Have a 400, bored .30 over. It's cammed, has headers, etc. Max rpm of the engine is a little over 6500. Has a holley 750 in it currently, is it too big, too small? Want the best set up.

 

2 bolt or 4 bolt block? What cam do you have? What cylinder heads? What is the rod length. You realley need a good 406 with alot of the RIGHT PARTS to spin that thing over 6500.

 

To be honest with you i'm not real sure, just know that driving or reving it in park the tach registers 6500 rpm.. dads project went over to me and i don't know too many specifics.

 

Ok, just figured out it is a 4 bolt.

 

Really irrelevant as to whether it's 2 bolt, 4 bolt, or what rod length, etc. It's a .030" over 400, so the only other concern I would really have is what type of cam, heads, and rear gear ratio it is using. If you don't have specifics, then I'd play it safe and go with a 650 Holley with vacuum secondaries. It should provide enough fuel without overcarbureting the engine.
But I would question the tachometer's accuracy? If you're holding the throttle long enough to really rev that 400 to 6500 rpm's, then it better be really well built! That big 400 wont take a lot of 6500 rpm hits if it's not a super strong lower end. I'd keep it under 6,000 and really more like 5500 most the time!

 

The 2 bolt 400 block are stronger then the 4 bolt blocks because of the webbing, just the nature of the 400 block. Rod length also plays a big part in how long the motor will last. The stock 5.56 short rod motor was never designed for a lot of rpm. Most everyone steps up to the 5.7 rod lenght motors and if you really want to wing it the 6 inch rod with splayed caps is the only way to go. You also need a good set of heads to feed those cubic inches, stock heads even with bigger valves is still just a truck motor. The best setup for the least amount of money spent is the 406 with 5.7 rods (be sure there clipped the rod bolts to clear the cam) and a set of ported vortec heads. For the cam the comp. EX-274 and a 750 carb and shift at 5800 rpms. The only thing that KILLS a motor is RPMs.

 

All good info, but it still doesn't have a lot to do with his choice of carburetor, as his original question asked.

 

The simple answer is....based on the c.i. and stated rpm limit, the 750 is a good size for your 400.

 

Thanks for an answer! I'll learn specifics when I get a hold of my dad.. just know everything is built on it to allow it to run that high of rpms. Think the gears are like 4:30's.

 

Your right on all counts. BUT if your trying to spin 6500 with a short rodded stock 400 assembley, you will probley be driving over the bottom end no matter what carb you have on. Once you woofumm big time, their mostly junk and hardly worth the time or money to fix. But yes the 750 vac. secondarys would be a good choice.