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Author
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Topic: Compression Ratio
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Buster
Gearhead Posts: 780
From: Orlando
Registered: May 2002
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posted 05-30-2003 05:12 PM
   
What would the ideal compression ratio for this combo, strip only max HP. This setup will have a 125hp shot of NOS as well. Also, recommended max RPM.Vehicle w/driver 3050lb. C4 tranny, break & 5500 stall converter. 4.000�� X 3.850�� SVO sportsman 2 bolt block (wire installed for copper gaskets)
Clark copper head gaskets 4.060�� X .042��
Main girdle
3.850�� Scat crank
Eagle 5.956�� H beam rods
Pistons To be determined Victor Jr. cylinder heads ported(w/stud girdle)
200 cfm exhaust 1.60�� valve Ferrea
300 cfm intake 2.050�� valve Ferrea Victor Jr. intake port matched to head
850cfm Holley Comp Cam No. 35-781-9
110* lobe separation
Lift
.696�� intake
.683�� exhaust
Duration @ .050
278* intake
286* exhaust Hooker Super Comp (1 5/8�� if I remember correctly) headers
No mufflers. [This message has been edited by Buster (edited 05-30-2003).]
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N266fords
Gearhead Posts: 557
From: Spokane ,WA USA
Registered: Apr 2003
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posted 05-30-2003 06:55 PM
Just a guess i would say you are looking at a 7500 to 7800 rpm motor..Probly 11.5 to compression if you want to run nos.other wise 12.5 to 13..I just build a 393 with stock victor jr heads forged crank from scat h-beam rods Je pistons (custom low comp )10.5 because of the street/strip car with hyd. roller cam 595lift. harland sharp..you should be putting some serious torque to the ground.Hope you get it to hook up ..Bruce
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Buster
Gearhead Posts: 780
From: Orlando
Registered: May 2002
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posted 05-31-2003 10:16 PM
Bumpage... more advice please. looking for lots of comments here
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steve'66
Gearhead Posts: 6522
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 05-31-2003 11:48 PM
You're running in 'my' uncharted waters.  Try Kuntz and company, Alex can give you the contact(s) when he gets back from his winning weekend. SteveW
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bigblocked85
Journeyman Posts: 41
From: Waterford,MI
Registered: May 2003
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posted 06-01-2003 12:14 AM
Not really sure. I would suggest to try out the 385 series site at Network 54. Thats where I found this site. It is a wonderfully informative site when it comes to the 385 series motors, there are many professional engine builders there that range from mild to REAL WILD combinations. I hope im not stepping on any toes here at M&M, i do like this site a lot but know you can get great guidance for your particular question there. I myself am building a 466 with a stock (decked out) crank, Scat H beam rods, Arias 13-1 pistons and a fogger system starting at 300 HP. Only time will tell! 
Good luck, Gordon
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Butch Jennings
Gearhead Posts: 582
From: No. California
Registered: Apr 2000
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posted 06-01-2003 12:14 AM
If it's opinions you're looking for, then I'll toss mine in. I think the cam is too big and the header is too small. I'd run a 1 3/4" header on it and run a cam that is more in the 265 or 270 @ .050 range, anything with more than 280 @ .050 isn't going to make any torque until way up in the rpm range. That cast crank won't want to see much over 7000 rpm on a regular basis. I've run plenty of nitrous through 12.5 and 13:1 engines, I've found that your window of error with nitrous is much smaller on a higher compression engine but it will make plenty of power if you keep the tune-up safe.------------------
Butch
460 powered 1967 Comet Cyclone (Broken)
10.271 @ 130.231
Butcher's Home Page
"Friends don't let friends drive Chevys"
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steve'66
Gearhead Posts: 6522
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 06-01-2003 12:57 AM
The Hooker SuperComps are 1 3/4 and the best you'll find unless you want a custom set fabricated.Butch is "right on", you'll have to have the nitrous tuned just right at the higher compression levels. Use all the safeguards and check the plugs. When an electrode is missing, it's time to worry. SteveW
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Buster
Gearhead Posts: 780
From: Orlando
Registered: May 2002
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posted 06-01-2003 01:36 PM
OK, now that I know the headers are 1 3/4�� and the cam is too big, btw Alex said that as well, but I had already bought the cam... he recommended advancing it. I have a gear drive but it only has 0* & 4.5* advance and retard setting. I have never advanced a cam that much before, I guess I could switch to a chain if needed. Also, this cam has a 110* lobe separation and should have a wider power band, not that I really know what it is yet, and I had hoped that would help the bottom end. I guess the main point I��m getting at is this... If I run a flat piston I will be around 12.2:1 CR. I have been running 13.5:1 ratio in the engine with the 3.5�� stroke crankshaft. And yes, I have burnt off electrodes in the past... that and a few head gaskets,  . It��s been my experience, with the Victor Jr. intake that the rear #4 & #8 cylinders lean out first. I was trying to stay at the same compression ratio as the 351, but I would need a dome piston. I haven��t bought the pistons yet... everything else I have. The 351cid has Ross dome pistons in it now. I was kinda hoping I would get the ratio over 13 with a flat piston but it didn��t work out that way and I don��t have the money for a new set of heads with a smaller chamber, thats what I really would like to do...a set of Blue thunder heads. I never really liked the idea of cutting that much off the heads, but that��s still an option as well. So, I guess at this point the questions are... 1a) Advance camshaft to 4.5 deg
1b) Change over to a chain for fewer degrees of advance.... 2a) Higher compression ratio of 13.+:1 using a dome piston, with flame travel Issues, leaving the head alone.
2b) Cut the heads and use a flat piston to get the ratio in the 13's
2c) Lower, 12.2:1 compression, using flat pistons with better flame travel, leaving the head alone. 3) Sell the house, move into a mobile home (RV) and buy an engine from Jack Roush. [This message has been edited by Buster (edited 06-01-2003).]
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Butch Jennings
Gearhead Posts: 582
From: No. California
Registered: Apr 2000
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posted 06-02-2003 11:21 AM
Regardless of what you do for a piston, I say sell the cam you got on Ebay and buy a better grind. You will not be happy fighting a cam that's too big, advancing it will help a little but it won't fix it. You've simply got the wrong cam.------------------
Butch
460 powered 1967 Comet Cyclone (Broken)
10.271 @ 130.231
Butcher's Home Page
"Friends don't let friends drive Chevys"
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