Help Rebuilding 350

[lmannyr]

This is my first engine rebuild. I'm learning everything as I go from books and online references. I will finish the rebuild myself too. Be easy on me, pretty please:redface:

The reason for the rebuild is I had taken it apart because it would not turn. After removing the exhaust, intake, heads there wasn't any damage noticed (except for the water in 3 cylinders) and a rusted valve (pics below). The engine still wouldn't turn. At that point I decided to pull the out drive. Viola, it then turned. Everything was basically out except for the block so why not rebuild? I WOULD LIKE to acheive 300-350 hp on pump gas.

Anyhow, I don't know the specs to the engine as it looks like it's been rebuilt already. I do know it is a 350 small block chevy with 2-piece rear main seal, 4 bolt mains, 4 bbl intake, rochestar q-jet carb. The crank and cam do not look healthy (pics below). I did not number the rockers nor the push rods. It has chipped #7 and #8 cylinder bases (probably why it was rebuilt before). The block is completely stripped down ready for the machining. Not sure if I should strip the heads too.

How can I acheive my 300-350 hp range with as little modifications.

If the crank is bad, I'll probably stroke it to 383. What else would need to change in this case.

I'm very opened minded here so please tune in and post you suggestion.

thanks!!!

 

[RCSConstruction]

Re: Help Rebuilding 350

Make sure your drive will handle the extra HP and TQ.
Getting 300 hp out of a 350 is easy, Vortec/ported heads with larger valves, manifold, roller cam, better carb. Stroker crank will get you higher..
Doesn't make it a good boat motor necessarily. Make your modifications to benefit the lower to mid rpm range.

 

[MikDee]

Re: Help Rebuilding 350

IMO, You may get to 300hp, but don't expect much more, because you cannot run as radical a marine motor, as a car motor, it has to be made stronger instead to pump through water. Compression can't be as high, a camshaft can't be as radical (has to be marine specific) and carburetion cannot be as big, simply because of marine condition's. Yes, you can bore it out, and or stroke it, raise the compression some, put Vortec, or good breathing heads on it, and fuel injection, but I don't know about blowers, or turbo's? If it's still available, look through a Mercruiser high performance marine engine brochure to get an idea of how they build up their motors, and what you can similarly do to your 350 block.

 

[Reel Poor]

Re: Help Rebuilding 350

If you are running an Alpha drive you are going to be limited to a maximum of 300hp. You can achieve close to that with a set of Vortec heads and a matching intake.

Stroking the engine could be hazardous to the outdrive.

 

[scott9398]

Re: Help Rebuilding 350

I have a couple of questions before you go any further. 1)When you say that the #7 and #8 cylinders are chipped are they actually missing part of the bottom of the cylinder (I cant tell from your picture)? 2) Which heads do you have? 3) Do you have a local machine shop which can rotationally balance the entire engine? 4) How serious are you about 350hp? Just going from what little info you have given, purchasing the new Mercruiser 383 might in the long run be your most reliable and economical route to take. Now before you say f@#k that and you're out of your f@#king mind let me explain. 1) If you do in fact have 2 cylinders which are missing a chunk of material off the bottom then don't waste your time rebuilding this block. It could evintually be the starting point for a cracked cylinder (metal fatique). 2) Judging from the picture of the block you have a dished pistons motor (lower compression probly 8.6:1 and lower horsepower) I highly doubt that you have the good Vortec or GM Performance Heads. This means they would need to be bought. 3) Most machine shops can balance a motor for rotating weight but fewer can balance while rotating. On a car this is fine however to make the kind of hp numbers you are after this motor will need to run above 4200 for extended periods and vibration is you enemy. 4) One of the main horsepower robbing component on a boat is the exhaust. You will need to convert over to thru hull (Really loud their cool sometimes and an annoyance most of the time) 5) Lastly you stated this is you first engine rebuild. I am not saying that you can't do this, even horsepower king Sonny Leonard had a first engine. However making 1 horsepower per cubic inch takes the right combination of parts and when you add up the cost of a new block, balanced rods, forged pistons, good heads, the right camshaft and all the other parts needed to make these numbers you will be really close to the price of that new Mercruiser. Only real difference is the professional assembly and warranty. One last piece of advise, with gas being 3.50/gallon and your boat not being a muscle boat you may want to look more seriously about simply doing a mild rebuild with a new set of vortec heads. That should be good for around 280 horsepower and be dependable. That's just my opinion I run a V-6 in my boat.

