More Ponies for 4.3

[marada1]

Sorry to bring up this subject again but I'm hoping to get a few questions answered.
Here goes...
I have a 1990 OMC Cobra 4.3L V6. It is a roller cam engine with 2bbl carb. and is rated at 160 hp. I have a set of 1996 Vortec heads (with rockers). I plan to buy an Edelbrock intake and 4bbl carb. (I run in fresh water only)
I've searched through hundreds of threads here and found many discussions on this. I'm hoping now to get some feedback from some people who have actually done these mods. (or have knowledge of) and learn of any problems I may run in to-and maybe some fixes for them.

Here's a few questions I have at this point:
Are the one piece (batwing) exhaust manifolds a problem with the vortecs?
Are the vortec pushrods different? If so, what is correct one?
Are there shift cable and throttle linkage brackets available that will bolt up to the vortec style intake manifold or will I need to modify the originals?
Is it worthwhile to change to the vortec heads? or is there more bang for the buck to just go to the 4bbl?

Thanks everyone for your input here!

 

[Bondo]

Re: More Ponies for 4.3

Are the one piece (batwing) exhaust manifolds a problem with the vortecs?

They Shouldn't be as the exhaust ports are in the Same place as the Non-vortec heads....
But,.......
The 1 piece Manifolds are a Problem all by themselves.......

I'm not Sure about the Pushrod lengths,....... I Believe they're the Same......

Are there shift cable and throttle linkage brackets available that will bolt up to the vortec style intake manifold or will I need to modify the originals?

With the Aftermarket Manifold,..... I believe you'll have to Re-engineer what you have.........

Is it worthwhile to change to the vortec heads? or is there more bang for the buck to just go to the 4bbl?

The 4bbl. Carb will net you about 20/25hp,......
The Vortec Heads will net you That Much Again.........

I've got the Heads,+ am hoping to complete the Swap this winter on My motor......

 

[marada1]

Re: More Ponies for 4.3

Thanks Bond-o,
What is the ploblem with the manifolds? I have had no issues with them so far. I have read something about water suck-back with vortecs. Anything to that?

 

[Bondo]

Re: More Ponies for 4.3

Changing the Heads shouldn't have Any bearing on it,......
Reversion is usually a Cam issue.......

I've never heard Anything Good about the 1 piece manifolds,+ Plenty of Bad News about them.......

 

[marada1]

Re: More Ponies for 4.3

I've read many posts that say "get rid of 'um" But never any specifics as to why. Only thing I see is they are "butt-ugly", but mine seem to do the job. Manifolds are expensive so until I have a reason, I guess I'm stuck with them.

 

[r33pwrd]

Re: More Ponies for 4.3

we did a intake manifold and 4 bar. carb on my friends 4.3 and WOW it was like we put a 350 into it! we did not do any linkage modifications.... the boat picked up 4 mph on GPS and the mid range power was amazing!

 

[Haut Medoc]

Re: More Ponies for 4.3

The problem with the one piece is that you can't inspect the insides at all....
You only know they are bad when they leak & ya get water in the cylinders.....
They are real expensive to replace & were hard to come by as well.....​

 

[marada1]

Re: More Ponies for 4.3

OK....Makes sense

 

[jdtower23]

Re: More Ponies for 4.3

I'm looking into doing something similar....have an '88 4.3 OMC....plan on getting a 4.3 Vortec longblock....I have the batwing manifolds but I'm not going to use them simply because they need replaced.....

I've heard you can possibly use a conversion kit for Mercruiser 1 piece manifolds since they are similar in shape....I think the main thing you need from that is an elbow that turns down....

Looked into the OSCO 1 piece replacement kit and they say not to use with Vortecs and heard from many sources that it is because of water reversion....i don't know why.....

Here is a pic of an install done by MichiganMotorz....they used the batwings with the Vortec....don't know how they rigged the shift bracket but you can see it's leaning and not going straight up.......

