My Upgrade Options..

[imported_TheMan]

I've got a 91 4.3L engine with 2 barrel carb. Like many others I am looking at upping the performance a bit. I've been reading over old posts as usual and just want to make sure of a few things.

RECAP:
I've got a set of used Vortec heads that I would like to switch out and am planning on getting a 4 barrel carburetor and intake. I've heard that all the AFB clones are basicallythe same, so I don't know what route I will go on that.. probably depends on what i can find on the cheap. The Mercarb quadrajets seem to be pretty cheap on ebay. Any issues with the 4.3L model in an advanced setup or would it be better to go with a larger engine model? I know that wca_tim said he had to change metering rods a few times to get his boat running well with the Edelbrock intake/carb setup. Would the parts from an edelbrock strip kit work on a Mercarb or are the threads and such different?

Another big question is whether the Edelbrock Performer 4 barrel intake (#2114) truly offers any increase in HP as compared to the GM 4 barrel intake. The claim is 18 HP on Edelbrock's website.. I'm a little bit doubtful, or at least pretty uncertain whether the price/performance ratio is worth it. Anyone actually done the Bondo 'seat of your pants' test?

Thoughts? Guesstimates on resulting HP? From other people's posts it looks like it should be in the 230 HP range.

Any advice is appreciated as usual.

 

[John_S]

Re: My Upgrade Options..

This link was posted by Mikdee. I think you will find it very useful: http://www.s10forum.com/forum/f107/the-holy-grail-of-4-3-info-131868/

Carbs:
- A mercarb is a Mercruiser specific 2brl carb.
- Q-jet is a 4brl carb, 750 cfm spreadbore.
- Edelbrock 1409, 600 cfm squarebore.
For your app, I'd suggest the 1409. There is a 4.3 kit for it, but I would buy the strip kit and just use the jets and rods choosen in that kit as a starting point.

Intakes:
I'm not up on the 4.3 vortec GM vs Edelbrock. The performer series is usually better than the stock intake. 10-15hp would not surprise me.

HP Estimate:
Your build is very close to a current stock 4.3L MPI. You will get slightly less than an MPI, because the induction is more efficient than a carb intake. So, around 210-215Hp at prop. Sounds like you are starting from a 2brl 4.3, which is about 155hp at prop. 60Hp is a decent increase.

Note: From a recent discussion, there was an indication that pre-balance shaft 4.3s have some additional hp. So you might have a few more hp than that.

 

[Lou C]

Re: My Upgrade Options..

I have a pre-balance shaft pre-Vortec 4.3 with the Rochester 4 bbl and it was rated at 205 hp but who knows how much it actually puts out.
One thing I would wonder about, is that I had heard that the Vortecs tended to pull water up the exhaust more than the non Vortec, don't know if that is true, but it would be worth looking into before re-doing the engine. Like did Merc/Volvo change the exhaust system when they went to Vortec?

 

[John_S]

Re: My Upgrade Options..

Lou,

The reversion problem is with the roller cam and not the heads. The V8 has it too, but reportly not as bad as the V6.

There was a recent discussion on hp of the 4.3L in of all places, a SBC V8 thread. I believe the hp numbers you are quoting are from engines that were rated at the crank vs the prop. The way all marine engines were rated changed in mid-late 80's.

 

[marada1]

Re: My Upgrade Options..

Almost done with this exact upgrade, just waiting on new exhaust manifolds. Should have it on the water in a month or so. I'll post some before and after numbers then.
I'm a little concerned about this "reversion" thing. Can someone give me more info? I have a 1990 pre-balance shaft roller cam engine. Is there something I need to do to prevent this?
Thanks

 

[Olds Eddie]

Re: My Upgrade Options..

I would put riser extensions on her. I have Imco stainless risers on my engine and have no reversion problems.

 

[wca_tim]

Re: My Upgrade Options..

I'm currently running a 4.3 with the pre 94 style block, electric fuel pump, vortec heads, edelbrock 1409 carb and performer intake, factory roller cam and exhaust and about a 10:1 compression ratio. I think it runs really well for a 6 cylinder - I easily keep up with the average 305 and even 350 rigs (given my boat is fairly light ca. 2500 pounds loaded, getting consistent 50 - 60 mph gps depending on prop and conditions). Based on what the previous owner indicated for the original 4.3 2-bbl, I'm probably running 8-10 mph faster than the stock 1988 2 bbl 4.3. I don't have a direct sat of the pants comparison for incremental upgrades, but especially if you add the greater flow of the vortec heads and more carb, it would seem the intake would net the claimed horsepower gains and don't forget the weight loss with the aluminum intake. The Edelbrock carb was trivial to set up and came with good documentation. Edelbrock's tech support people were right on the spot too when it ran too lean out of the box with my set-up. I'll be happy to look at my notes and see which metering rods and springs I wound up with if you like.

