305E Intake mod.
 

Got a new intake from Ed Snyder today. Thanks Ed!

So I looked at David Chadwell's 305E manifold modification and it looks like it'll be pretty simple. But, as I don't want to screw this manifold up...lol... Anybody got any tips an tricks? I'll be using a grinder and will be taking off a little at a time. I have a mig welder, and will be getting a carb plate either made or a spacer plate from Napa. Any tips would be awesome guys. Super excited to start working on this!

Re: 305E Intake mod.
 

If you got a Magnum manifold there won't be any need to do any welding, It's all about milling the top surface flat, cutting out a square bore pattern then fitting a carburetor spacer plate and drilling & tapping it. I've built two already and right now I'm building a third one, I'll post some pics.:ok:

Re: 305E Intake mod.
 

Ed has just informed me that the manifold is from a 305D.:banghead:At this point follow what David Chadwell did, that was is engineering expertise and the correct way to make a 4bbl distribute fuel without any restriction:thumbsup:

Re: 305E Intake mod.
 

Where do I find David Chadwell's modification? Is anyone running Holley 500cfm 2barrel 4412?

Re: 305E Intake mod.
 

Here's a link to the mod:

http://6066gmcclub.com/album.php?albumid=51

Re: 305E Intake mod.
 

Yeah, the manifold is from a 62 D series. I've always enjoyed fabricating so I don't mind the little extra challenge. Long as I don't screw this up beyond repair I'll be ok. haha!

Re: 305E Intake mod.
 

After you left yesterday, Tom, I realized that the manifold you bought from me was from the original engine (305D) out of my '62 Suburban that I replaced with a 401.

I'd recommend having a machine shop mill down the top surface for you. Then you could use a grinder to open up the hole and the insides if you're trying to do as much as you can yourself.

Re: 305E Intake mod.
 

Hi Ed! Thanks for the suggestion. A machinist friend of mine has a mill I believe so I could probably take it to him. Just need to call and make sure I can cause he's always super busy. haha

Re: 305E Intake mod.
 

Well the thing that really sucks is that all the machinists are going by the way side around here. I've got two more guys to ask, and if they can't, I'm going to have to use a grinder and sander and hope for the best. lol I'll update.

Re: 305E Intake mod.
 

Hi guys....will a 351 magnum manifold bolt up to a 305E? Got a line on one.

Re: 305E Intake mod.
 

Yes it will bolt up but use the 305 intake gaskets.

Re: 305E Intake mod.
 

Good to know!

Re: 305E Intake mod.
 

Do you happen to have any spare magnum manifolds for sale, original or converted for Holley 2bbl use?

I wonder if it's possible to mill one of these down and convert to a 4 bbl setup? Holley Street Avenger, Rochester Quadrajet, or Carter AFB???

Re: 305E Intake mod.
 

Here's some pics of two 4bbl manifolds I built, one uses a spread bore adapter so Quadrajet can be used and the other just uses a square bore spacer, both manifolds were milled down and the bases were opened up. The Magnum manifold already has 4bbl plenum in it because GMC actually did offer a dealer installed 4bbl option so the 2bbl version of the manifold was just cast with a different top base:thumbsup:Attachment 4647

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Re: 305E Intake mod.
 

Didn't know GM offered a 4 barrel option! Anyone ever use it that your aware of? That'd be one heck of a rarity!

Re: 305E Intake mod.
 

I don't have any extra manifolds.

Re: 305E Intake mod.
 

Well it's all bolted up and the motor is running like a Champ! Drinks the gas with No issues and pulls darn well. Really happy with how it turned out. Super easy to start compared to before to. :thumbsup:

Re: 305E Intake mod.
 

There was a wrecking yard in Southern California that specialized in GMC V6's and they had 1 factory 4bbl manifold for sale back around 15 years ago, unfortunately the wrecking yard caught on fire and is gone. There was also a 66 pickup with a 351E running around Santa Rosa California just next to the town I live in ,hat had a factory 4bbl intake. Not many are out there because hardly anyone knew about the option, GMC should have publicized on that more. Most engine overhaul gasket sets would come with the 4bbl base gasket and air cleaner gaskets for Magnum V6 engines.:upyes:

Re: 305E Intake mod.
 