 

[blh1972]

Re: Help Rebuilding 350

I rebuilt my 350 this year it was a 87-92 roller block. I swapped out the old heads for a new set of vortecs, edelbrock performer manifold, and a mercruiser grind roller camshaft. then only additional item was roller tip rockers and I picked up 1000 rpm's over the 260hp merc I pulled out.
So I figure I'm at 300hp, with a nice smooth idle and no problems with overheating etc. hop this helps.

 

[John_S]

Re: Help Rebuilding 350

I would add to what Scott said, if it has been rebuilt before, and already bored 0.030 over, means you will be going to at least 0.060. Many would consider that too far for a marine engine.

It sounds like you will have drive and other boat repairs to do. A crate motor will save you allot of time along with $. A 280-300hp 350 or a 320hp stroker (heed drive warnings) crate motor is worth considering.

 

[lmannyr]

Re: Help Rebuilding 350

Thanks for all the responses. I was watching them tick in last night!! THANKS!!!

Here is more info.

1987 Alpha 1 1.5 Gear Ratio
Head cast # 93417368 ( anyone know the specs on these?).

A Scat Stroker will cost 175.00 New. What do the Vortec's go for? What are the pros/cons to sticking to the same heads (and everything else) and swaping to the stroker crank? Depending on the cost to repair the stock crank, I may go this route. Then I'll need new rods.

 

[John_S]

Re: Help Rebuilding 350

Vortec heads are around 275 each plus S&H. Plus 170 for an alum intake.
You would need the vortecs to get to your minimum hp requirement for the 350. Until you have had all the cleaning and inspection done, to know what can be rebuilt vs replace, to do the analysis.

 

[FreeBeeTony]

Re: Help Rebuilding 350

If the block is good..............

I would change to a roller cam/lifters and buy a set of Vortec heads and intake manifold........

Keep it simple..........

 

[SuperNova]

Re: Help Rebuilding 350

From personal experience I can tell you, that all B.S. aside.
1- your outdrive will handle the extra power.
2-A scat crank won't last long in a marine stroker application.
3-To rebuild your 350 to the power range you want and have the proper parts for strength to make it live at steady 4800 or so rpm it is going to cost you a minimum of $3500. That is if you can get all the machine shop labor and the parts at jobber cost and do all the assembly labor yourself. $3500 without a doubt before it is all said and done. If you go 383 it will be more.

As stated before, if the cylinders are damaged in any way, I wouldn't even bother with it. If it has been bored before, you need to think about it real hard. And you need to do an assessment on how much rust is already in the coolant jackets. Looking closely at the cylinder wall after the core plugs are removed should give a decent indication, but a sonic thickness test is the true proof. If there isn't a lot of meat there, then you'll be throwing yur money away.
--
Stan

 

[DreamBoater]

Re: Help Rebuilding 350

one advantage you do have is that is is a small block chevy and you can buy after market parts that even exceed the marine spec parts fairly cheap compared to the fords, IE eagle rods, Crank, Pistons and such. but if I was gonna do it I would look for a clean std bore block and be very meticulous on what I get. I have built a lot of motors for the circle track that would stay a 5000rpm all day long but like SuperNova said bare minimum is gonna be right around 3500.00. With that said it sounds like your gonna have with this boat when you are done Good Luck.

Scott W