2F crankshaft in a 3FE?

[bigbrowndog]

#20
Mark W
IH8MUD Lifer

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Join Date: Jan 2005
Posts: 1,446

IIRC the shortened the stroke to drop the displacement to skirt below a 4.0+ liter tax penalty.
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certainly not for here as its based on 4,6,8 cylinders not on hp or displacement.
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200 CCs won';t make enough difference to matter. The longer stroke and rod of the 2f will make more torque for any given downward push on the piston from the burning fuel. The lighter rotating assembly and shorter stroke of the 3F will make for greater rpm cpability and a quicker revving motor.
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I am not trying to be arguementive but I have yet to see a 2F that is better running than a 3F, my 2 cents.

 

[Mark W]

Meaningless. Too small a sample, and too many variables unaccounted for.


I've built a few of both. I can't say that I can call one or the other smoother, stonger, or "better running" when they're put together right and tuned right.


Mark...

 

[bigbrowndog]

Meaningless. Too small a sample, and too many variables unaccounted for.


I've built a few of both. I can't say that I can call one or the other smoother, stonger, or "better running" when they're put together right and tuned right.


Mark...

LOL. The 2F is slightly better from an idle off but thats where it ends.The 3F develops more power and torque. The torque/rev band was raised to make the engine more suitable for on road use. So for full on rock climbing the 2F would be more suitable.

 

[sandcrawler]

Not to hi jack this thread, but you mentioned building up the 3FE - what would that involve? I'm assuming that you can gain some displacement with an over-bore; is there a cam for the 3FE that will improve things? Also, is there anything that can be done with the intake/header?

 

[Mark W]

LOL. The 2F is slightly better from an idle off but thats where it ends.The 3F develops more power and torque. The torque/rev band was raised to make the engine more suitable for on road use. So for full on rock climbing the 2F would be more suitable.

Let's not bother talking about stock engines.

FWIW, The 3FEs powered rigs that we got are not stronger on the road than the 2F powered rigs. But then they are saddled with an auto tranny too, so comparision based on that is tough too.

But they, like the 2F respond well to some tweaking.


Mark...

 

[Mark W]

Not to hi jack this thread, but you mentioned building up the 3FE - what would that involve? I'm assuming that you can gain some displacement with an over-bore; is there a cam for the 3FE that will improve things? Also, is there anything that can be done with the intake/header?

Boring an engine oversize does not really gain enough displacement to make a difference in anything. At least not in the kind of engines we are dealing with.

But they respond to the same things as the 2F (and most other engines). Increase the compression a bit. Install a longer duration/higher lift camshaft. Open up the exhaust. Makes a noticable difference.

I have not done the following, but I've talked to a couple who have, and I plan on getting around to trying this too... Mill out the throttle body and install a larger throttle plate to match (better intake flow). Install higher fuel flow injectors (or modify the existing ones...?)

I've been told that there is a company who can rework the ECU. (by someone who claims to have had it done.) I'm looking into this too.

The reputation that the 3FE has of being a dog is not fair. It is a good strong running motor. It benefits from its differences from the 2F as much as it sacrifices.


Mark...

 

[Moby]

I have not done the following, but I've talked to a couple who have, and I plan on getting around to trying this too... Mill out the throttle body and install a larger throttle plate to match (better intake flow). Install higher fuel flow injectors (or modify the existing ones...?)

I've been told that there is a company who can rework the ECU. (by someone who claims to have had it done.) I'm looking into this too.

Mark...

My 3FE has been rebuilt once (just a stock rebuild that now has a 20% leakdown in cylinder #5 and that just spit out the crank pulley nut, hence my engine work plans). But I digress... The ported TB does make a difference, at least on my engine (I had mine done by Downey). I've got the TLC4x4 intake tube, ported TB (I trimmed the TB gasket and port matched the TB to intake plenum). I've also got rebuilt & balance injectors, an MSD stacker ignition and coil and custom exhaust from the stock manifolds back.

All of these things together do wake up the 3FE nicely. Each time I added one of the above components I could feel the gain. Not enough to get me out of 3rd over the mountain passes that I drive regularly but gains none the less. I also run 4.56 gears and 31" tires for stock gearing. This was by far the best "performance" mod

I'd be very interested in feedback on the ECU reworking if you ever hear the outcome. I'm pretty convinced that even with my level of mods some fuel/spark mapping tweaks would be beneficial. ECUs may compensate to a degree for non stock systems but, at least from the studies I've seen, they can usually run better with some tweaking. However I'm not sure that doing it without the benefit of a dyno would be worthwhile.

 

[Mark W]

All of these things together do wake up the 3FE nicely. Each time I added one of the above components I could feel the gain. Not enough to get me out of 3rd over the mountain passes that I drive regularly but gains none the less. I also run 4.56 gears and 31" tires for stock gearing. This was by far the best "performance" mod

I am a firm believer in "packaged" modifications. You really have to modifiy everything together to get the best gains out of each of them.