Now that is neat. Hopefully one of these days I'll run across one. Be a Neat option to have.

Re: 305E Intake mod.
 

Wow, that looks fantastic! I want to do that now! Great work!

Re: 305E Intake mod.
 

Thanks! Sorry the pictures won't show up...waiting on admin to fix them. lol

Re: 305E Intake mod.
 

Ok....trying this picture upload once more. lol

Re: 305E Intake mod.
 

We have a running and driving video! Had no one to hold the camera while I was driving so I couldn't do a fast run....tried but failed. lol

https://www.youtube.com/watch?v=Gjpfx4YZzoY

Re: 305E Intake mod.
 

Been driving Crustine everyday to work and back and so I thought I'd do a review:

So, a stock 67 305E engine was advertised at 152 hp and 280 torque(?). That's with a small 2 barrel and small single exhaust.

My 1st step was a 600 cfm edelbrock adapted to my 305's 2 barrel intake using and old MR. Gasket 4 to 2 adapter. I figure about a 20 hp and 15 torque increase. Also a little more mid-rang and top end. But to much carb for single exhaust. So about 172 hp and 300 torque.

2nd step was dual 2.25 exhaust with flowmaster 40 series mufflers and 2.5 tail pipes. An increase was also felt with that as well....bout another 15 hp and 10 torque. So estimated power from last would be 189 hp and 310 torque.

Now the final. Scouted a 351M intake and milled it out. And again I felt a rather Large increase....I'm gonna say another 25 hp and 15 torque because it was noticeable. So 214 hp and 325 torque now after the manifold mod.

Could I be to high? Probably....but that motor is producing Much more power than before. And it's the baby!

Little more review......
Starting is Super easy. Two pumps of the gas and full choke...half a turn and it's sitting at a 1000 rpm warm up idle. I normally push the choke in to let it warm up at 700....anyhow, starting is effortless. Cold idle is 500 warm is 700.

Did do a plug check and plugs are burning the fuel nicely.

So was all this worth it for a 305 V6? I think so. The power increase justifies the work involved in my opinion.

And Yes a Magnum intake will bolt directly onto non-magnum heads. You will want to use 305 intake gaskets though.

Well that's it guys! Anything else you wanna know just ask....I think next I'm gonna make headers or try some magnum manifolds. I need a stinkin dyno! :lolsmack2:

Re: 305E Intake mod.
 

Stock figures for the 67 305E are 157 net hp and 263lbs ft torgue:ok:

Re: 305E Intake mod.
 

Since you're doing performance modifications, have you considered doing away with the points and converting to an HEI or Pertronix ignition?:thumbsup:

Re: 305E Intake mod.
 

BigBlock:

Thanks for the correct specs! Looks like I need to re-adjust my guesstimations! LOL!

I did consider HEI, but due to how clean the plugs are burning I didn't want to add extra spark that doesn't seem needed. It's hard to tell weather it would actually do any good or not. Plus I'm enjoying the fact I can run 89 in it. haha

Re: 305E Intake mod.
 

I found running the HEI in my 68 when it had the 305 enabled it to run much smoother at higher rpms, together with a 2 1/2 inch exhaust and Holley 500 it was a great combination and starting the engine from dead cold were instantaneous, barely touch the ignition and it fires up!

Re: 305E Intake mod.
 

That's the same thing that happened when I got a hot HEI for my 292. Only thing I'm worried about is that the spark will be to hot and I can't run lower grade fuel for fear of detonation. I do have the timing set at 10 initial. But I am considering! I thinking of getting the HEI that's on Ebay. Then I might upgrade to a 750 cfm. LOL!

Re: 305E Intake mod.
 

I've never had a detonation problem with the HEI. Also I always wanted to find spark plugs for my 478 that's in my 68 now that would have the .060 gap so I found AC 44XLS6 were compatible.

Re: 305E Intake mod.
 

A 750 cfm carb would be too much carburetion for a 305 V6:pullinghairout:, 650 cfm would be the maximum:ahhhh:

Re: 305E Intake mod.
 

