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  #16 (permalink)  
Old 10-16-2012, 06:02 PM
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Everything that's being said here is "what if". The what if question is.....What is the true static compression ratio of this motor. Until you know that for sure, you have no idea how to proceed. If the SCR truly is only 8.5:1, then the MAXIMUM cam I'd use in the motor would be 210 to 212 degrees duration @0.050" tappet lift. And even using a cam that small, when compared to the 8.5:1 SCR, will result in a weak DCR (dynamic compression ratio). If you want to rev the motor higher, as you have indicated it runs out of breath too early for you, then you will need more SCR in order to support more cam to support more rpm's. That's the bottom line.

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  #17 (permalink)  
Old 10-16-2012, 07:27 PM
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Originally Posted by Silver Surfer View Post
AP, you don't think the 200cc runners are going to be an issue???

It is going to take a big cam to make use of that. A big cam is not going to like that 8.5:1 CR.
Big runners are not as detrimental as people think. I have no idea where that came from other than people just wanted to feel better about having stock tiny ports. It won't need a big cam either, the one I listed would match the combo just fine and its fairly mild.
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  #18 (permalink)  
Old 10-16-2012, 10:29 PM
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Originally Posted by ap72 View Post
Big runners are not as detrimental as people think. I have no idea where that came from other than people just wanted to feel better about having stock tiny ports. It won't need a big cam either, the one I listed would match the combo just fine and its fairly mild.
Same reason you don't put a 850CFM carb on a 283.

Larger runners reduce intake charge velocity and thus require more RPM's to increase that velocity. Of course you need a larger cam to get get up there and take advantage of that. All this maybe fine at the track, but the OP said, "This is a street car, no drag racing." No one likes a soggy bottom end.
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Old 10-16-2012, 10:37 PM
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Wow. Lots of great information and suggestions. My first post on this forum and I have received some great responses. Thank you all.

And yes, I knew the question of the actual CR measurements was going to come up. I guess I could pull the intake manifold and the rear most head off to see what I have inside the motor. It is pretty much impossible to get the front head off with the engine in the car. Remember the engine goes across the rear of the car. I also not sure that I have the knowledge to do all the measurements around the CR either.

I agree with the thoughts that the heads may be the bottle neck. It may be that I remove the engine over the winter and tear it apart. Then I can determine what to do with heads and cam both. I am assuming that I would get some increase in compression with the right set of heads.

It is always a challenge when you buy a car modded by someone else and all I have to go on is their word for what is in the engine.

I was thinking $300 for parts for a cam, now that is looking more like $800 if I went with a roller. Yikes.

Lots to think about. I will get this car working correctly - it will be a fun little machine with 350 hp.

I think the first thing I will do is a compression test. It has to be done at some point I guess. Will a compression test give any hints as to CR?

I have just got the car on the road and have not driven it a lot yet. I was thinking it would have more low end torque, especially with the 4.11 gears and the four speed trans.
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Old 10-16-2012, 10:42 PM
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Originally Posted by Silver Surfer View Post
S No one likes a soggy bottom end.
I agree with this comment. Definitely takes the fun out of driving the car!
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  #21 (permalink)  
Old 10-16-2012, 11:13 PM
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Will a compression test give any hints as to CR?
Not unless you know the intake valve closing point ground onto the intake lobe of the camshaft.
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Old 10-16-2012, 11:15 PM
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Originally Posted by techinspector1 View Post
Not unless you know the intake valve closing point ground onto the intake lobe of the camshaft.
Ok, thanks. I think I will do the compression test any way just to see what it is. Thanks for all of your input and advice.
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  #23 (permalink)  
Old 10-17-2012, 08:39 AM
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Originally Posted by Silver Surfer View Post
Same reason you don't put a 850CFM carb on a 283.

Larger runners reduce intake charge velocity and thus require more RPM's to increase that velocity. Of course you need a larger cam to get get up there and take advantage of that. All this maybe fine at the track, but the OP said, "This is a street car, no drag racing." No one likes a soggy bottom end.
It won't give you a soggy bottom end, nor will running a 850cfm carb on a 283. It's an old wives tale passed on by a bunch of people who have never attempted such things and don't have a clue wth they are talking about. Going with a 245cc port would lead to problems, that head with the 200cc port will pick up power from idle on up over stock heads.
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Old 10-17-2012, 08:56 AM
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Originally Posted by ap72 View Post
It won't give you a soggy bottom end, nor will running a 850cfm carb on a 283. It's an old wives tale passed on by a bunch of people who have never attempted such things and don't have a clue wth they are talking about. Going with a 245cc port would lead to problems, that head with the 200cc port will pick up power from idle on up over stock heads.
I think I saw a Carcraft test of some sbc heads which were mostly 185 cc intake ports and one set had 200 cc ports. They noted that the 200 cc suffered no disadvantage and had very similar hp and torque numbers to the 185 cc heads.
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