Can I use a hyd flat tappet engine ('87-'97 w/ 1 pc rear seal) in '98 application?

[NormRinker]

Hey all,

Can I substitute my original '98 5.7L MerCruiser/GM 5.7L engine with hydraulic roller camshaft and lifters for one with the hydraulic flat tappet camshaft and lifters set up? It will still be of the '87 or newer variety with the one piece rear main seal. I suppose that's where it was different on the crankshaft rear bolt flange between pre '87 and post '87 designs. I want to stay with the newer one for my flywheel, starter, etc to bolt on if that's all direct bolt-on stuff I am thinking here. There are several nice crate flat tappet engines that I like, and some of them use Vortec cylinder heads. Besides the newer Vortec heads and intake manifold, What differences are there if any that I need to look out for going with a '87-'97 block in place of '98?

I can take care of the engine's top end as I will be staying with the Vortec stuff. I was more wondering if going with a hydraulic flat tappet camshaft and lifters won't affect anything with the Thunderbolt ignition system that's on there. I would think the engine wouldn't know what is what that's in there as long as the camshaft profiles and specifications doesn't differ too much.

I'm looking forward to seeing some of your replies on here. Blueprint Engines make some nice marine long blocks, crate engines, and there are some nice flat tappet GM Performance engines as well that might be marinizable. The cost difference between two type of valvetrain set-up is of a pretty good margin. I know most will say to stay with the roller lifters, but can a well thought out flat tappet engine work just as good in terms of moving the boat around with some power without affecting anything?

Thanks

 

[Coors]

Re: Can I use a hyd flat tappet engine ('87-'97 w/ 1 pc rear seal) in '98 application

The term "flat tappet" is confusing to us old farts; as that would be solid lifters. More knowledge will come in, but your rear seal has nothing to do with the gm cam- all are the same cam bearing size, one piece or two.

 

[180shabah]

Re: Can I use a hyd flat tappet engine ('87-'97 w/ 1 pc rear seal) in '98 application

You are correct in assuming that the accessories won't "know" what cam you are using. You will need to verify compatibility of your distributor drive gear though.

 

[John_S]

Re: Can I use a hyd flat tappet engine ('87-'97 w/ 1 pc rear seal) in '98 application

Bondo is the resident expert on SBC vintage and drive mating questions. From what I've read and learned from him, I don't know of any issues in those year ranges, but let him weigh in on the subject.

The roller cam has higher lift and shorter duration than the flat hyd lifter marine cam. The roller cam was available before vortec heads, and produced the same HP in standard head 350's. The vortec heads flow slightly better than standard heads at the higher lifts. There might be a neglagable difference in hp. The main thing you will be giving up, would be reliability from reduced lobe wear.

Mercruiser, like GM, used the melonized distributer gear on their roller cams. It is my understanding, but need to check, that it was also used with the flat hyd cam. You probably have elec fuel pump, so don't have to deal with the different pump rods.

I forgot why you were replacing your engine, (and too lazy to go back and find posts) but think it was due to water in the cyl and need to bore. If so, at least check out all the roller cam components, and reuse if possible/cost effective.

 

[NormRinker]

Re: Can I use a hyd flat tappet engine ('87-'97 w/ 1 pc rear seal) in '98 application

Bondo is the resident expert on SBC vintage and drive mating questions. From what I've read and learned from him, I don't know of any issues in those year ranges, but let him weigh in on the subject.

I can see why he is the resident expert on that. I will wait and see if he will come in here and answer. I recall he is using an older block in his build up but I do not know what it is going to mate up with, etc. I have a Bravo III so that's what I will be mating up to with the original '98 flywheel, starter, and so on.

The roller cam has higher lift and shorter duration than the flat hyd lifter marine cam. The roller cam was available before vortec heads, and produced the same HP in standard head 350's. The vortec heads flow slightly better than standard heads at the higher lifts. There might be a neglagable difference in hp. The main thing you will be giving up, would be reliability from reduced lobe wear.

I wonder how much reliability is given up between both designs. I would think a flat tappet set up can run for a long time.

Mercruiser, like GM, used the melonized distributer gear on their roller cams. It is my understanding, but need to check, that it was also used with the flat hyd cam. You probably have elec fuel pump, so don't have to deal with the different pump rods.

I wondered about that. It's good to know there is a chance this melonized gear can be used with the flat hyd cam with no adverse effects. I will have to look further into it to be sure. Yes to the electric fuel pump.

I forgot why you were replacing your engine, (and too lazy to go back and find posts) but think it was due to water in the cyl and need to bore. If so, at least check out all the roller cam components, and reuse if possible/cost effective.

Yes, due to water ingestion. The motor ran beautifully before the overheat incident. The valve rockers, springs, push rods, and hydraulic roller lifters looked brand new looking into the engine from the top. I would have to pull the rollers one by one (and mark their original location) to inpect the roller surfaces as well as the cam lobes surfaces. I was wondering if some of the flat tappet engines I've looked at can be used to replace a hydraulic roller engine. Perhaps Bondo might answer that one.

....

 

[John_S]

Re: Can I use a hyd flat tappet engine ('87-'97 w/ 1 pc rear seal) in '98 application

I know that the ICM grew in size and # of pins on '98 V8 vortecs. More pins, usually means more sensors. As long as are transferring all the sensors and wiring to the new engine, probably OK. Follow all the wires and make sure you know how mounted. A MPI mapping might not be perfect, but the carbed T5 set-up shouldn't know the difference. But, it sounds like your cam/lifters are fine. Mic them, and if good, reuse them. You will just need to confirm that the crate engine is '87 up, and roller cam capable.

Note: If there is a crank sensor (I think that is only on MPI) you would need the composite timing cover which came on '97 and latter SBC.

Also, if reusing your heads, the crate engine will need recessed pistons or comp ratio will be too high.