Compression Ratio Question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Longhorn Al · 04-06-2002, 03:27 AM

I was wondering what kind of compression ratio I'll be looking at with my engine? I'm not sure what info y'all need, so here's a quick run-down.

It's a 383 with KB hypereutectic flat-top pistons, and a CompCams 270H. I'm planning on using the Performer RPM intake and heads along with an Edelbrock 750cfm carb. I also want aluminum roller rockers. What other info do you need?

I wanted to know this because I've been seeing guys here suggest dished pistons to get a good ratio and be able to run on pump gas. I've already bought the pistons, so it's a little late for that. Will my engine be ok on the high octane with whatever compression I'm going to have?

------------------
1970 C-10 named HOSS
350/350, PS, PB, 3.07 gears
Future Motivation: 383 stroker, KB flat-top pistons, RPM intake and heads, 750cfm Edelbrock, & headers.
For pics of my truck go here: http://communities.msn.com/1970HOSS/shoebox.msnw?Page=1
Future Projects: 1969 Pontiac GTO and 1974 International Scout II

Hook 'Em from Austin, TEXAS

sam's 72 · 04-06-2002, 03:49 AM

We need to know more about the heads. What CC are they? 58, 64, 72 cc. We also need to know the deck height on the block, has the block been decked, or is it stock? If you decked it, then the piston is further up in the hole, and this make a difference! Also, what thickness of head gaskets are you going to use?
Sam

Longhorn Al · 04-06-2002, 04:03 AM

I'm looking at 64cc. I know the shop decked the block, but don't know how much. I have no idea on the gaskets.

sam's 72 · 04-06-2002, 04:07 AM

Big al,
Are the heads alum. heads? You can get awy with more compression with alum, then you can cast iron
and you need to find out how much they decked the block, cause the other thing you need to look out for is clearance with pistons and valves.
Sam

REPO1 · 04-06-2002, 09:55 AM

Here is a link. http://www.mustangii.org/tech/calculators/cr.shtml

You need all the info they ask for.

Reid

------------------
Sylvan Lake, Alberta, Canada

1970 Chevy C20 Custom Camper
#s matching 402BB Turbo 400 trans.
Air conditioning, power steering, manual brakes.
73,600 Original Miles!!
(Add on 2000 more from raod trip!)

69 longhorn · 04-06-2002, 11:24 AM

I have a 70cc chamber edelbrock perf rpm with flattops. The eng is decked ,but not to min specs.....9.8 to 1. You can run to about 10-1 with aluminum heads. Good luck....69 longhorn.

04-06-2002, 03:27 AM	#1
Longhorn Al Texas Longhorn For Life Join Date: Jun 2000 Location: Austin, Texas Posts: 698	Compression Ratio Question I was wondering what kind of compression ratio I'll be looking at with my engine? I'm not sure what info y'all need, so here's a quick run-down. It's a 383 with KB hypereutectic flat-top pistons, and a CompCams 270H. I'm planning on using the Performer RPM intake and heads along with an Edelbrock 750cfm carb. I also want aluminum roller rockers. What other info do you need? I wanted to know this because I've been seeing guys here suggest dished pistons to get a good ratio and be able to run on pump gas. I've already bought the pistons, so it's a little late for that. Will my engine be ok on the high octane with whatever compression I'm going to have? ------------------ 1970 C-10 named HOSS 350/350, PS, PB, 3.07 gears Future Motivation: 383 stroker, KB flat-top pistons, RPM intake and heads, 750cfm Edelbrock, & headers. For pics of my truck go here: http://communities.msn.com/1970HOSS/shoebox.msnw?Page=1 Future Projects: 1969 Pontiac GTO and 1974 International Scout II Hook 'Em from Austin, TEXAS __________________ 1970 C-10 named HOSS 400SB/TH350, PS, PB, 3.07 gears \m/ Hook 'Em from Austin, TEXAS

04-06-2002, 03:49 AM	#2
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	We need to know more about the heads. What CC are they? 58, 64, 72 cc. We also need to know the deck height on the block, has the block been decked, or is it stock? If you decked it, then the piston is further up in the hole, and this make a difference! Also, what thickness of head gaskets are you going to use? Sam __________________ 72 LWB chevy truck. Pasadena, Texas

04-06-2002, 04:03 AM	#3
Longhorn Al Texas Longhorn For Life Join Date: Jun 2000 Location: Austin, Texas Posts: 698	I'm looking at 64cc. I know the shop decked the block, but don't know how much. I have no idea on the gaskets. __________________ 1970 C-10 named HOSS 400SB/TH350, PS, PB, 3.07 gears \m/ Hook 'Em from Austin, TEXAS

04-06-2002, 04:07 AM	#4
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	Big al, Are the heads alum. heads? You can get awy with more compression with alum, then you can cast iron and you need to find out how much they decked the block, cause the other thing you need to look out for is clearance with pistons and valves. Sam __________________ 72 LWB chevy truck. Pasadena, Texas

04-06-2002, 09:55 AM	#5
REPO1 Shortbox wanna-be. Join Date: Mar 2002 Location: Fort St.John, British Columbia, Canada Posts: 773	Here is a link. http://www.mustangii.org/tech/calculators/cr.shtml You need all the info they ask for. Reid ------------------ Sylvan Lake, Alberta, Canada 1970 Chevy C20 Custom Camper #s matching 402BB Turbo 400 trans. Air conditioning, power steering, manual brakes. 73,600 Original Miles!! (Add on 2000 more from raod trip!) __________________ 1970 Chevy C20 Custom Camper 402BB Turbo 400 trans. (Slowly becoming a '70 shortbox 1/2 ton) '71 Camaro SS 402/T400 resto '97 Z28 (11.41@127MPH)

04-06-2002, 11:24 AM	#6
69 longhorn Registered User Join Date: Aug 2001 Location: rock island,il,usa Posts: 5,382	I have a 70cc chamber edelbrock perf rpm with flattops. The eng is decked ,but not to min specs.....9.8 to 1. You can run to about 10-1 with aluminum heads. Good luck....69 longhorn. __________________ http://community.webshots.com/user/hotrodhorn



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