Carb and Distributor Recommendation

[eoseitz]

Hey Everyone. I'm almost finished with my engine build and I'm needing to choose a carb. I'm leaning toward a 650 edelbrock to match my intake. Would a 650 be good or should I step up to a 700? My other question is about the distributor. I have a 74 corvette and I need an MSD tach drive (or knock off) to run my RPM gauge. However, the websites I'm viewing is saying it will only work on vehicles up to a 74. Is there anything different about the gear on the bottom that would make this not work in my setup? I've list full build details below.

Heads

1965 Chevy Double Hump 3890462
2.02 Intake 1.60 Exhaust 64 CC combustion chamber

Pistons

Unknown Brand….Stamped 0.30

Block

1982 LT9 350 Bored .030 over.

Rocker Arms
Brand:COMP Cams
Manufacturer's Part Number:17002-16
Part Type:Rocker Arms
Product Line:COMP Cams High Energy Die-Cast Aluminum Rocker Arms
Summit Racing Part Number:CCA-17002-16
UPC:036584215943
Rocker Arm Mounting Style:Stud
Rocker Arm Ratio:1.6
Rocker Arm Style:Full roller
Stud Size:3/8 in.
Shims Included:No
Rocker Arm Material:Aluminum
Self-Aligning:No
Rocker Arm Body Style:Standard
Rocker Arm Nut Styleolylock
Slot Style:Standard

Push Rod
Brand: Elgin
Pushrod Model Or Series: Heavy Duty
Year: SB Chevy
Engine: SB Chevy
Tube Diameter: 5/16"
Tube Wall: .075" Wall
Length: 7.8
Material: C1010
Heat Treated: Yes
Use With Guide Plates: Yes

Rocker Arm Studs
COMPETITION SCREW-IN ROCKER ARM STUDS
C.A.T Power part # RAS 3750
Comparable to Mr Gasket part # 1075
A 7/16"-14 tapped hole in the head is necessary for installation. Stock heads do not have threaded holes.
Top 3/8"-24 thread size (for rocker arm nut/polylock)
Bottom 7/16"-14 thread size
2-1/2" overall length
Hex base up - 1-3/4" long

Lifters
Brand:Sealed Power
Manufacturer's Part Number:HT-817
Part Type:Lifters
Product Line:Sealed Power Hydraulic Lifters
Summit Racing Part Number:SLP-HT-817
UPC:724956565054
Lifter Style:Hydraulic flat tappet
Lifter Link Bars Included:No
Link Bar:None
Lifter Outside Diameter (in):0.842 in.
Lifter Offset:None

Cam
Hi-Flow 1H
Erson E110421
RPM Range 2750-5750
Duration @ .050 Lift 228 deg
Valve Lift .472 in
Lobe Separation 108 deg
Advance 0 deg

Intake
Edelbrock 2701 Performer EPS

 

[Hib Halverson]

If yours is a 74, then the MSD tach-drive distributor, which BTW, is an excellent product, will work fine. It's for Corvettes up to and including the 1974 model year.

With that 82 block, unknown pistons and the heads with 64-cc chambers you may want to make sure you're not going to have problems with compression ratio. Are the pistons flat-tops with four valve reliefs?

As for a carb, I'd retain the QuadraJet which came with your car but have it modified to work with the cam and head combination you have.

 

[eoseitz01]

I don't have the original engine or quadrajet in the car anymore.

The Pistons are flat tops. I'm not sure about the reliefs.



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[kpic]

Back in the day, GM used Holley on the 350-370, Z-28 302 and 396-375. I'd do what GM did. Personally, I'd get the dual feed (separate fuel inlets for the primaries and secondaries) 750 or 780 cfm Holley and set it up for mechanical, not vacuum secondaries. Mechanical hits harder and quicker than vacuum.

 

[Vettehead Mikey]

That's a shame the original Qjet carb and manifold are gone. Other than bragging rights, there's not much to gain by having a carb bigger than 650 CFM on a relatively mild engine.

 

[Hib Halverson]

Flat tops and 64cc heads may result in a fairly high but not excessive compression ratio. It depends on any valve reliefs in the pistons and the deck height. If you're not sure of the CR, you need to be careful with your spark calibration.

Those 64 cc heads do not have hardened valve seats so make sure you're using a Lead Substitute product. A good one is Red Line Lead Substitute.

