High compression 2.9L?
 

I dont know how many of you guys have looked into this, but I found something interesting while doing some unrelated research. It looks like you could use pistons for a 2.8L V6 in a 2.9L V6 and pick up a lot of compression. See specs here:

http://webpages.charter.net/beckracing/slvpg43.htm

Essentially what you could do here, is replace the stock 2.9L piston, with it's 13cc dish, with a flat top from a 2.8L. I'm not sure what compression ratio this would give you, but I'd think it would be at least 10:1. Is this old news, or has this been done before?

Thoughts?

The 2.8 itself was a lower compression engine than the 2.9. I think all you would gain would be the stroke of the 2.9, and I doubt that would be anything signifigant. Blocks were basically the same.

Did you actually look at the piston specs?

You're missing the point. The 2.9L has a dished piston, whereas the 2.8L has flat top pistons. Replacing the stock 2.9L pistons with 2.8L pistons should give a sizable increase in compression.

Hard telling. Some sources list the 2.8L and 2.9L as the same bore size, the manufacturer of the two pistons I listed does not. See here:

2.8L piston: http://www.kb-silvolite.com/spistons...etails&S_id=88

2.9L piston: http://www.kb-silvolite.com/spistons...tails&S_id=580

Now THEY list the bore as the same size.

Also realize that you may not want to just swap pistons. The bores could have taper or a ridge that could break rings. I would suggest going to the nearest oversize of 2.8L pistons and bore the 2.9L block to fit, along with a complete balance of the bottom end.

In short, yes. There will be a ridge left on both ends of the ring travel, not just on the top. Plus you'll want to bore it anyway to get the proper piston to cylinder wall clearance with the new pistons.

Do you really think it would give a creditable increase in compression?

Yes I do, and it absolutely would increase compression. You're going from a piston with a sizable dish to a flat top. The compression height is actually a bit higher on the 2.8L piston, though IMO not enough to cause problems. That too will give you more compression.

I'll put it this way. The combustion chamber volume of my 4.0L heads was 60cc. The 2.9L heads I have out in the garage have visibly smaller combustion chambers. When you go from a 13cc dish, to a flat top with no dish, how much do you think this would increase compression?

Have you looked at the chamber on the 2.8 heads??? Its the same size if not smaller than the 2.9 chamber. The 2.8 was a 8:1 compression engine and the 2.9 was a 9:1 engine. For the 2.8 to have 8:1, it would have had to have a dramatically smaller compression height than the 2.9. The 2.8 has 96-7% the displacement of the 2.9 not 88% which would explain the rise in compression according to stroke. If all things were equal except for stroke, the 2.8 would have 96-7% of the compression ratio of the 2.9, or 8.7:1. Now the kicker is the dish in the 2.9 piston. That means that the compression height of the 2.8 piston is going to be even lower or the chamber cc's is going to be higher (or headgasket thickness, which I doubt is the case). Somebody has their numbers wrong. If you put a 2.8 piston in a 2.9, I doubt you would gain compression, in fact, you might lose it.

Well send an email to KB-Silvolite then.

For the record, I've seen two different heads with chambers that looked identical, and one had a much higher combustion chamber volume than the other. The only way to really tell is to CC the heads.

True, but Im talking about a significant difference, At least as much as the dish in the 2.9 piston. For example, You can most definately tell the difference between an early 302 (58cc) and a late 302 (69cc) head chamber size by looking. All I am saying is that you cant just assume a piston is going to have a higher CR just because it is a flat-top design.

True, but I can assume that if the compression height of the flat top is slightly higher than the dished piston! Like I've shown, it's listed in two different places. Like I said, an email to KB / Silvolite is about the only way to resolve this IMO.

Lol, if you wanna email those guys, be my guest. I dont care enough about the subject to put that much effort into it. Im just going by the factory CR's and displacements.

I turn tho this, http://www.fordracingparts.com/download/charts/217.pdf everytime I want to pull an engine measurement, I encourage everyone to bookmark it. It sure makes it handy when trying to scheme up a low budget JY part swap engine build lol.
The only incorrect info I have been able to find is either the 2.9L or 4.0L deck height, they are listed as the same when in fact they arent, the 2.9L deck height isnt correct.

To figure out if there will be a significant increase in compression use this calculator, or we have one in our calculator section (FTE) but I dont know how to get to them lol so here http://kb-silvolite.com/calc.php?action=comp I dont know the head CC volume otherwise I could figure it out.

Notice the FRPP catalog I posted also notes the 0.17" difference in compression height between the two pistons, with the 2.9 being shorter.

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! :-X22

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.

