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Old 04-20-2013, 09:41 PM
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Carb selection advice: SBC Mild cam

Here are the specs

350 SBC 4 bolt main
.040 overbore
76CC heads from 74-80
9 to 1 compression
Performer RPM intake manifold
Hugger headers
manual trani

Currently I have a 600cc holley single pumper 4 brl that seems to run OK, but just doesnt have the power or response that I am looking for. I used to have a throttle body fuel injection setup (Holley) that made substantially more power and torque and performed flawlessly until the ECU died and I had to go back to carbs.
I have had the carbs dyno tuned a couple of times in the past by a very good tuner extremely familar with holleys and I am not happy with them, The power breaks up substantially in the upper rpm's and the torque down low is just not what it should be (half what it should be..). The latest dyno a year ago was 235rwhp and 295rwtq (Power valve changed and some other stuff, still broke up in top end and just felt sloppy). The same dyno 4 years prior was 245rwhp and 275rwtq with about 25% drivetrain loss. When fuel injection was used it had 50more hp and 100 more tq to my butt dyno which has been very accurate to date

Im looking for a carb that will let me tune it better and fit my performance needs better.

I do road racing very occasionally but mostly mountain runs and drift days in the car, but it is 90% a street car.

I was thinking a holley 670 street avenger, can anyone confirm this would be good?

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Old 04-20-2013, 09:51 PM
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what kind of car, weight, gearing, max rpm, fuel type.
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Old 04-20-2013, 10:21 PM
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73 Porsche 914, 2300lbs, close ratio 4 speed, 6500 max rpm, CA 91 octane.



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Old 04-20-2013, 11:05 PM
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750? Really? That seams like a lot of carb.

I dont really think I need better heads, The power level I had with the fuel injection (650cc TBI) was plenty, Im just trying to get to that power level and close to the drivability with carbs.
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Old 04-20-2013, 11:37 PM
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holley 390 with vacuum secondaries
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Old 04-21-2013, 12:07 AM
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390? Your joking right?
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Old 04-21-2013, 01:27 AM
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Quote:
Originally Posted by Andyrew View Post
750? Really? That seams like a lot of carb.

I dont really think I need better heads, The power level I had with the fuel injection (650cc TBI) was plenty, Im just trying to get to that power level and close to the drivability with carbs.
2300# curb weight, manual trans, a set of decent alum heads and a 750dp would make for a seriously fun street car.
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Old 04-21-2013, 01:57 AM
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Nobody has asked about the cam yet??????? The SCR is 9.0:1. If you using a big cam with that SCR, there's the problem.
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Old 04-21-2013, 02:06 AM
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Tech inspector, Mild cam. Here are the details on it. If I remember it was an RV style cam. (We tried to eliminate low end torque, trani does not fair well with high torque)

It's an Elgin "Pro Stock" Cam
These are the specs on the box.
DURN DUR. @ .050 CAM LIFT Valve Lift Lobe Centers
IN Ex IN Ex IN Ex IN Ex IN Ex
291 291 218 218 0.303 0.303 0.455 0.455 105 115
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Old 04-21-2013, 02:16 AM
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Quote:
Originally Posted by F-BIRD'88 View Post
Ditch those old smog era 200 horse heads. What are they 882's?
Yup 882's.

We've already had the 600 tuned to what the local tuners can do with all new parts, 4 hours of dyno work, and really I havent noticed enough difference to justify any more work at $100 an hour, Even they said its as much as they can do on that carb as its sacrifice this direction or sacrifice that direction.. So its time to move on to new hardware..

I'll look at the option you presented me, I appreciate the breakout
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Old 04-21-2013, 03:02 AM
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So this is what I would be looking at if I went the Proform route? Note the carb donor is a mech secondary whereas the proform is vacuum.

http://www.summitracing.com/parts/pro-67101c/overview/

Holley 700 Double Pumper Carburetor | eBay
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Old 04-21-2013, 09:32 AM
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I agree with f-bird,a 4779 holley or HP series or,,,if you can build the carb yourself? I really like using a 4777 holley as is except,,change the base plate to a base plate off a 4781(850). Build that carb,it will flow785 ish.The throttle response is excellent,small venturi Vs 850 Base
plate. If you modify the 650 add replace able air bleeds
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Old 04-21-2013, 01:03 PM
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F-bird,

Its so bad right now I am thinking that I have some other issue.. It feels like 100hp right now. Im going to start with the fuel filter and see where that gets me, and then pull the plugs to see what it looks like.

Again, when I had fuel injection it felt amazing.. Like I could break the tires loose at 50mph by just stomping on it.
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Old 04-21-2013, 02:28 PM
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Nope carb pump.

I was trying to dial the engine in after I had done the major tuning myself. Didnt do much..
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Old 04-21-2013, 02:40 PM
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dyno

Quote:
Originally Posted by Andyrew View Post
Nope carb pump.

I was trying to dial the engine in after I had done the major tuning myself. Didnt do much..
what he is saying is;even if you find a few ponies the cost is too high for such a low return. Your 914 is the second v-8 Ive seen. what amount of power will your trans axle accept?
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