4bbl on a 4.0

jcisworthy wrote:

This is the intake in question

http://ep.yimg.com/ay/yhst-12260461708320/dorman-4-0l-jeep-intake-manifold-3.jpg

As was mentioned earlier that manifold is designed for dry flow (absent of fuel until the injector). I'll say it this way, the POSSIBILITY exists in the pathways that fuel MIGHT fall out of suspension or cling to the walls with wet flow using a carburetor. But it might not. Until it gets tried everything is just theory.

I watch a lot of head porting videos. The porter will claim that a 5% increase in flow is "massive." And maybe in the upper regions of airflow where every little bit is hard to come by, and races are won by hundredths of a second it does matter. But to the guy on the street it doesn't. In the end I don't think anyone will know unless they try such as you are proposing. And your expectations and willingness to accept tradeoffs might be different from those of others giving advice.

If you already have the manifold, have access to the machines that create the proper surface and weld the adapter, and you see this as a "hobby" it could be worth your effort. Only you can decide.

'63 American Hardtop

INTERESTING..., it ran better with a carburetor than an injection system. I did notice that the adapter that came with the kit necked down like it was a 2bbl.. On the alternate 4 bbl. adapter they used the sides went down into the manifold.

This seems to take some of the plenum volume (might not be a bad thing) and the air/fuel mixture seemed to enter the plenum about 1-1/2" deep. That may cause the mixture to balance better for distribution..., or it might make for a sharp edge for the mixture to pull over in the negative especially for the top center runners that sit high.

In any case this video presents the concept as practical and showing decent results with the caveat that it is for peak HP and doesn't present drivability between idle and max RPM. Still it is cool when you see someone do what has been in your mind for years.

'63 American Hardtop

There using a spacer anyhow, so an open flange and switching between open or 2 or 4 hole spacers would be easy.

Sure makes you wonder about the throttle body and how the the electronics held it back on that intake vs the carburetor that much.

Was reading an article on a port injection vs throttle body that only made 20 HP and 4 Ft/Lbs difference on a 700HP+ V8 with there dyno runs.

Great video!

Spacer is welded on with time-set threaded inserts and making some pulls tomorrow.

600 CFM Quick fuel BR-67270 carb

PAC Racing springs 130 seat 265 open to replace the factory 85/200 that started to float at 4300 ish

Specializing in dyno services, engine building, and cylinder head porting

rbjracing.com
Phone Number 518-915-3203

This should be cool John.

Have a bigger carburetor on hand, just in case the large plenum shows it's going to go lean?