Stock compression for an 87 5.0 HO???

Wally · 10-04-2002, 12:06 PM

Well let me start off by saying HI to everyone. My friend picked up an 87 5.0 HO to put in a 66 Bronco that he’s doing a frame up restoration on. We thought we would do a compression test to see what shape the motor was in before we started. The Mustang that it came out of was rolled and was upside down for a while so one cylinder shot oil a crossed the garage. The compression test went from 140 psi to 190 psi. on one side and 180 psi to 195 psi on the other. I haven’t seen a stock motor have that kind of compression of I figured I would ask the 5.0 experts here on the board.

What should the stock motor have for compression?

I’m thinking the motor has a lot of carbon built up on the pistons that it causing the high compression.

Thanks for your input.

7000rpmisheaven · 10-04-2002, 12:24 PM

From what I know its not the actuall number that is the most important. Whats most important is that the value you get for each cylinder is about the same. I think you want to lowest number to be no more than 10% off from the highest. I recently peformed a compression test on mine. I did three tests for each cylinder and out of all the tests on each cylinder the highest I got wast 155 and the lowest was 145.

mike72678 · 10-04-2002, 12:25 PM

when i tested compression in my brothers mustang (88 gt) bored .040 over with just standard pistons (about 9:1) and the stock heads milled .030 , he had 160 psi +/- about 5 psi in all cylinders , i think that his compression ratio was about 9.5:1 to 9.75:1 . hope this might help . sounds like you got a lot of compression .

10-04-2002, 12:51 PM

What should the stock motor have for compression?

Stock 87HO motors in mustangs have a 9:1 compression ratio

10-04-2002, 12:06 PM	#1
Wally Registered Member Join Date: Oct 2002 Location: Santee CA Posts: 1	Stock compression for an 87 5.0 HO??? Well let me start off by saying HI to everyone. My friend picked up an 87 5.0 HO to put in a 66 Bronco that he’s doing a frame up restoration on. We thought we would do a compression test to see what shape the motor was in before we started. The Mustang that it came out of was rolled and was upside down for a while so one cylinder shot oil a crossed the garage. The compression test went from 140 psi to 190 psi. on one side and 180 psi to 195 psi on the other. I haven’t seen a stock motor have that kind of compression of I figured I would ask the 5.0 experts here on the board. What should the stock motor have for compression? I’m thinking the motor has a lot of carbon built up on the pistons that it causing the high compression. Thanks for your input.

10-04-2002, 12:24 PM	#2
7000rpmisheaven Registered Member Join Date: Nov 2001 Location: germantown MD Posts: 283	From what I know its not the actuall number that is the most important. Whats most important is that the value you get for each cylinder is about the same. I think you want to lowest number to be no more than 10% off from the highest. I recently peformed a compression test on mine. I did three tests for each cylinder and out of all the tests on each cylinder the highest I got wast 155 and the lowest was 145. __________________ 85 GT 4bbl roller cam 2 ch. Flowmasters, O/R H-pipe Performer intake and carb milodon water pump, FMS 9mm wires, aluminum driveshaft, king cobra clutch

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Stock No More	Stroked408	Windsor Power	9	06-12-2002 08:19 PM
What is the stock compression........	Barrfight	Windsor Power	7	05-12-2002 03:24 AM
For whoever it was considering using stock ported heads	2FastLX	Windsor Power	5	10-11-2001 01:53 PM
Ported Stock Heads...	FivepointOH	Windsor Power	5	03-12-2001 03:47 PM
LT's vs. shorties vs. stock headers	jonnyk	Windsor Power	9	01-01-2001 11:28 AM

10-04-2002, 12:25 PM	#3
mike72678 MW Link Sponsor Join Date: Sep 2002 Location: rochester , ny Posts: 79	when i tested compression in my brothers mustang (88 gt) bored .040 over with just standard pistons (about 9:1) and the stock heads milled .030 , he had 160 psi +/- about 5 psi in all cylinders , i think that his compression ratio was about 9.5:1 to 9.75:1 . hope this might help . sounds like you got a lot of compression .

10-04-2002, 12:51 PM	#4
Mustanguy Guest Posts: n/a	What should the stock motor have for compression? Stock 87HO motors in mustangs have a 9:1 compression ratio