79 400 Compression Ratio Trivia
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79 400 Compression Ratio Trivia
Ok, I've always wanted to know this. Maybe you guys out there can give me a good guess on what my compression ratio actually is.
I have a 79 400 2V, and what I did to increase the compression ratio in it was to install flat top pistons from Badger, and also shaved the stock heads down 18 mills. I didn't do anything fancy with the head gasket, just the regular ones from Felpro. That's about it. I didn't have the block shaved. Just the heads.
The engine runs great, but I'm just curious as to what the new compression ratio probably is.
Any guesses?
I have a 79 400 2V, and what I did to increase the compression ratio in it was to install flat top pistons from Badger, and also shaved the stock heads down 18 mills. I didn't do anything fancy with the head gasket, just the regular ones from Felpro. That's about it. I didn't have the block shaved. Just the heads.
The engine runs great, but I'm just curious as to what the new compression ratio probably is.
Any guesses?
Last edited by Torque1st; Jan 29, 2006 at 12:44 AM.
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I read the article, but the only thing of note to me was that the '71 flat topped pistoned 400 had 9.0:1 compression, so I think it's safe to say that the Badger flat tops I put in my 400 alone would bring the CR up to 9.0:1, assuming the '79 is the same except for the low compression pistons.
So now I need to know how much more the CR would have risen due to the shaving of the heads 18 mills.
Thanks.
So now I need to know how much more the CR would have risen due to the shaving of the heads 18 mills.
Thanks.
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Aftermarket piston's compression height and valve relief size vary. So do factory block deck heights + or - .005". Figure 3.5 to 4cc was removed from the chamber and compression is probably 9.3 to 9.4:1.
http://www.fordmuscle.com/calculators/compression.shtml
http://www.fordmuscle.com/calculators/compression.shtml
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With the quality control of the '70s, it's possible that the block heights can be off more than the +-.005, but even with that tolorance the CR would be hard to guess.
Is there a way to use a compression tester to figure out the CR? The meter I have for a compression tester doesn't measure ratio, just PSI.
Is there a way to use a compression tester to figure out the CR? The meter I have for a compression tester doesn't measure ratio, just PSI.
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Unfortunately using a compression tester to determine compression ratio has tooo many variables, it can be approximated, but not nearly as accurate as you want.
Compression pressure, approximate @ cranking speed :
8.0---140PSI
9.0---160
10.0--180
11.0--200
Compression pressure, approximate @ cranking speed :
8.0---140PSI
9.0---160
10.0--180
11.0--200
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This is a bet you would lose, my friend FastFord59. I have a 400 in my '79, and it's stock. I am as sure as the sun shines, the wind blows, and the snow falls on that.
Ford made the 400 up until 1983.
Ford made the 400 up until 1983.
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From: Eastern Pa
Another variable is the cam. Did you do a cam change in the engine? Depending on the cam it may also change you dynamic cr. Theres a calculator that works nicely figuring in some of the variables on the kbsilvolite site. We would assume you have a 400 crank in there or it would run terrible as the badgers would be way down in the hole.
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From: Northern Illinois
Originally Posted by fastford59
I bet yopu don't have a "79" 400, they didn't make them in '79.Better do some more research on your engine #s.
Here are 2 VIN's from my Bronco's.
1 is a U15H and the other is a U15S.
H=351M and the S=400
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I put the Comp Cam 265DEH K kit in it. Lots of goodies in that kit. I was happy as can be putting that in. It was beautiful!
I'm guessing that with what I did during the build, it's at about 9.8:1 compression. I imagine it's close to that.
I think the confusion with the 400 might be that it's not in a truck. Although I own a Ford truck, this particular vehicle is a '79 Town Car that came with a Ford 400 as the only engine available for that year for Town Cars.
I'm guessing that with what I did during the build, it's at about 9.8:1 compression. I imagine it's close to that.
I think the confusion with the 400 might be that it's not in a truck. Although I own a Ford truck, this particular vehicle is a '79 Town Car that came with a Ford 400 as the only engine available for that year for Town Cars.
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From: PacNW
351M/400 production stopped at the end of model year 1982.
If the stock Badger flat tops are being used they have a 9:1 nominal compression ratio when installed in a completely stock engine. Their compression height is also .010 lower than the factory pistons to make up for the fact that the block and/or heads may need to be decked. If you took .018 off of your heads then you may be around 9.2:1 if that but the only real way to tell is to measure the total amount of space above the piston and calculate it out.
If the stock Badger flat tops are being used they have a 9:1 nominal compression ratio when installed in a completely stock engine. Their compression height is also .010 lower than the factory pistons to make up for the fact that the block and/or heads may need to be decked. If you took .018 off of your heads then you may be around 9.2:1 if that but the only real way to tell is to measure the total amount of space above the piston and calculate it out.