Should I modify my 750dp, or just go bigger?

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metallidart

metallidart

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I have my Holley 750 double pumper (4779) all apart for a rebuild (I got it used), and I just had a few questions. I have rebuilt a ton of carbs, so no issues on the "how to" in that respect.

I was just curious to see if there was any worthwhile way to increase the airflow on the 750 to make it a better match for my 422 sb. Or, would it just be easier to look for an 850dp or even a 950hp? 10.8:1, W2 2.08/1.6, [email protected] Lunati solid flat, 3.73 gears, auto w/appropriate stall.

I am kind of thinking whatever I do, it will just be a crutch and I need a bigger carb.
 
What RPM are you typically spinning the motor to? Is this a street car or will you be seeing some track time?

Unless you're turning upwards of 7,000 RPM, I can't see the motor needing much more than a properly tuned 750DP.

Definitely interested in what others have to say on the topic.

-Mike
 
Its going to see upwards of 65-6800, or as high as I need to go lol. The W2s will be ported, and I am leaning towards the Lunat Voodoo solid 288/296 259/[email protected] .586/.606 110lsa cam, although the one below it in size isn't out of the question. My goal is to break into the 10's once its all set up. My compression is an educated guess, I havent cc'd the heads yet, they are listed at 70cc so I figures after polishing etc it will be around 73cc.

I have thought about the proform main body alot. It seems like it would definitely help the airflow. I'm just wondering if it would be enough? Depending on what thread you read, what day it was posted, what the posters had for breakfast, etc, the 750 would be ok, it would be ok for now, an 850 would be ideal, a 950hp would be ideal, an upside down gas can would be best, etc. Inkjunkie even pours the fuel on himself.

I'm willing to bet the 750 with the proform body would be super responsive, and probably more streetable. 90% of my time will be on the street, but 75% of that time it will more than likely be driven like it is at the strip.

If there were more than one E85 station around here, I would probably go that route.
 
Never had one of those Proform main bodies myself but a friend just went thru a carb for a customer. Looked sweet on the surface till he mentioned that the venturi's & plate did not line up well. He wasn't too impressed. I'm sure many just slap those together & call it an upgrade. I'd do a little research before buying one myself.
 
If I did go that route, I wouldn't be afraid to match it all up and blend it with a dremel and some sanding rolls. As long as all the internal ports lined up.

I think the one thing that keeps bouncing back and forth in my head is 1) Put $120 or so in my 750 or 2) sell the rebuilt 750 for $175 or so and put that towards a used 850, or bigger.

It would be cool to try the proform just because I have never used one before lol.
 
I would get a 950. They have them on ebay for around 450 rebuilt. But it doesn't coem with HP center, but you can buy one off there brand new for like 60 bucks.
 
HP950 and not worry anymore.
I use similarly rated Street Avenger 870s on engines that never go above 5500, cruise at 2200, and idle at 800. Strokers love them and really respond well. Even in terms of gas mileage.
 
Thats not a bad price, I looked a little the other day but just at 850s lol. As long as it is complete, a used one needing rebuilt isn't out of the question. Unless it was rebuilt by someone I personally trust, I would probably tear it down anyway. I will have to check out prices again tonight. Kinda kicking myself for selling my new, in the box, 850 on here last year for like $300.

What about an 850 with the aftermarket main body?
Another question, other than the obvious "better flow" from the missing choke horn, etc, how much to they actually increase the flow? Do they increase the volume, or is that more relative to the engine, or butterfly size? Or do I need some schooling on what carb airflow numbers actually measure? I didn't sleep much, and just got home from the dentist, so my confusion level is higher than normal lol.
 
moper said:
HP950 and not worry anymore.
I use similarly rated Street Avenger 870s on engines that never go above 5500, cruise at 2200, and idle at 800. Strokers love them and really respond well. Even in terms of gas mileage.
Click to expand...

Thats basically what I was understanding from alot of guys. This is my first stroker, first experience with W2s, cam bigger than 240ish @.050, first solid cam, first engine over 9.5:1, etc. Pretty steep learning curve, especially since it seems like strokers behave quite a bit differently.
 
Least expensive way to go large is the proform mainbody.

Will flow about the same as the 80496 950hp carb.
 
crackedback said:
Least expensive way to go large is the proform mainbody.

Will flow about the same as the 80496 950hp carb.
Click to expand...

Thats the part that has me stumped. I know in the end its just numbers and whatever works best, works best, but the numbers help me understand it lol.

So, it would let the same amount, or similar, to the 950hp. Are the throttle plates the same diameter? I haven't done alot of research, and I know I shouldn't assume, but I am lol. I assumed the 850 and larger Holleys would have larger bores/plates, and like anything larger, on the same engine the bigger ones would flow more air, just slower. So, am I right assuming the 750 with a proform body would have more velocity? And the increase in flow would come not from volume, which would basically stay the same, but from less restrictions in the path of airflow? That would lead me to assume a carb like that would have better street manners, response, etc.

Am I overthinking this?lol

I guess, bang for the buck, would be either my 750, or an 850 (they go for about the same price used) if I sold my 750, and get a proform body for either of them. Tthat would get me behind the wheel the quickest!

Maybe down the road I could get a 950hp, when my finances are a little better. Hell, for that matter, I could get a main body when my finances are better.

This train of thought brought me back to selling my 750 and finding a good used 850.

Back to the question, and the above million questions, other than the main body swap, is there really anything else you can do cheaply to increase aiflow on my 750?

Btw, thanks for the answers so far!
 
I suggest running what you have if you need a carb now and call a few places with your car and engine specs and see what they recommend and how the carbs would be set up. Save your funds for a carb that is suited to your combo then sell the 750 when it arrives.
 
Rocket said:
I suggest running what you have if you need a carb now and call a few places with your car and engine specs and see what they recommend and how the carbs would be set up. Save your funds for a carb that is suited to your combo then sell the 750 when it arrives.
Click to expand...

I agree,, its not the always the amount of CFM that gets the job done,,all carbs are mast produced,,they dont know or care what cam you have,,rear gear,,,tire size compression,,chamber size, or how much the car weighs,,or what you plan to do with it,,,

if your want the car to perform on the street and strip its different then just a track car,, there is a carb guru near me,,that works wonders with mostly holly carbs,,,he come from the boating and drag racing world,,his sons hold a lot of records at a local drag strip in south jersey,, he ddi wonders to the carbs i had on a street drivn blower motor,,my carbs went from 650 cfm to 862 each,, but all the internals were reworked for driveablitly on the street, most blower cars have to wait for the blower to build heat before they can get them to idel,,, not the oen i had,,,

but special tuning doesnt come cheap,,,get a carb built to your needs out of the box doesnt always work perfectly,,,
 
a no cost idea, take a look at a holley hp carb and note the entry. the way it is smoothed out and then do it to your 750. this allows more air to enter it smoothly. this mod you'll have to add more main jet and you'll make more horsepower.
 
Is this a full blown race car that your leaving at 4500 or higher on the transbrake? Then go bigger where low speed drivabillity and part throttle are not needed. If its a street strip car, then stay with the 750. This is why i dyno everything, there is no guessing as to what the motor wants vs what i think it needs.

Example. My new 426 wedge 520 HP used 630 cfm. So the AED 750 HOM i have is perfect, its crisp resonsive, it accelerates great no bogs farts of stumbles.

There is a 428 stroker ford small block on the dyno now, big compression victor heads big roller cam etc, it has a 1050 dominator on it, and it is using 930 cfm. So thats perfect, he has a light car, leaves off the button. he made 780 HP

Decide what your doing with the car and get the carb that best suits your needs. Dont over carb your combo you will have more problems than you need.
 
To get a proform main body to work on a 750 db look at the numbers on throttle plates
180 will work, 172 are too small to work.
 
I like Fisher's response, 100%. chassis Dyno is the way to go. First hand experence. No time for Details just "Cliff Notes" (showing my age) .Dialing in Cars one weekend at Track (all friends). Running Big Block (Built) heavy car. went to 850 cfm DP at Track pulled off friends car running that weekend also. (Built Carb, high dollar, close specs. on total car combo.) 60 ft. times dropped, E.T. dropped BUT Trap speed was UP. re-jetted the 850 ALOT to try to work it in. Best we could do was a few 10ths (yes I know they all add up) . Long story short,put 750 DP back on played with MY 750 all weekend DID NOT MESS WITH ANYTHING ELSE. Just so I had no X-tra variables. After all was said and done I was back to the same jetting and ended up with the only change was I Went to 50cc accelerator pumps .60 ft. times dropped, Slicks spun a tad more off line and dusting all the way through 60 ft. mark. Dropped .5 off total ET. After this LONG build up to qualify this statement. You have to dial every carb. into YOUR total combo at a Track to see what works for you. Try not to touch anything else so you can see if you need another Carb. MERRY CHRISTMAS !
Tim :-D
 
I will agree with using the ProForm center section. I used one with my old 650DP Holley and it made all the difference at the higher RPMs,
 
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