1990 OMC 4.3L Equivalent and Swap Complexity???

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Your problem is adapting from the outlet of these new risers to the inlet of the Y-pipe if the diameters are different. That is what Bondo is saying.

Okay, I took some measurements and this is what I came up with. The i.d. of the original manifold riser outlet, is 3" which dumps into a 4" coupler connected by a couple boots or bellows. The angle of the original riser is 30 degrees, and I can get a 30 degree riser for the new manifold. The i.d. of the new riser is less than 3", but the o.d. is 3", but I'm not sure if the smaller i.d. is enough to cause concern. The only accessories on the original manifold are the water inlet from the thermostat housing and the pitcock drain, both of which are on the new manifold. The only change is that the port inlet will be on the backside of the manifold instead of on the front. I think I could live with that. Any comments, details I may be missing?? I really do appreciate all the insight, fellas. Your knowledge and expertise is invaluable, to me. Thanks!!

 

[bruceb58]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Why are you worried about the ID of the riser outlet when the hose goes on the outside?

 

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Why are you worried about the ID of the riser outlet when the hose goes on the outside?

Well, my only real concern is the amount of, if any, back pressure the smaller diameter might generate. Is that a non-issue? I just don't want to miss any details that could come back to bite me after the rebuild. The way it's looking, I think the exhaust system I found will work pretty good. Can you see any reason to think otherwise? Thanks.

 

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Hey Fellas.... I just wanted to update and get some feedback on this whole crazy idea me and a buddy have cooked up. First of all, I finally got the engine out after a very long delay. The engine is stripped and ready to be blasted and sent to the machine shop. She actually looks pretty good. So, the end result of the swap idea, is to just rebuild the 4.3L that's in it. It's all about the same price anyhow, and this way I get to spice things up a bit, which leads me to my next quest for knowledgge.

I want to beef up this engine a bit. I'm not cool with 175HP. My plan is to bore & hone the cylinders .030, re-surface the heads, replace the pistons with a flat top hypereutectic four valve relief set, using Total Seal gapless file fit rings (2nd ring), replace the rocker arms with 1.7 roller tip rockers, replace the stock roller cam with an L79 cam GM part #10051147, complete port, polish and port matching, and so on and so on.

The final dig should be around 275 - 300 horse power when all is said and done, and it's really a comparable cost to buying a factory replacement. I also plan on using a triple exhaust setup. The things I am unsure of, are the capability of the outdrive to handle the horse power increase. I know the Cobras were used on V8s too, so I was wondering if anyone could offer me some feedback on the outdrives range of torque. I plan on rebuilding the outdrive, but are there things I should consider before I proceed? Also, how can I make sure I get the right prop for my setup? Is there a formula or anything? I appreciate any and all insight. Thanks, guys.

 

[Tommywalton]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Fuel and air in the right ratio+ spark at the right time+enough compression= running engine. You already have compression and its you said it still wont run when you dump good fuel in it. Fix the ignition

 

[Tommywalton]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Oh i didn't see that last post. Sorry

You are about to spend MONEY

 

[Bondo]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

I want to beef up this engine a bit. I'm not cool with 175HP. My plan is to bore & hone the cylinders .030, re-surface the heads, replace the pistons with a flat top hypereutectic four valve relief set, using Total Seal gapless file fit rings (2nd ring), replace the rocker arms with 1.7 roller tip rockers, replace the stock roller cam with an L79 cam GM part #10051147, complete port, polish and port matching, and so on and so on.

The final dig should be around 275 - 300 horse power when all is said and done,

Ayuh,.... Looks like you, 'n yer Bud have been readin' to many Hot Rod magazines....

The .030" over-bore doesn't increase horsepower, it just cleans up the cylinders...

Insteada flat-top pistons, you should be lookin' at Vortec heads, 'n D-dished pistons,...
With the quench cut down to .042" to .046", 'n the compression ratio at 9:1 or slightly Better,...
The Vortec heads will provide yer Hp boost...

I donno the Spec's on that cam, but would like to know,... I'm guessin' it's probably Too Big...