If you don't have the original carb, I'd either go looking for a QuadraJet, then have it properly calibrated, or put a small duel-feed Holley on it...say 600-700. Ignore earlier comments about mechanical secondary Holleys. They don't work very well on the street unless the engine is very radical and the duty cycle is more racing than street. The comment about vacuum secondary carbs not hitting hard is ridiculoius. Properly calibrated, a vaccuum secondary Holley can "hit" real hard especially with the right axle ratio. In fact, the opposite is true, in most cases. In a high-po street application, a mechanical secondary Holley will often "over-carburate" right at secondary opening.

The comparison between your applcation (mild 350 w hyd cam) and the 350/370 (70 LT1) 302/290 (67-69 Z/28) and 396/375 is not logical.

Good luck!

 

[eoseitz01]

My heads were redone. I probably should have mentioned that. I don't know all the specs anymore. I know they have hardened valve seals and some other valve work done. I'm pretty sure there are stiffer springs and the valves may have been enlarged. I recall him saying something about a port polish maybe when I bought them.


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[Vettehead Mikey]

I wouldn't worry about hardened seats one way or the other. Engines in Corvettes don't get worked hard enough for it to be an issue.

 

[eoseitz01]

So should I be looking at 600 or 650 carbs? The auto store in town has a 600 in stock.


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[Hib Halverson]

My heads were redone. I probably should have mentioned that. I don't know all the specs anymore. I know they have hardened valve seals and some other valve work done. I'm pretty sure there are stiffer springs and the valves may have been enlarged. I recall him saying something about a port polish maybe when I bought them.


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It's "hardened valve seats" not "hardened valve seals".

As for "Vettehead Mikey" suggesting that valve seat recession is not an issue, my experience has been that Corvette engines may see severe duty and severe duty is what causes valve seats to recede in the absence of some kind of seat lubrication, either leaded gasoline or some form of lead substitute. Conversely, if the engine is always driven easy, then, I agree with "Mikey" in that the need for hard seats or lead substitute is not that critical.

 

[Crimson Thunder]

I have the 670 Holley Street Avenger carb on my car. My cam and engine specs are fairly close to yours. I put the yellow spring in it and it hits as hard as a mech. secondary carb. I've been happy with it.

 

[eoseitz01]

Ok. I'll look into that. Thanks for the responses.


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[Hib Halverson]

How "hard" the carb "hits" is going to be governed by many characteristics

1) Spark curve
2) RPM at vac secondary opening point
3) Vac secondary opening point and opening speed.
4) air fuel ratio during accelerator pump action.
5) air fuel ratio at part throttle just prior to secondary opening
6) air fuel ratio during power enrichment
7) vehicle weight
8) final drive ratio

Get all that stuff right and you can be assured the carb will "hit" hard.

 

[tnovot]

I have the 670 Holley Street Avenger carb on my car. My cam and engine specs are fairly close to yours. I put the yellow spring in it and it hits as hard as a mech. secondary carb. I've been happy with it.

I also had a Holley Street Avenger 670 on a ZZ4 crate engine in my '75 before I sold it. Loved the carb - good starting, excellent response at all RPM's. Here is a cut and paste from an earlier reply to a question a few years ago:
"I run a Holley 670 SA on my ZZ4, it screams! But swap the #68 secondary jet into the primary side and pick up a #76 for the secondary (as per Lars' recommendation). Easy to do..."

I left the jets in mine unchanged and it may have been a little lean but was fine for normal street driving with an occasional hard run through the gears.
Terry

 

[kpic]

In a no-holds-barred performance application, a mechanical-secondary carb does have advantages over a controlled-secondary configuration. Assuming it's properly sized and fine-tuned for the application, due to its quicker-opening secondaries, when you slam the throttle full-open, a double-pumper carb has the potential to generate better throttle response and make more power than a controlled-secondary carb with the same airflow (cfm rating). Until its secondaries fully open, a controlled-secondary carburetor has more pressure drop under the throttle plates compared with the mechanical-secondary unit; less pressure drop below the throttle plates translates into the engine receiving a denser air/fuel charge. Greater charge density translates into higher engine output.

Vacuum or Mechanical-Secondary Carburetor? - Hot Rod Magazine

It is what it is.

 

[eoseitz01]

So just for clarification, a 650 would be ok?


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