Competition HP TQ and Carb question

[4xquadrod]

I'm not sure where to post this so here I go.

I have a car that produces 419 tq and 290 hp at the rear wheels. The Dyno guys told me that the edelbrock 750 cfm was at its peak and couldn't supply any more fuel at the top end. It was at 14:1 fuel air ratio. They told me a 750 holley would do the trick.

I had a 870 duel float holley so I installed it. Went back to the Dyno and ended up with 400 tq and 335 hp at the rear wheels. I think it ran better the other way, I didn't gain any rpms.

Is there a breif way to explain the change in numbers due to the carb change?

Thanks
Steve

 

[Forrest Nearing]

best way I can think to explain it is, "Edelbrock carbs are junk"







they're for slow show cars...



there's a reason Vic Edelbrock Jr. put a Holley on his daughter's car...



14:1 A:F is SUPER LEAN...



it may run better around town w/ the Carter... er... I mean Edelbrock on it, but it'll make a big difference at the track w/ the Holley.



FWIW, if you're only making 335 at the rear wheels, that you might like a 750 better... I'm assuming you're running an automatic, which will eat a little more power, but I made 328rwhp on a little 302 with a 650 double pumper.



step down to a smaller holley, and drivability around town will improve



Forrest

 

[4xquadrod]

I agree, I was just wondering about the dynamics of why.

 

[paulb]

I take it the 14:1 was at WOT (wide open throttle)? If so that it WAY lean. 12. 5:1 at WOT would be much better. What was the vacuum at WOT? It should have been less then 2-3". If it was then more then likely you have enough CFM. Try jetting it richer and see what happens.



As far as the 870 making more power. I suspect it was jetted a little richer.



Paul

 

[4xquadrod]

The edelbrock could not be richened up any further (so the shop said). The 870 was richer and they brought it to the 12+:1

I was wonder more about the relationship between gaining hp and losing tq with the change.
I guess I just don't know how to articulate my question well enough to get my thoughts across.

Thanks Guys!

 

[Forrest Nearing]

the torque probably comes from the smaller carb...



you can fatten up edelbrocks, but I'm not sure how far. have you played w/ those metering rods or whatever they use? (I wouldn't mess with the edelbrock personally)



what size engine? I'm assuming 350-400cid based on the torque numbers

 

[EbarA]

I think they use metering rods as well (I use to use Holley as well). Size of the Carb or CFM should not (in itself) change your ratio. You just need more fuel for the air your pulling in. As a thought, might check your fuel pressure when you are at WOT. If you drop, it can cause a lean condition at top end.



I would think the 750 CFM should be enough for the numbers you are pulling. A lot of times, larger carb can result in higher peak HP but less TQ. At the lower rpms, the air has more speed as it flows through the ventura on a smaller carb giving it more TQ. A bigger carb has a bigger opening and the air slows done in low-mid range rpms causing the power to fall off till the motor pulls enough air in to bring the "air speed" back up ... causing better atomization and all that good stuff.



Just because a motor puts our more peak HP does not mean it will run better then a motor with more broad range TQ. Just ask the guys/gals on this site.



Just my $. 02.