Honestly, I think a mild cam upgrade would do wonders for the current set-up I have and really wake up the midrange and add a good bit on the top end - it clearly runs out at about 4600 - 4700 rpm... I'm in a light boat though, if a heavier rig ,the torque out of the hole right now is great! I'm taking this engine out in the next month or so so am not going to play with it any more at this point. I would also bet that I'm not using all of the carb flow capacity - based on presumed volumetric efficiency, displacement and the simple fact that the last bit of throttle doesn't really seem to net any additional horsepower or speed, just a little more noise and different sound... This wasn't unexpected though and doesn't seem to hurt anything on the lower end with the current jets.

Not sure what you're specifically trying to do, but I have a spare set of heads that might be usable for a porting experiment, the original roller cam and parts valve train out of a similar 4.3, etc... I don't know that you would have any use for them, but seeing as I only live about 35 min up 43 from you, let me know if you might make good use of them... They're not doing anyone any good showing the first signs of rust on the back porch...

Finally, I'm currently using (new) factory exhaust running through prop with exhaust tube and have seen no signs of inversion.

Hope this is helpful.

 

[wca_tim]

Re: My Upgrade Options..

OH! I just remembered that the 350 I bought to use as a starting point for the current build came with the factory quadrajet and 4-bbl manifold... I'll have a look and see what the carb looks like when I get home from the office later today...

 

[imported_TheMan]

Re: My Upgrade Options..

Well.. I guess I would like to go faster and have more power... eventually

I really only use the boat for wakeboarding at this point and time. I am planning to build a tower eventually here.. Buying a house soon so I don't really have the time or spare money right now. I was able to get up and cruise along on the 3L earlier, but for other people (my 220lb brother) it wasn't so easy. The 3L also was unable to power through turns. I am also pretty competitive and one of my friends bought an '88 Liberator with a 350 (OMC... boo). He goes faster, so I would like to faster too. So I bought a junk boat with a decent 4.3L to swap out of it for $660. I sold the trailer for $200, 3L motor for $550, and have some additional spare parts off of it I would like to get rid of (hydraulic cylinders, trim pump, loads of SS, bell housing, gimble ring, etc.). All in all, I expect to come out about even on the project at this point... I wasn't trying to make any money off of it, just recouping some dough. I expect my UPGRADES to cost me a bit. (I'm thinking $400-500 for everything I want to do engine related)

I have NOT switched outdrives yet. I plan to likely purchase a complete SEI outdrive with the proper gear ratio in the future, but I am just waiting for the right time. Thus I am running the 2:1 gear ratio for the time being and am going to experiment with some props to see what happens. If it shears to bits, it shears to bits. Currently I was running a 17p prop that was on the boat before. It put me at 36mph with the 3L at 4500 RPM or so. With the present engine I have not had the tachometer calibrated right and just got a separate inductive tach to verify numbers. I was running at 42 mph WOT and would guess I was overrevving the engine above recommended numbers at around 5200 RPM. Obviously I want to get the most bang for my buck for the present situation so I am gonna try out a 23p prop and see what happens. I'm gonna also experiment with a 21p to see as well.

The difference between the 3L and 4.3L for me is amazing. I kind of suspect that the 2:1 gear ratio provides me better hole shot than I would get with the 1.84:1.. but that might be in my head as I haven't sat down to really calculate it out. I'd like to beef up the power the engine has just so it is there for acceleration purposes. Top end really isn't that important to me, although it is nice.

Like I said, I've got the Vortec heads on hand and will probably port them for the sake of doing it. I just haven't decided whether to essentially build it to the stock GM settings or go with the Edelbrock setup. I'm probably leaning towards the Edelbrock, especially if I get a bonus of some sort this year.

My 230HP estimate was based on the engine not being a balance shaft engine. Although I have no personal experience, other users have said the balance shaft eats 25HP. 205 HP + 25HP = 230HP. It's probably not that cut and dry, but oh well. If the Edelbrock intake improves it at all over stock, I would think it would be pretty close.

You live in greenville, tim? If you could find your notes on the carburetor settings it would be much appreciated.

 

[marada1]

Re: My Upgrade Options..

Hey Tim, I would also be interested in your notes on tuning the carb.
Please post!

 

[John_S]

Re: My Upgrade Options..

If you are looking for stock v8 settings: http://forums.iboats.com/showthread.php?t=189135

From '94 Merc Tech Manual: http://www.boatfix.com/merc/Techbk/94/94hg5c.pdf

Great Q-jet tuning info: http://www.florida4x4.com/tech/quadrajet/QJet_Tuning_Paper.doc

Sorry, couldn't find any Merc Q-jet setting for the 4.3L, just weber 4brl.