The 1.7 rockers, 'n the port, 'n polish is nothin' but a waste of time, 'n money....
Valve lift, 'n timin' is done with the Cam, not the rockers,....
'n the port, 'n polish don't do squat at the rpm levels We run boat motors at....

 

[Tommywalton]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

I have to agree with bondo this time. You can bench race all day and put a hot street engine in a boat. A street engine hates a loaded heavy boat trying to plane at 3000rpm when it wants to peak at 5500. Ive done it already and now im doing what bondo is talking about. Vortec 5.7 heads are designed to flow best below .450 valve lift. They are astonishing between .300 and .400 lift. Your vortec heads w the d-dish pistons are the way to go

 

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

Ayuh,.... Looks like you, 'n yer Bud have been readin' to many Hot Rod magazines....

The .030" over-bore doesn't increase horsepower, it just cleans up the cylinders...

Insteada flat-top pistons, you should be lookin' at Vortec heads, 'n D-dished pistons,...
With the quench cut down to .042" to .046", 'n the compression ratio at 9:1 or slightly Better,...
The Vortec heads will provide yer Hp boost...

I donno the Spec's on that cam, but would like to know,... I'm guessin' it's probably Too Big...

The 1.7 rockers, 'n the port, 'n polish is nothin' but a waste of time, 'n money....
Valve lift, 'n timin' is done with the Cam, not the rockers,....
'n the port, 'n polish don't do squat at the rpm levels We run boat motors at....

Thanks for the comments, Bond-o, but this isn't a hotrod magazine day dream. My buddy is a certified GM high performance guy and the specs we are looking at come straight out of a GM high performance factory manual.

Boring .030 over does more than clean the cylinder walls, hence the need for larger pistons and rings. If it was just a matter of "cleaning" them up a simple honing would do. While it may not give me a huge increase in compression alone, when coupled with all the other improvements it will find it's place.

I don't see a real need to swap the heads. The Vortec heads are not that impressive and the same effects can be achieved through other areas of modification. The flat top pistons coupled with the gapless rings will create an equal, if not higher, compression ratio as the D-dish with vortec heads.

The L79 camshaft is actually a GM specific replacement for the 4.3L 90degree V6 factory roller cam. The L79 is the same size as the factory cam with a modified lobe design that actually increases duration rather than lift. The extra lift is generated by the repositioned fulcrum center of the 1.7:1 rocker arms.

I really don't understand why you believe porting and polishing is a waste of time. Creating superior flow and volumetric pressure have everything to do with a more efficient and complete burn. The numbers of its gains have been proven on flow benches for decades, so I think you must be confused. And the cost is irrelevant when you do the work yourself. It's not a complicated procedure, but worth the time. Unless you're a Mopar guy who just like to burn fuel and doesn't care about the efficiency of his engine.

As it is clear that we have different ideas about what is a better route to take concerning the engine build, what about the outdrive? The purpose of my post was to find out if there will be any issues with using it with the new engine configuration. Will the outdrive play nice with the increased HP or do I need to consider a swap or something? Thanks for the input, fellas.

 

[Bondo]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

I really don't understand why you believe porting and polishing is a waste of time. Creating superior flow and volumetric pressure have everything to do with a more efficient and complete burn. The numbers of its gains have been proven on flow benches for decades, so I think you must be confused.

Ayuh,.... Maybe, probably not though....

Marine exhaust manifolds are like a Brick Wall to yer plans,....
They're an open plenum, common passage, then stuffed underwater through the prop....
Oh, 'n thru-hulls don't change a Thing,... it's the Manifolds/ risers....

Boat horsepower, ei: Torque is made from idle to 4800 rpms....
Nothin' you can do will pay the benefits of a properly set up Vortec headed SBC....

The 4.3l is still the little sister,... same rules apply....

Vortec heads, decked block to .043" quench, 'n D-dish pistons is the near perfect startin' point of a Boat motor...

Still don't know what the cam is,... If it came stock in a Truck,... it'll work pretty darn Good...

Good luck anyways,... Go read the 383 threads in the non-repair I/O forum for some pointers....

