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Discussion Starter · #1 ·
I have an good running low power original 1976 Pontiac 350 2bbl with TH350 in my Firebird. The motor has 6X heads with 2.11 / 1.66 and 7.6 cr with 160 horsepower. I would like to have more power cheaply without the suitability for everyday use suffers. It should be driven regularly in the city in summer. So not a racing engine with extreme consumption. If 300 hp were possible I would be very satisfied. I know that a 400 would be better and the 350 are very unpopular. There is also almost no information on 350 conversions. But I come from Germany and Pontiac engines are hard to come by here. That's why I want to keep the 350. I could get an old Pontiac # 13 cylinder head with 72cc, 2.11 / 1.77 or a head with 1.96 / 1.66. Would the engine withstand it, if only the camshaft and the cylinder heads as well as an Edelbrock Performer intake and an Edelbrock carburetor were exchanged and how much performance would result? Can you recommend a combination. Or is that a pointless attempt on an original engine with 120,000 miles?
Thank you
Tom
 

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Well, the #13 heads have 2.11 1.777 intake and exhaust valves. Thats good.
The 350 bore is a bit tiny and the bigger valves may hit the top of the cylinder bore when open as they are a bit to large. But I see you already have large valve heads.
350 blocks , at least from around 70 up , are chamfered at the top of the bore to provide clearance for the valves and to improve flow as the chamfer "unshrouds" the valve . Since you already have big valve heads, I suspect it may not be a problem, BUT if you change the heads, and put in a larger cam, you will want to check the valve/ piston clearance as well as checking the valve to cylinder wall clearance.
Raising compression will work for more power, as it enables a larger duration cam.
Rebuilding the engine would be a real good Idea. Forged rods are paramount to keeping the bottom end together, In My Honest Opinion

You could get a stroker kit from butler. Stroking it would automatically raise the compression ratio, so you may not even need different heads


Not sure where you are at with the budget so I will wait to hear about that before I make any suggestions
 

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I would put a new oil Pump and Timing chain it along with a New Cam and call it good.
Forget the Edlbrock Intake and Carb their HP looser! Find a stock pontiac 4 barrel intake, its best for street and use a good stock Qjet best on street for a Pontiac.

6X heads are good heads.
It will spin the tires and have enough torque to put a grin on your mug and be reliable as long as you dont go to big on the cam and Jet the qJet properly.
Use a Good stock HEI distributor and run dual exhaust! no need for headers but they are worth 20 hp.

If you overhaul it do get the forged rods, rods were the weak link in these engines, 6X heads can be ported to flow good air by someone like Butler that knows what they are doing.
 

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I bet it has the original Turbo 350 in it thats probably been rebuilt a Few times by now and I bet it still has the converter for a 400 in it.
Gears would help it be a little quicker but he just wanted a little more reliable power without breaking the bank or building a race car.

The 350 wasnt a bad engine, it could be built too make good power is it a 400? no, but still it will make good power.

A friend of mine Craig Hendickson of HO Racing had a 326 CID Pontiac in a 3600lb tempest that would run 11's all day long he even had some national records with it.
I havnt seen Craig in a while now I need to go by his house and visit him.
 

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I would say 300 horse is easy on a 350 Pontiac.
Op need some #15 heads , not # 13.

15 are an 85 CC chamber, 13s are a 72 cc chamber.
85 cc puts the CR right at 9 to 1

13s are 72 CC , puts the cr at 10.3 ish to 1

The 15 heads can be milled to 80-82 CC easily and will put the CR right at 9.5 to 1( if you want to get tight with it)
9 to 1 will run the cam ( 2801 summit)
Some mild port work. 4 barrel for fun. Tune the dizzy correctly.
Put in a 2801 summit cam
Boom , pump gas motor. Pretty sure it would be at 300 horse.

