[lts70]

I have been looking for a 400 or 455 for quite a while now with no luck in my area. I am thinking I want to look at rebuilding the 350 that came with our 1973 Ventura. I wish the motor was original to the car but it is not, I also tied to find a 1973 350 to match the car numbers better with no luck in my area.

The plans for the car is a fun street car to cruise but with enough power to have fun in. It is automatic but we plan on swamping to a 5 speed. Trying to keep the cost on the motor reasonable so that we can go the TRX 5 speed route.


The 350 motor we have is a 2 barrel 1970 255hp #11 heads 8 to 1 compression motor. The block date code is E110 and block casting number is 9799916. The #11 heads have a date code of E210 and when we checked the CC's they were at 82cc before any valve work.

I picked up a used Edelbrock performer and Qjet already. The cam is toast. I am going back and forth of how to build this motor.

Option 1
I am leaning towards milling the heads down to get the compression up and getting a good cam to support going to a 4 barrel. Hoping I could bump up into the 300hp +/- range.

Option 2
But I also love my Chevy 383, So I was looking at the Pontiac stroker kits.
Buttler performance has a 383 kit for $3,329 and a 407 kit for 2,399. Anyone know why there is a $1000 difference?

Would love to hear from you guys that have had experience building these 350 or 350 stokers. Every one around here only has experience with the 400 or 455. If I find one of those for a good deal, great. But hoping to move forward with the 350.

[ponchjoe]

I would build it to 69 350 HO specs of going 350. These were rated at 320 hp.
You’d need to find some better heads like 48, 12, 13, 62. These are big valve screw in stud heads.
The Pontiac 383 stroker is cool but expensive compared to 400 stuff. Surprised there’s no 400s around Idaho. If you’re considering the money for a stroker why not just have Butler, Kaufman, or Pontiac Speed Shop (my preferred) build a short block and ship it to you. That’s the best bang for the buck in my opinion.

[Verdoro 68]

We'll likely be keeping our 350 when the time comes to rebuild, too. I think the 4" stroker kits are more expensive partially because they use 6.7" rods vs. BBC 6.8" rods. If I was going to stroke the 350, I'd go with the 4.25" kit. No substitute for cubic inches. If you stroke it, you're going to want some better flowing heads. I probably would anyway since 11s have small valves and press-in studs.

If you're sticking with a 350, I like the '69 350 HO spec as a model. Kind of like the combo Dennis recommended in this thread: https://forums.maxperformanceinc.com...11#post6526811

[Quad]

"Buttler performance has a 383 kit for $3,329 and a 407 kit for 2,399. Anyone know why there is a $1000 difference?"

The 4" stroke cranks are forged in the 383 kit. The cheapest 407 kit starts with a cast crank.

[lts70]

May have found a set of 68 350 HO #18 heads. But he wants $450 for the set and he doesn't believe they are screw in rocker studs. those work good with the 69 HO specs? Bad price?

[unruhjonny]

This is absolutely my unfiltered opinion

Skip milling the heads;
Just do a simple rebuild without getting carried away, and I'd be willing to wager that it will make sufficient power for you to have fun cruising around with.

I have long held the opinion that the P350 is unfairly maligned - almost entirely because they cost the same to rebuild as a larger displacement engine, and what's the old saying?
"There's no replacement for displacement"

Honestly even a lower compression P350 is a great engine...

As to the milling or head swap:
1) you would be surprised how much power can be made with "small valve" heads - they are the same size valves as the earlier "large valve" heads.
2) I believe that the 1970 #11 heads have a combustion chamber size of 80cc;
I also believe (if my memory isn't failing me) that this is the same size as 1970 #13, or 1969 #62 heads.
3) screw in rocker studs are a nice assurance, but unwarranted if using a smaller cam profile.

Just don't pick too large of a cam and you should be good.

[lts70]

This is great. Thank you for responding!

My good friend has a engine machine shop so milling the heads would not cost me anything but the use of my forklift when he needs it. I have no problem installing screw in studs I have access to the correct equipment for that as well.


The #18 heads come with a 350 out of a 1974 Pontiac. The whole engine minus the carburetor would be mine for $800. See Attached pictures.


Would the #18 heads be a lot better, I cant find a lot of info on them?

[johnta1]

The 1968 #18 head would be 10.5 cr (advertised) on the 350. So small chamber already. 1.96/1.66 valves. Probably pressed in rocker studs

[b-man]

The #18 heads have value to people looking to correctly restore a 1968 350 HO. They’re quite rare and sought after.

The #18 heads have press in studs and a smaller combustion chamber volume than the common #17, #47 and #11 small valve 2-barrel 350 heads. The ports are essentially the same on all of them. Choose whichever head gets you closest to your target compression ratio.

[SD455DJ]

Originally Posted by lts70

May have found a set of 68 350 HO #18 heads. But he wants $450 for the set and he doesn't believe they are screw in rocker studs. those work good with the 69 HO specs? Bad price?

Buy those heads! As B-man said, they are quite rare and all you really need to do is to have the press-in studs pinned. I have 2-sets of small valve heads where we just had the studs pinned. One set is '70 #15's for the YH 455 and the other are '70 #16's for a 330 hp 400. The 455 has a Summit 2802 cam (224/234/114 at .466"/.488" lift) and the 400 has a Summit 2801 cam (214/224/112 at .444"/.466" lift). I shift the 455 at 5200 rpm and the 400 at 5600 rpm without any studs pulling out or breaking. I wouldn't go much higher than a .488" lift cam with pinned studs and the valve springs have 120 lb seat pressure and 270 lbs. open at .488". That is if you decide to keep pressed-in studs. It never hurts to convert to screw-in though.

