The Ford Barn

46fatford · 08-10-2011, 07:22 AM

I want to install my newly purchased Offy 375 heads on my engine. The engine is a 8RT that was a reman w/ low miles. I took off the pan, intake, exhaust etc and it was clean inside. I also checked all the bearings and they look like new. The engine is a good runner, no smoke, no noise, good oil pressure. I really don't want to pull it back out and install a cam right now, but would like put on the heads and a 2 pot manifold with 1 of Bubba's converted chevy distributor w/ pertronix. My question is, will installing these heads hamper the breathing w/ out changing out the cam? I really like the look of finned heads, but if it requires the cam change they can wait. If no on the heads for now, I'm still going to be installing a 2 pot manifold and hotter ignition anyway. I know I would gain more performance wise by installing a cam, doing some porting and the heads, intake, but the car is just a cruiser and won't be raced.The engine is in a 46 business coupe with the stock 3:78 rear and 3 spd. Any advice is appreciated.
thanks
Matt

Walt Dupont--Me. · 08-10-2011, 07:31 AM

The 375 heads should work fine with a stock cam. Those are pretty tight heads and most performance high lift cams you will have to have the heads valve pockets machined out some. Walt

Ol' Ron · 08-10-2011, 09:17 AM

The heads will work fine as is. However, It will improve performance and fuel economy if you tighten up the combustion chamber by checking piston to head clearance. This should be .040-050" and can be checked by using little aluminum balls stuck on the pistons and squashed by rotating the engine. Some use the old method, using clay. Check near the edges and center. This doesn't increase compression much but increases turbulence in the chamber before ignition getting a cleaner burn. Two carbs work well o a stock engine if tuned right. Check A/F in cruise and acceleration. The SBC is a good move.

Ford Flathead · 08-10-2011, 09:37 AM

clay the pistons and valve clearance for sure.

blown49 · 08-10-2011, 01:49 PM

With stock bore and stroke you're looking at a nominal compression ratio of 8.41:1. You will probably have to have the valve pockets enlarged when you change the cam. Thos heads are no longer in production and are hashed in black on the PDF files mentioned below.

Here's a link to a post I made earlier this year with a PDF file of various comptression ratios of various heads on diffrerent blocks. Each head is listed at different strokes and bores as well.

The link has the connection to the PDF file at the bottom of the first post in that thread.

Hope this helps.

Jim

http://fordbarn.com/forum/showthread...ht=compression

46fatford · 08-10-2011, 06:45 PM

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The heads I'm going to use are going on a .060 over 8RT with a 3 3/4 crank. They have already had the plug area unshrouded and have been massaged to work with an isky 400 jr cam. They came off an old race engine a friend of mine had. He ran them with a new 400 jr cam and never had any issues with clearances. Also will raising the compression this much cause premature wear or oil useage? The engine is a low mileage reman and the cylinders all look really good with cross hatch and compression is good across all cylinders 120+ .I just don't want to hurt it. If you guys think it could I might just swap out my 8RT heads for my set of 59ABs and save the offys for a future rebuild. I like the looks of the earlier heads more. While I'm at it I could have them shaved too. Can anyone tell me if they noticed a difference in running temp between the earlier style heads and the later 8BA heads, with all other variables the same, ie ignition, carburetion, and water pumps?
Thanks
Matt

Ol' Ron · 08-10-2011, 07:01 PM

You're looking for too much information, nothing is perfect. You'll have to do some thinking. When you say all the clearances are correct, that was on "HIS" engine. There are several ways to clearance for valve clearance and one removes too much material and lowers the CR drastically. However, 8.5:1 CR on a stock cam can cause trouble with the ignition system and using a SBC dist can cure this, but you'll have to understand this information isn't in a book someplace. Not to mention the A/F iws also important here. This might scare you some, but what your doing has been done by others quite successfully with great results in performance and economy. Modifying an engine requires some thought. Good luck