I've also tossed around using small block Ford 5.090" con rods with 2.3L HSC pistons - if I can fit the rods onto the crank, as I believe the wrist pins on the 2.3L HSC pistons are the same diameter as on those rods. Someone had mentioned something about using 3.3L Mopar pistons with 4.0 rods (doubt it would work) on a 4.0 crank to stroke the 2.9, but I have a feeling it'd be better (if you can fit them to the crank) to use the SBF rods or have some custom made. There are a few threads on FTE floating around discussing the 2.8 and 2.9 and what can be done to bore & stroke them, etc. I have been looking into this and there are only a couple of options as some places will NOT export their parts, but a couple will. I wouldn't mind fitting a 3.5 kit into both the 2.8 and 2.9, personally. IF I felt like spending that kind of cash! Even the 3.0/3.1 kit for the 2.8 into both would be a nice little bump in displacement that might be worthwhile. I'll probably keep brainstorming on this and see if I can come up with a off-the-shelf or junkyard parts buildup. I just wished I had all the pieces and parts to play with here so I could tinker around with it in my free time.

So, 'splain to me why there are as many (if not more) aftermarket systems that use MAP instead of MAF? Most of the ones I have looked at use MAP sensors vice using the MAF as the 4.0 does. I'm not dogging the 4.0 swap, but you might as well figure on buying the aftermarket heads for it when rebuilding. Either way you go about it, you're going to spend money - so the choice is up to the person making the decision, IMO. I haven't ruled out doing a 4.0 swap myself :p

I've actually been looking at finding an early (90-94) 4.0 for some experimentation. I believe the early 4.0s had the distributor hole with a plug in it at the top rear of the block as the 2.9 does. I'm sure if there was room for it, might be able to install the 2.9 distributor and sensors (if needed) and not have to mess with any wiring much at all - unless, of course, you wanted to do a MAF conversion in the process. Yes, I'm 'different' and like to look at things from more than one angle ;)

the 91 sploder I had with the 4.0L, had the hole at the back of the block. It has the bottom part of a dizzy there (not literally, but its what it looks like) to drive the oil pump off the cam gear. The 2.9L dizzy afaik doesnt fit, I looked into it myself...and what I heard from others had something to do with shaft size and cam gear...not to say you couldnt find one of something else. Also from what I saw on my 4.0L it didnt look like there was much room for a dizzy there with the upper intake installed, making you have to run a boxed upper, which is no good unless you run forced induction...and if you run forced induction you definately want a MAF system for better tunablilty.

With the 4.0L crank in a 2.9L youre inceasing stroke nearly half inch (0.485") The rods are 5.14 and the pistons have a 1.461 pin height. So you have to lose 0.242125" (half the stroke, half goes up, half goes down) roughly between the piston and the rods. We will round that number to 0.24". With the 5.0L rods you loose 0.05" so you would have to loose another 0.19" to have the piston up the bore the same amount as from factory. This would leave you about a 1.27" piston pin height. Thats not too bad, except you have to worry about the skirts hitting the crank because you shortened the rods and increased the stroke.
Youre going to want to compare a finished rotating assy to a 347 stroker, because the stroke and deck height are near the same
347 stroke is 3.4", rods ARE 5.4", pistons IIRC ARE 1.1" (edited) and block deck height is 8.206"
4.0L stroke is 3.32", 2.9L rods are 5.14" and the 2.9L deck height is 8.084"


good luck, im not trying to tell you not too, Im just sharing my past experience. I concluded that if I were to run a v6, it would be a 4.0L and Id spend my money on a supercharger and tuning and be happy.

I guess if I were to attempt a 2.9 distributor / ECU setup on a 4.0, I would probably have to use the gear on the oil pump drive shaft assembly that is in the block, then check fitment and 'machine fabricate' as necessary. Honestly, looking at a 2.9 without a distributor in it with the upper and lower plenums installed doesn't 'look like a distributor will fit in there', so the only way to find out is try it. The only thing I could see is if I would have to figure out how to shorten the height of the installed distributor. At least that is a little further down the road on that brainstorm as far as info than I was before - I hadn't had a chance to tear into things first hand.

