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.
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.
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 ******* 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
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.):
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.
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.
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.
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.
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
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.
Hi the 2.8 height pin is 1.546 inch the 2.9 is 1.461 inch this is why you will have a raise in compression when swapping the 2.8 piston into the 2.9 block and also the piston are flat which bring the combustion chamber a lot smaller at the very least by 13 cc these two factor alone bring your cr by at least 10 to one when I read some of your post I which you could do a little more research thank