Ford Model A & B Motors

[PC/SR]

Hardtimes: I was referring to piston/head clearance, guess that was not made clear. Thanks Zephyr gear set with the 4.56 would be interesting. Yeh, lots of combinations available.

[hardtimes]

Originally Posted by PC/SR

Hardtimes: I was referring to piston/head clearance, guess that was not made clear. Thanks Zephyr gear set with the 4.56 would be interesting. Yeh, lots of combinations available.

Head clearance, got it Wow, .045 is going to be what...8:1 or better

I'm easily confused these days, eh. Did you say that I still owed you that money .
Talking gear ratios makes my grey matter hurt. I've got the better/higher zephyr 2nd ratio, but then I go to kiwi quick change rear and big tires ..and got lost

[old28]

hardtimes / PC/SR / Mr B -- Can I get 8.1 CR with 7.1 heads and a .o45 piston top clearance? Or will I have to mill the 7.1 head a bite?

Better to buy a 8.1 head and set piston top clearance to .o45?

[PC/SR]

Don't know. Depends on gasket thickness, flycut depth(or not), piston popup, combustion chamber size. Bored out will add a bit to the CR. Lots of things to think about and consider.

[hardtimes]

Originally Posted by old28

hardtimes / PC/SR / Mr B -- Can I get 8.1 CR with 7.1 heads and a .o45 piston top clearance? Or will I have to mill the 7.1 head a bite?

Better to buy a 8.1 head and set piston top clearance to .o45?

These guys will set us straight, if I say something off key !
Model A stock pistons from Ford....'popped up' about .031. So, it makes sense that you will have to have either piston head reliefs cut in the head, or piston heads which are ordered and/or cut FLAT with top of block. This keeps interference from occurring and breaking things...with flathead heads ! So, you can get a flathead head and cut the flycuts off of it (see the pictures that I showed you earlier) to increase cr, but you have to keep in mind expansion rates and things growing as rpm grow ! Now there is an exception to this , but it does not involve flathead. If you have an OHV Head with say a 'hemi' type comb chamber...now you can popup maybe lots to increase cr. With flathead, remember what PC/SR was just saying about piston clearance at .045. IMO, that is darn close...too close? Maybe

PC/SR also thinks/types faster than I do !!

[old28]

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hardtimes -- With all the information you have put out there I still have questions until I get Mr B's book. With a stock A motor are the pistons .031" above the block top at TDC? If you cut the pistons flat so the pistons meet the top of block do you have to cut Intake/Exhaust valve clearance in 6.1 head or a 7.1 head? This is for a stock motor. What if you have 1.70 Intake? Are there any 7.1 heads out there with the clearance built in that still have .050 piston clearance?

[hardtimes]

Originally Posted by old28

hardtimes -- With all the information you have put out there I still have questions until I get Mr B's book. With a stock A motor are the pistons .031" above the block top at TDC? If you cut the pistons flat so the pistons meet the top of block do you have to cut Intake/Exhaust valve clearance in 6.1 head or a 7.1 head? This is for a stock motor. What if you have 1.70 Intake? Are there any 7.1 heads out there with the clearance built in that still have .050 piston clearance?

Go back and study post #23 , the first two pictures. One picture shows head with .050 'flycuts' , above the piston heads. Other picture shows same head with flycuts removed. However, if you look at the valve pockets, you will notice that there is still plenty of depth in head to accept the biggest cam (lift) that an A will or can use. Even with the .050 cut that took away the flycuts, there is still PLENTY of valve head room...even for 1.70 intakes ! You can enlarge the valve head areas of any head to improve flow somewhat, but this head is doing such a great job driving the attached B engine, that no such enlargement work will be done or indicated as needing done.

Yes as said before, the stock Ford A engine had about .031 piston popup. You cannot run popup pistons with a head cut like the one shown.

There IS one exception to this statement though....you can run more than one head gasket or have a solid copper head gasket made to order to provide the exact piston to head clearance that you wish to have (counter-productive to have popup pistons and have to install two or more head gaskets to get clearance...shoots the heck out of cr then.

At any rate, you have to clay the piston to head clearance to determine your clearance...WITH head gasket in place. Same claying can be done with valve heads, if you want to know what you have.

Finally, answer to your last question; is there 7:1 head with clearance built in , and still have the .050 clearance ? I do not know of any This is because a 7:1 flathead IS going to look like the one pictured...without the flycuts !!
Comp ratio is a combination of a number of things. When all said and done, relative to a 7:1 flathead....the CLEARANCE (and thereby the cr) between piston top and head surface would be set by use of proper head gasket and cc of valve areas in head.

Contact Tod and tell him that you are interested in obtaining a 7:1 cr head... You will most likely be buying a head that looks like the one pictured in post #23.

[old28]

Question, With a stock piston at .031" above the top of the block with a 7013 R3 gasket & 1.70 intake valve will a standard 6.1 iron head work with no other motor modifications? Does a 7.1 iron head have to be fly cut to work in the same situation?
What's an easy way to get 75 -90 HP from an A motor with the least amount of machine work? I will port/polish the block at home and build a 2 x 2 intake with 94 carbs. Will have stock size exhaust & 1.70 intake. Looking at a 330 or 340 cam.
Just trying to get some combinations to think about.

[johnneilson]

An Old Banger Racer told me in the beginning of my exploits, "you will never spend so much money on a motor to go so slow as a Model A".
The other advice he gave, "Start with a B Model, it is half way modern".

