help with block i.d. - Pontiac GTO Forum
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post #1 of 10 (permalink) Old 04-24-2006, 10:40 PM Thread Starter
 
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New block question

my block has a 400 stamped by the front freeze plug on the drivers side.
it also has a 77 stamped by the back distribitor and numbers g197.
it also has a (yu) stamp in the front upper passenger side near the water pump.
500557 is also stamped in the back passenger lower corner.
GM-3 d N is on the passenger front lower corner.

These are the numbers that I found.
I know the numbers g197 are july 19 1977
Can I assume that this is a 400 or did they use 400 blocks to make 455's.
Does anyone know what these other numbers are?

Last edited by matt68gto; 04-25-2006 at 07:48 PM.
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post #2 of 10 (permalink) Old 04-25-2006, 09:55 AM
 
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You have a 1977 180-horse 400 block. No, 400 blocks were never used to make 455s. The 455 is a large-journal block, and the 400 is a small-journal block - you can't directly swap cranks between the two.
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post #3 of 10 (permalink) Old 04-25-2006, 01:48 PM
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Matt,

500557 is the casting number for a 400 starting in 76 and ending in 77.

Randy


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post #4 of 10 (permalink) Old 04-25-2006, 07:44 PM Thread Starter
 
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Since I have 1968 heads on that 77 400 block what do you think the horsepower would be? Assuming a moderate cam. Also what makes A 400 in the 70's have so much less horsepower? Is it the heads, cam, pistons, combination? What do you think the percentages are?(meaning mostly smogheads, or cam ect...)
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post #5 of 10 (permalink) Old 04-26-2006, 11:18 AM
 
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The 400 shortblock (less cam) was the same all years: cast flat-top pistons used from '67 through 79, so the bottom end has the capability to make the same horsepower regardless of year. Same rods were used, and same crank.

The difference in the engines was the cam and the heads (and the intake manifold). If you slap a set of 68 - 69 GTO heads on a mid-70s 400 block along with a cam that's equal to or better than the GTO "068" cam, and install a good intake manifold, you'll produce power identical to a "real" 68/69 350-horse 400 GTO engine.

The low 70s hp ratings were a combination of low compression heads with small valves, mild cam, and poor-flowing EGR intake manifolds.
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post #6 of 10 (permalink) Old 04-26-2006, 07:38 PM Thread Starter
 
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Thanks lars for all your help. The car does have a oversized cam although I don't know what it is. I am going to have the car dinoed soon and i will post the results.
matt
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post #7 of 10 (permalink) Old 04-26-2006, 10:19 PM
 
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Matt, I see you are still on the Pont 400 research warpath!

The heads are the heart of the engine and the block doesn't really matter so you have a good start. Actual power will depend of the rest of the parts, how well they match up and the general condition of the engine. As Lars said you should be well into the 300+ HP range at the crank if the engine is set up correctly.

Next time you post why don't you tell us what you do know about? What kind of intake and carb, ignition system, exhaust, manifold/headers etc. Stock vs aftermarket?

A dyno test will tell all, but with the good heads and 4spd your car should be able to boil the tires and pull strong through 5,000 RPM, if not then there are some weaknesses to deal with.

Walt
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post #8 of 10 (permalink) Old 04-27-2006, 06:52 PM Thread Starter
 
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Walt or anyone with advice
The intake is a edelbrock torker 1, the carb is a new edelbrock performer series 750cfm, ignition is factory HEI out of a 1975 pontiac boneville, and it does have old headers I'm guessing from 1985 because that is when the motor was rebuilt. If the guy I bought it from was truthful. Should I upgrade anything? I know they now have a torker 2. I dont know if that is much better. Does a edelbrock carb have the same deck as a quadrajet carb? Should I do anything to the ignition? It does have the vaccum advance. The guy I bought it from said it is bored 30 over. Does that do anything for performance. It also has an oversized cam. Any advice or sugestions is very helpful? I am learning a lot form all the help. I just put back on the orignal rally 11 rims that I bought from Vintiques and new Bf goodrich tires. My next investment will be the anti hop bars Lars told me about.
matt
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post #9 of 10 (permalink) Old 04-27-2006, 08:57 PM
 
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Well at least now we have a better idea of what you have. Upgrades depend on what you want compared to how good it runs and looks now. And there are lots of opinions on this! Do you want the engine bay to look "stock" or does power have priority? If you are looking for more power do you want to use old or new technology. That sort of thing.

I'd start by ordering up catalogs from places that specialize in 60's engine perf and restoration parts, especially Pontiac-specific. Then start reading. You will find answers to a lot of your questions in the catalogs. I don't know who is out there these days, but Nunzi's, PAW and Jegs come to mind.

My opinions? My goal was never to build a street car into a race car but I could often get into the 13's anyway. I actually like the stock 60's intake manifold, a good Q-jet that is set up right works fine but my favorite was a Holley spreadbore double-pumper. Going too big on the carb is a common mistake. I think the torqer manifold is OK, I don't know anything about your carb. As long as the HEI works good it is fine, but watch out because heat can kill the module and leave you stranded. Dual exhaust is a must, headers can only help.

Assuming that your engine is in good shape and everything is working right then the cam has by far the biggest impact. The right cam is key to making it all work. Too "big" a cam is a common mistake, but with the manual trans it is not as critical. By the way it is just about impossible to tell what a cam is by looking at it, unless you can match up the numbers. Read up about cam design so that you understand what duration and lift means. Pontiacs like dual-pattern cams with more lift and duration on the exhaust. Changing a cam is not a job for a novice, but its actually pretty easy to do for someone with experience.

All that said, hopefully you will determine that your engine is already "right" and all you need to do is enjoy it!

Walt
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post #10 of 10 (permalink) Old 04-27-2006, 09:36 PM Thread Starter
 
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Walt,
Sounds like good advice. I am tring to decide on how much performance I want. I do like the stock look to the car. I would be happy if it ran in the 13's.
I am looking forward to taking the car to cruz nights this summer. I will let you know what the dino numbers are soon.
thanks Matt
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