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 Porting 305 "601" heads project 
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Post Porting 305 "601" heads project
Last spring a good friend of mine bought himself a 91 C1500 pickup as a toy. It has a 305 TBI motor that runs perfectly fine, but.....it definitely won't set any land speed records! So an upgrade is in the works! So while this project doesn't specifically involve an F body, it does involve a 305 which many of our cars have, so I thought I'd share as I progress!

The owner has 2 goals for the this project. Number one is he wants the truck to sound cooler...….easy enough.....its difficult to make a SBC sound bad! Number 2 was a little more power. He isn't looking for maximum all out power, just being able to merge onto the 400 without fear of getting run over would be great.

Not wanting to have the truck out of service while the engine was being upgraded, he struck a deal for a 305 (turned out to be from a 1986 F body after we ran through the stampings on it). The engine came with an Edelbrock carb and HEI ignition that were worth well more than what he paid for the entire engine, so he reasoned even if the motor was junk, it wouldn't be a total loss. After tear down, it appears the motor just needs a refresh and it should be perfectly usable, so he brought me the 601 casting heads to see what could be done to them to coax some extra steam out of this engine.

So here is what I'm starting with.

Image20200224_131500 by Hewitt Shane, on Flickr

Image20200224_131517 by Hewitt Shane, on Flickr


Look at how badly shrouded these valves are! Going from memory, I measured and there is not even 80 thou gap between the valve and the chamber...…..that's terrible!! Lol!

Imagereceived_244512419903828 by Hewitt Shane, on Flickr


Mon Mar 02, 2020 10:55 am
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Post Re: Porting 305 "601" heads project
Before I go any further into this project, keep in mind I make no claim to be any sort of expert on porting cylinder heads. Take what I'm doing here with a grain of salt...…...I may well be turning these things into flaming turds!!

But, on with the project.

I took some measurements of a few things as I usually do.

Minimum cross sectional area of these heads comes in at 1.70 square inches. That is actually similar to most stock 350 heads and quite generous for a 305. So there wouldn't seem to be any significant gains to be had hogging out the intake ports, especially given the rpm range this motor will be operating in (think truck......less than 5500 rpm max). I'll obviously give them a clean up, but there won't be any hogging them out going on here.

Throat under the intake valve measures in at 1.60". If you follow the thought that the throat should be 90%'ish of the valve size, then these throats need to be opened up into the 1.66" range (and smoothed out considerably)

Throat under the exhaust valve measures in at 1.23". Following the same 90% rule means the exhaust throat will need to be opened up to the 1.35" range.

Then there is the valve shrouding to deal with.

All in all it would seem that the bulk of the gains from these heads will come from within 1 inch of either side of the valves.


Mon Mar 02, 2020 11:12 am
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Post Re: Porting 305 "601" heads project
The first thing I decided to tackle was the shrouding.

Spent some time with my cutters & cut the chamber wall back, & put a preliminary 3 angle valve job on it.

Imagereceived_198443618072067 by Hewitt Shane, on Flickr

Same treatment on the exhaust side.


Imagereceived_125532345554711 by Hewitt Shane, on Flickr

The difference in the shrouding is remarkable.

Image20200228_195404 by Hewitt Shane, on Flickr


Mon Mar 02, 2020 11:25 am
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Post Re: Porting 305 "601" heads project
The thing that still baffles me about these old iron heads is that there as absolutely no symmetry or uniformity from one cylinder to the next at all. This isn't unique to the SBC heads...….I'm currently finishing up a set of Olds 455 J heads that were similar.

Image20200301_122545 by Hewitt Shane, on Flickr

Both of these intake valve seats were cut to the same height. Look at how much extra material came out of the throat area of the intake valve on the left compared to the one on the right to get the same 70 deg cut under the 45.


Last edited by auto_god on Mon Mar 02, 2020 11:50 am, edited 1 time in total.



Mon Mar 02, 2020 11:34 am
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Post Re: Porting 305 "601" heads project
The cut I made to unshroud the valves needed to get blended into the rest of the chamber and the bowls needed to be blended/smoothed into the bottom of the 70 deg cut of the valve job.

Image20200302_082610 by Hewitt Shane, on Flickr

Tear dropped the valve guide and gave the port a clean up.

Image20200301_170832 by Hewitt Shane, on Flickr

The intake on this cylinder is basically ready to go!

That's as far as I've got so far. I did this 1 cylinder just to evaluate if we should proceed with these heads or move on to something else. At this point I would say these are likely going to work pretty well...…….probably a pretty significant improvement from the swirl ports on the owner's current 305.

Now I have to get back to the Olds 455 heads and finish those up before I go any further with these.


Mon Mar 02, 2020 11:45 am
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Post Re: Porting 305 "601" heads project
Well the Oldsmobile heads are done so now I can get back to these ones!

The plan has changed somewhat though in the meantime.

Back when I took these heads apart, I noted the valves had some play in the guides. After measuring the stem diameter I determined the valve stems were worn several thousandths, so replacement valves were going to be in the game plan going forward.

Also, going back several months now, I purchased an old Wolf Valve Refacer and have been in the process of refurbishing it to get it back into service again. It's working absolutely perfect now.

Image89544274_2506100829705714_766708630782214144_n by Shane Hewitt, on Flickr

Last weekend after finishing up checking the brand new Oldsmobile valves (6 of the 8 brand new intake valves needed to be trued up surprisingly enough......1 valve was alarmingly out), I dug out one of the sets of 1.94/1.50 SBC valves I'd saved out of other heads I scrapped to see how well they would clean up.

Well after 5 mins or so in the grinder, I'd say they turned out pretty good!! Before on the right, after on the left...….both those intake valves were from the same head.

Image20200510_155936 by Shane Hewitt, on Flickr

Similarly pleased with the exhaust valves.


Image20200513_071616 by Shane Hewitt, on Flickr

So given how well these leftover, free parts turned out, the decision was made to upgrade the 601 heads from a 1.84/1.50 valve package to these refaced 1.94/1.50 valves.

So I spent a couple hours Monday afternoon cutting the intake valve seats to accommodate the larger 1.94 valves.

Image96804188_880522775798186_6804861809149870080_n by Shane Hewitt, on Flickr

So that is where the project stands at the moment. All the seats in the first head are cut and the porting for the first cylinder is complete. This week I hope to get back out to the valve grinder and do the complete set of valves for both heads


Wed May 13, 2020 6:57 am
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Post Re: Porting 305 "601" heads project
Spent a couple hours at the valve grinder over the weekend getting a complete set of 1.94 / 1.50 inch valves refaced, back cut and ready to go.

Image98330020_235413357911713_8329839172214849536_n by Shane Hewitt, on Flickr

Should be a considerable upgrade.

The original 1.84" intake that came out of these heads on the right, the 1.94" intake that is going in on the left.

Image98183203_247668669881328_4206667338239442944_n by Shane Hewitt, on Flickr

Time to get the grinder back out and give the bowls and ports some love.


Tue May 19, 2020 7:40 am
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Post Re: Porting 305 "601" heads project
Wasn't in the mood to be hunched over grinding away this weekend, so decided to media blast the first head instead.

Image98022149_2681502475418301_4970673232001630208_n by Shane Hewitt, on Flickr

The owner is going with black on this engine, so attended to that detail too.

Image98349169_271822393969912_1503292025942835200_n by Shane Hewitt, on Flickr

Nothing left to do but get the grinder out next weekend!


Wed May 20, 2020 9:24 am
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