There is a ton of opinion about heads a chambers.
I had a 8:1 Winfield repop here that would not flow enough air to make 70 hp. This is a dilemma for the side valve motors. Not to say that it cannot be done, just beware of snake oil salesmen.

[Tom Wesenberg]

Turbocharge it for the most bang for the buck.

[old28]

forever4 -- That may be true, but a smart man asks a lot of questions before he starts throwing money into a project.

johnneilson -- Well taken. As I want to increase the bore to 4" (.125 over) I was leaning towards the thicker (they say) A block. I know what you say on the oil salesman, I have read a few threads from real life conditions that said they could not see any noticeable performance between a 5.5, 6.1 or a 7.1 head. I am with you on dollors/speed on an A/B motor. I have recently built a few 6 cylinder race motors and spent twice what I did on my BBC motors to run slower.

Tom Wesenberg -- Turbo's are out as per the rules in TROG.

[johnneilson]

old28,

just think about this, 4" bore on a motor with bores on 4.250 centers. It doesn't matter A or B. I have seen 4.030 bores, not for my stuff, thank you.

IMHO, a B block with full pressure drilled crank and inserts makes sense. I know of many who have run babbit very successfully, again, not for my stuff.

The best part of this is that there isn't a catalog like Summit or Jegs to choose from, if you want to go fast, you have to massage the parts, gently.

[old28]

johnneilson -- As this motor will be for the TROG race twice a year I want to go with a big inch setup as in a 4.00" bore. I plainned on center main pressure oil & babbitt bearings (both rods & mains). As the motor will be run maybe 10 1/8 mile passes on hard sand I can't get my pocket book around full insert bearings. May change my mind before I start building, I will see what I learn in next few weeks.

I have done years and years of Summit & Jegs with my BBC dragster & altered and I am up for this new game with the A & B. Just got my copy of 4 Bangers & me from Mr B so I have a lot of reading & learning to do for the next few weeks.

[old28]

What is the compressed thickness of a Fel-pro 7013 R3 ?

What is the compressed thickness of a Best #509 ?

If I order pistons with a CH that will have my pistons even with the top of the block at TDC, Is there a head gasket that will provide .050" piston to head clearance with a 7.1 CR head with no piston fly cut?

Or do you have to set up the motor with the pistons .010 - .013 in the hole?


The more I read my book (Mr B's) the more questions I have. I am learning more each day. Hope you guys with all the right answers don't get tired of the questions from the new guy.

[PC/SR]

The Best gasket compresses to .050--.055. I run it with pistons with no popup or flycut. Be really sure to measure the deck height from the pan rail to the deck. (11.5" stock.) It is critical to calculating popup. I bought a "new" block and took the sellers word for how much he took off and got popup I did not want and the valve lengths were off. Finally measured it and it apparently someone sometime took off more, threw the initial measurements all off.

[old28]

PC/SR -- Thanks for the information. I am thinking that the FelPro-7013R3 will be the same as the best at .050-.055 compressed, but I would like to hear from someone that has used one.

So if I know the block height I can order pistons with a CH that will place the flat top piston even with the block top. Then using a 7.1 iron head with no fly cuts, install a Best 509 gasket and I should have (.050-.055) piston to head clearance. Am I correct or have I missed something?

Are Egg & Ross both good for custom pistons (CH) as I am going to use cast not forged in this Hot Street type build? Piston rings will be the small modern style type.

[old28]

With your years of Model A building knowledge go easy on use new guys that are just getting started in this A & B sand box.

As per the answer from PC/SR above I was unaware that there were two models of the Best 509.

CH -- Compression Height

At the young age of 70 this ain't my first rodeo, been building by own drag race motors for 50+ years but this A & B stuff is a new game and it's like starting over.

[old28]

forever4 -- Thanks for the information. I am working towards a hot street type motor to run in the TROG in Pismo Beach, CA. This car will make maybe (10) 1/8 mile passes on compressed sand at the beach once or twice a year. The more I read Mr B's book the more I am looking at a lower HP mark.
I think a motor for this project in the 65-75 HP @ 380-4000 RPM would work great and do what I want it to do & not have to be working on it all the time.

As this motor will only be run a few passes I would still like to build cubic inches as large as I can at 4" bore (.125" over) and with a uncut 7.1 head and a compressed gasket at (.050-.055) and the original pistons Up .031" out of the hole, how do you maintain a .045-,050 piston to head clearance?

Do you have to flycut the head in the piston area about .031" with the above setup? How much does this lower the CR on a 7.1 head?

Open to other/better ways to get to 65-75 HP. All the normal cam, intake, carb, P&P, will be done. This is not a high buck build, just a fun setup for a fun race, Ain't the Salt or the dry lakes, even thow I love them.

[Spokes]

Originally Posted by old28

Thanks CarlG Unable to find it on Amazon, other places I can try?

Jim B. is a Member on Fordbarn. I have his Book every interesting and complete. Jim is also helpful with Banger Questions. Two Great Magazines on the Subject FAST and Secrets Of Speed both have Web Sites. Hill Climbs, Meetings Ect.

[George Miller]

If you worked on drag engines for 50 years you must know about O ringing the head for stainless steel O ring. Why not do that. That is how I sealed the Olds 455 head on my Model A engine for hill climbs.