Yes, Mister Whately walked me through the same procedure at about the same time. we called the late F head the "Bathtub" chambered head IIRC. Accepts domed 2F pistons just fine. I'm still running that engine, now with Chevy valves and a little porting and polishing.
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- #22
As I understand, a domed piston with an open ( .5 head from 1974) configuration has higher compression than a flat piston with a closed configuration. Probably a domed piston will not work with a close configuration.
Do you already have the closed head? If so, you can measure the diameter.
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- #23
Compression:
domed piston+open head </= flat piston+close head < domed piston+ open F head / "Bathtub"/ from 1974
domed piston+open head </= flat piston+close head < domed piston+ open F head / "Bathtub"/ from 1974
Anyone have a ballpark how much this would increase HP?
You should charge money for straight lines like that. Off the top of my head:
1) Um, none?
B) I got stickers that add more HP.
III) It just makes a tractor engine into a slightly better tractor engine maybe,
The Head bolts for the F1.5 are unique to that engine (longer). Are you all using the 2F head bolts?
What I recall from reading a Mark A. post on the subject is that the Late F block was drilled and tapped for longer head bolts. I don't know if the 2F block will take the longer head bolts. I think that I am using regular 2F head bolts, I have a few to choose from
I did. At the time it was what I had. I also don't recall any discussion during the LCML days of needing to use F1.5 head bolts.
School me- what would be the goal of increasing compression?
HP increase. When I had the 1.5F head on the 2F the compression was bumped up to 195, stock is 160. The power increase was noticeable, but how much can't say since it was never measured. Seat of the pants increase - on the interstate one day I decided to let the 2F run. I had the FJ40 up to ca. 95 mph when I backed off and it was still pulling.
Damn that’s wild- something for me to think about…
Thank you. I currently have a pretty good running 78 FJ40 with a 2F motor. I am looking into the future at a rebuild and want to do it right. This site is a fantastic collection of information. I'm not sure if I can stay with the domed pistons in the future with the paucity of replacement.
If it won't go fast, chrome it!!
Do you know the casting number for the 74 1.5 head you used? That seems like at least as good of a solution as shaving my 61031 78 head. Thank you for the information.
Mike Haberthur
Now that may be what I am looking for. I need my FJ40 to maintain 65-70 up hills and be able to pull a 5spd overdrive transmission. Easy to do with a V8 swap, but the stock six might be good enough.
Thank you
Mike Haberthur
Thank you. Not interested custom pistons!
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- #37
I took her on the freeway for the first time today, going 75 mph. She sounds like she could go a little faster, but the 55 mph speed limit is stopping me from pushing her further. She also has 7.00x15 tires, which make for a bit of a bumpy ride.
that's awesome!
That is great. At what rpm is she doing 75ish?
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- #40
Good question. I was so excited that I forgot to look at the gauge.