08-10-2011, 07:22 AM	#1
46fatford Senior Member Join Date: Jun 2010 Location: Indiana Posts: 338	Flathead questions I want to install my newly purchased Offy 375 heads on my engine. The engine is a 8RT that was a reman w/ low miles. I took off the pan, intake, exhaust etc and it was clean inside. I also checked all the bearings and they look like new. The engine is a good runner, no smoke, no noise, good oil pressure. I really don't want to pull it back out and install a cam right now, but would like put on the heads and a 2 pot manifold with 1 of Bubba's converted chevy distributor w/ pertronix. My question is, will installing these heads hamper the breathing w/ out changing out the cam? I really like the look of finned heads, but if it requires the cam change they can wait. If no on the heads for now, I'm still going to be installing a 2 pot manifold and hotter ignition anyway. I know I would gain more performance wise by installing a cam, doing some porting and the heads, intake, but the car is just a cruiser and won't be raced.The engine is in a 46 business coupe with the stock 3:78 rear and 3 spd. Any advice is appreciated. thanks Matt __________________ "..Nothin' outrun my V8 Ford" (Chuck Berry) S.M.I.B.

08-10-2011, 07:31 AM	#2
Walt Dupont--Me. Senior Member Join Date: May 2010 Location: Gardiner Me. Posts: 4,200	Re: Flathead questions The 375 heads should work fine with a stock cam. Those are pretty tight heads and most performance high lift cams you will have to have the heads valve pockets machined out some. Walt

08-10-2011, 09:17 AM	#3
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,860	Re: Flathead questions The heads will work fine as is. However, It will improve performance and fuel economy if you tighten up the combustion chamber by checking piston to head clearance. This should be .040-050" and can be checked by using little aluminum balls stuck on the pistons and squashed by rotating the engine. Some use the old method, using clay. Check near the edges and center. This doesn't increase compression much but increases turbulence in the chamber before ignition getting a cleaner burn. Two carbs work well o a stock engine if tuned right. Check A/F in cruise and acceleration. The SBC is a good move.

08-10-2011, 09:37 AM	#4
Ford Flathead Member Join Date: Jul 2011 Location: La Crescenta, CA Posts: 92	Re: Flathead questions clay the pistons and valve clearance for sure.

08-10-2011, 01:49 PM	#5
blown49 Senior Member Join Date: May 2010 Location: West Union, Ohio Posts: 113	Re: Flathead questions With stock bore and stroke you're looking at a nominal compression ratio of 8.41:1. You will probably have to have the valve pockets enlarged when you change the cam. Thos heads are no longer in production and are hashed in black on the PDF files mentioned below. Here's a link to a post I made earlier this year with a PDF file of various comptression ratios of various heads on diffrerent blocks. Each head is listed at different strokes and bores as well. The link has the connection to the PDF file at the bottom of the first post in that thread. Hope this helps. Jim http://fordbarn.com/forum/showthread...ht=compression __________________ Visit my Blown '49 Merc website @ http://www.blown49.com

08-10-2011, 06:45 PM	#6
46fatford Senior Member Join Date: Jun 2010 Location: Indiana Posts: 338	Re: Flathead questions Sponsored Links (Register now to hide all advertisements) The heads I'm going to use are going on a .060 over 8RT with a 3 3/4 crank. They have already had the plug area unshrouded and have been massaged to work with an isky 400 jr cam. They came off an old race engine a friend of mine had. He ran them with a new 400 jr cam and never had any issues with clearances. Also will raising the compression this much cause premature wear or oil useage? The engine is a low mileage reman and the cylinders all look really good with cross hatch and compression is good across all cylinders 120+ .I just don't want to hurt it. If you guys think it could I might just swap out my 8RT heads for my set of 59ABs and save the offys for a future rebuild. I like the looks of the earlier heads more. While I'm at it I could have them shaved too. Can anyone tell me if they noticed a difference in running temp between the earlier style heads and the later 8BA heads, with all other variables the same, ie ignition, carburetion, and water pumps? Thanks Matt __________________ "..Nothin' outrun my V8 Ford" (Chuck Berry) S.M.I.B.

08-10-2011, 07:01 PM	#7
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,860	Re: Flathead questions You're looking for too much information, nothing is perfect. You'll have to do some thinking. When you say all the clearances are correct, that was on "HIS" engine. There are several ways to clearance for valve clearance and one removes too much material and lowers the CR drastically. However, 8.5:1 CR on a stock cam can cause trouble with the ignition system and using a SBC dist can cure this, but you'll have to understand this information isn't in a book someplace. Not to mention the A/F iws also important here. This might scare you some, but what your doing has been done by others quite successfully with great results in performance and economy. Modifying an engine requires some thought. Good luck