Which Carb to Buy?

[85/Silverado]

The motor is pushing over 400 hp. SBC 4 bolt main. Edelbrock RPM Intake.
I want either a 650 or 750 and a quality carb. I would like to stay under 500 dollars.

Thanks

[68post]

If your intake is a spreadbore the best street carb is a Qjet , if it is a squarebore intake the 750 or 800 edelbrocks can give good mileage , but a Quickfuel is a great carb for power.

Over 400 HP - I wouldn't be looking at 650 carbs.

[85/Silverado]

Is there much trouble with a QF carb and Auto Trans?

[rich weyand]

400 hp at 5500 rpm in a 400 SBC is 600 cfm. Over-carbing it will reduce horsepower and mileage due to reduced stack velocity.

Look at the Qjets from SMI carburetors. Sean Murphy was one of the founders of Jet and knows what he is doing. He will tune it to your setup based on his voluminous notes.

[Drizzle]

I noticed a significant power increase replacing my ed 600 with a holley 750. 4150 with electric choke and vacuum secondary. Given my edelbrock was having issues but I don't think power was effected after half throttle. Polished all for a little over 300 bucks.

[68post]

You do have the option of buying a spreadbore Holley also. They were produced in 650 and 800, double pumper or vacuum secondaries. (I think that only the 650's are still sold new )
Spreadbore carbs make better street carbs in my opinion.


$.02

[85/Silverado]

What about a Mechanical Fuel Pump? Do I need the Push Rod for it? I sent my Specs. to SMI to see what they suggest for CFM's will see what they say before I buy.
I just took the motor to a guy to have him measure the pushrod length so I know what to order. And he will install them and the rockers, Dist. Water Pump, Intake and water neck & thermostat for 300 bucks.

[MikeB]

Is this a new engine? What are the specs - size, cam, heads -- and intended usage?

600-650 CFM is perfect for 90% of 350s, the exceptions being high RPM racing engines. But some carb models work better than others with big cams.

[popsthebuilder]

I've heard good things about the quick fuels.

[Jake Wade]

If you are needing a square flange carb, I like the Quickfuel 680 Hot rod series.

otherwise.....Qjet

[68post]

A 600 carb on a 400+ HP engine would be best on a single plane intake , but since the engine only sees half the carb on a dualplane it likes a little more carb.

That said - I did use a 500 AFB on a dualplane manifold years ago, my main concerns were mileage and torque below 4,000. The engine was a 350 with; an AL intake , headers, mild cam ( 260* advertised duration), and quicker advance ignition. Aprox. 320 HP.

It would fall on it's face around 5,000 rpm, but got great, for a 3/4 ton, mileage !

A 350 in a truck needs a dualplane usually, a 400 + hp engine doesn't need a 600 Edelbrock - but a 650 Holley may be a minimum. IMHO

Here's a great carb for only $334.03

http://www.quickfueltechnology.com/c...fm-street.html

[bnoon]

I run about 425 horse and am limited on the top end by my Summit Racing 600 CFM carb (Holley 4010 based design with many improvements). At about 5700, the 600 is done. If I end up keeping the 350 that I have for sale, a 750 Holley (3310 with Proform main body) will climb on top and will gain a good 20-30 horse on my combination.

[kalbert]

400hp? Says who? How are you measuring it without a carb on it? To pick the right carb you need to evaluate more than a horsepower estimate. How many cubic inches? Compression ratio? Cam? Heads? Exhaust? Highway, town, road racing, drag racing? Then we can talk carburetor.

[MikeB]

Originally Posted by kalbert

400hp? How many cubic inches? Compression ratio? Cam? Heads? Exhaust? Highway, town, road racing, drag racing? Then we can talk carburetor.

Bingo!

[UKNOWME]

Originally Posted by kalbert

400hp? Says who? How are you measuring it without a carb on it? To pick the right carb you need to evaluate more than a horsepower estimate. How many cubic inches? Compression ratio? Cam? Heads? Exhaust? Highway, town, road racing, drag racing? Then we can talk carburetor.

I'm grabbing some popcorn. This may get interesting!

[85/Silverado]

Here is all the info on the engine.
Cam http://www.compcams.com/Company/CC/c...x?csid=79&sb=0
Stroked 368 ci
Alum heads 200cc intake runners. 2.02 intake, 1.60 exhaust, springs .550
Compression Ratio 10.4 to 1
Long Tube Headers
Mostly city driving to shows and occasional trip to town to pick up large things

[MikeB]

All those engine parts are begging for a 3.73 axle and a 650-670 carb on that Edelbrock Performer RPM manifold.

I'd call QuickFuel Technology and Holley to see what they recommend. The key is being able to adjust idle mixture and get a consistent idle speed with that cam and the 200cc intake runners. Both conspire to create low vacuum and "lazy" air flow at low RPMs. However, your engine should be awesome once it gets past 2000-2500 RPM.

[stansilverado]

I made and researched multiple threads about carb size. I even used the Calc but could not pull the triggger on a 600cfm carb for my 383. I ended up using a QF750.. The carb not only started my truck and kept it running on the first try.. It only needed slight adjusting for optimal performance. Best carb Ive ever purchased. Fan for life now.
383 stroker I went with a Quick Fuel (Quick Fuel Slayer Series Carburetors SL-750-VS)

[school boy]

Well I wasn't going to post because of fear of being burned but oh well. I ended up picking the Summit 600 with vacuum secondarys. Started my mild 406 on first try and easy to tune on our test stand. The 406 is mild with factory crank, gm 5.7 rods, keith black pistons, ported gm 113 aluminum heads, LT4 hotcam (218/228 @.050), and summit stage 3 intake. What sold me was the anualar boosters and bowl design. Those anualar boosters are great for low signal air speeds. I know the 600 is a tad small but knew I wouldn't be spinning this over 5700 rpms and doing that very little. I mostly wanted the low end torque.

[MikeB]

Originally Posted by school boy

The 406 is mild with factory crank, gm 5.7 rods, keith black pistons, ported gm 113 aluminum heads, LT4 hotcam (218/228 @.050), and summit stage 3 intake.

LT4 roller cam in a GM 400 block?

[school boy]

Originally Posted by MikeB

LT4 roller cam in a GM 400 block?

It's the lt4 hot cam which is the roller cam

[MikeB]

Originally Posted by school boy

It's the lt4 hot cam which is the roller cam

Hmmm. That cam has a stepped nose and must be held in place by a retainer plate that bolts to the front of an 86-up block. But factory 400 blocks do not have that feature. I have never heard of an OE roller cam being used in a non-roller block. So I'm curious to learn how you secured the cam, and what type lifters you used.

Thanks.

[school boy]

Took me a minute to find the exact article but heres where most of the info I used come from.
http://www.superchevy.com/how-to/148...ic-roller-cam/
If I remember correctly:
factory roller cam
modified cam retainer
cam button
roller cam timing chain
roller timing cover
I used Howards retro roller lifters

[MikeB]

So nothing magic then. Just treat it like a retrofit roller cam including the way it's supported in the front. But it was probably less expensive than buying an aftermarket cam.

The GMPP HT383/RamJet 350 cam I'm using in my 97 block cost me only $120-something as a brand new take out! The latest GM roller lifters, as used in the LS7/LS2, were also $120-something.

Thanks for the info.

[school boy]

Yea the cam was $200 from summit I think and everything else I was buying anyway just now for roller cam. I done a lot of research before I built it.