"http://www.michiganmotorz.com/article_info.php?articles_id=7

Let me know how this progresses

Thanks

 

[180shabah]

Re: More Ponies for 4.3

DO NOT skip the Vortecs. You already have them, use them.

4.3 w/Vortec heads, stock cam and Edelbrock(2114 I believe) manifold will net you an honest 225-230hp, quite a jump from 160, and more than most 5.0's(the EFI's w/vortecs were rated 250-270). If you really want a screamer, call Comp Cams and they will halp you with the PN's for marine use, end result you can have a 4.3 puttin' out approx 260 horses while weighing more than 130 pounds less than a 5.0L

For those of us with balance shafts, the gains are the same +/- but we have to subtract 25-30hp accross the board, that thing sucks up some power to spin.

 

[marada1]

Re: More Ponies for 4.3

Thanks guys. The heads are going on for sure. I think I'll get to look'in for some two piece manifolds too.
Anyone got any ideas about the pushrods?

 

[180shabah]

Re: More Ponies for 4.3

Sorry, pushrods are same length.

 

[marada1]

Re: More Ponies for 4.3

Took my Vortec heads to the machine shop yesterday. I was talking to the machinist there about this upgrade and he wondered if the piston geometry in a Vortec engine might be different. I'm thinking the compression ratio difference is due to the cyl head only. Does anyone here know for sure?
Thanks

 

[Bondo]

Re: More Ponies for 4.3

I'm thinking the compression ratio difference is due to the cyl head only. Does anyone here know for sure?

Ayuh,......
The Vortec Heads Do in fact have a smaller chamber,......

Have you pulled your Heads,+ Looked to see which pistons the motor has in it,..??.....
Some are Better than others,...... But they'll all run with Vortec Heads.....

 

[marada1]

Re: More Ponies for 4.3

I know what pistons I have 423NP. Don't know what the vortecs have.

 

[Bondo]

Re: More Ponies for 4.3

I know what pistons I have 423NP. Don't know what the vortecs have.

Ayuh,.......

Unfortunately,...... That means absolutely Nothing to Me.........

Are they Flat-Top pistons with Valve Reliefs cut in them,..??... How Many,..??...
Are they Dished Pistons,..??.....
How far down the cylinder are the tops, when at TDC,..??..??...

 

[marada1]

Re: More Ponies for 4.3

Ha Ha... sorry dude. It didn't mean anything to me either, thought it might to you guys. It is a dished piston with valve relief.
Here's the specs....
http://info.rockauto.com/SealedPower/423NP.html
Have not pulled my heads yet so this is all I have right now.
Here's a pic
http://cgi.ebay.com/ebaymotors/Chev...emQQcategoryZ33623QQihZ002QQitemZ120153332079

 

[Bondo]

Re: More Ponies for 4.3

Ayuh,........

That's Not the Best Choice for getting All there is to Get from the Vortec Heads,.........
But,......
If you can get the Quench of the Top of the piston to .040,......
That'll be as Good as it Gets........
That's why you need to know How Far down th cylinder the piston rises to,+ the Thickness of your Head Gasket.......

 

[marada1]

Re: More Ponies for 4.3

I've got the Heads,+ am hoping to complete the Swap this winter on My motor......

So Bond-o, what pistons do you have in your 4.3? What model engine ,etc.?

Just looked at Rapido's site. The pics they show of thier 4.3 Vortec looks like the same piston.

 

[mtnrat]

Re: More Ponies for 4.3

I think he means some thing like this D dish or "quench" piston.

The flat area on the piston corresponds to the flat area on the heads. At the end of the compression stroke the air fuel mixture is squished out from between the two flat areas causing turbulence in the air fuel mixture and a more complete burn. They are generally used when a flat top piston results in too high of a compression ratio. An interesting side effect is because of the efficient burn a higher compression ratio can be run without detonation. The ideal space between the flat spots is about .040" made up of the cylinder height above the piston at TDC, and the crushed gasket thickness added together.