3900 heads on the 3500~!

[CNCguy]

throw that 3900 head gasket on a 3500 and take a picture and see what it looks like. maybe all you need is a .020 or .040 overbore to address the piston to valve and piston to wall issues.

I don't have a 3500 here but I will see if I can round up a 3500 gasket to set on the 3900 head. That way everyone can see where the valves are relative to the cylinder wall.

For those wanting to see a better comparison of the 3900 to 3400 ports, I made a paper template of the 3900 port and layed it over a 3400 port for visual comparison. It's not the best template but good enough to see the differences in port sizes. I put some red layout dye on the 3400 LIM to help give it contrast.

[MidnightriderZ24]

thats a huge port!!

[sil]

throw that 3900 head gasket on a 3500 and take a picture and see what it looks like. maybe all you need is a .020 or .040 overbore to address the piston to valve and piston to wall issues.

can you do a bore like that though ?
bore more of one side than the other ? lol


mmm i wonder how much you can take off a 3900

[Superdave]

hey CNC guy, if you want a 3500 head gasket just let me know.. i've got 2 used ones sitting on the floor in the garage...

[Joseph Upson]

I don't have to do it to know it's likely to have problems. Having larger valves as well as larger bore diameter could not only cause interference with piston to valve clearance but also valve to cylinder wall. If you remember that the 3400/3500 valves already take up so much room that there isn't much space to put a larger valve in those combustion chambers, it stands to reason. Plus the larger combustion chambers on smaller bores is going to change the quench area. I don't like the idea of that at all.

Then there is the question of potential you brought up... people seem to be exploring the potential of these engines already with 3500 top end swaps. It hardly seems that the port and valve size of the 3900 is needed without the extra half liter of displacement. IMO without forced induction all that is going to do is lower the air velocity in the ports and lose torque. Especially without being able to take advantage of the variable cam timing and variable intake manifold the 3900 has.

And what LIM gasket problem are you talking about. With the revised gasket and proper installation there ARE NO PROBLEMS anymore. Case in point, I've been running mine for 57,000 miles with no problems at twice the stock HP level.

Bottom line is, I didn't just blurt out some stupid opinion like you seem to think. I've thought this thru and it doesn't seem worth the headache or cost to me to get the 3900 stuff to work for questionable benefits. It's just too much of a different animal from the 3400/3500. The 3500 top end swap seems like a much more justifiable option.

There are some very, very, important points mentioned here that many seem to be taking offense to rather than a wise consideration. So let me humble myself and give it a try;

Note the valve reliefs in the 3900 pistons posted in the other 3900 thread, which are absent in the 3500, 3400 and 3100.

There is also valve to cylinder bore interference in the 3100, if it clears the 3400 or 3500 it will be close and I've heard no mention of shrouding yet.

From personal experience with overzealous head-runner porting, a considerably larger runner design having more volume on the same engine will reduce the intake charge velocity and therefore your power output at every point on the rpm range where that scenario exists. I remember so well the machinist I dismissed as not knowing this for sure that warned me before hand so well. The power loss was so great that eventhough it was a TPI 383 stroker turning 3.73 gears in a Z28 with stock tires, the old 305 it replaced might have given it trouble. And that's comparing the engine before my hacking to after.

Combustion science is high tech stuff and way out of my league but with the little I do understand, I certainly would not want to cross a factory tested quinch area with cliffs and over hangs from improper alignment. There's something pretty special about being able to run a 9.8:1 compression ratio on 87 octane that says fragile.

I believe we all should hit the reset button and reconsider what amounts to valid points. An actual mock up setting is not always necessary to be certain the idea has more cons than pros.

The idea is a good one, it's the practicallity and proper function that is in question due to pre existing facts regarding combustion dynamics.

And the likelyhood a salvager is going to break up a good engine of this nature having only been on the market 2yrs or less to sell in pieces is probably neil. The 3500 has been out 4yrs and look at how tough it is to get those parts used.

[Guest]

A-wrong your post is nothing but speculation. I love the fact that you are acting like it can't be done or that its a bad idea and you have non of the parts in front of you to know for sure. Just STFU already.

We wont' trully know untill we line things up or try to bolt them down. If it doesnt' work then it doesn't work. But if it does I am going to be on your case even moreso then I am now.

[SappySE107]

Be on his case somewhere else.

[rickykline]

would be interesting to see... but as said before i also doubt it would work(properly..)

