Adrenolin

So I called Edelbrock today regarding heads, intake and carburetor for our 351w. The tech said agreed that on a stock 351w the 600cfm to 650cfm carbs would be best however with our build be highly recommended the larger 800cfm AVS Thunder series carb which kind of surprised me. He said their testing showed that at 350cid and 370hp the 650cfm carbs didn't offer enough and stepping up to their 750 or 800 showed a performance increase. Since we should be 357cid pushing 440ish hp/torque we'd be farther ahead getting the 800cfm AVS and adjusting the secondaries to kick in a bit later. Explained to me that the primaries on the 800AVS are smaller than on the other performer and RPM carbs. Also with this setup he stated that we'd get better fuel mileage due to the smaller primaries.

Our tentative build consists of the RPM 2.020 heads (602519), RPM intake (71811), Comp Cams hydraulic roller cam, lifter, timing chain, retro-fit kit (SK35-424-8 or SK35-421-8/ 31-1000) and Keith Black Hypereutectic pistons (KB-303.030-8).

So as the saying goes... things to make you go Hmmm.

kalli

I would kinda trust what the manufacturer is telling you, but I believe the most important part here is: how high do you want to rev the 351? 6000? 8000? that makes all the difference. not only how many CID are pulling, but how often in a given time ...

Kalli

my77stang

i gotta ask why your even looking at a edelbrock carb? its well known that by not going with a holley design you WILL be leaving horsepower on the table.

1971mach1

I have a 351C and put on a Edelbrock Performer 750 (vs) and couldn't be happier.
Drivability is now great, almost like it had fuel injection and right out of the box, no tweeking needed. And by the seat-of-the-pants dyno, it feels like it gained about 20hp over the origional (rebuilt) Autolite 735 (using stock manifold with sq-bore adapter).
I've had the Edel on now for about 1.5 years and it still performs like new, with no tweeking.
Back in the 1970s-80s, Holley had the best replacement carbs, but I think Edelbrock is now a step above.

fakesnakes

At any given moment on any given car related forum the debate of Edelbrock over Holley carbs rages on!

I had a 750 Edelbrock on my Ford racing 392 (stroked 351w) and it performed well (same engine that originally had EFI stacks on it). Where it fell down, like all Edelbrock carbs do, is at the upper end of performance. If you rarely or don't ever play in this space, you probably don't realize what you are leaving on the table. In my case, almost 20HP! Varying the size of the primary jet (as Edelbrock does through the stepped rod controlled by vacuum) works great for moderate driving. The problem is in transition to the secondaries at various rpm and load it is unpredictable, particularly in high VE engines. This is where the simplicity of the Holley power valve in conjunction with correct accelerator pump tuning shines.

Let's not make this a debate about Edelbrock vs. Holley, but more about the engine and type of driving. A well built, well tuned engine intended for strip and "spirited" street driving works better with a Holley design.

1971mach1

That's funny, I felt it had the MOST gain at the upper end (3500-5500 (my limit)), but it also gained on the low end too. A different engine though (mostly stock 351C 4v heads).

Looks like the old addage, "your results may vary" certainly applies here.

Carlos Pineiro

I'm no mechanic, so from a layman's point of view, all I can say is my EB 650 Thunderjet AVS gives me a balanced, responsive ride up through 6000 rpm on my 302. It doesn't suck that much more gas than the 500 cfm carb I replaced (according to my MPG), but I must be sucking a lot more air because the increased HP I got was significant. I probably would have done fine with the 600, but I got a deal on the 650 at the time, so I took it.

The nice thing about the Thunderjet series is the ability to easily adjust the secondaries with a screwdriver without any hassle.

CP

Adrenolin

Kalli.. thats the funny thing about the manufacturers suggestion. I've made 2 calls to them and the 1st told me a 650 while the 2nd told me the 800. Today I called in for a tie breaker and hit the Carb option in the phone menu. Today the 3rd tech recommended that both carbs would function well however the 650 for low end and the 800 more so for top end with your foot in it. The final outcome was that he suggested that the 650cfm AVS carb would be best for a fun street car and perhaps tuning the secondaries to kick in a bit sooner.

As for the RPM I'll likely be setting a limit via the new MSD 6AL-2 at about 6300rpm. The springs in the Edl 602519 heads are rated for 6500. I figure 6200 will keep away from any valve float issues and keep her from blowing it up.

my77stang.. I knew the debate regarding Edelbrock vs Holley carbs would hit. Don't care, I'm not racing the car or looking for every single HP I can find. Without commenting on the known issues BOTH have... I'll be installing an Edelbrock carb.

1971mach1.. What did you have on it before the 750? I'm looking for the lower end power and the tech today said the 650 would be better for this.

fakesnakes.. the intent on this car will be strictly street by the wife whose mainly a light footed driver. She can't wait to kick her foot into it but for the most part an easy going driver. A few people we know do the strip thing so I'm sure it'll see the tree once or twice but thats it.

Carlos.. your correct in the ease of adjustments on the Thunder series. Was one of the reasons I've decided to go with it. I've got an older 600cfm (1406 I think) that needs a rebuild on the 289 sitting in the corner. Figured I'd get a new carb for the 351w and leave the 289 complete for later.

my77stang

*cough* proform *cough*

1971mach1

The origional Autolite 735 was on it.
650 would probably be better for your purpose though.