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3.5 - 4.0

2959 Views 17 Replies 6 Participants Last post by  MrSpool
I have a rover with a 4.0 in it but am trying to drop in a 3.5, it is obdii which means no distributor. what would i need to do to put this in? I have heard they are both the same engines just with different displacement. thanks.
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I got the history on why you want to do this, from the previous thread, but, as Disco says, what would posses you to put a 3.5 in to replace the bad 4.0?
A 3.9 would make more sense, as you wouldn't notice a power difference. but the 3.5 is going to feel like your 4.0 on 6 cylinders.

The bottome line is, if you were willing to go to the bother ( alot of labor is going to be invested here, not to mention the cost of parts to convert the 3.5 to a GEMS block) is that you would need to strip the front cover (oil pump and distributor) off, and replace it with the front cover and oil pump from the 4.0. Also the intake manifold from the 4.0 must be put onto the 3.5 as the fuel rail and throttle body( including the 4.0 MAF) must be retained to satisfy the GEMS ECU.

Thinking about it, I suppose you could leave the 3.5 front cover, including the distributor, in place, just changed over the top end. Man would that blow some mechanics mind when he opened the hood and saw no wires coming off the distributor to the plugs.

Personally, if it were me,and knowing what a pain in the ass it is to pull these hunks of aluminum out, I would only go through it once. If the money was an issue, I'd go find my own 'Desperate Housewife' and be her bitch.
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MrSpool said:
That makes alot of sence. The reason I was going to try to put in a 3.5 was that there is one that is relitively inexpensive, .
Ever hear the expression "Penny Wise, Pound Foolish"?

I have to say, even if it was free, I would not put a 3.5 in anything. You're going to do alot of work, and in the end, be completely dissatisfied with the resulting performance, be very lucky to sell the truck, not to mention probably taking a loss on it.

As Okie says, and I can attest to, having done many, it's more than a days work.

a 3.9 will say just that, on the top front of the plenum, cast right in, in big numerals "3.9" , whereas, as 3.5 won't have anything on the plenum
John C said:
How about a 3.5 in a Series truck? That would be pretty cool!!!
Yeah? That's called a Stage One, and they are rare for a reason, they were awfull even when new.
onslow said:
Sorry chaps but I totally disagree (as usual) :dunno:

Sorry, Ons, but in this case I have to disagree with you. The reason Spool indicated choosing a used 3.5 was cost savings. That being said, how much is any cheap engine after you tear it down to change the cam, cam bearings replace the lifters (You wouldn't put an ancient set of lifters atop a new cam would you?)
He would then have to either polish the ports himself, or send the heads out to have them done, polished and port matched. I don't know what your shop charges, but most automotive machine shops around here don't come cheap.(yeah, I know, you do it yourself right, so do I but Spool hasn't indicated he would) So, basically, he is completely rebuilding a 3.5, and it would have been more prudent to have taken all those steps, but on his original 4.0 (and not have wasted the $$$ on the 3.5 to begin with)
After all thats done, he still can't put the 4 barrel on(4barrel and manifold, another $800), as most states won't permit it, and it won't pass emmissions, and most states are now testing that too. He's working with a GEMS ecu system, and there will be problems in the ecu isn't seeing a running engine, and GEMS is also security critical, imobilizer and all Any 3.5 is going to 8 years old now, and probably a high miler. True that 3.5 engines never ( I never heard of one) had liner shifts, though they are know just as 3.9 and 4.2 for needing head gaskets as they age, steel head gaskets simply don't last forever.
So his "reasonable" 3.5 is now, conservatively, pushing $2500.

I just recently did a total on a 4.2 and with shop work and parts, was over $2k, and I don't put any price on my labor.
He hasn't indicated, but if it's a standard (R380) it isn't as critical, but if it's a ZF4, the gearbox govenor is likely to delay his shift. I agree, a removal can be done in a day, but he's not going to 'pop' the new one in the next day, as there are loads of bit and pieces to swap over, unless he's prebuilt the new 3.5, and gotten the flywheel with it (or torque converter plate)
I wouldn't disagree, a 3.5 with a Holley is basically what every healey owner wanted 25 years ago (There were lots of these around from Buicks) an I have one sitting out on the shop floor right now with a top mounted turbo and side draft carburator, and it will probably still sitting there when I'm dead and gone.
A 3.5 in your S1 must make it go like snot, but the S3 Stage one was a piece of Heath Robinson if I ever saw one, whoever designed that trans should have been shot.
I stick by my original statement; puting a 3.5 in his Disco would be a mistake.
(Besides, he seems to have gottewn religeon, and says he will seek out a 4.6, Now that's going in the RIGHT direction.
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MrSpool said:
That settles it then, I will put a 4.0 in it or a 4.6. now about the install. Do I pull the trany with the engine or just pull the engine and leave the tranny? Most rear wheel drives I have done I pulled both, but this is awd so I am not sure. Thanks.
No, Trans & Transfer case stay' in the car.

Unbolt the torque converter from the engine while it is still in the car. Put the new engine in with torque converter attached to trans input shafts. DO NOT try to put it in with it bolted to the engine as you will very likely damage the gearbox pump. There is only one bearing there, in front of the pump, and jockying the engine around with the force on the input shaft is hazardous.
There is no flywheel, per se, on an automatic. It's just a thin steel plate to which the ring gear, and torque converter are attached.

First thing you're going to do, is remove the small aluminum plate at the bottom of your bellhousing, front side. Then, rotating the engine with a socket on the front pulley/bolt, remove the bolts holding the torque converter to the adapter plate. If you remove the torque converter afterward, when you slide it back onto the trans input shaft be certain that the pump drive is engaged. There are two keys on the end of the TC spud, which engage into two slots on the pump drive. It is possible to not engage these, bolt up the engine and the first time you start it, the two keys promptly wipe out the pump drive.
You've got it right, now get on with it and let us know how you make out.
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