mikeys68

I recently bought a 68 shelby gt350 clone that has a 351w that was supposively professionally built, but I question that now. My problem is the Holley street avenger 770 has been "tuned" by a local race/tune shop, but still "spudders" and "loses power" briefly at about 3/4 to full throttle. They tell me the carb may be very large cfm for the motor and maybe a smaller better carb would be better. They also claim the street avenger is low quality Holley equipmt. I'm just now getting back into the muscle car scene after many years and don't really know much at all. The engine supposively has roller rockers, eagle rods, aires pistons, ceramic coated headers, Trick flow heads, comp roller cam, pro race harmonic balancer, edelbrok performer RPM intake, holley race fuel pump, many MSD parts etc. Any thoughts appreciated!!!! I'm leaning towards just buying a new carb but would like advice what to get. I'm not planning on racing the car, but would like to have the most hp with smooth ride. By the way, it dyno-ed at their shop at 305 rwhp with 347 tq. Should a 351 with the above be better than that? Better stop with the questions....

Soaring

The original GT350's used a Holley 600 CFM carb. Sounds like yours is just too big.

Colorado_Mustang

The carb just isn't tuned right. Part of the problem may be the vacuum secondaries. There may not be enough fuel entering the venturi when they open up initially under a light load, causing the hesitation you're feeling.

Other problems may be related to the accelerator pump or other parts of the enrichment circuit.

It doesn't sound like you have a very big cam if you're only gettin 300hp out of a 351W. Do you know the specs? A 650cfm carb may be well what you need...and if you want to eliminate having to tune the vacuum secondaries, just get a classic double pumper.

85lebaront2

See the GT350 carb thread. 1965-67 GT 350s used a 715 cfm Holley, not a 600 cfm. If you could find one, it would be great on a 351W. The 65 was a Holley R3259, 66 R3259-1 both of which had the NASCAR float bowls. The 67 was more conventional with cathedral bowls. I don't remember that Holley number. A 69 428 CJ 735 cfm would be a good size as that is what the old muscle parts catalog recommended. If the heads weren't opened up, all the other work in the world won't help.

4reboy

back in teh day 351w had 290 hp (4 barrel), so I think yours should be way more than that considering what is done to it. But then again i don't know if the 290 hp is at the wheels or at the crank.

valley firearms

It's not ading up. Unless your car is tuned poorly, with all that stuff it should be getting more HP than that. Especially if you have trick flow heads. Are they aluminum? You need to post some pics.

mikeys68

I'll try to post some pics if you or someone can tell me the basics on how to. I'm new to this forum thing. I see a photo gallery section, but not sure where to add from there?

Also, Do you think the Trick Flow Heads are "a good thing"? If so that's great, because I posted the same paragragh to a different forum and had a reply that those heads on a 351 would make it a QUOTE "DOG" of an engine. I know people have different opinions here all the time i'm sure, but maybe Trick Flow has a website or more info somewhere, I haven't looked yet.

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mikeys68

The tune shop tells me now the issue may be the MSD Ignition Box if it's not the carb. The coil is a MSD Blaster 2 i think. Has anyone seen a bad MSD cause issues like I'm having?

Colorado_Mustang

If it's the box, you'll lose your high rpm's no matter how much throttle you're using. It won't just hesitate.

deadcarnahans

I have TFS heads on my 351. No complaints here.