5.7 engine build

[1979 Quartermasters]

Good day people:

Finally got around to dismantling a 1998 5.7 GMC Vortec engine I acquired last summer. I swapped it out for another for a friend of mine and he let me keep the old one. I thought it might be a head gasket, but they didn't show any obvious damage. So I'm thinking its a cracked head as he over heated it a couple of times. It had a nice thick milk shake in it and when i took it apart, #8 had some coolant in it. The pistons came out easy (little or no ridge), and everything seemed to be in pretty good shape. All the passages were full of the redish sludge. There is some rust in the top of cylinder #8.

The current engine is a 1995 5.7 bored .030 over and other wise stock with about 550 hrs on it. I do have Corsa switchable exhaust.

So here is my plan.

Block cleaned and checked for damage. If it is good, I was thinking bore it .030 over and get it decked.
The crank looked good, but I'll get it checked and repaired as needed.

I would like 300 to 350 hp and convert it to a carburetor.

I am aware of the reversion problem, but would like as lumpy of a cam as possible (cool factor)

I can turn a wrench, but have never built an engine from scratch.

I don't understand all the lingo of lift, duration and all that stuff, so I was hoping some of you guys would advise me in that department.

I see the fuel pump mount is there, but there is no hole to the cam. Can this be machined or do I have to use an external fuel pump?

Is this a feasible start, or am I out to lunch on this.

All input welcome........

Thanks, Ken

 

[NHGuy]

The fuel pump will need to be electric. But that's a good thing any way.
Lumpy cams revert. I'd recommend getting a marine specific cam from Comp. Also get their lifters and valve springs, those work out best in sets.
If you go with vortec heads and get a high lift cam you may have to mill down the valve guides since vortec heads have some limitations there. There's a DIY tool available for that for around $50.
If you really want to go all out you'll have to spend an extra $1000 for long tail exhaust, then you can go cam wild. But to do that the switchable exhaust goes away and you are loud all the time. Unless...you do exhaust turn downs outside the transom. They can handle aggressive cams without making so much sound.
.030 over 5.7 is a 355. Nice.
Oh also, learn about combustion chamber shape and size, piston shape, quench etc. Your goal is .040 quench distance and about 9.4 to 1 static compression ratio.
350 HP is what to expect.

 

[1979 Quartermasters]

Thanks NH. I'll look into getting the cleaning and machining done and take it from there. Do I need to have a deffinite plan before it gets bored and decked?

 

[Scott Danforth]

yes, you need to plan out everything

why are you going to a carb? Im assuming your MPI currently. I would just get the ECM tuned to what you build.

If your buying a new rotating assembly anyway, get a 3.75" stroke crank and build a 383. Scat rotating kits are inexpensive for SBC's use reverse dome pistons and vortec heads. zero deck the block, and use an 0.041" head gasket to give you a nice quench.

your limited to 268 degrees of duration on the cam with wet exhaust. its not really lumpy thru the leg, however would be with switchable exhaust.

 

[NHGuy]

Well, I have been doing a 383. There's quite a bit of effort to clearance the block for the stroke. Aside from that, no issue.
But I think it's worth it to get almost 10% more displacement.
I'd expect efi to have more tuning problems going up to a 383 though. I'm doing mine over with a carb which I understand. And I can set it up at home or out on the lake with an AFR meter. Or I can take it for a dynamometer set up.
My concern with efi is I've read that some require shipping ecm's back and forth to get the tune physically "burned" into the efi controller. I don't know if that is the case on the OP's system. But it's worth checking.

 

[1979 Quartermasters]

Thanks for all the info. I don't have all the computer stuff as it stayed with the truck. My current motor, in the Searay is pre Vortec and I was hoping to use intake and carb from that motor. I was also hoping to use the original crank with new pistons, heads and cam. I was told I could hit 350hp easily provided I used the right combination......

