Advice on new carb purchase

[dgc333]

I have been running a Holley 4160 600cfm vacuum secondary carb on the 360 in my 68 Barracuda and I want to purchase a new carb. The car runs very well with the 600 but I want soemthing new that is sized more appropriately for the engine.

The 360 is a 10.6:1 magnumed headed motor with a comp XE268H cam and a CrossWind dual plane intake.

The car is 99% a street car so max high rpm power is not a priority and I want to stay with a vacuum secondary.

I have narrowed my choices to a Holley Street Avenger 670 or a Barry Grant Road Demon 725.

What do you guys think and why?

Thanks

 

[smythge]

I just got a new Street Avenger 670, had to increase the jets and and accelerator pump, but it works great now, no hesitation, great low end and high end power. The electric choke works great. I tried 2 edelbrocks with no luck

 

[rumblefish360]

IMO, the 725 Raod Demon is a better size CFM for the build and what I would go with myself.

 

[dgc333]

Well I purchased the 725 Road Demon. Installed it last Friday and did some tuning over the week end. Overall it runs very well (once I got the t-cable sorted out, was only opening the throttle blades 2/3) but it seems a little rich.

My question is; Does Barry Grant number his jets differently than Holley? the Road Demon comes with 78's on the primary side and 86 on the secondaries. I checked the specs on several comparbly sized Holleys and they numbers were much smaller. 65-72 on Primary and 68-75 on secondaries. If they do is there a cross reference out there?

 

[ramcharger]

The jets are identical. You can use your holley jets in your demon carb.

 

[dgc333]

I know the jets phyiscally are interchangeable but I though I heard/read that the way the sizes are marked was not consistent between the two companies. Are you confirming the a #75 Demon jet flows the same amount of fuel as a Holley #75 jet?

Seems strange that two carbs intended for the same application and with equivalent CFM ratings and based off the same design would have such different size jets in them.

Thanks!

 

[388dart]

"equivalent CFM ratings" - not true. BG carbs are wet flowed and will flow more air/fuel mixture than a holley of comparable cfm rating - at least until you get to the Dominator series.

Drop down 4 jet sizes front and back (74/ 82) - maintaining 8 differential at all times. I think you will find a far crisper throttle response and better overall operability. Check plugs and get them to a light brownish colour if you can. I have a 750 mighty demon on a 388 with BLAH, BLAH and am down to 74/82s and will be trying 72/80s this weekend.
The final jet sizing in a particular carb has a lot to do with the cam, head flow, exhaust, timing, combination.

 

[dgc333]

I thought the street avenger series of Holley carbs were wet flowed too. IT was the 670 and 770 I gave the jet range for.

Thanks on the jetting tip. I will give it a shot this week end.

 

[dgc333]

FYI. I called Barry Grant's tech support and they confirmed that the jet sizing is the same between Holley and Demon carbs. They also explained why the there carbs tend to require a larger jet than an equivalent Holley. It's the desing of the bleeds in the metering block, there are more than in a holley.