The Ford Barn

1931flathead · 04-23-2016, 02:52 PM

what a good compression ratio for a street engine with out having problems with it

Karl Wolf · 04-23-2016, 03:34 PM

Please put this in perspective.
What engine
Car
Useage

Karl

1931flathead · 04-23-2016, 03:46 PM

flathead ford v8 in a model a model 59 with 125 over bore and 4 1/4 stroke crank

Kahuna · 04-23-2016, 04:26 PM

I, personally, would want no more than 9:1.
You have a large flathead at about 292 cubic
inches, if my math skills are correct. It may
be a bit difficult to obtain a ratio like that.
Do your homework on combustion chamber
volumes on various heads to make a good
decision and head selection.
JMO
Jim

1931flathead · 04-23-2016, 04:35 PM

they say with a 74 cc head gives you 10:1 I will have to cc the block first to see what I got just trying to get a good idea what I should shoot for I don't want to buy a set of alum heads and cant use them thanks

Kahuna · 04-23-2016, 05:49 PM

Sponsored Links (Register now to hide all advertisements)

Keep in mind, I haven't done much of this in years, but
my calcs seem to indicate that with a 74cc chamber you might be very close to 9.1:1.
Someone else can correct me
Jim

1931flathead · 04-23-2016, 09:20 PM

just going buy what ross is saying on there web site

Ol' Ron · 04-23-2016, 10:26 PM

Last year we built a 294ci engine with L-100 cam, we used edelbrock 74cc heads Milled for .045" piston clearance. This gave a Cr of 8.7. The L-100 bleeds of some of the pressure as the dynamic CR is around 7.5. Using a SBC dist set for 16 degs mechinical adv and 8 degs vac weve been running 87 oct gas with no problem. Check the AF as well, cruise should be around 15 and power 12.5. It;s in a 38 PU with Toyota 5 speed. Nice ride.

1931flathead · 04-24-2016, 08:26 AM

Thanks Ron I will have to cc my block and go from there to see what heads I should buy

Kahuna · 04-24-2016, 11:36 AM

Is the block relieved? That'll make a difference

1931flathead · 04-24-2016, 12:01 PM

No I'm going to get it done

JWL · 04-24-2016, 01:24 PM

O'Ron touched on an important point. It depends on what your cam timing numbers are. With a stock cam and low grade(regular 87 octane) about 8 to 1 is in the ball park.

1931flathead · 04-24-2016, 01:39 PM

425 camshaft is going in it

04-23-2016, 02:52 PM	#1
1931flathead Senior Member Join Date: Feb 2016 Location: central minn Posts: 1,025	compression ratio what a good compression ratio for a street engine with out having problems with it

04-23-2016, 03:34 PM	#2
Karl Wolf Senior Member Join Date: May 2010 Location: Mill Valley,Ca. Posts: 1,509	Re: compression ratio Please put this in perspective. What engine Car Useage Karl

04-23-2016, 03:46 PM	#3
1931flathead Senior Member Join Date: Feb 2016 Location: central minn Posts: 1,025	Re: compression ratio flathead ford v8 in a model a model 59 with 125 over bore and 4 1/4 stroke crank

04-23-2016, 04:26 PM	#4
Kahuna Senior Member Join Date: May 2010 Location: NorCal Posts: 2,617	Re: compression ratio I, personally, would want no more than 9:1. You have a large flathead at about 292 cubic inches, if my math skills are correct. It may be a bit difficult to obtain a ratio like that. Do your homework on combustion chamber volumes on various heads to make a good decision and head selection. JMO Jim

04-23-2016, 04:35 PM	#5
1931flathead Senior Member Join Date: Feb 2016 Location: central minn Posts: 1,025	Re: compression ratio they say with a 74 cc head gives you 10:1 I will have to cc the block first to see what I got just trying to get a good idea what I should shoot for I don't want to buy a set of alum heads and cant use them thanks

04-23-2016, 05:49 PM	#6
Kahuna Senior Member Join Date: May 2010 Location: NorCal Posts: 2,617	Re: compression ratio Sponsored Links (Register now to hide all advertisements) Keep in mind, I haven't done much of this in years, but my calcs seem to indicate that with a 74cc chamber you might be very close to 9.1:1. Someone else can correct me Jim

04-23-2016, 09:20 PM	#7
1931flathead Senior Member Join Date: Feb 2016 Location: central minn Posts: 1,025	Re: compression ratio just going buy what ross is saying on there web site Last edited by 1931flathead; 04-23-2016 at 09:27 PM.

04-23-2016, 10:26 PM	#8
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,860	Re: compression ratio Last year we built a 294ci engine with L-100 cam, we used edelbrock 74cc heads Milled for .045" piston clearance. This gave a Cr of 8.7. The L-100 bleeds of some of the pressure as the dynamic CR is around 7.5. Using a SBC dist set for 16 degs mechinical adv and 8 degs vac weve been running 87 oct gas with no problem. Check the AF as well, cruise should be around 15 and power 12.5. It;s in a 38 PU with Toyota 5 speed. Nice ride.

04-24-2016, 08:26 AM	#9
1931flathead Senior Member Join Date: Feb 2016 Location: central minn Posts: 1,025	Re: compression ratio Thanks Ron I will have to cc my block and go from there to see what heads I should buy

04-24-2016, 11:36 AM	#10
Kahuna Senior Member Join Date: May 2010 Location: NorCal Posts: 2,617	Re: compression ratio Is the block relieved? That'll make a difference

04-24-2016, 12:01 PM	#11
1931flathead Senior Member Join Date: Feb 2016 Location: central minn Posts: 1,025	Re: compression ratio No I'm going to get it done

04-24-2016, 01:24 PM	#12
JWL Member Emeritus Join Date: May 2010 Location: Fitzgerald, Georgia Posts: 2,204	Re: compression ratio O'Ron touched on an important point. It depends on what your cam timing numbers are. With a stock cam and low grade(regular 87 octane) about 8 to 1 is in the ball park.

04-24-2016, 01:39 PM	#13
1931flathead Senior Member Join Date: Feb 2016 Location: central minn Posts: 1,025	Re: compression ratio 425 camshaft is going in it