2000 rpm stall

Done
 

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Discussion Starter · #7 ·
Thank you for the many tips and hints. I will find out what the cylinder heads and machining costs. Now I at least know what is possible and see if I can even get the parts here in Germany. Possible 300 hp sound tempting, I hope that the car will still be suitable for everyday use in city traffic. Should I look explicitly for a Firebird Quadrajet from 1976 350 or what would be important?
 

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You don’t need a quadrajet unless you really want one.
An Edelbrock 1406 600 cfm carb with electric choke will be good. Edelbrocks need a couple additional things though. A fuel pressure regulator set to 5 psi and a heat spacer. About 100 US more over the carb price.
Edelbrocks are simple carbs. Easily tuned. Quadrajets are more complicated.
What’s your budget like?
Do you need to pass emission tests?
 

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Discussion Starter · #9 ·
Yes, the car has to pass an emissions test. My budget is tight so I'm trying to figure out what a good quality upgrade would cost. It is an everyday car, so it should work reliably. If necessary, I would then save some money or, if possible, upgrade gradually. I heard that the Edelbrock carburetor was already running well in the factory settings and that 40-year-old quadrajets are hard to find here in Germany. Or mechanics who can adjust them. But now I have learned that many prefer the Quadrajets. May be I start with a rear gear change
 

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Discussion Starter · #12 ·
In Germany, the cars are connected to the computer with a measuring probe in the tailpipe and newer vehicles (from 2006 up) are also connected to the computer (OBD plug). My car passed this test.
And my budget is tight because how you say, I am doing the other things like wheels, interior, suspension( another question: would you go with rubber oder polyurthane bushings).

I just got an offer for an Pontiac intake and cylinder head. I wouldn't have looked for these parts myself yet. You notice that I have no idea about the engine conversion and wanted to find out whether the parts fit and make sense.
That's why I'm considering buying the parts and storing them. When I have the money for the rest of the engine conversion I
would do that later. The camshaft that you recommended is cheap but I don't know what other costs will be added.
The machine shop in particular is likely to be very expensive here in Germany.

So thank you again for your experience that helps me a lot.
 

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It will need to be a richer mix than the stock setup as the cam will impose the need for more fuel.Mileage will always suffer when you start making more power. More fuel consumed, more emissions.
You could put an A.I.R. pump on the exhaust, and run it when you go for a smog test. It would dilute the exhaust and aid in burning some leftover Hydrocarbons.It would also probably give you one hell of a rattle in the pipes..LOL
 

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Discussion Starter · #16 ·
Can you help me with the cylinder heads again?
The heads I wanne buy have the number 15 and D0218 and D018 cast in.
Is it correct that these heads are from 1968?

I found two pieces of information about heads 15 on the internet.
It seems the 15 heads

in 1968 for 400 cui, 1.96 /1.66, 10.5 cr
and
1970 for 455 cui 1.96 /1.66, 87 cc

are diffrent

I have now 1976 heads 6x-4 with 2.11 / 1.66, 94 cc in my Firebird and ask me if it makes sense to install the 15 heads?
Thank you for your help

525039
525040
525041
525042
525043
525045
 

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I have seen most of the time, pontiac heads with the date codes a few days, to a few weeks apart.Not sure why, but that is the way I have seen it on many engines that have never been taken apart, so I assume it is common from the factory
 

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Still going to be a major obstacle to get any compression in a little 350 with 87cc chamber....you need heads down around 72cc just to get somewhere near 9.2:1 compression wtih a flat top piston.
With an 87cc head you need a 15cc piston dome just to get 9.2:1 compression.

Math don't lie...compression ratio calculator here is easy to use and had pre-input button for Pontiac engines bore and stroke.
 

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120,000 miles and passes emmisions. Leave it alone.

Focus on the transmission and rear end to make best use of what you have.

If you want to do modifications make them reliablity modifications. Cs130 alternatior in place of the si10. Updated carburatior with better jetting. Updated better flowing catalitic converter and muffler. Nicopp brake lines. Etc.
 
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