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post #1 of 20 (permalink) Old 06-11-2011, 12:53 PM Thread Starter
 
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Cam Question

I bought ny 68 GTO about 2 years ago. The person that sold me the car had only owned it a short time and did not know much about it. Well, I got lucky. The car is in excellent shape. Engine was recently rebuilt. You can see new gaskets everwhere on engine. Seller only knew that engine had been built, but did not know any details. Engine runs great, no clicking or tapping,does not smoke and runs really smooth. It has the numbers matching 360HP H.O. engine with 4-speed and 3:55 rear gear. Told you I got lucky, the seller didn't know it and I don't think he would have known what he had if he had know it. I sent off for the PHS papers and everthing checks out. It is the real deal. My question is this. The engine has a very smooth even idle. I would think that the H.O. would have a bit of a choppy idle. I am wondering what type of cam rebuilder used. Is there anyway to find out? I am tempted to pull top end down and inspect cam, but engine runs so good I am scared to mess with it. I took it to drag strip a while back. Made 3 runs. First run I bogged real bad off line and just aborted that run. Next run with pretty good off line traction and granny shifting at 5,000 she turned a 14:26, next run was a 14;44. Both runs were around 98 MPH. What do yall think, is that what a stock 68 H.O. is expected to turn? It also has a set of hedman headers. I sent Qjet to Cliff's High Performance Qjet for rebuilding and sent the HEI dist to Sun Tuned for set-up. If I decided to replace cam and lifters, what would ya'll recommend. I would want Rhoads lifters. Thanks

Last edited by Pontiacdude; 06-11-2011 at 12:55 PM. Reason: trying to remove the things in middle of post
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post #2 of 20 (permalink) Old 06-11-2011, 02:51 PM
 
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I think the cam should sound a "little lopey" mid 14 secs aren't that great. BEFORE you tear the motor apart, make sure every thing is tuned and hooked up properly.....it's a lotta money to see what cam you have! I would think you should turn mid 13 with that car.....E



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post #3 of 20 (permalink) Old 06-11-2011, 04:55 PM Thread Starter
 
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I agree. I think that the correct cam was not put in engine during rebuild. I think it is one of these 'RV" cams that are supposed to run smooth and get better gas mileage. I could have probably knocked a tenth or two off if I was more aggressive on the gear stick, but I didn't want to hurt car. I wish you could hear it idle. Everything on the engine is set correctly. One thing I have noticed, the car has never "spark knocked". I have run 87 octane gas and it still runs good. I don't think a H.O. would do that unless cam or pistons had been changed for unleaded gas and lower compression. One other thing, I put a bore scope down one of the spark plug holes and you can clearly see two big round valve reliefs side by side on the pistons.

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post #4 of 20 (permalink) Old 06-11-2011, 07:07 PM
 
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If it's a smooth idle, thats a good time. Did you drive the car like you hate it, for drag racing it's drive on kill or you'll never get the true potential out of the car. Do you want the car faster? Stupid question, lol.. Not knowing what you have limits what cam you can replace it with. You can read some of Mr. Pbodies threads and see the cams he recommends, that is what I am going to do if I need one. How radical do you want it, you have a 4 speed, you can run however radical you want. Sounds like a really nice car, whatever you do, decide what you want to do with the car before you go to far and the car isn't fun anymore. Also, did you have the car tuned to kill, or just running good?

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post #5 of 20 (permalink) Old 06-11-2011, 07:57 PM
 
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Cam Question

A stock 400 HO tuned to factory specs should detonate on pump gas, even premium. Sounds like somebody replaced the pistons to lower the compression. There is an excellent explanation on Pump Gas Compression Ratios on Rock and Roll Engineering's website under FAQ's at Pontiac Engines : Rock and Roll Engineering I think your et's are representative of a stock 400 HO
driven conservatively. Even with matching numbers cars there is no real way to know what is inside an engine.
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post #6 of 20 (permalink) Old 06-11-2011, 08:33 PM
 
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The quickest and cheapest way to lower compression is with a head swap. What is the casting numbers?
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post #7 of 20 (permalink) Old 06-11-2011, 10:49 PM Thread Starter
 
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It has the number 16 heads. One head has a date code of January 15,1968 and the other is January 16, 1968. About the only option it has is the Rally Instument Cluster with indash tach ,H.O. engine,posi, and 4-speed. It has no power steering or brakes, no console, no hideaway headlights. So, it appears whoever ordered it new , ordered it to run.
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post #8 of 20 (permalink) Old 06-12-2011, 09:41 AM
 
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If you can run 87 without pinging it is down on compression, or the timing is retarded. If the pistons are flat tops with valve reliefs, the compression would still be up, probably 9-1 or better. With no power brakes you can run a bigger cam, as you don't need the vacuum for brakes. You can run a compression test and that will give you an idea of the compression ratio or engine condition. I would advance the timing til it pings lightly then back it up a smidge. Also run premium gas with the advanced timing, then you'll see the cars true potential.

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post #9 of 20 (permalink) Old 06-12-2011, 11:53 AM
 
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.....87 Octane pump wee wee should make a "correctly built and tuned" HO motor rattle "like 2 skeletons makin' love on a tin roof during a hail storm"......



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post #10 of 20 (permalink) Old 06-12-2011, 12:21 PM Thread Starter
 
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There is no question about the valve reliefs. They were very visible on top of the pistons. I think I will start advancing the timing until I get a ping and then back it down a little. Will let you know. One thing I had forgot is when the 87 octane was put in, the tank also had some 91 octane with some octane boost in it also. My gas gauge does not work and I am scared of running out of gas, so I stop and put in gas practically every time I drive it. It may have had enough 91 octane and octane boost to cancel out the 87 octane.
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