Pop Question about 2F Piston/Head Tradeoffs (1 Viewer)

[rstoddard]

Mark Whatley wrote this in 2006. Can anyone help me understand what Mark is saying about the trade off between using the ‘75 (“early”) head versus the “later” (years?) head to achieve higher compression?

I have a ‘75 2F I’m looking at rebuilding and I’m wondering if this comment from Mark suggests that I should consider replacing the domed pistons with flat head pistons and using a later model head “milled to achieve higher compression”? Is he suggesting using the domed pistons with the later model head and milling it so they don’t contact and to create a tight combustion chamber?

“Flat top pistons with closed (quench) chamber heads is a more effecient setup that domes and open chamber heads for the type of rpm and flow rates that you will see in a 2F. Any 2F.
If you run flat tops in the open chamber head, compression drops a lot. Bad thing. If you run domes in the closed chamber head, the piston and the head try to occupy the same space at TDC. Worse thing.

If you want to run the earlier head, mill it to reduce the volume of the chamber to bring compression back up some. In the real world (as opposed to the dyno) you will never notice an difference in power or economy over the later head with this approach. But if you start with the later head and mill it too, you can attain higher compression.
Mark...”

 

[White Stripe]

Mark Whatley wrote this in 2006. Can anyone help me understand what Mark is saying about the trade off between using the ‘75 (“early”) head versus the “later” (years?) head to achieve higher compression?

I have a ‘75 2F I’m looking at rebuilding and I’m wondering if this comment from Mark suggests that I should consider replacing the domed pistons with flat head pistons and using a later model head “milled to achieve higher compression”? Is he suggesting using the domed pistons with the later model head and milling it so they don’t contact and to create a tight combustion chamber?

“Flat top pistons with closed (quench) chamber heads is a more effecient setup that domes and open chamber heads for the type of rpm and flow rates that you will see in a 2F. Any 2F.
If you run flat tops in the open chamber head, compression drops a lot. Bad thing. If you run domes in the closed chamber head, the piston and the head try to occupy the same space at TDC. Worse thing.

If you want to run the earlier head, mill it to reduce the volume of the chamber to bring compression back up some. In the real world (as opposed to the dyno) you will never notice an difference in power or economy over the later head with this approach. But if you start with the later head and mill it too, you can attain higher compression.
Mark...”

He is saying closed chamber heads are more efficient. Which you use with flat top pistons. Then you mill the head to raise compression. What year heads are closed chamber should be easy to find out doing a search, but I don't know personally. For such a setup you would run a sniper with timing control. I would also run a aftermarket performance cam and port the heads. However if I were building a performance 2f myself, I would seriously consider using a Ford 300 instead. Would have similar soul of a 2f but more potential because of parts availability. Would be really cool.

 

[rstoddard]

He is saying closed chamber heads are more efficient. Which you use with flat top pistons. Then you mill the head to raise compression. What year heads are closed chamber should be easy to find out doing a search, but I don't know personally. For such a setup you would run a sniper with timing control. I would also run a aftermarket performance cam and port the heads. However if I were building a performance 2f myself, I would seriously consider using a Ford 300 instead. Would have similar soul of a 2f but more potential because of parts availability. Would be really cool.

Interesting concept. Certainly less expensive but it would present challenges installing it.

 

[rstoddard]

So you (and Whatley) are saying that the Closed Chamber Heads, milled to raised compression, and Flat Head Pistons provide the highest compression 2F engine, correct?

 

[Grayscale]

Mill either head, and larger pistons for either type, and you will have higher compression. Not sure that I'd really want a thiner waterjackets, playing the whole muscle car mods game.

 

[SergP]

Not sure if this help.
In my project, PO installed (and probably drive it) an older head (1974) on 2f (1976) with domed pistons.
But the engine is rusted and didn't start, I rebuild it,.. but never try to start or test it. I have found 1977 2F in "better" condition

this picture from this setup:

 

[rstoddard]

Mill either head, and larger pistons for either type, and you will have higher compression. Not sure that I'd really want a thiner waterjackets, playing the whole muscle car mods game.

I’m not trying to build a muscle car. I just want to build a respectable 2F with good low end torque. I understand that the open chamber heads with domed pistons have a lower compression than the closed/flat and we’re designed primarily for smog control. If I’m going to rebuild a 2F I want to get the best performance I can. That doesn’t mean I’m trying to build a high performance engine, just trying to optimize with what Toyota engineered over the years.

 

[flx]

My understanding was that domed piston allowed (in stock form) for a better compression than flat ones (by filling more of the chamber).

The statement from Mark in your first post may be missing the context it was posted on? I'm wondering if this statement was made for the specific case of a rebuilt engine, as domed piston are NLA and if you use flat pistons in an engine/head made for domed piston you obviously get the worst result.

 

[cruiserkev]

Previous owner did this on my 40 in the 90s. Shaved 74 F head on a 76 2F block with flat top pistons. Cylinder compression was around 140 if I remember correctly. Quick on the street with plenty of torque for the trail, loved it. Apparently this was a common trick hot rodders did back then. Unfortunately after a few years, I developed a crack in the head. Could not find another F head at the time and replaced it with a 2F one which worked but performance definitely suffered.

 

[aztoyman]

Bumping your compression (within reasonable limits) is a great way to increase low end torque.

If domed pistons are NLA as mentioned I would run the closed chamber head if you have one. If you run the closed chamber head and flat top piston you can still mill the head to achieve more compression but you should calculate that out. CC the chambers and know your compressed head gasket thickness. The machine shop should be able to help you with that.

