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Discussion Starter #1
We have been needing to source a replacement motor for our P38 for years, and finally found a good parts truck! It’s a 4.6 GEMS motor though, ours is a 4.0 Bosch though. I know the displacement isn’t really an issue, but I made a list of all the things I believe we need to swap and would like some assistance in making sure we didn’t miss anything.

Remove GEMS crank sensor mount and have a replacement Bosch one put in place
Swap the flywheel from our Bosch motor to this block
Bosch style cam gear (was planning on anyways to do a Stage 1 or 2 Crower. Thoughts on this as well?)
Obviously swap our SAI heads and all the intake goodies. This motor is going to be top hat lined so we would get it back as just an assembled short-block.

Anything we seem to be missing? Thank you all!
 

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If you're starting from a short block, there's not much to it, just reuse everything from the Boch engine. You might find some mountings are different, including for the crank sensor IIRC. Camshafts etc are identical, only the cam wheel is different.
An uprated cam is a good upgrade for not a lot of money. We always use a Piper or Kent high torque.

Filip
 

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We have been needing to source a replacement motor for our P38 for years, and finally found a good parts truck! It’s a 4.6 GEMS motor though, ours is a 4.0 Bosch though. I know the displacement isn’t really an issue, but I made a list of all the things I believe we need to swap and would like some assistance in making sure we didn’t miss anything.

Remove GEMS crank sensor mount and have a replacement Bosch one put in place
Swap the flywheel from our Bosch motor to this block
Bosch style cam gear (was planning on anyways to do a Stage 1 or 2 Crower. Thoughts on this as well?)
Obviously swap our SAI heads and all the intake goodies. This motor is going to be top hat lined so we would get it back as just an assembled short-block.

Anything we seem to be missing? Thank you all!
The Crankshaft Position Sensor in different on Bosch and GEMS engines. The bracket for the sensor is different as well. You will need to cut off GEMS bracket and have a Bosch bracket welded in place. The brackets are available. The welding part is trivial for any shop that has a decent AC TIG welder. The sensor needs to be positioned correctly, measurements will need to be taken on the original Bosch block to re-create the same setup. Last time I had it done, the shop charged a little a hundred and fifty bucks. It's not as bad as it sounds.

There may be an issue with the knock sensors, I don't remember. The rest should be a direct bolt-on. The oil pan and front cover are different on Bosch and GEMS engines. If you are reusing the front cover - replace the oil pump gears. Also replace the camshaft bearings in the replacement block, even if they look good. Replace the freeze plugs and clean out oil galleys.
 

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Discussion Starter #4
There may be an issue with the knock sensors, I don't remember. The rest should be a direct bolt-on. The oil pan and front cover are different on Bosch and GEMS engines. If you are reusing the front cover - replace the oil pump gears. Also replace the camshaft bearings in the replacement block, even if they look good. Replace the freeze plugs and clean out oil galleys.
Looking at the knock sensors, I think I have some ideas that'll work for mounting them.

A new oil pump was always in the cards, no point in a rebuilt motor with an old pump! Now, I have a hard time telling the difference between the GEMS cover and the Bosch cover? Is there any advantage/disadvantage to keeping the GEMS cover/oil pan, or should we just swap a Bosch unit onto it? I know also we will need to take the Bosch oil pickup if we take the Bosch cover & pan as they don't clear the GEMS setup.
 

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As you're starting from a Bosch, it seems logical to reuse as much parts as you can, and only replace with GEMS parts where needed.
 

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Discussion Starter #6
As you're starting from a Bosch, it seems logical to reuse as much parts as you can, and only replace with GEMS parts where needed.
Other way around, GEMS motor from the parts car into our Bosch car.

I was even planning on getting a set of cylinder heads from Pick N Pull this weekend, as well as a Bosch front cover + oil pan + oil pickup, that way more of the motor can build outside of the car before installation. I'd grab an intake manifold too but it's easier to install the motor with the manifold off. ARP head studs? Much harder to install with the block in the car haha
 

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ARP head studs? Much harder to install with the block in the car haha
No they aren't. Much harder if you screw the studs into the block and then try to fit the heads but if you drop the heads into place and then screw the studs in (using the hex hole in the end provided for this exact purpose) the same as you would with bolts, it's no different.
 

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Other way around, GEMS motor from the parts car into our Bosch car.
That's what I meant, your base vehicle is a Bosch. It does complicate matters if you want to leave the original engine in as long as possible. If you take it out first, you can easily swap all the bits and only use the GEMS parts you really need.
I'm in a similar situation, building a 5.0 with Bosch manifold etc, but as I'm still driving the Bosch donor car I don't really have access to the parts...

I do find it easier to install and torque the intake manifold on the engine stand. Which is one of the reasons I'm waiting to install my engine.

Filip
 

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Put 4.0 liter HC pistons in your 4.6, this will raise your CR to about 10.7:1 if I'm correct.
Keep in mind, you lose bottom end power with another camshaft, with a Kent 180 you deffinitly do
 

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JACK'S GRANDAD
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Put 4.0 liter HC pistons in your 4.6, this will raise your CR to about 10.7:1 if I'm correct.
Keep in mind, you lose bottom end power with another camshaft, with a Kent 180 you deffinitly do

Be very careful doing that with no other modifications. I've always used 4.6 pistons for the engines I build, with good reason
 

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Discussion Starter #12
Be very careful doing that with no other modifications. I've always used 4.6 pistons for the engines I build, with good reason
Yeah that I do not plan on doing. Other than the main issue of driving the 4.0 until the weekend of the swap, it's risky.

The Kent 180 seems to be a good mid-point between the Crower 229/230 cams. One of my buddies has a 4.6 in his D2 from Turner with the 180 and the difference at the bottom end isn't really noticeable, but once you past ~2.3k its very apparent that it's got some extra get up n go!
 
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