I would use the Summit 2800 cam (204/214/112 at .422"/.444" lift) in a 350 as it is similar to the 067 factory cam that came in the '69 350HO engines with the TH400 trans.

Dennis

[tom s]

JMO,make up your mind on what you want to do with CI before buying and heads!If I was in your position I would use a 4in stroke rotating assm.Tom

[se428bandit]

I'm just reading this thread and wonder what you ended up doing with the 350. I've had some pretty good luck with the Pontiac 350. This an old video. https://youtu.be/P7S38kFsIq8?si=f0neaDeaHDbrLeMY

[Shiny]

I don't remember this thread but I hope he bought the 18 heads.

As I understand, the 11 heads are more like 87 or 88cc and the CR on a 1970 350 might not even be 8.0:1.

Rocky Rotella quoted some engineering specs here:

Link to Rocky Rotella comment re: #11 heads

[srmmmm]

Advertised CR on the 1970 350 cu in engine with the 2 barrel carb was 8.8:1

I went the 4.25" stroke option on mine and with an .060 overbore got 413 cu in. With flat top pistons set even with deck height and 6X-4 heads, the calculated CR is 9.3:1

[SD455DJ]

This conversation has got me curious…

For the 350 (354) and 400 engines with #11 heads to have the same advertised compression ratio of 8.80 to 1, the 350 heads would need to measure 77.2 cc’s and the 400 heads would need to measure 88.3 cc’s (both with ‘zero’ deck, 8 cc piston valve reliefs, and 0.040” quench using the Butler on-line compression calculator).

With Rocky’s information about the #11 heads having a design cc of 87.17, the 350 (354) would have 8.04 to 1 compression and the 400 would have 8.88 to 1 compression cc’s (both with ‘zero’ deck, 8 cc piston valve reliefs, and 0.040” quench using the Butler on-line compression calculator). Using a thicker head gasket (0.052” as per Rocky’s info), the 400’s compression drops to 8.69 to 1.

According to the Pontiac Parts Catalog – Models Thru 1975 (circa May 1979) - the “1970 400 2-B.C. w/8.6 ratio” uses #9790911 head gasket that measures 0.048”. This would increase the compression slightly to 8.75 to 1.

However, since factory engines were built with pistons at least 0.015”, or greater, below deck and head chambers 5-7 cc’s larger than advertised, the compression ratios are a good half point below advertised as well.

I have both the factory ’70 WU code 350 and XX code 400 2-bbl engines, so I’ll get them Whistlered to see what their actual compression ratios are.

Dennis

[Shiny]

Does a whistler measure static CR? I'm ignorant but curious how valve timing doesn't affect this?

[SD455DJ]

Originally Posted by Shiny

Does a whistler measure static CR? I'm ignorant but curious how valve timing doesn't affect this?

The Katech Whistler is an electronic device that accurately measures an engine’s compression ratio without disassembling the engine.

The Whistler Compression Ratio Tester is designed to determine the static compression ratio of virtually any engine quickly and accurately. It is widely used by race sanctioning bodies like NASCAR and SCCA to enforce compression ratio rules, as well as by engine builders to verify actual compression ratios without relying on volume calculations.

The device operates using acoustic principles. Air is injected into the cylinder through a spark plug hole, and the Whistler measures the resulting tone as the piston moves to top dead center (TDC). This tone correlates with the combustion chamber volume, which, combined with the number of cylinders, engine displacement, and temperature, allows the Whistler to calculate the compression ratio to the nearest hundredth of a point. Accuracy is reported at ±0.05 actual static compression.

The pictures below are of the RAIII in the '70 Formula; original engine before rebuild being tested on the Whistler.

Dennis

[Shiny]

Thanks Dennis

Wow, that's a fancy tool!

That 10 number must be nice to see!

Sounds like it is basically measuring air volume using some kind of sonic resonance response... then comparing max to min..

I'll look at their site to see if it spells out why valve opening doesn't affect it.

I predict 7.9 to 8.0 for a 70 350... just because I believe many #11 head measurements shared on this site that align with the engineering doc quoted above.

And the comment made about a gasket thickness difference between 350 and 400 2bbl engines in 1970 is curious... why would they do that?

Very bizarre to me that Pontiac would intentionally engineer different gasket thicknesses to somehow make the same head work on different engines, then advertise a known inaccurate number like 8.8... ??? Makes me think the transition to emission compliance caused a lot of decisions that were driven more by schedules than by design.

Mike

[SD455DJ]

I should have mentioned that you rotate the engine so both lifters to the cylinder you're testing are on the base circle (compression stroke). It is a resonance difference between the two extremes. You can hear a faint 'whistle' differences when testing.

Good questions that I certainly don't know the answers to. They sure played the numbers game for some reason that doesn't make sense on the surface.

Then 350 had its own unique head gasket for the smaller bore diameter. I don't have any information on the thicknesses unfortunately.

Dennis

[srmmmm]

Originally Posted by SD455DJ

Then 350 had its own unique head gasket for the smaller bore diameter. I don't have any information on the thicknesses unfortunately.

Dennis

The 350 block has chamfered cylinders for the large valve heads. That may be contributing to the actual/calculated compression ratios, as well as necessitating the special head gasket.