

How about a vacuum secondary 870 Holley? They have some great ones out-of-the-box now. Very driveable and you get the flow the engine needs at the high end.

As Damon said, the Q-jet airvalve carb acts like a vac.sec. carb as it opens airvalve based on demand. My OHC 230 Pontiac I6 (1966) had a 750 Q-jet stock. That might have been one of the first uses of that carb, BTW.

My $.02

 

IMO, 870 is way too big for that motor, if it was me, id get a 750 double pumper or 750 road demon. An 800 might be suitable for the dual plane, but Switch intakes to a victor jr. and get rid of that messed up cam too, what kind of cam is that BTW, crane, comp?? Id go with a bigger cam than that, too much duration and not enough lift. Id get a hyrd. roller in the .550 range with about the same duration and some dual springs. Just my 2 cents.

 

take a look at the holley 770 steet avenger pt#080770

 

Do you have any specific reasons for recommending the street avenger? I've noticed this carb has been heavily marketed lately.

I don't see what makes them different than any other Holley. They come pretty close out of the box. Was Holley just trying broaden their market? Increase sales?

IMO, a 750 4150 Holley tuned with a wideband would be an even better choice.



Ben T.

 

i work for a speed shop and i bet we sell between 5-7 street avengers a week anywhere from the 570 up to the new 870 i have never heard a bad report from any of the customers who have bought these carbs i saw that he drives this car a lot on the street the carb takes very little work out of the box to run good if this was a race car i agree 750-800 cfm mech. secondares carb would probley be a better choice