[AaronGTR]

There are some very, very, important points mentioned here that many seem to be taking offense to rather than a wise consideration. So let me humble myself and give it a try;

Note the valve reliefs in the 3900 pistons posted in the other 3900 thread, which are absent in the 3500, 3400 and 3100.

There is also valve to cylinder bore interference in the 3100, if it clears the 3400 or 3500 it will be close and I've heard no mention of shrouding yet.

From personal experience with overzealous head-runner porting, a considerably larger runner design having more volume on the same engine will reduce the intake charge velocity and therefore your power output at every point on the rpm range where that scenario exists. I remember so well the machinist I dismissed as not knowing this for sure that warned me before hand so well. The power loss was so great that eventhough it was a TPI 383 stroker turning 3.73 gears in a Z28 with stock tires, the old 305 it replaced might have given it trouble. And that's comparing the engine before my hacking to after.

Combustion science is high tech stuff and way out of my league but with the little I do understand, I certainly would not want to cross a factory tested quinch area with cliffs and over hangs from improper alignment. There's something pretty special about being able to run a 9.8:1 compression ratio on 87 octane that says fragile.

I believe we all should hit the reset button and reconsider what amounts to valid points. An actual mock up setting is not always necessary to be certain the idea has more cons than pros.

The idea is a good one, it's the practicallity and proper function that is in question due to pre existing facts regarding combustion dynamics.

And the likelyhood a salvager is going to break up a good engine of this nature having only been on the market 2yrs or less to sell in pieces is probably neil. The 3500 has been out 4yrs and look at how tough it is to get those parts used.

Thank you! I'm glad at least one person understands that I am merely trying to point out some potential problems with this swap and not just blurting out nonsense (like shaun does so often). From what I've been reading lately about the combustion cycle and especially on the effect the quench area has not only on detonation resistance but also on fuel efficiency and torque production, I wouldn't want to mess with that. The 3400/3500 heads already have very good quench areas that are largely responsible for this engines higher detonation threshold compared to the L67 V6's (along with the aluminum vs iron heads). I've run AFR's at rpm that would have resulted in Kr of 5-6 degrees or more in grand prix GTP's according to guys on the tuning boards. I'm not going to mess with a good thing just to try and get some bigger ports when the 3500 heads will flow plenty. That's the only reason I'm saying it won't be worth the risk. I'm giving an opinion, thats all.

[SappySE107]

Im pretty sure the combustion chamber overlap with the cylinder would cause head gasket issues if you put 3900 heads on a 3400 or 3500.

[Guest]

Thank you! I'm glad at least one person understands that I am merely trying to point out some potential problems with this swap and not just blurting out nonsense (like shaun does so often).

YOu mean like the time you said the Beretta pace motor used a custom stroke crank because there was no way in hell the aluminum block could be bored out to a 3.4L. You sweared up and down about it till I posted the pic showing that you were wrong. And how you got all pissed and started using swear words at me because you were publically made a fool?

You mean nonsense like that?

OWNED!

[prophiseer]

fucking childish, y'all - save it for the Ford boards.

In my opinion, I also don't think it's a great idea, either; if you really want that much port and runner volume, you should just drop the whole 3900 in because you'll need the larger cylinder volume to draw enough air through the runners to any make decent power.

[AaronGTR]

YOu mean like the time you said the Beretta pace motor used a custom stroke crank because there was no way in hell the aluminum block could be bored out to a 3.4L. You sweared up and down about it till I posted the pic showing that you were wrong. And how you got all pissed and started using swear words at me because you were publically made a fool?

You mean nonsense like that?

OWNED!

Grow up you douche bag.


Everyone already knows this history... how soon you forget though. I said that you couldn't bore it out that big without resleaving the block because it made the cylinder walls too thin and risked distortion. GM did it on that car anyway because it was just a concept car and not meant for service use. Someone else pointed out that in the GMP catalogue they don't recommend boring that block out to more than 3.3L without resleaving it, so the people who actually make the block said the same thing I did... and everyone pretty much agreed with me and that you were a fucking moron. End of story. So who owned who? I don't really care though. I wish you would just grow up and stop dragging up this stupid non-sense. You seem to be the only one who can't let it go, and your useless baggering of me and other members on this board sure doesn't do anything to help the 60v6 community. Real mature there shaun.

[bszopi]

Glad to see I get to close another thread because 2 people can't seem to just leave each other alone. Well, looks like I get the last word. Shaun already knows he is on thin ice....