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Lets see what we can do with this 3.5

3K views 18 replies 5 participants last post by  Ruggels 
#1 ·
Ok well in my new classes this semester im taking engine reconditioning and automatic trans rebuild classes.

in the engine class we may supply our own parts and by the end of two semesters you should have a engine build 100% to spec ready to run, was going to grab an engine for my dads durango seeing as its at 240k miles but they wanted 450$ at the yard for one, while it was only 150$ for my trep. durango's are only in the "premium yard". so we pulled a 3.5 from a 95 and called it gravy.

anyway in the class we literally have everything you could need to machine a engine however you like, the teacher even calls the class "engine machining" not reconditioning. well i would just feel like im missing the potential if i do not "update" this engine as much as i possibly could.

From what ive researched so far the design has been around about 18 years from 93-11, with the end result a 46hp and 44tq increase from its release, with versions 2.7, 3.3, 3.5 and ,4.0

it seems the increases from the 1st gen 3.5 to 2nd gen as many if you likely know is from the heads, with softer springs and wider intake valves, and the differences in the block the pistons are lighter 2nd gen, with heavier rods (i dont know how much that really makes a difference) also i think the pistons have a flat top on 2nd gen and that increases the compression and makes it inteference?, the first semester of the class consists entirely of the heads so ill start with that, widen the valve seats, port, polish intake, throw in the 2nd gen valves/springs, i have the specs from 94, compared to 04, and the valves/guides are exactly the same besides the intake head diameter, intake valve lift is .40 mm more in 2nd gen, i still need a bit more research on that but it seems entirely doable, and that can take up my time while i research the more adventurous idea...

Now someone once told me that the 1st gen could not be modded into a 4.0? i didnt look into it at the time but now i ask why not? i assume its something to do with the oil pan, as i believe the blocks are exact same in 2nd gen except iron not aluminum? many small differences can be handled easily, i noticed the 2nd gen guys having to grind out some on bottom of cylinder for crank clearance, i still need to do much more research on the project but im curious as to why i was told it couldnt be done?
 
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#3 ·
Sounds like just the thing to do!!!

The only thing you may run into is the lack of computer support to make it run right - mechanically it will be potentially flawless - but if you can't feed it, no point. I don't know, but bigger injectors are the first thing I'd find before you go modifying the heads too much.

Perhaps custom injectors (using standard Bosch style injectors) and a custom injector rail (top feed, rather than bottom feed) would be a solution? Of course there is always a megasquirt.

Very exciting to see where you go with it.
 
#4 · (Edited)
yea i need to look more into the fuel delivery, among many others, i was deff planning on new injectors, and need to look into a computer to run it, i saw the guys with 2nd gens had larger then needed injectors with a computer controlling it to better compensate for fuel differences between idle and WOT, i was gunna look into something like that for a 1st gen computer... a better fuel rail would be nice as well, maybe i could look into getting a higher pressure threw the lines for better spray, haven't looked into that yet, hehe so much research to do, im having the hardest time finding the 4.0 rebuild specs

my teacher was telling us how they are putting 20,000 PSI threw diesels to make them quite as a gas engine, irreverent but interesting as hell, esp when you can cut steel with water at that pressure.

Edit: i actually just checked and see that dodgebob ran stock injectors for a while before upgrading, makes sense to be ok as the stock would likely be enough at lower rpms while your still breaking in the engine, but fuel delivery is deff high up on the list.
 
#6 ·
my teacher was telling us how they are putting 20,000 PSI threw diesels to make them quite as a gas engine, irreverent but interesting as hell, esp when you can cut steel with water at that pressure.
Diesels are getting up in the neighborhood of 30,000 PSI now with up to 7 injections per combustion using common rail fuel systems. If memory serves me right, it takes a little over 30 or 40 thousand PSI to cut steel with water alone but its still pretty darn cool.
 
#7 ·
Gasket matching the ports will do much for you, Increasing the small I believe 48mm Throttle bodies with a 3.3 s 58s on both side will help air flow. Fart as polishing it will not do much. The biggest area to work with is around the valve to help improve swirl and flow.

The Viper and the 3.5 share the same type of injectors, which are bottom feed. keep that in mind. Also, OBD II First gen PCM will not respond very happily to timing differences or at least in a 3.3 they will not.
 
#10 ·
i figured as much, the guy i talked to on the phone at the dealership said something about other things they could have changed between obd 1 and 2 so i just went with what he said, but i dont think it will matter at all really, if anything i could see OBDII as being more restricting on the tuning side, but thats just a wild guess.
 
#12 · (Edited)
well got to work on em a bit today, got everything taken apart ready to be cleaned, i was also able to get the 2008 4.0 dodge nitro engine specs from the school resources, it would seem that the 4.0 has a few differences but seems Chrysler followed suit of what they did from 1st to 2nd gen....

even lighter pistons then the 2nd gen trep, (which is even lighter then 1st gen), for a difference of 515g in 1st gen trep to 375g in the nitro, thats around 140g per piston, heavier connecting rods from 626g in first gen to 693g (total weight), resulting in + 73g, so becides the deeper cranks the rotating assembly is a full 767g thats almost two pounds off your crank!