And IMHO, gearing appropriately is very very important, even more so with this engine/tranny combo thsan with the 2Fs and manuals.


Mark...

 

[cruisermatt]

No problem

Not a problem.

2F stroke= 101.6mm
3F = 95mm
stroke difference= 6.6mm
compression height difference= 3.3mm

A set of custom pistons w/ pins moved up 3.3, or
A set of custom rods that are 3.3mm shorter
is all that is required.

Call any one of several custom engine parts suppliers and have them hog a set of slightly shorter rods or pistons out of billet. They will happily do the work and take your money.

That being said, a fuel injected chevy might be a cheaper swap.

Bringing a neat idea back from the dead.

Just to clarify about needing a piston with shorter compression height, is that 3.3mm shorter then a 2F piston or 3FE piston?

2F compression height is 1.87", correct? If so, a 3FE piston has compression height of 1.74", and the piston needed for putting a 2F crank and rods into a 3F block would need to have a compression distance of 1.61", right? Obviously 1.56-1.6" would be more realistic taking decking into consideration.

 

[crashmonk]

 

[LAMBCRUSHER]

do it Matt! I couldn't afford the pistons...

 

[cruisermatt]

View attachment 1628810

So helpful...

 

[cruisermatt]

do it Matt! I couldn't afford the pistons...

Don’t really need expensive pistons for this if my numbers are right.

 

[RockDoc]

You are looking at 3.3mm difference from 3FE piston/rod to fit the 2F crank. If you are thinking about this, I'd strongly recommend going with a 2F bottom end. The strength of the 3FE is the top end, strength of the 2F is bottom end geometry. Build a stronger cruiser engine, not a weaker 3FE.

(disclaimer: I was deep into this stuff 8-10 years ago, not so fresh in my mind now)

 

[RockDoc]

View attachment 1628810

Keep your sprinkles, and I'll stick with the s***-eating grin that appears with a 2FE barking at 5000 rpm.

 

[FJ40Jim]

Bringing a neat idea back from the dead.

Just to clarify about needing a piston with shorter compression height, is that 3.3mm shorter then a 2F piston or 3FE piston?

2F compression height is 1.87", correct? If so, a 3FE piston has compression height of 1.74", and the piston needed for putting a 2F crank and rods into a 3F block would need to have a compression distance of 1.61", right? Obviously 1.56-1.6" would be more realistic taking decking into consideration.

The numbers reflect changes to 3F parts to accommodate the 2F crank.

Compression heights of pistons are somewhere in a previous post.


BTW, this is not a neat idea. It's a bad idea because the 3F already has inferior rod geometry. A longer stroke in the cutdown block just makes it more badder. It's a lot of expense and hassle just to end up with a 3F with a weaker bottom end.

 

[cruisermatt]

The numbers reflect changes to 3F parts to accommodate the 2F crank.

Compression heights of pistons are somewhere in a previous post.


BTW, this is not a neat idea. It's a bad idea because the 3F already has inferior rod geometry. A longer stroke in the cutdown block just makes it more badder. It's a lot of expense and hassle just to end up with a 3F with a weaker bottom end.

Ok, carnage averted then.
I do have a complete 2F shortblock on hand anyways. I was just wondering purely from a possibility standpoint.

So, next question while I’ve got your attention, what’s the biggest bore 2F you’ve seen? Assume custom pistons/machine time are no problem. 3.800 safe? 3.900?

 

[RockDoc]

Just to add a bit more with respect to the wisdom of stroking a 3F block vs. swapping in a full 2F bottom end.

Help me plan for a 2FE (post 199 if it doesn't go straight there)

A couple of pictures in this post show how far the pistons drop with respect to the bottom of the cylinder bore in the stock 3FE and 2F. The 3FE piston is already shorter than the 2F piston, and drops further out of the bore. Adding stroke within the 3FE block will mean dropping the 6 or 7mm further.

From what I understand (from Mark Whatley's posts IIRC) over-revving a stock 3FE leads to piston skirt failure as the most likely first step in engine failure (poorly supported piston, high rod angle). With a 2F, the rod bolts stretching / failing is the likely starting point of failure from over-revving, and at a higher rpm than 3FE failure. I've had my 2FE to at least 5000 rpm without issue, I think I've seen 5500 to 6000 stated as where rod bolts are in danger. Some have fit ARP rod bolts for insurance.

 

[LAMBCRUSHER]

I’ve had my 3fe well north of 4 grand... amazingly deceptively smooth...

 

[LAMBCRUSHER]

The numbers reflect changes to 3F parts to accommodate the 2F crank.

Compression heights of pistons are somewhere in a previous post.


BTW, this is not a neat idea. It's a bad idea because the 3F already has inferior rod geometry. A longer stroke in the cutdown block just makes it more badder. It's a lot of expense and hassle just to end up with a 3F with a weaker bottom end.

Where is your sense of adventure?!!!