cam question

[SUX2BU99]

Don't be afraid to think a 600 will be too small for a 400. It takes fairly deep breathing to really require a 750. What heads do you plan to run on the 400?

What happened when the 305 blew up? Was it just running okay and then quit or was it a high-RPM run and then boom!  lol

[eventhorizon66]

I would run a 750 Holley on a 400 or a 383, no question.  I also have it on pretty good authority that, so long as proper attention is paid to atomization, they'll work very well on a hi-perf 350.

[team39763]

Doesn't Job Gibbs make a oil that's supposed to be good?  Joe Gibbs Driven - http://www.joegibbsracingoil.com/whyuse.html.  I read about a few racers who use it in their rides.

[SUX2BU99]

Event, do those Vizard books you have contain a chart with CFM vs displacement? I've been told that even with a volumetric efficiency of 100%, a 350 doesn't even need 600 CFM. 750 might still be even more than a 400 could ever consume. I don't have a reference source handy to me though.

[VileZambonie]

Understand VE is going to change throughout engine rpm, engine load, temperature, humidity etc. A carburetor rated at 850 CFM will work just fine as long as it is tuned correctly. The cfm rating is a max flow rating. Proper jetting and metering is all you need.

[SUX2BU99]

That's all true, but VE will also never go past 100% either unless it's a pretty hairy race motor and part-throttle conditions lower VE at that moment even more. I'm not trying to debate theories or anything about VE and how real-world conditions actually dictate things. I know of this one engine builder who is constantly saying how to go smaller on carbs, heads and cams to produce better power down low for mild motors. He likes 525 cfm Holleys on most any sub-450 HP small block. To listen to him at first you have to wonder, but to keep listening it sounds like he is speaking from experience. But anyway, I digress a little. I wouldn't do a 750 personally unless I had a more radical motor but that's just me. QJ's are 800 CFM and came on low-power, short-revving smog motors right? Go figure.

[eventhorizon66]

Event, do those Vizard books you have contain a chart with CFM vs displacement? I've been told that even with a volumetric efficiency of 100%, a 350 doesn't even need 600 CFM. 750 might still be even more than a 400 could ever consume. I don't have a reference source handy to me though.

Yes there are general guidelines on carburetor sizing in several of his books.  But he places most emphasis on venturi size and booster gain relative to the engine combination.  To illustrate this he has used carefully blueprinted 1200+ cfm 4500 series carbs on both street and race 350s with very positive results.

Grab a few of his books.  He seems to be brilliant on the subject (fuel mixture preparation seems to be his specialty).

http://www.amazon.com/How-Build-Horsepower-David-Vizard/dp/1884089143/ref=sr_1_2?ie=UTF8&s=books&qid=1243984023&sr=8-2