while from 1st to 2nd gen trep they increased the intake valve head diameter by about 1.5mm, and softer springs (some say the main cause of the gains from the 1st to 2nd gen is from these two things) and while in the 4.0 the valves stay the same size they actually have .85mm more lift for intake, and around .5 for exhaust valve over 1st gen, and about .5 more both intake and exhaust compaired to 2nd gen, as well for the 2gen it uses softer intake and exhaust springs then the 1st, while the 4.0 keeps the softer intake, the exhaust are more similar to 1st gen rather then 2nd in terms of tension.

so more research on interchangeable springs, valves, etc... i cant figure about where the extra lift in the valves comes from, i think it may be both the cam and exhaust valve together.... the 4.0 exhaust valve overall length is .5mm longer then in 3.5s that explains the lift their, but the intake is the same, as well all cam specs are the same but it does not give me the size of the lopes on the cam (i think thats what they are called)

im going to make a thread with all the 4.0 specs later tonight, the info i have is just printed out so just engine build specs no full section on engine from FSM... yet :spiders:

edit:
The only restriction to tuning would be in the computer.
yea i was meaning on the computer side of things i would think a OBD1 ECM would have less strict programming then a OBDII, and more comparing with the 2nd gen guys rather then the two engines i was looking at but like i said its just a wild guess guess with no merit behind it :emmm:
 
#14 ·
yessir, i plan to essentially do as much upgrades on the engine as my budget will allow, i wont have to much worry about machining as the school has everything i could need there. so i can focus my money on parts. ill either sell the old engine or see if i can find a body to throw it in and sell that.

im trying to get the modifications i want to do in a priority order, i dont want to throw in the deeper crank and leave the valves the same, i could see it restricting the engine with the larger differences between 1st and 4.0, im finishing up my research on the mechanical aspects now i need to look into parts costs and interchangeability.
 
#15 · (Edited)
so went in and more cleaning, cleaned the valves, noticed one of the heads was rebuilt before, the valve guide covers were in 3 diff colors, and could see they were milled before, started to pop out the valve guides and noticed that the chamber is different on each of the heads! :facepalm: seems someone threw on the wrong head for a repair, the doner car only had 87k miles on it.

one head obviously gives a higher comp ratio then the other,




anyone know what year the higher comp ratio head came out? i checked all the intake valves and they all seemed to be the same size, i know 2nd gen runs larger intake valves so is this from a first gen i believe, and the doner car is a 95 concord

Edit: so a bit of research has lead me to find the head in the top pic is from a a 93/94 and the lower head is from 95/96/97, and further research has lead to me find that the 2nd gen and 4.0 heads use the design in the lower pic, so a 93/94 head will give a higher compression, that coupled with 4.0 internals will make these heads the most efficient and powerful. available.
 
#16 ·
Early Years aka 93-95 I believe are the higher end compression years.

Far as Cams, I will repeat that last time we tried to change duration, in a OBD II LH car the computer refused to run it properly on a driveable scale. I am hoping OBD I would not care as much. We tried a 3.8 cam which had just minor extra lift and duration. PCM would not drive it at any reasonable pace.

Also, 2nd Gens got some of the extra power from tighter tolerances, hence they are interference motors. Softer Springs would not increase or decrease seeing that as one valve is opening another is closing so they equal each other out to be honest. If anything with higher RPMS you want higher seat pressure from a spring to prevent valve float. Also the PCM prgormaing, and re-designed-everything pretty much is the cause of power.

Far as lift, cam and rocker arm ratio is what controls the measurement. Once again you are playing with internals that can "kiss" so watch out. The fact the first gen 3.5 can snap a belt and not automatically grenade is a great thing.
 
#17 ·
did you swap the sprocket from a 3.5 onto the 3.8 cams and the PCM would not run it? or did you use the 3.8 timing sprocket from what i can tell from this thread http://www.dodgeintrepid.net/showthread.php?t=290738 and talking with my teacher the ecm should be able to run the 4.0 cams so long as we could adapt the timing sprocket on correctly, and of course like you said i need to look into clearances very carefully, im still debating if i should make it interference with a higher comp ratio or not
 
#18 ·
did you swap the sprocket from a 3.5 onto the 3.8 cams and the PCM would not run it?
They were doing this on a 3.3 engine, not a 3.5 - the 3.3 and the 3.8 engines are essentially the same engine with some larger dimensions - the cam gears are the same.
 
#19 ·
so the semster is winding down i got the head that i want all rebuilt and its ready for larger valves/seats when i get a chance, still need to get another 93-94 head and rebuild that. found i need a new set of rocker arms, i need to look into cost of replacing individual rocker or if i should just get a whole new assembly. im leaning towards new so i don't have to worry about the rest of the rockers failing.

i was misunderstood and thought the block class was the semester following this one but it seems it starts in fall, but honestly thats better for me as it gives me more time to save for parts, so now i got it all home took the block apart and snapped some pics.


Some very ground up journal bearings



The nick in the crankshaft that im unsure if it will be able to grind out, oh well the 4.0 needs the new crank anyway just more motivation.



The broken rocker's you can see the tips on some of the rockers have been smashed in and float for about 1/8" up and down while others are rock solid and i cant push them down without really trying to do it.

Broken next to what it should be



what it should be



And we have a thrown connecting rod cap, the 4.0 needs new rods anyway so these would not have been reused unless the project is abandoned.



Connecting rod bearings are not in great shape either at least they are not as bad as the journals


And here you can see the effects of the two different heads the motor was running when i pulled it



now some block pics




and from early observations the block is in ok condition, no cracks, gouges, or disasters, now its time to save every penny for the next 3 months till this project picks back up
 
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