Next question, intake
 

Hey all, here's my next question...
I'm looking to try and do the "best practices/upgrades" for building my engine up. One of the common swaps I see is the carb (or TBI, but I'm not sure I'm up to that). I have the option to use the 305e intake manifold, or a 351e manifold. I'm guessing the 351 would be the preferred to use?
I've seen some debate over 350 vs. 500 cfm carbs, with mention that the engine can't draw enough to make the 500 worthwhile. What's the thought? Is this a case of "better to have and not need" the volume with the 500, or KISS with the 350?
The TBI sounds great, but it looks rather extensive in the work and parts to make it function correctly. Is this correct, or is it just fear of the unknown on my part?
As always, I am thankful for your help.

Re: Next question, intake
 

If you try the 350cfm carb there will not be any noticeable change what-so-ever, don't waste your time and money on one I've tried one and it was a disappointment. The 500cfm carb is a difference of night and day for performance and overall drive ability. In some cases 305 V6's have ran too rich from the 500 but the remedy for that is to re-jet it and the problem is solved. I first did this conversion back in 1975 at the age of 15, I wanted better performance out of my father's 68 KM-2500 (Now mine) there was no aftermarket 4bbl conversion around or anything performance but I figured the 305's 2bbl base was standard GM issue so then a carb adapter for GM 2bbl base would work and it did. The truck was already upgraded to dual exhaust, 16 years later I built an HEI for it. The engine never seemed over carbureted or running to rich and would always pass the California biannual smog test far above average.:thumbsup:

Re: Next question, intake
 

Funny how the 500 holley ran to rich when I am running a 600 eddy 4 barrel on my 305E. lol

The 351 with the large base 2 barrel would be the one to get. I got a 351 Magnum intake for mine that I opened up for a 4 barrel conversion. Didn't even need an HEI. :thumbsup: Plugs burned clean, but I don't lead foot it and if I do I wait until the right rpm so the secondaries kick in. :teehee: I am running a pertronix which helped a tad...mainly for easier startups. Don't even waist money on a 350 2 barrel. They are a rip off for their size.

Re: Next question, intake
 

I wouldn't use the 351E manifold on 305 or 351C (non-Magnum) heads. The smaller head ports will create a 'ledge' where the intake meets and could cause flow problems. Not sure if non-Magnum heads could be ported to match a 351E intake manifold. Peter?

Re: Next question, intake
 

I did this and have had no problems. :thumbsup:

Re: Next question, intake
 

TJ, to clarify, did you port the heads to match the intake, or leave it as is?

Re: Next question, intake
 

I don't think non Magnum heads can be port match to the Magnum intake either. It is working on TJ's 305, I've also heard from others that done the same manifold swap and no problem:ok:

Re: Next question, intake
 

Years ago I ran a Chevy 327 in my daily driver. The intake had larger ports than the heads and it apparently suffered no noticeable ill effects.

In fact, the car ran very strong, and made 165 RWH on a factory gross HP rating of 250 with the TH400 automatic transmission.

Re: Next question, intake
 

Left as is, the magnum ports really are not much bigger. The main difference is Magnum is Open ported and non-magnums are split. But there is a slight size difference none of which I have had to worry about. Did a plug check and it's burning super clean. And that's with a pertronix and the plugs gapped at .035! :thumbsup:

Re: Next question, intake
 

Can't argue with success!

Re: Next question, intake
 

That was my thought as well, that the open port vs. split seemed like an advantage. I'm no engineer, but it seems to me having access to a larger volume of air/fuel mixture in the open port compared to the split port could only help mixing and amount that could actually be pulled in to the cylinder. It seems the most restrictive part then would be the head and intake valve, and not those PLUS the intake manifold channel.
I guess i'll be cleaning and painting that 351 manifold... and looking at the 500cfm carb.

Re: Next question, intake
 

If you're going to be running A 500cfm Holley 2bbl there is no need what so ever for the Magnum manifold whether it's from a 351E or any larger Magnum V6.:ahhhh: The discussion for using the larger Magnum manifold was for a 4bbl conversion:pullinghairout:, furthermore adapters are no longer being manufactured to install a 500cfm carb on Magnum manifolds. Your present 305 manifold only requires a Mr. Gasket #1937 adapter to use the Holley carb, it's a simple bolt on installation.:ok:

Re: Next question, intake
 

What Pete said. I do have a 4 down to 2 adapter that will work on a 305e and should work on a 351M manifold, but the results are rather a waist of time. I tried it and felt a little difference, but had I cleaned and rebuilt the 2 barrel it probably would have been the same. haha Not until I got a manifold and actually opened up the plenum did I notice much. But that's with a 4 barrel....two barrel doesn't really Need a manifold mod. Like said, if you do a 500 best to get an adapter and put it on. The 500 mod is the most common...I think 3/4 of the v6's here have it! :thumbsup:

Re: Next question, intake
 

The other thing is with the 305 manifold you can free up the restriction by opening op the base hole of the manifold with a die grinder to match the larger diameter throttle bores of the 500.:upyes:

Re: Next question, intake
 

I'd try it, but it would be a down grade from the 4 barrel. :lolsmack2: