In the new issue of "Chevy High Performance," there is a great article about their 305 project. The engine is a 1992 with TBI injection. There is a lot of info about using Chevy HP Vortech cast iron heads on the 305 and it explains what needs to be done to get these heads to produce 9.6:1 compression. In addition, I just got off the phone with the HP guys at Sallee Chevrolet in Oregon. The ZZ4/HO aluminum heads--P/N 12556463, Casting 8113--will bolt right up on 1986 and earlier 305s with TPI. These heads come with a 58cc combustion chamber and can be taken down to 53cc for the higher compression. By using these heads (or the Vortech) machined as the article notes, valve lift is increased to .570, allowing the use of many hydraulic roller cams.

I also have a question. How much of a problem is it to lose the TPI and go with a carburated version?

Stu

 

I think swapping tpi for a carb has been discussed alot, just search a little.

Thirdgen.org even have a howto on it, https://www.thirdgen.org/newdesign/tech/carbswap.shtml

 

 

if youre really set on building a 305, the zz4/l98 heads are the ones to go with. going carb would be a good idea, fi costs more, and is more expensive, but it also has many good perks. anyways, IF i was to ever build a 305, start with a good bottom end. you get what you pay for, so i suggest something like willie is running, splayed 4 bolt main, all forged, so the bottom end is pretty much bullet proof. im not sure if you can go bigger then the stock valves on those heads with having interference with the cylinder walls so they would be the restriction, but you could still do some porting on them, allowing like a lt4 hot cam to be good. then get a good flowing intake, and a good carb and youd have a nice tiny mouse

 

well, since spendin the cash to splay the mains on a 305 would be a waste of cash, rebuild one to stock specs on the bottom end, but blanace it. i used stock bottom end with the hotcam and l98 heads with a slight port on my 305. had the lt1 converted intake. good enough for mid-low 13's on motor with 3.42's and 2700 stall. no problems, good running motor. cheap, too

 

AND the best part about chosing the parts i did, was that they all will transfer over to a 350 with ease. so think ahead

 

I believe the article you're referencing is a 305 TBI not a TPI.

I don't thing I would go nuts with a whole forged bottom end and 4 bolt. From what I've been told, a 2 bolt will hold up to 500+ HP. Now I'm not saying that's set in stone, but that's what I've been told.

 

yes, i know he was refering to a tbi or car setup, but the hard parts are all the same, just different intakes

 

don't do it. if you've got a 305 TPI there should be no reason whatsoever to go to a carb. TPI is perfect for a 305, the fact that it is EFI makes it easier to tune, diagnose, and also a lot better for daily use. you should have no problem making as much HP as you want (can squeeze out of) with a TPI intake on a 305. if you had a TBI I'd say go for it because TBI isn't as efficient and still operates the way a carb does, albeit "smarter" but is a lot more restrictive...

 

Machining heads has nothing to do with making a 86 down hydraulic block magically a 87+ hyd. roller block.

 

I don't understand your post. Sallee Chevrolet (a GMPP shop) and GMPP both tell me that the LT1/HO aluminum corvette heads will work on the 1986 TPI, particularly since the heads match the TPI manifold. All I'm saying is, that if milling the iron Vortechs got higher compression at 53 cc, why wouldn't the aluminum heads? They are both 58cc. If it would somehow make a difference, I'd like to know what it is.

Stu

 

sure, milling the heads will affect the cc of it, but as far as making the block from a hydraulic to a hydraulic roller, it will not.

 

added note, LT1 heads will not work on an SBC block without modification to the coolant passage. doing all that work to put mediocre heads on the car is not cost effective or smart. in fact most LT1 guys shell out the extra cash to get SBC heads converted to LT1 style so they can use a larger variety of heads and/or 18 degree heads and so forth. if you've got an 86-down block you need to use a retrofit roller cam for it and a cam button, can't just swap over parts.

 

Okay, you're confusing me, man. According to GMPP and the parts guy at Salee Chevrolet here in Oregon, these heads will bolt right up without the problem you note. Here's where I guess I'm lost, and I don't claim to know it all. If valve lift is increased to .570, like the '87 in CHP with the Vortech iron heads, why wouldn't the lift in my '86 get the same result? And, although a roller cam might be groovy, I'm probably going with an Engle Racing hydraulic with .450/.450.


I just retired after many years as a capital defense investigator and I have time on my hands. So, I'm trying to learn as much as I can before I start the major work. Frankly, I'm a little tired of the so-called advice "not to waste [my] money." In the first place, it's my money. Second, I had a 1980 Z-28 with a totally built 383. It was the Millenium Falcon of Eastern Oregon--the fastest hunk-of-junk around these parts. Now I have this 305 and, frankly, all of this jabber about "get a 350" is just making me want to do this out of spite. Tell ya what. When I'm done, you tell me where you live. I'll come with my car and I'll buy time at a strip near you. Then we'll see who's right.

 

i think you mean the l98 aluminum heads. they were on vettes from 86-91 i believe. i think the new zz4 crate motor heads are exactly the same, maybe even zz3s? theyre 58cc with the d shaped exhaust ports. with port work and 2.02/1.60 valves, theyre very good heads. the thing is, those big valves will hit the cylinder walls on a 305, BUT, there is a member name Willie that has those size valves on his 305 by having valve reliefs on the block. i highly suggest talking to him about building a 305s. its the blocks that are different as far as lifters are concerned. i dont know much about lifters, but i do know everything up to 86 were flat tappet, and starting in 87 hydraulic rollers started. the way you can tell it if you have a hydraulic roller block is if there are indents in the block right above the lifter bores.

as for the building a 305, power to you. my high school class motto was something like "we did not take the path well traveled, or the path less traveled. Instead, we went where there was no path and left a path behind us"

 

You are right about the L98 (I don't know why I keep saying LT1) and, if I remember right, it is basically the same as the HO head used on the ZZ engines. That's what Salee Chevrolet said. According to the guys at Edelbrock (I was thinking of Performer RPMs, but the chambers are 64cc), if you use a cam with .450/.450 lift (or less), the valves will not hit the cyllinder walls.

 

ah, so thats why you wanna run such small lift. what kinda duration on that cam?