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Compression ratio

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Compression ratio
#1
Engine
Colonel musturd 79 Avatar
Colonel musturd 79 Michael McKinney
Winchester, Virginia, USA   USA
1978 MG Midget 1500 "Colonel Mustard"
1987 Pontiac Fiero "SILVER BULLET"
I have a midget 1500 it has been bored .020 over and I am using dished pistons. I want to acheive a 9 - 9.5 CR , I have a tkc3239 cylinder head . If anyone could tell me how much I need to mill my head to get there.



Amore della Strada
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Ken Plumstead Avatar
Smithers, B.C., Canada   CAN
1965 MG MGB
1968 MG MGC GT
Good Morning Colonel,

Try this site. You can 'play' with the numbers to get what you want.

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

Ken



MG: Transforming gasoline into Fun!!!

Speedracer Avatar
Speedracer Platinum Member Hap Waldrop
Greenville, SC, USA   USA
1967 MG MGB Racecar "The Biscuit"
In reply to # 3641302 by Colonel musturd 79 I have a midget 1500 it has been bored .020 over and I am using dished pistons. I want to acheive a 9 - 9.5 CR , I have a tkc3239 cylinder head . If anyone could tell me how much I need to mill my head to get there.

More than you want to cut off the head, with a flat top piston it take a cut of .100" to get to those numbers. Add to that you really can not deck the block more than minor clean up due to the recessions around the bores for the head gasket. Even with "9.0 to 1" flat top piston in the NA 1500 you are only netting 8.3 to 1 with virgin block and head decks, your engine with dish pistons is like 7.5 to 1. Bottom line of you don't go with the flat top piston you are not going to get there, and trying to make higher CR with extreme LC pistons will erase any future option you may have, it is really bad way to do it.

The RSR CR calculator, Ken linked is a good source to use, once you have your data.



Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com



Edited 1 time(s). Last edit at 2017-12-09 08:05 AM by Speedracer.


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