Mercruiser 350 MPI rebuild
08-08-2024, 09:36 PM
#1
Mercruiser 350 MPI rebuild
Hello, everyone, I have some engine building questions to ask, it seems like there is more of an engine building crowd here.
One of the two 5.0 MPIs in my new to me boat turned out to be seized up due to water getting into the cylinders. I went ahead and picked up a 98 5.7 vortec truck motor to use as a core (will get another tomorrow). I will trade my 5.0 ECMs for 350 MPI ECMs. I do have a couple of questions though before I order parts and such. Just to be clear, I want to build bone stock 350 MPIs. The most important thing in the build by far is for the stock ECM555 controller and tune to play nice with the engine. Here are my questions:
1. Is a compression height of 1.56, piston volume of 12cc, and squish gap of 0.040 correct?
2. Summit pistons ok for this purpose or are they a no no? Any other brand?
3. Is there a difference between the 811658 and 866022T cams? Difference in ECM calibration? Or are the interchangeable with the same ECM?
4. Where should I check for cracks in the block?
5. If I decide to make a 6.2 out if it, will the 811658 cam that I have screw up the 6.2 ECM? or is it interchangeable with the 5.0?
I am sure I will have more questions as I go along
Thanks!
One of the two 5.0 MPIs in my new to me boat turned out to be seized up due to water getting into the cylinders. I went ahead and picked up a 98 5.7 vortec truck motor to use as a core (will get another tomorrow). I will trade my 5.0 ECMs for 350 MPI ECMs. I do have a couple of questions though before I order parts and such. Just to be clear, I want to build bone stock 350 MPIs. The most important thing in the build by far is for the stock ECM555 controller and tune to play nice with the engine. Here are my questions:
1. Is a compression height of 1.56, piston volume of 12cc, and squish gap of 0.040 correct?
2. Summit pistons ok for this purpose or are they a no no? Any other brand?
3. Is there a difference between the 811658 and 866022T cams? Difference in ECM calibration? Or are the interchangeable with the same ECM?
4. Where should I check for cracks in the block?
5. If I decide to make a 6.2 out if it, will the 811658 cam that I have screw up the 6.2 ECM? or is it interchangeable with the 5.0?
I am sure I will have more questions as I go along
Thanks!
Yesterday, 03:47 PM
#2
Hello, everyone, I have some engine building questions to ask, it seems like there is more of an engine building crowd here.
One of the two 5.0 MPIs in my new to me boat turned out to be seized up due to water getting into the cylinders. I went ahead and picked up a 98 5.7 vortec truck motor to use as a core (will get another tomorrow). I will trade my 5.0 ECMs for 350 MPI ECMs. I do have a couple of questions though before I order parts and such. Just to be clear, I want to build bone stock 350 MPIs. The most important thing in the build by far is for the stock ECM555 controller and tune to play nice with the engine. Here are my questions:
1. Is a compression height of 1.56, piston volume of 12cc, and squish gap of 0.040 correct?
2. Summit pistons ok for this purpose or are they a no no? Any other brand?
3. Is there a difference between the 811658 and 866022T cams? Difference in ECM calibration? Or are the interchangeable with the same ECM?
4. Where should I check for cracks in the block?
5. If I decide to make a 6.2 out if it, will the 811658 cam that I have screw up the 6.2 ECM? or is it interchangeable with the 5.0?
I am sure I will have more questions as I go along
Thanks!
One of the two 5.0 MPIs in my new to me boat turned out to be seized up due to water getting into the cylinders. I went ahead and picked up a 98 5.7 vortec truck motor to use as a core (will get another tomorrow). I will trade my 5.0 ECMs for 350 MPI ECMs. I do have a couple of questions though before I order parts and such. Just to be clear, I want to build bone stock 350 MPIs. The most important thing in the build by far is for the stock ECM555 controller and tune to play nice with the engine. Here are my questions:
1. Is a compression height of 1.56, piston volume of 12cc, and squish gap of 0.040 correct?
2. Summit pistons ok for this purpose or are they a no no? Any other brand?
3. Is there a difference between the 811658 and 866022T cams? Difference in ECM calibration? Or are the interchangeable with the same ECM?
4. Where should I check for cracks in the block?
5. If I decide to make a 6.2 out if it, will the 811658 cam that I have screw up the 6.2 ECM? or is it interchangeable with the 5.0?
I am sure I will have more questions as I go along
Thanks!
2. Get a good forged piston. I have no experience with the Summit branded pistons. OEM were hypereutectic. I use SRP forged.
3. I did not find cam specs but both cams are used in a metric **** ton of Merc small blocks. Kind of like the GM "395" hyd roller, very common.
4. Where ever the magnaflux detects them. Not trying to be a smart ass. FWIW my original 1995 got minor cracks between the #5 and #7 lifter galleys at about 725 hrs. Was discovered on a rebuild but not the cause of the rebuild if that makes sense. I did not reuse the block.
5. The motor is not going to screw up the ECM but the tune can screw up the motor. With a stock motor/cam/heads going from a 300 to 350 or 377/383 will require minor tuning in the fuel tables. I will lay money down that a bone stock 350 tune will start and run a 377/383 right out of the barrel (I have done it). It won't be perfect (in fact it will be closer than you think) but it will run. HOWEVER you would NEED to run wideband and see what the AFRs are doing. Tuning the 555 is going to be the biggest issue.
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