Ken

 

[NHGuy]

You can do it with the bits you propose, and you might be able to work with the Vortec heads too if they are in good enough condition. If they need much work though it starts to become more effective to replace them as you have said. Is your boat ignition Thunderbolt IV or V?
There's a company selling pistons on ebay with compression heights that fit a .010 decked block. So If your block is in good shape you can keep more material there to resist warping and damage.
The prevortec intakes don't all match up to every head. When selecting heads this is something to know. I think it's some intakes use 8 bolts and others use 12.
Also the valve covers can be center bolt or perimeter bolt. If you go for better rockers there can be clearance issues inside the valve covers too. I gutted the interiors of the valve covers on a set of prevortec heads to clear roller rockers on my 87 5.7. You can't use real tall valve covers because they will touch the exhaust risers.
I'm hoping my wallet allows me do do these, so I cab go for a bigger cam.

 

[1979 Quartermasters]

It currently has thunderbolt 1V

 

[Scott Danforth]

my 88' center bolt factory stamped valve covers only required "adjusting" the breather baffle with a pliers to get them to fit with my roller rockers.

 

[1979 Quartermasters]

Sounds like we're getting close. A lot of this motor building language is Greek to me, but I'm trying to absorb it. Does decking mean flattening the area where the heads are bolted on? Do I need to know which piston I want to use before this is done?

 

[1979 Quartermasters]

Right now , I have the block, crank and heads laying in the back of my truck. I'm not going to have the cash to buy the parts I'll need, but thought I would get these parts check and machined. Then put them aside and wait till I have enough cash to purchase parts. Besides, the difference between your money and our is kinda stupid right now.

 

[Scott Danforth]

I would wait on machining the heads until you know which cam and springs you will be using. I assume you will be going with screw in rocker studs and the associated guild plates, or if you use roller rockers, you would not use the guide plates.

it goes back to the whole planning thing.

 

[1979 Quartermasters]

I'm pretty much assuming the heads, or head is cracked. I was planning on just working on the block and crank. It was over heated badly a couple of time and from what I understand, that pretty much guarantees cracked heads. Vortec heads don't like heat.

 

[Scott Danforth]

Check out racejunk.com. you may find a complete set of machined vortec heads with springs and stainless valves for $400. I did

 

[1979 Quartermasters]

Cool. Thanks Scott.

 

[burtonrider11]

Not to rain on anyone's parade...however, I see you have an Alpha 1 drive. At 350HP you will be stretching the limits of reliability in that drive. They typically rated for about 300HP. Just keep that in mind......So long as you aren't firewalling it on take off, you'll probably be okay. Probably also since it's not a big block, it will help since it won't have as much torque....Either way, it might be a really good time to go thru the drive to make sure everything is in really good order

Good luck with the build and keep us posted, I'd love to do that with our boat and 5.7 as well. Maybe just a bit milder though

 

[1979 Quartermasters]

Well, I took the block in to get cleaned and assessed. I've been reading thread after thread and many article. You guys are amazing how you get to the numbers you want and then turn it into piston, gaskets, cams, etc. I'm not really absorbing all this quench, squish and cr stuff. The cam, lifters and bee hive springs I think I'm understanding. Comp cams can help me set this up. Pistons I have no idea.

 

[NHGuy]

You want to get the flat part of the piston to come up to .040 from the head. To do this you have to work out the compression height of the pistons and the head gasket thickness. You also need to get the compression ratio to a correct goal. I'd go for 9.4 or something close.
Check out uempistons.com and go to their calculators. Your engine uses 3.48" length connecting rods. Figure which size head combustion chamber you want. And figure out which piston capacity and head gasket thickness will then get the right quench distance (the .040" I mentioned), AND also will get the right compression ratio...whew! You select the piston capacity (in cc's) to get along with the heads you are doing,
Or, in my case I had the pistons so I worked the other items.
Example: on my engine I already had small cc pistons, only 4 cc's, so I got a bigger capacity 76cc head combustion chamber to keep the compression ratio from going so high I couldn't use certain fuels. The reason to keep down the compression ratio is to be able to run pump fuel and avoid detonation. Detonation occurs in engines with higher compression and not enough octane. It causes engine damage, you just can't allow it. If you can keep down the compression ratio you can run lower octane fuels, which are easier to find on the water , and cheaper.

 

[Scott Danforth]

if your running vortec heads, you want the dish to mirror the combustion chamber.

something like this http://static.summitracing.com/globa...890CP60_xl.jpg

this style piston will give you the most quence/squish which gives you the most torque.

if your piston looks like this, it will produce much less power

 

[cptbill]

Just don't forget to make sure your drive can handle the HP in cress