3500 heads on 3.500" bore (2.8/3.1)

[sharkey]

this is something ive been considering for a while now to replace the ironheads. with my pistons i calculate it out to be 11.2:1 compression with 3.1 gen 2 head gaskets. this is about what im looking for, however there is the one isue im unsure of.

would a 3500 head work with the small 3.500 bore of a 2.8/3.1??? i know the 3500 is 3.700 bore, leading me to beleive that this combo will not work.

any thoughts???

[bszopi]

No, it won't work. Somewhere on here, it is discussed as to how the combustion chambers actually go past the bore.

[sharkey]

thats what i was figuring.

hmmm, well that sucks. i guess without building a new motor i am stuck with these cursed ironheads.

[ForcedFirebird]

Ben showed pics...
http://60degreev6.com/showthread.php?t=35296
And I measured the widest point of the 3400 and 3500 heads...

http://i158.photobucket.com/albums/t...s/100_3027.jpg

http://i158.photobucket.com/albums/t...s/100_3028.jpg

The 3400 heads can be easily modified in the combustion chamber to work with a high compression engine. If you unshroud the valves and get rid of some of the sharp edges, you should be ok on pump gas. I calculated removing 1cc of material in each chamber should get you down to 11:1.

Here's what bjornmk1 did to his 3400 heads (note how similar they look to 3500 chambers)...

http://60degreev6.com/showthread.php?t=36794&page=2

[sharkey]

that may be an option. i realy dont want to build another short block, if i can swap some heads onto it i would be very happy, although it still means building new headers, changing all the accessories, timing cover, oil pan, ect.

im still tossing around the idea of just turboing what ive got, its only 9:1 compression, ive got stainless valves and forged pistons, its the perfect recipe for lots of boost. now if the turbo headers i payed curtis (turboz24) for now over 4 months ago would ever show up, id be happy.

[ForcedFirebird]

The accys aren't that bad to deal with. I was able to rotate some brackets and enlongate some holes to make the stock ones work (maybe a little different for your FWD), but the accys were in my way for my turbo plans. Even if they didn't work, it's easy for you to get some from the JY from a 3x00 engine sice you have FWD.

The headers will still work if the primaries are 1 5/8's or bigger, the bolt holes on them just need to be enlongated as well (ports line up). timing cover also should not be an issue for you, I have to take off the top bolt hole tab with a grinder because when I turned the LIM 180* (so the tstat neck is in the front) the neck interfered. The cover doesn't even need to be removed for this mod, but I don't think you will have that problem since your tstat neck is going to end up over the bellhousing, correct?

Throttle cable is another snag for me, but again it's because I have a RWD and my TB pulls from the back.

[CNCguy]

Throttle cable is another snag for me, but again it's because I have a RWD and my TB pulls from the back.

Thats not too hard to work around. On a stock TB you can remove the throttle plate and rotate the shaft 180 degrees so it pulls to the rear. You have to drill & tap a new hole for the idle stop screw and remove the little tang on the TPS so it can be rotated 180 also. The billet TBs are already setup to operate this way.

[ForcedFirebird]

Thats not too hard to work around. On a stock TB you can remove the throttle plate and rotate the shaft 180 degrees so it pulls to the rear. You have to drill & tap a new hole for the idle stop screw and remove the little tang on the TPS so it can be rotated 180 also. The billet TBs are already setup to operate this way.

It's not only because of the direction of pull, but length as well.

I already modified a n* TB from Ryan, all I have to do is thread the hole and the cog from my stock TB will bolt on. I sent it to another member here for him to make a UIM for my MPFI top end, but I haven't seen him on any sites, and haven't heard from him in a couple of weeks. I might have to do something different.

Also I'm going to be using a MegaSquirt1 because of cost, and it doesn't support the IAC's anyways.

[sharkey]

for me anything around the timing cover is an issue. the j-body ironhead motor was an oddball. if you look in my sig you will notice the alternator and power steering pump are in oposite spots compared to a gen 2 motor. the alternator would be in the way of the manifold.

[Superdave]

for me anything around the timing cover is an issue. the j-body ironhead motor was an oddball. if you look in my sig you will notice the alternator and power steering pump are in oposite spots compared to a gen 2 motor. the alternator would be in the way of the manifold.

I think you'd end up using the gen3 timing cover anyways.. easy enough swap and you'll probably get better cooling with the newer water pump style.


the hybrid swap guide on Domesticcrew should give you an idea..

http://www.domesticcrew.com/hybrid.html

your headers will work fine, just elongate the holes a little.. i used iron head flanges for the first set of headers i built, they fit the 3400 heads fine after a little filing.