BajaBuddy

I am replacing stock carbs (Weber) on 7.4 litre motors with Holley 750s and was wondering if it is worthwhile to also replace the intakes at the same time, maybe with something like an Edelbrock Performer. Does anybody have any thoughts or experience on this? Thanks.

formula31

The stock intakes are built for spreadbore carbs. The square bore holley can be used on them with an adaptor but I would think the air flow would be strange with the 2 small holes in front and the the 2 big secondary holes. Id change it.

Krumbsnatcher

I would change it but not before I knew what the motor will require in CFM's.

Does anyone know what that motor will pull?

Here is a link that will calculate your CFM.

http://www.csgnetwork.com/cfmcalc.html

Griff

Weber carbs are square bore carbs. The intake manifolds on engines with weber carbs are also for square bore carbs. The Holley will bolt right on without an adapter and the intake is tapped for both Holley and Weber carbs. As far as changing it, if it was a Magnum intake, I'd say NO. With a stock 7.4 low rise intake, I'd say YES.

BajaBuddy

Thanks for replying already. Motors aren't 454 mags. Also, according to the CFM calculator, at 83% volumetric efficiency (if that's correct) is requires 604 CFM.

FWK

It is a low rise intake with a adapter for the weber.

formula31

Learn somethin new everyday, thanks Griff.

MACDAD260

As Griff said, Weber carbs are square bore carbs, also. The Holley will bolt on but, there is more to it than just changing the carb. You will also need to change the linkage plate and the fuel line if you convert from the Weber to a Holley. If yours is like my '93 than you will also have to fab a bracket to remount the Mercathode since it mounts on the Weber linkage plate. The linkage on the throttle lever will need to be changed as well.

The intakes on the 7.4 and Magnum motors are actually spreadbores for Rochesters. When they quit making the Rochesters and went to the Webers they just used a Mr. Gasket adapter. There might be a slight advantage in going to a genuine squarebore manifold but, I doubt if it would be very much. If you're going to change the manifold then I would go to a high rise dual plane like a Performer Rpm or an Airgap. Unless you also change the cam and do some head work you probably will not see enough difference in performance to make it cost effective to also change the manifold. The biggest difference that you will notice with the Holley is better starting after setting for a week or two. The Webers are famous for long crank times unless you start it up every day or two. Otherwise, they run well if tuned correctly.

formulaF302

I have had nothing but problems after going to squarebore holleys on top of my spreadbore intakes last year. I had been using a square bore style bracket below it to tie my throttle linkage in, and did not have any other adaptor. I could'nt get my rear four plugs to burn anything but solid black on both engines. I am enroute to the marina as soon as I finish reading todays posts to install my new Merlin dual plane intakes that I bought last week and finally got painted. If you change don't forget to use the correct marine gaskets on your thrmostat housing...they have a couple metal rings on them which maintain the ground contact to your intake so that your overheat alarms will function.
I'm just hoping this takes care of my problem.....

blown1500

MACDAD260 seems to have the right idea. As for the spreadbore intake with the correct adaptor, I have never seen any improvement on the dyno, in the boat or in the car. If you want the ultimate opinion, call Edelbrock or maybe someone at Barry Grant.