Engine quandry...

[RustyMule]

Hello, still somewhat new here, but I have a question. I have a 75 K5 with a 350 sbc. Somewhere down the line of ownership, previous to when I got it, the heads on the engine were swapped out for a set of centerbolt 87+ heads. I looked up the #'s and found they are from a 305, meaning slightly smaller intake valves (1.82 ish as opposed to 1.92 ish) but they are Vortec (swirl ported) heads. I am wondering if the "vortec" properties will outweigh the fact that it has smaller valves. It has good power and decent gas mileage. Does anybody know of any pros and cons of this setup? I have the intake and headers off as we speak so this would be the time to do something about it. Thanks for any input anybody might have.

 

[dyeager535]

First off, I'd make SURE those are Vortecs. Vortec head are NOT swirl port heads, which is why they work so well.

The smaller valves are going to hinder a 350 somewhat, BUT Vortecs are pretty efficient, even 1.94's on strong engines work well.

If they are working for you, I wouldn't swap them, regardless of what they are.

 

[RustyMule]

I thought that vortec meant that it had swirl port heads. I was confused. They were the same heads that they used on the 305 from 87 to 95ish so I had assumed they might be vortec. I think I might pull them anyway just to make sure they're ok and clean them up. Thanks for the help.

 

[aj johnson]

true vortec heads didn't come into play until 96.
the biggest advantage of the 305 heads is that they have a smaller combustion chamber which gives you slightly higher compression, IIRC.

 

[aj johnson]

also, vortec heads have a "heart" shaped combustion chamber.

 

[u2slow]

If they were Vortec, they would be 96+ heads. They only use 8 vertical intake bolts instead of 12 angled.

305 chambers are often smaller, raising your compression when used on a 350.

 

[scrappyk5]

i didnt think you could put vortec heads on the old style sbc. ?

are you sure the engine hasnt been changed all together?

 

[dyeager535]

i didnt think you could put vortec heads on the old style sbc. ?

You better come tell my 355 that.

Anyways, if they are pre-96 SBC heads, they are not Vortecs. Swirl port heads suck as cast.

Like I said before, as long as they work for you, why mess with them?

They will raise compression on a 350 (again check that you really have a 350 at this point) but unless you change pistons, I would imagine you'd HAVE to run something like 89 octane or higher due to the compression increase.

 

[RustyMule]

I didn't realize that vortec weren't around until 96. Learn somethin new everyday! Anyway, I know it is a 350 block. It's the one that came with the truck and it's not a 400 or a straight six. I pulled the heads and I have some new-fangled combination of crap I don't think anybody has tried on purpose. The pistons are 40 over and are alloy or aluminum. Who knows whats goin on in the lower half. That, in combo with the smaller heads, has made me start looking for a crate engine so I can save some sanity for X-mas. I'll keep ya'll upraised of the situation. Thanks

 

[dyeager535]

My point was, what is stopping it from being a 305?

I'd just be checking the suffix code (passenger side behind where the alternator sits typically, where the head meets the block) in case.

You didn't make any reference to it running poorly beforehand, thus my statement as to not mess with something that isn't broken.

All pistons (we deal with in these engines) are aluminum: cast, hypereutectic, or forged.

 

[scrappyk5]

You better come tell my 355 that.

Anyways, if they are pre-96 SBC heads, they are not Vortecs. Swirl port heads suck as cast.

Like I said before, as long as they work for you, why mess with them?

They will raise compression on a 350 (again check that you really have a 350 at this point) but unless you change pistons, I would imagine you'd HAVE to run something like 89 octane or higher due to the compression increase.

like i said , i didnt know , but that is cool that you can use them.