Keep in mind that if you go too high with compression, your octane requirements go up even with retarded timing. So find out the ideal compression ratio for your intended use.

If all you have is an open chamber head and all that is available is flat top pistons you will loose compression and performance unless you bring compression back up by milling the head or find domed pistons. It will still run with the lower compression but you will notice the loss of performance.

What head do you have?

 

[rstoddard]

Bumping your compression (within reasonable limits) is a great way to increase low end torque.

If domed pistons are NLA as mentioned I would run the closed chamber head if you have one. If you run the closed chamber head and flat top piston you can still mill the head to achieve more compression but you should calculate that out. CC the chambers and know your compressed head gasket thickness. The machine shop should be able to help you with that.

Keep in mind that if you go too high with compression, your octane requirements go up even with retarded timing. So find out the ideal compression ratio for your intended use.

If all you have is an open chamber head and all that is available is flat top pistons you will loose compression and performance unless you brig compression back up by milling the head or find domed pistons. It will still run with the lower compression but you will notice the loss of performance.

What head do you have?

I don't know for certain... I picked up the engine recently not knowing the year. I cleaned off the SN (2F 037791) and from the MUD Spreadsheet determined it was a 1975 Engine. I'm going with the assumption it's an open chamber with domed pistons. I'm just wondering if I should be thinking about trying to find a closed head. I can probably swap it for one. I haven't started pulling it apart yet and I might not do so until next year, so I won't know for a while. Just thinking ahead.

BTW, I'm in Tempe, just north of you.

 

[rstoddard]

My understanding was that domed piston allowed (in stock form) for a better compression than flat ones (by filling more of the chamber).

The statement from Mark in your first post may be missing the context it was posted on? I'm wondering if this statement was made for the specific case of a rebuilt engine, as domed piston are NLA and if you use flat pistons in an engine/head made for domed piston you obviously get the worst result.

What is "NLA"? From everything I have read, the domed piston was used to make up for the larger chamber, which was made to increase flow for smog purposes, but it lowered compression and created a larger quench area. The Closed chamber and flat pistons had a smaller, more efficient quench and higher compression that can be increased by milling which makes the quench area smaller.

 

[71cruiser71]

I increased the compression of my 2f when it was rebuilt. Now I need higher octane gas for it to run right. 87 doesn't cut it anymore, im assuming the higher compression has led to this, idk if this helps you in anyway... just additional info I guess

 

[Unimogguy]

What is "NLA"? From everything I have read, the domed piston was used to make up for the larger chamber, which was made to increase flow for smog purposes, but it lowered compression and created a larger quench area. The Closed chamber and flat pistons had a smaller, more efficient quench and higher compression that can be increased by milling which makes the quench area smaller.

NLA—->No longer available

It would be interesting to know the compression of the @FJ60Cam motors. I don’t know if this is something someone who’s had one rebuilt would provide? It could give you an idea of what they do.

Use search term: cop motor
By: WNGROG

 

[rstoddard]

I increased the compression of my 2f when it was rebuilt. Now I need higher octane gas for it to run right. 87 doesn't cut it anymore, im assuming the higher compression has led to this, idk if this helps you in anyway... just additional info I guess

I’ve heard that you need to do that.

 

[rstoddard]

Is there a demand for used domed pistons and open chamber heads? Can I sell the parts and keep the block and crank?

 

[FJ40Jim]

The 81-87 closed chamber 61040 head and flattop piston setup is more efficient for various reasons. Unfortunately, the 81-87 head casting was lightweighted and the casting is thin in places, leading to thermal cracking either because of an overheat or just a lifetime of thermal cycling. They are getting hard to find, uncracked.

The open chamber 61030 head gives away a little quench and a little thermal efficiency. But it's an early, heavier casting that has to be BADLY overheated before it cracks.

 

[rstoddard]

sure if this help.
In my project, PO installed (and probably drive it) an older head (1974) on 2f (1976) with domed pistons.
But the engine is rusted and didn't start, I rebuild it,.. but never try to start or test it. I have found 1977 2F in "better" condition

this picture from this setup:

View attachment 3198520View attachment 3198521

Wow… that really looks great. Are those the original pistons and valves? Did you just clean and hone the block? What did you have done to the head?

 

[rstoddard]

The 81-87 closed chamber 61040 head and flattop piston setup is more efficient for various reasons. Unfortunately, the 81-87 head casting was lightweighted and the casting is thin in places, leading to thermal cracking either because of an overheat or just a lifetime of thermal cycling. They are getting hard to find, uncracked.

The open chamber 61030 head gives away a little quench and a little thermal efficiency. But it's an early, heavier casting that has to be BADLY overheated before it cracks.

Yeah, I came to the conclusion that the best thing to do would be to rebuild what I have with the original block, head, pistons and valves if things are still good and within tolerances. I pulled the head and I don’t detect any significant ring ridge, so if the head, block and valves can be cleaned up like @SergP’s that might be a decent engine. Hopefully if won’t require major machining.

Merry Christmas everyone !!!

 

[SergP]

Wow… that really looks great. Are those the original pistons and valves? Did you just clean and hone the block? What did you have done to the head?

I believe so. Someone swap this head for increased compression.
I have cleaned the block and hone it as much as I can.
But #4 cylinder wall still looks bad. The engine needs to rebore.
I clean the head and pistons and install new piston rings. I want to try it... but find a better engine from 77

the head is in better condition, I just cleaned everything.