Built 350?

[Josh in Pa]

I have a 350 in my '92 GW invader. It was professionally rebuilt last year. (Heads were not rebuilt). I am thinking about putting on the vortec heads and intake this year, but wonder if the compression will be too high with the new flattop pistons? Are their any other things I can try for a little more oomph? It has a 4 barrel. The motor was rebuilt with a "marine performance cam" (no known numbers) and it has a real smooth idle, and very good low end power, but I am thinking a different cam might help my mid to higher rpm? Any other ideas? I know the best idea is to probably leave it alone, it seldom gets driven real hard, but I like to tinker. Thanks for any help,
Josh

 

[Fishermark]

Re: Built 350?

I am thinking about putting on the vortec heads and intake this year, but wonder if the compression will be too high with the new flattop pistons?

You should be fine with the flat top pistons. You might need to run premium... but maybe not.

I know the best idea is to probably leave it alone, it seldom gets driven real hard, but I like to tinker. Thanks for any help,
Josh

"I like to tinker" - that can get expensive quick... but is a problem most DIY's have. I would suggest doing one thing at a time. Put the vortecs and intake on first and see how you like it. I think messing with the cam will add too many potential problems with no real value. Most of the high performance cams will either cause reversion problems or will only see benefits above the red line rpms for your engine.

 

[FreeBeeTony]

Re: Built 350?

I like to tinker also................it's dangerous.........

Just a thought looking ahead.........if you do the Vortecs, keep in mind that they do not handle too much lift stock...........if you think you might change the cam at a later date I would look into modifying the Vortec before you install them..........

I have been thinking of doing this if I ever need to remove my engine again........

 

[Fishermark]

Re: Built 350?

Tony brings up a good point with the vortecs - even with your existing cam. Since it is not stock, and you don't know the specs - you need to at least find out the lift. Vortecs can handle up to .480 inch without any modification - more than that and it will require some machine work.

 

[Bondo]

Re: Built 350?

but wonder if the compression will be too high with the new flattop pistons? Are their any other things I can try for a little more oomph?

Ayuh,...

If you don't know what you've Got,...
It's kinda hard to tell you which direction to proceed......

 

[180shabah]

Re: Built 350?

Have you considered a prop change? Don't know what you are trying to accomplish, but you may not need to get into the engine.

 

[TilliamWe]

Re: Built 350?

I am thinking about putting on the vortec heads and intake this year, but wonder if the compression will be too high with the new flattop pistons?

My 1997 5.7LX EFI Gen + engine had Vortec heads & flat top pistons, straight from Mercruiser. And a compression ratio of 9.2, I think. Anyway, it ran just fine on 87 octane.

 

[Josh in Pa]

Re: Built 350?

I have an idea what I've got. I believe the stock heads are 72cc, and a vortec head is 64 cc. From reading, the 64cc with flattops will put comp over 10. Also from reading, this will run in a car (on premium pump gas) but maybe not so well in a heavier vehicle. I'm wondering if anyone has done it in a boat before? I don't want to change props, I currently have a 21" and WOT is about 4400. I'd like to keep the same prop, and spin it a little faster, maybe have a little better acceleration too.
Josh

 

[Bondo]

Re: Built 350?

Ayuh,...

Without knowing how far down the bore TDC is,+ the thickness of the headgasket,...
You're still shooting in the dark...
And,..
Without a Casting # for what you're calling the Stock Heads,...
There's No way of knowing the chamber CCs....

 

[John_S]

Re: Built 350?

My 1997 5.7LX EFI Gen + engine had Vortec heads & flat top pistons, straight from Mercruiser. And a compression ratio of 9.2, I think. Anyway, it ran just fine on 87 octane.

Do you have pictures? If you check part numbers, it shouldn't have had them. As far as I know, the recessed pistons started in late 80's/early 90's, when they went to 64cc heads (not-vortec, 217s?). There were some slight pistom changes, but the recess stayed through the vortecs. The recess accounted for approx 10-12cc.

 

[TilliamWe]

Re: Built 350?

I will try to find the pictures. I too was surprised to see the pistons it had. They looked NOTHING like the pistons in a 1987 truck engine that we installed in a boat. Those had an obvious dish to them, mine did not.

 

[Fishermark]

Re: Built 350?

I built the engine in my car - the one pictured in my avatar. It is a 350 from an 88 Suburban. I bought new Vortec heads from the Chevy dealer. I used flat top pistons - which, if memory serves me correctly, had either two relief or four relief cut outs for the valves, but were not dished at all. At the time I figured the quench, etc with the head gasket thickness. but those exact numbers escape me now. Anyway, the engine runs great and runs just fine on regular, 87 octane gas. If it gets in a situation where it wants to "lug" it will certainly start pinging pretty quickly. That's something you want to avoid of course, so you will need to listen and get to know what your engine "likes." You don't want to load it up so that the WOT is only in the low 4000's that's for sure.

 

[180shabah]

Re: Built 350?

....I don't want to change props, I currently have a 21" and WOT is about 4400. I'd like to keep the same prop....

You may or may not get your wish, your engine will tell you what IT want after you get it back in the water.

 

[Mkos1980]

Re: Built 350?

Heres pics of my 90 5.7L that I put the Vortecs on. The stock 217 heads had 64cc and the new vortecs do too so nothing changed. I added the roller valvetrain. It was flat tappet before. Pic of LT4 HotCam going in.

 

[Mkos1980]

Re: Built 350?

Looks like flat tops to me with 4 valve reliefs. Also with the combo I went from 4400 RPM with the 21P Laser I was running and now I'm running right around 5400RPM's with the 21P Laser

 

[TilliamWe]

Re: Built 350?

And to me, those look dished. I remember mine looking even flatter than that with valve reliefs. But I could be "mis-remembering", and the wife deleted the photos.