*84TA

It has come time for me to put a new carb on my car. My old edelbrock 1407 is shot! I could re-build it, but I could never get tuned just right...

I thought I would throw this out there for suggestions from the highly knowledgeable member we have here.

Here's what I have.
-ZZ4 short block .020
-Iron Vortec Heads
-Eldelbrock Performer RPM Intake.
-Comp Cam Xtreme Energy XR288 Hydraulic Roller Camshaft
Lift: .520''/.540''
Duration: 288°/294°
Lobe Separation Angle: 110°
RPM Range: 2500-6000
-T5 trans
-3:42 gears.

I know its a loaded question, but what carb would you buy?

Night rider327

iTrader: (13)

As 20 people and you will get at least 10 diff answers. Heck, I'm gonna give you 4 answers lol.

Heres the math formulas to go by.

street carb cfm = rpm x displacement / 3456 x 0.85
street/strip carb cfm = rpm x displacement / 3456 x 0.95
racing carb cfm = rpm x displacement / 3456 x 1.1
engine CID x volumetric effiency x max RPM / 3456 = cfm.

Myself.. For pure street use on that one I would run a 600 vac sec,
street performance 650/660 vac sec,
street/strip 650/660 dp,
more strip than street 750 dp

On my camaro I run a Holley HP 4150 750 dp.. 355, brodix IK 200 heads, 249/252@.050" , .570"/.579", 106 lsa cam, 3.89 gear.

On my street S10 I run an edelbrock 600 cfm, 355, vortec heads, 214/228@.050, 3.42 gear.

skinny z

That's about a sensible answer as you're going to get.
The multipliers (.85, .95, 1.1) in the first three equations are an estimate at the volumetric efficiency (VE). That can be a tricky decision as it's largely a guess. VE is function of the whole engine package. Assuming the compression ratio and exhaust system are spec'd properly, it's the cam and heads that determine the VE. On any given engine, mine for example, the VE could range from 85% to 100%. The max rpm is critical too. Calculate where your engine makes peak power (also largely a guess as a lot of us have never dyno tested our combinations) and add a couple hundred rpm for overspeed. While you may rev more than 200 past peak HP, the VE drops off too so it's basically a wash in the calculation.
As an example, my 355 makes peak power around 5700.rpm. That's from some dyno testing and similar engine build results. Max RPM is 5900. I think I'm optimistic at a VE of 85% and that's due to an inefficient exhaust system. While my headers are well spec'd for my engine, my exhaust piping is not. A single 3" to a small flowing (cfm) muffler in the stock location doesn't due much to relieving back pressure or enhancing flow. That said, I still use 85% as my target.
355 x 5900 x .85/ 3456 = 515 cfm.
From that, it's plain to see how engines get over-carbed. My best choice is less than 600 cfm.
Take that example but use a VE of 100% (which isn't unreasonable with my cylinder heads but with an exhaust system that works like open headers) and the numbers are
355 x 5900 x 1.00/3456 = 606 cfm.
If I went up in cam, say to something like your 288, then peak power might be in around 6300. Add 200 rpm for overspeed and keep the VE the same:
355 x 6500 x .85/3456 = 570 cfm.
At 100% VE:
355 x 6500 x 1.00/3456 = 667 cfm.

It's your guess at volumetric efficiency and max rpm that really make those decisions critical.

skinny z

This is not meant to enter the vacuum secondary vs mechanical secondary debate.
But I will if you want to!

*84TA

I would like to hear your input

RamIt

With the 5 speed? 600-650 dp. Super crisp at the expense of some mpg.
"I" have never been able to tune a vac secondary carb to come close to having the response of a Holley DP with a stick.
Factory quads are better for the ham footed driver.

skinny z

If you never drive your car at less RPM than peak torque output, then your DP is good enough. That is to say, you're never less than say, 3500 rpm or so depedning on your engine specs. Drag racing engines are an excellent example. Big stall converters or dropping the clutch at high rpm won't benefit from what a VS carb has to offer. The performance is equal when tuned.
If power below peak torque is of any concern then if you learn to tune the vacuum secondaries properly, I'll guarantee you'll not only be AS fast at the dragstrip (or faster if your combo is less than ideal as in stall speed or clutch capacity) but you'll win in the MPG department especially in and around town.
Fact.