Going back to topic, here are the numbers I crunched for deck clearance with the noted pieces and parts (using either stock 2.8/2.9 con rods or Small Block Ford rods) installed as part of the rotating assembly (NOTE: I have heard that the Mopar 3.3 V6 pistons will fit and clear the crank, and comparing them to other options, it looks to me as if they will clear the counterweights, etc.):

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

3.3L Mopar V6 pistons, 4.0L crank, SBF rods:
= 8.084 - (.5*3.32) - 5.090 - 1.260
= 8.084 - 1.66 - 5.090 - 1.260
= 0.074


3.3L Mopar V6 pistons, 4.0L crank, 2.9 rods:
= 8.084 - 1.66 - 5.140 - 1.260
= 0.024

And with these numbers, as both options have clearance for deck, also noteworthy is the fact that the 3.3 pistons will fit the 2.8/2.9 blocks as far as piston diameter (STD bore is 93mm and the oversize numbers are the same as the 2.8/2.9 pistons) - the only factor here is having to ream out the wrist pin holes in the pistons to fit either SBF rods (0.0111" of reaming required) or stock 2.8/2.9 rods (0.0441" of reaming required) and whether or not the SBF rods will fit the 4.0 crank (bore diameter and rod thickness/width), even with a little machining magic on the rods and/or crank. I wished I had the dimensions for the stock 3.3L Mopar V6 con rods to compare, though.

Yeah, it'd be a lot involved and not necessarily cheap, but doable. A 4.0 with a supercharger (I thought only the OHC versions had a kit for that?) or turbo would be fairly impressive - a guy I know on another forum is installing a custom turbo setup on a 4.0 OHV engine, so I am waiting to see how that goes. There are stroker kits for the 4.0 as well. I'm personally not looking at anything radical, and have kept my options open - even doing a MAF conversion to a 2.9 or TBI conversion to a 2.8 (or even installing an Offy 4-bbl intake and converting the ignition to a Duraspark, etc.) as part of either build, whether or not I bore and stroke 'em. At least I have something that I can try vice ordering a much more expensive kit or short block, and both the 2.8 and 2.9 bored .020-.040 over will still yield about 3.4L displacement, but not sure what the compression ratio end results would be without more info.

2.8 pistons in the 2.9 engine
 

Getting back to the question of using 2.8 pistons in the 2.9 engine, the Keith Black website gives the following information:

2.9 piston part no. 1199, deck height 1.527", dished
2.8 piston part no. 1164, deck height 1.511", flat top
2.8 piston part no. 1174, deck height 1.535", flat top

All pistons listed as fitting 3.661" bore size. All have same 0.945" piston pin size.

One doesn't need to do involved arithmetic to see that using the 1164 piston would increase deck clearance by 0.016", whereas the 1174 piston would decrease it by 0.008".

Thus the 1174 piston will give a higher compression ratio due to the lack of the large dish and the slight decrease of deck clearance.

Other concerns include weight differences and skirt shape, i.e. will the skirt of the 2.8 piston clear the crankshaft counterweights. Presumably they will since others have done this conversion and did not mention interference. If weights are different, rebalancing will correct.

:-drink

I'll have to take a look at those two pistons. I think one is for the older 2.8 V6 (71-74) - there are differences, and I think I know which two pistons you are referring to from past 'research'. I don't recall if the 170 cid inline engine had the same bore size and pin size. I'd rather be safe and use the piston with the shorter compression height. At least then, you'd probably have a lesser likelihood of valves impacting the tops of pistons.

Piston heights and such.
 

Well the KB site lists the 1164 as 1974-75 application, and it is the lowest compression height of the three. I didn't notice an earlier 1971-74 listing in the KB lists.

Using the desireable(?) 1174 piston will move the piston top up only 0.008", which is unlikely to cause any valve interference problems.

A good plan would be to check the piston to deck clearance of the engine when the heads and old head gaskets are removed. You can research "quench distance" to see if it is desireable to increase or decrease it.
If the block deck surface is to be milled, then it might be a good option to use the lower compression height 1164 pistons.

:-drink

I forgot to add that the inline 170 engine has a 3.50" bore so its pistons are not candidates for the small V6 engines.

Yeah, I knew there was a difference in the inline piston bore sizes, just didn't recall specifics. '71-'74? I thought the 2.6 was the 'biggest' Cologne engine during those years and the 2.8 hit the streets in '74. I could be wrong. I'll consider all the options once my project comes into being. Even a mildly stroked 2.8 with a decent cam and fuel injection (or 4-bbl intake and carb) would be better than stock for the '84 BII I may be getting. Sort of off-tangent to add to this is I am brainstorming how to reverse-engineer the TK-to-SBF bellhousing adapter so I can bolt up a T18/19 or NP435 and NP231 t-case behind it. I just wished I had the numbers in front of me for the difference in bellhousing depths and input shaft lenghts :(

Here's one extra little bit of information I gleaned while reading the 1991 Escort manual. It regards the 1.9L four cylinder engine, but perhaps is a general rule of thumb:

They give a "squish height" or quench distance specification of .039-.070".