Ah ok, That's a big gap! I think mine are at .040 or .045. Just pulled some plugs again after hauling a couple heavy loads of lumber....load on truck and load on trailer....plugs are still looking new. :thumbsup: Did notice some carbon build up on one around the ridge....but nothing to be concerned about. I'll post some pictures of the load in my build thread. I was joking about a 750. haha The 600 is plenty for that motor, not enough RPM to justify the air....but those jugs sure draw some vacuum!

Re: 305E Intake mod.
 

600CFM definitely sounds good for the 305, is there a noticeable increase in acceleration when the secondaries kick in? When I was 17 years old I tried a Holley 780 dual feed carb on the 68 with that same adapter you first used, vacuum leaks, fluctuating idle and excessive gas consumption:ahhhh:. No way would it work so back went on the Holley 500 2bbl:lolsmack2:

Re: 305E Intake mod.
 

You can feel them kick in I know that. lol Mainly depends on RPM....I'll gun it from 2000 to 3000 and that's about it. But it pulls much better now that the manifold is open! Here's a picture of the load in tow this morning. lol Unloaded those by hand......

Re: 305E Intake mod.
 

Wow... quite the load there TJ!
I'd like to toy with the idea of adding a SMALL 4 bbl carb (Carter AFB or maybe Rochester Quadrajet, maybe Holley Street Avenger) to the 351, but on a 351, 600 cfm would really be the useable limit. These engines were intended for low rpm, they have no harmonic balancer even. Doing mods than are only beneficial at 4000+ rpm will tear up these engines.

I think a 351 may be able to get even better fuel mileage if I were to run a small 4 bbl on it.

600 cfm on a 305 is just overkill. You'd likely get better low end response with a smaller carb. Having your cam reground to add about .020" lift and running custom higher compression pistons to be able to run magnum heads on a 305 (otherwise the big chambers will drop your cr below useable), that would require a little more carburetion, and make great power.

The thing that always gets me in the hot rod automobile community vs vintage motorcycle community, is that the bigger automotive engines mask mixture issues more than a smaller bike engine, so people never bother changing out carb jetting to fine tune the engines!

I have a wide and o2 sensor and AFR gauge/controller tailpipe sniffer setup nowadays. I have yet to put it on the GMC, but will when I run the 351C with the Holley 500 conversion. I hope to add an X pipe to the exhaust at some point, and maybe get some custom headers made. Dual exhaust is overrated, that's why H pipes became common and now the superior X pipe dual setup is popular. Same reason everyone started making 4 into 1 headers for 4 cylinder race bikes following Pops Yoshimura's lead...

Re: 305E Intake mod.
 

Thanks for the info Chuck! The overall performance was greatly increased, even with an over kill carb. The motor has no issues burning the fuel with stock points and a pertronix coil. I've lost a tad bit of low end, but not enough to where it's really noticeable. When towing I can shift at 2700 RPM and still pull through the gears whereas before I had to shift over 3000. That load I towed there I never shifted over 3000 rpm with! I may try getting a 500 edelbrock and jetting it down a bit, or a quadra bog. But I just recently pulled some plugs again and they still look really good! Gas mileage I got a rough estimate of 10. lol But I have been doing a lot of towing and stopping and going. No real highway driving. Part of that problem to would be the 4.11 gearing and 29 inch tires. I plan on 31's or 32's in the near future as I finally got a set of 16 inch rims. Even the inside of the exhaust is not as black as before. I've been playing with the idea of getting that MSD fuel injection unit. lol

Re: 305E Intake mod.
 

Can this mod be completed on a 1960 single barrel intake?

Re: 305E Intake mod.
 

I don't believe so. Best thing to do would be to find either a 305 two barrel intake or a 351 magnum intake. The magnum is way easier to modify so that is why I went with it.

Re: 305E Intake mod.
 

Thx, I have an extra 2 barrel and can do the mod on that. I guess the old 1 barrel is paperweight material now.

Re: 305E Intake mod.
 

The 1bbl manifold does not have a big enough plenum to accept any kind pf modifications. The best is the 66 and up Magnum manifold used on 351E,M,401M, 432 and 478M engines because theses particular manifolds have a 4bbl plenum that just needs to be opened up.:thumbsup: