Perhaps the longer stroke of the 2.9 was the cause of the dished piston head...this would give enough clearance between the piston and an open valve at TDC. Are you sure a Flat top piston would not hit an open valve. I'm pretty sure a dished piston is designed to maintain a certain stroke with enough clearance for valves when they are open, such as on the exhaust stroke.

 

This is a legitimate concern which would have to be adressed by the engine builder.

Lets take a look at some things here:

The link shows the stroke and deck height to be different between the 2.8L and 2.9L. Lets figure up deck clearance:

Deck clearance = deck height - (.5 * stroke) - rod length - compression height

2.8L deck clearance = 8.084-1.35-5.14-1.539 = .055"
2.9L deck clearance = 8.084-1.4175-5.14-1.461 = .0655"

Now then, a 2.9L with 2.8L pistons:
Deck clearance = 8.084-1.4175-5.14-1.539 = -.0125

So you'd be .012" above deck with 2.8L pistons. Which would probably be alright with a thick head gasket. Or, you could have the pistons shaved about 13 thousandths and have zero deck.

Then you could check valve clearance as has been done for years. Preassemble the motor and check! If you need valve reliefs, a machine shop can do it cheap. People do it all the time. I really doubt they'd be needed though. For one, the 2.9L cam probably doesn't lift all that much, and is nowhere near full lift when the piston is at TDC. Next, and the big factor, these are not wedge heads. The valves in these motors are at a 90 degree angle to the deck. Any valve relief would have to be a perfectly circular plunge cut. Really though, I dont think the valves at full lift would even contact the pistons at TDC. I dont think there's any interference there to begin with!

Also note that they have the 2.9L deck height wrong. It should be 8.084", not the 8.858" like the 4.0L block uses.

 

110% i agree, and I thought I mentioned the 2.9L block height being off.

 

Indeed you did!

However, I thought it would be good to mention it again just in case someone missed it the first time.

 

good idea, thats the only thing wrong Ive found on that page so far.

 

The 2.9 deck height is the same as the 2.8, its nearly the same block.

 

heres another idea to check valve clearance at top of piston some have used alittle clay on top of piston rotate the assy on on cylinder and see what marks if any are left into top of piston by the valves kinda the same principal as checking bearing clearance.

 

I don't have the numbers on the top of my head but 2.8l pistons will work.

i recently built a flat top pistoned 2.9l. the numbers work out for the clearance and the compression is somewhere just north of 9:1.

Quick question.

why won't a 2.8L camshaft work in a 2.9L?

 

Because the 2.8 has timing gears, and the 2.9 is chain driven.

 

I know this is fairly old. And I dont know if anybody will answer but here goes. It was said that this idea works which is great. Ill be rebuilding a 2.9 in very near future and would like a lil more power out of it. Am I right to assume in doing this it would be my answer to getting the most I can get outa my 2.9? Ive never really built a hi po motor before so I really dont know of how things are done. If I could get a lil bit of a guide line into what parts I would need to build this Ill do it. Thanks

 

If you have the money, Morana Racing (Canada) sells a 3.5L stroker kit for the 2.9. Otherwise, from my best guess, the only way to make this work is to use the 2.8 pistons and 2.9 rods. I have been doing some research on stroking both the 2.8 and 2.9. My main focus now is figuring out the rod lengths and deck heights (kind of stumbled upon this thread poking around) to see what may or may not work without a whole lot of machining involved, other than what is absolutely necessary. There are other threads in this part of the forum and one in the Bronco II forum related to this. The chart in a previous post doesn't take into consideration the BII / Ranger 2.8, which IS an identical bore size from everything I have found.

 

Geez.. Talk about a fair chunk of change... 2500 U.S. dollars. Convert that over to Canadian dollars thats like 3051.50 And then add taxes onto that and shipping and what not. By the time your done. Your spending close to if not more than $5000. 0 Bucks on the motor alone.. And what for? So a guy with a slightly done up 5.0 can pound the crap outa ya? seems hardly worth it.
Thanks for the insight there Kernal. And as for answering my other post about the suspension as well thank you.
Could I be so bold as to ask you a few more QWuestions about our trucks? If I may.. Could you e-mail me and we'll take it off board.
Thanks.

Wolf_Pack-316@hotmail.com

 

Yeah, buying the parts, kits, etc. to do it with a 'pre-built' kit or short block is crazy expensive - which is why I have been looking into 'compatibility' using 'stock' Ford parts. Even with a slight bore and stroke, it's still not going to be cheap - but I personally am not after a street sleeper, just looking for a little bump in power for on the trails. I know, I know... why don't I just swap in a 4.0, right? I don't feel like snatching the motor and other pieces and parts only to rebuild an engine anyway before putting it in as I have noted issues from Explorer owners that have had their OEM heads crack, and really do not feel like doing all of the extra wiring work, etc. Not that I am not open to the 4.0 swap at this point, but I dare to be different sometimes

 

Actually I was talking to a guy that I know. And he says that a 4.0 l swap is a big waste of time. Its a huge headache that really isnt worth it. Just keep the stock motor and maybe boost its power up a bit like what you want to do. I think your onto a good idea.

 

the only thing that ever stops me from building a 2.9L is the fact that I would spend the money stroking it to come in under 4.0L. When I can buy a complete junked explorer for $500 and rebuild the engine and have everything I need to swap plus a more powerful engine and a better fuel management system.