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Discussion Starter · #1 ·
Alright, I have a few questions regarding an engine that was built in my 75. The car originally had the 165HP options. That engine cam with 8.5 compression. I am thinking my current engine doesn't have enough compression for the cam that is installed. It is a regular 350 with the same stroke, and the bore is only 30 over. So, basically a 355. The heads are double hump heads with 2.02/1.6 and 64cc chambers. The pistons are the stock flat tops that came in the original style engine. The gasket is stock size. What would my compression be?

The cam is a Duration @ .050 228/228 Lobe sep 107 Max lift .480/.480.
http://www.cranecams.com/index.php?show=browseParts&action=partSpec&partNumber=100072&lvl=2&prt=5

Also, I would like a horsepower if you guys could help me with that. With all of that information it has an Elderbrock RPM intake, Holley Secondary Advance 750, and headers. I'm thinking with that cam and the combination that I will need a 3,000 stall and have my power range from there to 6,000. That is, if the compression isn't too low.
 

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My first thought here is that the flatop pistons and 64cc chambers you've got 8.5 with a 4 inch bore. Now you've made that 4 inch bore .030 bigger, and that should have made your compression ratio lower. Not much, but a little. Maybe 8.3? Someone else will have to do the math on that.

:cheers:
 

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355ci with 64cc heads and flat tops yields a compression ratio of 9.5:1 (without getting into specifics of head gasket thickness etc...). The LSA of 107 is probably why you're thinking you're cam is too big. It's going to be very rough. You'll be fine with a stall of around 2600. Anymore and you're creating way too much heat. Sounds like a very streetable enjoyable combination.
:cheers:
 

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:spanked: I'm corrected, I missed the head change from the original '75. I think they used 74cc heads OEM.. OOPS
 

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My first thought here is that the flatop pistons and 64cc chambers you've got 8.5 with a 4 inch bore. Now you've made that 4 inch bore .030 bigger, and that should have made your compression ratio lower. Not much, but a little. Maybe 8.3? Someone else will have to do the math on that.

:cheers:
More CI into the same size chamber = more compression.

Get on a static compression calc. web sight and plug in the numbers. My old 355 with .038 quench - 5 cc two valve relief flat tops with 186 casting double hump true resurfaced to 64 cc is more like 10.43

It always was on the verge of detonation with a Crane 272 cam So i had to install the bigger 278 power max

This will get you close.

http://www.csgnetwork.com/compcalc.html
 

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the COMBO of a 3.73:1 rear gear and a 3000rpm stall converter will make a huge improvement :thumbsup:
the cams designed to operate in the 3000rpm-6000rpm band so the drive train must match that rpm range to operate correctly :laughing:
example
if youve got a stock or nearly stock stall converter and a 2.87-3.31.1 rear gear its going to be miserable to drive
 

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Discussion Starter · #7 ·
Exactly what I was thinking Grumpy. That's what my dad and I came to the conclusion of. I was just wanting to know the compression to see if I was safe with the combo before anymore work is done. With a 3000 stall/3:73 rear, that cam and combo, what do you think it will run in a quarter? weighing in at about 3700 pounds. I am going to personally guess 12.8. Maybe I'm wrong. Chime in and tell what you think. Thanks all for your help. :thumbsup:
 

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One version of my 355 with the Crane 278 cam 1.6 RR and I highly recommend using larger springs with 130 pound seat pressure. I had a very consistant 12.70's 3300# car on 9X28 slicks. 3000 stall totaly done TH350 3.55 rear gear.

I used 186 casting ported & polished screw in studs and guide plates Manley Proflow valves 2.02/1.6 7000 rpm red line. Single plane intake ,headers true duals W/O cats.

I spent way to much money on the 186 casting heads, but you also have to look at what was really availiable back in the early 80's. I later went to a solid cam with P&P 200 cc heads with 2.055/1.6 valves and was able to get it down to 12.30's
 

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heres some calculator links you might want to save someware

http://www.rbracing-rsr.com/compstaticcalc.html

http://users.erols.com/srweiss/calccr.htm

http://www.kb-silvolite.com/calc.php?action=comp2

http://www.wallaceracing.com/dynamic-cr.php

http://www.diamondracing.net/cocalc.htm

to maximize the tq/hp on a street combo ID keep the dynamic cpr close to 7.8-8.0:1 and the static cpr close to 9.8-10.5:1 and THE QUENCH TO BETWEEN .038-.042 AND youll be fine with that 3000rpm stall and 3.73:1 rear gear with 92 octane in that 355 OR IN A SIMILAR 383

btw my calcs put your combo at about 10.1 static cpr, you might need to retard the cam 4 degrees to lower the dcr but a cam swap might be another option
 

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Discussion Starter · #10 ·
Thanks Grumpy, that is exactly what I have been needing. I've always wanted to learn more about cam, compression, and valvetrain geometry. I'll save the calculators and use them on future builds. :thumbsup:
 
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