rsbcruiser
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I am considering using a 74 f engine head on a 2f engine. My understanding, doing so wil increase the compresion of the motor. If so then how much? What would the final compresion be?
74 f engine head on a 2f
- Thread starter rsbcruiser
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rsbcruiser
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- #3
Perchance sir, Mr. Pighead, have you ever run a compresion test? By your comment I assume you are running the setup I mentioned. If so I have many questions. My motivaton is better gas mileage. Has the higher compresion helped your gas mileage?
Interested too. My 74' head is off and at the machine shop. Would you know what compression ratio starts to hint at premium gas? Seeing as it's 7.8 to 1 now, it seems a little bump would be okay without switching to 91?
I run an early 2F block with a late F (F.5) head. I recall the block had to be milled some, don't know how much, and probably the head had been milled in the past...
I have done a compression test, got readings in the low 140s IIRC.
Better gas mileage? Hard to say, what with 35" tires and no speedo correction. I'd like to think I'm around 13MPG highway...
I have done a compression test, got readings in the low 140s IIRC.
Better gas mileage? Hard to say, what with 35" tires and no speedo correction. I'd like to think I'm around 13MPG highway...
I am in the process of doing exactly that, putting an f.5 head on an F block. I know I need to take the split rocker arm and oil tube pick up from the F, but are you sure about milling the block? I wasn't aware of having to do that.
Was that because your f.5 was milled larger so you had to do the same to your F block?
A little bump above 7.8 for an iron head engine will be fine. 8.5-9 would be close to the dividing line before it's time for higher octane.
Cool, I was thinking about .030 off would be okay. What do you think?
Sorry for the highjack...
rsbcruiser
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- #10
Ya, know problem Ziffdaddy, I heard 0.03" would be okay from the head. Tend to agree with doubters though, save the extra material. just making sure we are all on the same page here. See, what we were talking about is putting a 74 f head on a 2f. The 74 head has a slightly smaller chamber than a 2f head. The early 2fs and the 74 f engine had pop up pistons. Putting a 74 f engine head on an f motor with flat pistons will drop your compresion I think. In that case you might have to shave the heads. I am surprised to hear that the 74 had 7.8 to 1 compresion. I thought it was 9.3 to 1.
rsbcruiser
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140psi? If so your compression isn't causing the detonation me thinks. An earlier f engine design should give 150psi. or so.
Texican
s-Moderator
I've done this, the 74 F had smaller domes on the pistons than the 75-80 2F this is what raises the compression.....as far as the boost Mark Whatley said you gain a full point without milling. I did not have to use premium fuel.
If you tried to install it on an F motor you would loose compression, same deal on the late 2F as both these have flat top pistons
On an F you would have hell trying to oil the rockers......reckon you would have to use the old rocker/rail and plumb an oil line to it.
I have one of these heads off and ready to go, also a 77 era head, if I did a liquid volume comparison does anyone know how to figure the compression gain?
Butch
If you tried to install it on an F motor you would loose compression, same deal on the late 2F as both these have flat top pistons
On an F you would have hell trying to oil the rockers......reckon you would have to use the old rocker/rail and plumb an oil line to it.
I have one of these heads off and ready to go, also a 77 era head, if I did a liquid volume comparison does anyone know how to figure the compression gain?
Butch
I had this setup for a year before the head cracked, '74 F head on a 2F block with domed pistons. Engine had been rebuilt and the compression across all cylinders was 190-195. Timing was set at 11 degrees and I ran 93 octane to keep pinging under control. Mileage was around 15 mpg with 4.11's and 35's.
Except for the need for 93 octane that sounds like a really nice combo. There's a lot of torque to be had by upping the compression just by one or two points.
yeah, I just talked to my machine guy and he said the head had been milled a little before (don't know how much) and he had to take .022 off just to get it flat again and ended up with about .050 off total. (plus whatever was done previously) He also said that with a starting point of 7.8 to 1, that taking .050 off wasn't gonna get me to 9 to 1 anyway but will give it a nice little bump. He's a pro with Landcruiser heads...which is nice.
From what my machine guy said, 'the head is a long skinny block of iron that can easily warp over the years'......so in checking for straightness on the head, he had to remove .022 from it just to get it flat again. As for the block, it's, apparently a bit more resistant to warping, and a bit tougher to drop off at the machine shop for a little milling, especially if it's still in the truck. So, if nothing is out of true then you wouldn't need to have it milled, but it's tough to tell on your own so it would be good to have it checked before putting it back together and have it leaking everywhere.
Hope that helps a little...
rsbcruiser
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- #20
Very interesting Godwin, wondering though, do you think the cracked head was caused by the higher compression? I suppose there is no way to really tell, but was the head cracked through the combustion chamber? I'm thinking that if it was then the higher compression can't be ruled out as a cause.
