Drax240z Posted September 16, 2001 Share Posted September 16, 2001 Yeah John, at 14.7psi (1 bar pressure, or 2 atmospheres) there is twice as much air in a given volume, so a engine running 1 bar boost is effectivly ingesting twice as much air as it would without boost. ie: my 168ci engine running at 14.7psi boost would be roughly the equivalent of a 336ci engine without boost. (of course efficiency plays a large part as well) Did you ever get any track/gtech times with your old motor? It would be interesting to compare to the 383 once all is done... Quote Link to comment Share on other sites More sharing options...
John Scott Posted September 16, 2001 Author Share Posted September 16, 2001 Until the 383 is ready to install, (only 2/3 the way there, financially) I can't help tinkering with the old motor. Probably going to save it for another project....maybe an AWD viscous coupled (Syclone) 67-72 Chev PU. I know I know, another topic/forum. Anyway, I'm convinced my engine is way over carbureted with the 600 dbl. pmpr. According to ATI a cfm rating is nearly doubled at 15 psi. Hmmmm, I doubt my engine could ever ingest 1200 cfm, let alone 1000, but the 500 should have a better delivery. I'll post results once its on. JS Quote Link to comment Share on other sites More sharing options...
Guest Tom Scala Posted September 16, 2001 Share Posted September 16, 2001 John,2 barrel carburator air fow is rated at a different pressure drop than 4 barrels are. The 500CFM Holley 2 barrel only flows about 350-375CFM of air if the air flow is measured the same as a 4 barrel. I found this out the hard way when I bought one to go on a Ford 351C 2V motor once. I thought I was smart and would get cheap & easy 4 barrel performance but it didn't work out that way. Quote Link to comment Share on other sites More sharing options...
John Scott Posted September 16, 2001 Author Share Posted September 16, 2001 What ever the actual cfm is I'm still going to try it. Still might be closer to my engine's needs, then again.... Drax, I have a Gtech log, numbers all over the place! I can't believe how much difference a hot day makes. You think a naturally aspirated car runs a little slower on a low density day.., but when a large percent of your hp is based on forced air, I guess it makes sense. JS [ September 16, 2001: Message edited by: John Scott ] Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 16, 2001 Share Posted September 16, 2001 John, glad to hear your going 383, although your 6 is pretty killer. You run blow through carb with a supercharger currently right? What mod's did the carb require, I mean I know nitryl floats is probably a must, but what all else did you have to do to it? Regards, Lone Quote Link to comment Share on other sites More sharing options...
John Scott Posted September 16, 2001 Author Share Posted September 16, 2001 Lone, pretty simple. Mill the choke horn (nice way to say hacksaw) remove choke linkage and fill hole with JB quickweld, and like you mentioned change floats. Thats it for the carb. Also needed is boost indexing a mechanical pump or boost regulated regulator with a good healthy electric. I use the Mallory. JS [ September 16, 2001: Message edited by: John Scott ] Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 17, 2001 Share Posted September 17, 2001 Thanks for the info John. Appreciated. Regards, Lone Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted September 20, 2001 Share Posted September 20, 2001 If I recall (wasn't too interested in 2bbl carbs at the time, and that hasn't changed) a 4 bbl is rated at 1.5" Hg and a 2 bbl at 3". I have run Holley's of various sizes on 289, 302 and 351C engines along w/a ffew various size Chevy's, and can tell you that if you have even a mild V8, you really need a 4 bbl. Start w/600 vacuum secondaries for a mild/smaller engine, and go up from there, depending upon rev range. Remember that the smaller 4 bbl carbs from Ford on 289's were rated around 450 cfm - the Autolite carbs on 351C's were 750 cfm, of their own peculiear spread-bore pattern. A 289 whighrise intake and headers, small cam used a 600 to good effect (780 too much). Funny thing about the 351C, when using a Double Pumper Setup, It ran much better with a 700 than a 750 - the SBC liked the 750 better. Both using similar manifolds. Only reason to use a 2 bbl is to stay in class rules in racing - the 4 bbl will get better mielage AND perform better. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.