Ozz1967

iTrader: (4)

I would keep the CC Qjet. Properly tuned, it'll run like a raped ape, give you the same power and better MPG's than any Edelbrock or Holley.

Your performer intake will be the bottleneck in your set up but that's a restriction in keeping the factory hood.

I'm running essentially the same set up you have with a slightly smaller cam (.515/.530 lift, 268/272 duration, Lobe Sep 112.

skinny z

It's been eons since I tuned a quadrajet but if anyone ever produced a carb with primaries and secondaries like the Q-Jet based on a 4150 style, I'd buy one in a heartbeat. You really can't beat those tiny barrels while cruising and those massive secondaries when you mean business.
I've got too much invested in my 4150 platform to re-invest in another carb style but I see your point entirely with the Rochester.

camarito

I used a Speed Demon 650 vacuum secodary on mine for a few years, i have a widebande and vacuum gauge installed and was able to tune it almost like fuel injection i was very happy with it.
A few month ago i got a great deal on a almost new Proform SS 750 mechanical secondary so i give it a shot, it was extremely rich in it's stock form so i used the jets and power valve from the BG 650 and it got spot on on AFR, 14-15:1 at cruise, 13:1 after the 8.5 power valve, 11:1 WOT (a bit rich but i'll get to it in the spring).
For my surprise and contrary to some people advice, the response is much better, the car accelerates faster and has higher top speed, gas mileage didn't suffer at all still the same 16-18 mpg average.
So for my experience and in my setup the 750 mechanical secondary works better.

camarito

i still have the Speed Demon 650 VS if you want to buy it

skinny z

In all fairness that's not really apples to apples.

skinny z

I'll pass on the Speed Demon however the Proform 600 VS looks very interesting.
http://proformparts.specialtyauto.co...ategory_id/182
Adjustable air bleeds (HSAB, LSAB and IAB), four corner idle...If you really want to tune like fuel injection, these are the elements you need to work with. The Speed Demon has none of those except the four corner idle.
14-15:1 is nice but consistently bouncing off 16:1 at cruise with only two barrels functioning will boost the mpg considerably. Not having a 2nd accelerator pump active while cruising through town will also boost economy. (That's only follows).
As for accelerates faster, unless you're engine was starved for air with the 650, I'd say that with a day at the track and some serious tuning, the 650 would perform every bit as good as the 750, perhaps better if your engine runs at less than peak torque at any point in a race. I'm guessing it does.
Well done on your tuning nonetheless. Seems the art of working with a carb is slowly dying. I've got a long season ahead working with what's probably too big a carb (albeit with annular boosters so that helps) and my highway mileage has dropped off some. New track and elevation to work with as well.

camarito

True the Speed Demons don't have adjustable air bleeds but they were perfectly matched ( i did drill the IAB and PVR a bit) but everything else was just jet and power valve change and it was god to go, and i had that carb apart 100 times for small tweaks and experiments with PV and PVR ports as i needed a bit more fuel at power enrichment due to the small primary jets, on the Proform PVR's are also adjustable, and it weights less than 1 third of the Speed Demon, damn thing is heavy
It does hit 16's sometimes with low load but going one size lower in jet will lean it a bit too much for the hot summer, 180* t.stat and high cruise timing (46*), it will ping a little, 14-15 it's just right for my setup, the Vacuum drops allot quicker on the 750 so the power enrichment responds faster than the 650 with the same power valve.
It's not a track car just a fast street machine that i enjoy driving around, a track car it's tuned for WOT, going WOT on the street for more than 5 seconds it's suicide...lol