 

[Tommywalton]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

I just assembled mine today. Factory 98 vortec with edlebrock rpm and marine 600cfm. Ill let you know how it runs. Also an omc will grenade on you if your transom shift cable is all wacked out. I dont know if in my case a cobra could handle a 5500 rpms for long anyway at 375 hp. Oh yeah if you build that engine do yourself a favor and us glm manifolds at least.

 

[Tommywalton]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

On thr prop question. I have a 23' boat that does double duty. When its loaded up i run a 4 blade 15" 15 pitch prop. I also have 3 blade props in 17,19 and 21. No calculator ever worked for me. One prop does well for cruising with light load, one for heavy load. One for high speed light load, on for any load towing/wake boarding. I have a wrench that floats and carry extra nuts and pins. Change them often. I run the 17 pitch the most

 

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

http://www.mooreperformance.info/volvoV6kit.html

Ayuh,.... Maybe, probably not though....

Marine exhaust manifolds are like a Brick Wall to yer plans,....
They're an open plenum, common passage, then stuffed underwater through the prop....
Oh, 'n thru-hulls don't change a Thing,... it's the Manifolds/ risers....

Boat horsepower, ei: Torque is made from idle to 4800 rpms....
Nothin' you can do will pay the benefits of a properly set up Vortec headed SBC....

The 4.3l is still the little sister,... same rules apply....

Vortec heads, decked block to .043" quench, 'n D-dish pistons is the near perfect startin' point of a Boat motor...

Still don't know what the cam is,... If it came stock in a Truck,... it'll work pretty darn Good...

Good luck anyways,... Go read the 383 threads in the non-repair I/O forum for some pointers....

Thanks Bond-O, for the reply.

Actually, the GLM exhaust manifold found http://www.mooreperformance.info/volvoV6kit.html uses individual runners rather than an "open" plenum.

The torque that you speak of is actually made at 5250RPMs, and that is the standard for all gasoline engines capable of making the RPMs. My configuration puts that number at 300ft/lbs of torque with 325HP at 5250RPMs, which is why I went with the L79 camshaft. The lashpoint duration is 318/318, the tappet lift duration is 222/222, lift is .447/.447 and a 114 degree lobe centerline. This camshaft was made for V8s, but GM made a V6/90 version. If you look at the data from the Desktop Dyno, in the image below, you can see where the torque for this configuration sits after plugging in most of the numbers.

The heads that are on my engine are more than sufficient for achieving maximum torque and are actually the first generation vortec design complete with factory swirl porting.

I appreciate your input Bond-O, and I am not trying make it seem like you don't know what you know, but in turn, I know what I know too.

What I would like to know, Bond-O, is how the outdrive will handle the higher torque? Any insight on this little matter would be greatly appreciated.

 

[genuinegemini]

Re: 1990 OMC 4.3L Equivalent and Swap Complexity???

On thr prop question. I have a 23' boat that does double duty. When its loaded up i run a 4 blade 15" 15 pitch prop. I also have 3 blade props in 17,19 and 21. No calculator ever worked for me. One prop does well for cruising with light load, one for heavy load. One for high speed light load, on for any load towing/wake boarding. I have a wrench that floats and carry extra nuts and pins. Change them often. I run the 17 pitch the most

Thanks for the info, Tommy. I read a lot about the shift cable issues with these outfits. I didn't realize you needed to have that many prop options available to you. I know a bit about engines and things, and I know a good bit of terminology in regards to boats, but I don't really know boats very well at all, hence the forum posts. Everyone here is very helpful and knowledgeable about a lot of different areas surrounding boats and engines and whatnot. Thanks for the GLM suggestion, but I already had it saved in my favorites. I searched for a good long while trying to figure out that aspect. I kept getting all this "not compatible" feedback and it really had me wondering, but after some serious investigating and logical thinking, it became obvious that the only real, bonafide difference is the wet exhaust. The more I read and understand the more I see where there is lots of room for modification and one-offish fabricating.

The chevy V6/90 is essentially a SB V8 with the #3 and #6 cylinder removed and then "smushed" together, so to speak. Many people think they are just "chopped off" at one end or the other, not so. I would be interested to hear how your engine performs after your recent assembly. I'm going to investigate the prop situation a little more thoroughly before making and finalities. Thanks again, Tommy, for the insight. It's much appreciated.