350 head/exhaust differences???

C

clutchdust

Millionaire Playboy
Joined
Mar 27, 2008
Messages
1,726
Location
In transition
So I'm STILL working on this fucking Suburban. I got the engine all put back together. As I stated in another post, I went to the junk yard and pulled a whole motor from a '90 3500 (I got the whole motor because it was a 4-bolt main). The idea is to keep that other block as a foundation for the Vette and just use the heads for this Suburban. They checked out good, no cracks, so I just lapped in the valves, new seals and bolted them down. I get the engine in today and I'm thinking I'm finally going to start this thing, all I have to do is bolt on the accessories.
Didn't even make it that far.
I started to bolt the exhaust manifolds up and I could get four bolts in but not all six. Either a front and center or back and center but not all six bolts would go. Upon further inspection it looks like the bolt holes are drilled about 1/8" farther apart (outside hole to outside hole) than the manifolds will accept.
WTF?
These are factory cast iron heads. How the hell are the ports farther apart than the heads that originally came in this Suburban? I mean SBC is a SBC right? First gen anyway.
My current theory is that these heads actually aren't original to the 3500 the engine came from. For one thing, it had, incorrectly, the pushrod guide slots in the head AND self aligning rockers. Also had a broken push rod, probably because of that issue. I also noticed that for some reason it has larger exhaust valve stems in this than the original engine had. I didn't compare the overall diameter and it's almost impossible to tell 1.5 from 1.6 visually so that may be the difference there. But the original Suburban heads had .341 valve stems whereas these heads have .375
So now my plan is to pull the manifolds back out and just hog out the outer port bolt holes a little. All I need is maybe 1/16" on each and I should be fine. What a PITA this thing is turning into!
 
I've seen exhaust manifolds draw up when they were removed. A few of them I've heated with a big rosebud and spread them back apart. PITA. I've seen a tool that goes between the center and one end that looks like a turnbuckle- install that and start cranking on it to spread the manifold.

There was a couple of years there was one of the exhaust manifold bolts that was set away from the port on the end = it was a good 3/8 farther away than the rest. I've got a plate that was designed to correct that. It uses short 3/8 bolts with allen wrench and a flush type head in that one place, then the normal bolts go in the rest of the holes.
 
Twin_Turbo said:
Are you perhaps using vortec heads?
Click to expand...

Is there a difference between pre-Vortec head exhaust holes and Vortec heads?

I've seen the ones Tim's mentioned.... but I've honestly never had the issue with stock, cast manifolds.... I'll have to look at some ramp heads I have - maybe those are different (IIRC started in 88 through 93) truck heads with a ramp cast in the intake port to swirl the mixture)

I have all three types of heads (882s, ramp heads, Vortec) in my shop.... I'll post up a side-by-side tonight if that would help
 
The holes used changed, early heads & manifolds use the outer of the outer bolt holes, and not all heads have 2 holes at the end. The later ones all do those manifolds use the outer holes. I think it changed somewhere in 83 but the year his engine came from it might even be a vortec head, which means the intak won't fit either


Vortec head, or similar to SBC head with only 1 outer hole

p177892_image_large.jpg


SBC head with both holes

Pro_Torker_SBC_iron_head.jpg


Notice the difference? the outer of the 2 is lacking on the vortecs


All headers will bolt up to either, it's the cast manifolds that gie the problems. There are tons of cast gm manifolds that use the outer of the 2 holes. Willing to bet the same is true for that truck.



Manifold spreader
http://www.summitracing.com/parts/WMR-W80663
 
Well, they are different casting numbers but otherwise not that different. I mean, we're only talking about maybe 1/8" difference. I'm almost leaning to what Tim was talking about with the manifolds drawing up. Both sets are centerbolts and both have the ramps on the intake ports.
Maybe what I'll do tomorrow when I get off work is pull the manifolds back out and throw them up against the cracked heads and see if they still line up. If not, then the heads are definitely different. If so, it will pretty much confirm Tim's theory.
I will post results later. Thanks for all the replies.
 
No on cast iron heads the center bolt angles changed to 72 degrees (corvette alu heads kept 90 deg) exhaust patterns are the same.
 
On a side note, my head has 2 bolts in a certain location on the exhaust side (forgot where) This could be an indication that manifolds could have different bolt patterns. TT is right I think.

My headers had slotted holes as well. Still was a thight fit.

I know that on the intake side, heads from 86 and up are different as well.

Not sure this would help, but I thought I would add.
 
When I bought my '72, the rebuilt OEM engine had the stock rams horns on it, with operating heat riser valve on that bi metal spring......they went on/off fairly easy, and I put on the first TPI, using that heat riser flapper trick for the O2 sensor location, single wire unheated version, car ran on two road trips from DC to Florida, during which time I noticed the mani's on both sides turned kind of a white/gray color, and the iron surface looks like it was krazy with stresses or high temps, something went on kinda strange, never noticed it in more normal driving up north, maybe 2 hours on the freeway at a time.....it was a 336 rear and Muncie trans....so doing 10.5 hours one was at 80 mph, well, I dunno what to think.....

I sold the whole shebang after putting in the present roller engine......
the manifolds went on/off ok, even after the oddball observations....

:amazed::twitch:
 
TimAT said:
I've seen exhaust manifolds draw up when they were removed. A few of them I've heated with a big rosebud and spread them back apart. PITA. I've seen a tool that goes between the center and one end that looks like a turnbuckle- install that and start cranking on it to spread the manifold.
Click to expand...
<DING! DING! DING!>
Winner, winner, chicken dinner!
Ended up just hogging the outer holes with a bit just about 1/32" bigger. Still tight but I was able to get all the bolts started.
Think it was because the old heads got so hot?
 
For some reason, the cast iron mix they used just shrinks sometimes. No idea why. Way back there, when the 427's in the dump trucks were ruling the streets around KC, you could pull a perfect cast iron manifold off, carefully lay it on the bench, do the valves or whatever, go get that same manifold, and it'd have a crack in it you could throw a cat thru. Never dropped or even bumped. It'd crack. On the engine, it was fine. Go figure. And not all of them would crack either. :twitch:
 
You must log in or register to reply here.

Latest posts

Back
Top