What carb?

David Murray · Post by **David Murray** » Sun Apr 23, 17 6:08 pm

Currently looking at carb options for my 512 stroker build (10:1 CR, Crower Street Roller Cam), which will be completed and fitted into my Polara over the next few weeks. I don't want to re-use the Quick Fuel 735 Vac Sec that is on the current 440 and don't particularly want another QF carb, though do want to stick with Holley or Holley derivatives. Time for a double pumper perhaps....950 CFM maybe, or is that too big....850 better?

This will remain primarily a street car (A727 with 3.23 gears...but may go up to 3.55's), though I will want to run it down the track every now and again. Any comments/suggestions appreciated.

Blue · Post by **Blue** » Sun Apr 23, 17 6:58 pm

950, those big block strokers love CFM. I Had 2 750 double pumpers on my 400 based 512 in a light car, never had an engine with throttle response like it, the thing was brutal.

TW71 · Post by **TW71** » Mon Apr 24, 17 10:46 am

I have a 950 HP Holley on my 512, although I believe its UNDER 850 cfm, the heads are max wedge port size, it needs much more cfm, I have a 1150 4500 but will use the smaller carb for now but it needs at least 1150 imo.

who wants fuel economy!

David Murray · Post by **David Murray** » Mon Apr 24, 17 11:43 am

Thanks guys. It was actually the Holley HP (either Street or Classic...not sure of the difference) or possibly the mega expensive Ulta XP that I was leaning towards. Sounds like 950 CFM (or at least an advertised 950) is the bare minimum.

Blue · Post by **Blue** » Mon Apr 24, 17 4:09 pm

Pro Systems build some nice carbs to suit your combination, that's what I had. Have a look at their website you can get an online quote.

David Murray · Post by **David Murray** » Mon Apr 24, 17 6:13 pm

Thanks. Just submitted an online form for recommendation and quote.

David Murray · Post by **David Murray** » Tue Apr 25, 17 7:19 pm

Okay, just taken the plunge and ordered a carb from Pro Systems....a custom build based on the Holley 950HP I believe.

Mick · Post by **Mick** » Tue Apr 25, 17 8:55 pm

I have a HP1000 4150 carb i was going to sell.

DaveB · Post by **DaveB** » Wed Apr 26, 17 10:04 pm

I would have used the 735 vac sec,unless you have some real good heads,big roller cam(.650 and up)and rev it to 6800 rpm,you wont need 950 cfm.
your vac sec will support 500hp/550 ft torque.
Putting the motor on the Dyno tells the story

David Murray · Post by **David Murray** » Thu Apr 27, 17 7:20 pm

Interesting point...I've seen a LOT of debate on the kind of setup I'll have, with carb recommendations ranging from 650 CFM vac sec to 1050 dominators.

I've never been entirely happy with the QF carb....hours of tuning with jets, IAB's, IFR's and power valves, but still a big lean spot at part throttle. So, I'll definitely start with the 950 double pumper and see how it goes. Actually, I probably will dyno it so maybe I will stick the 735 vac sec back on then and compare.

Mick · Post by **Mick** » Thu Apr 27, 17 9:19 pm

TW71 wrote:I have a 950 HP Holley on my 512, although I believe its UNDER 850 cfm, the heads are max wedge port size, it needs much more cfm, I have a 1150 4500 but will use the smaller carb for now but it needs at least 1150 imo.

who wants fuel economy!

A HP 950 has a 750 base but they have very good shift recovery, i took an 850 DP off my challenger and fitted my HP950 off my Dart and it picked up .15

Mick · Post by **Mick** » Thu Apr 27, 17 9:20 pm

TW71 wrote:I have a 950 HP Holley on my 512, although I believe its UNDER 850 cfm, the heads are max wedge port size, it needs much more cfm, I have a 1150 4500 but will use the smaller carb for now but it needs at least 1150 imo.

who wants fuel economy!

A HP 950 has a 750 base but they have very good shift recovery, i took an 850 DP off my challenger and fitted my HP950 off my Dart and it picked up .15

TW71 · Post by **TW71** » Fri Apr 28, 17 3:27 pm

They have good response Mick but they were thought to flow 950 cfm and they dont, not sure what the figure is but a lot of punters as I did believed they were 950, hence I believe thats why they brought out ''Ultra'' version