4.3lx intake manifold question

[Lt1z350]

I found some posts on this but no one says I gained x from the swap. Some are 2bb to 4bb so those don’t work.
I got a 94 4.3lx non vortec heads. I see edelbrock has an intake and they claim 18 hp vrs the stock merc cast iron. I have not taken off the carb but stock looks to be open plenum single plane which has been proven to be terrible from idle to 4500 rpm vrs any kind of dual plane intake and that’s the range on this motor. So that alone says the Edelbrock should be much better in the 4.3 rpm range.
What I was hoping to find was someone that did it and posted I was 43 mph with stock and now 48 mph with new intake. More air probably will lean it out there seem to run a little rich stock on this 4 bbl stock carb. I might do the 1409 at same time which I did find guys that posted what jets and rods worked best. Unfortunately no way to put a wideband sensor and tune it perfect as I have a stand alone setup for tuning cars. So tuning your plugs and peak mph will net the most hp.
I just re proped the boat to a 4 blade 19p and hole shot is excellent now but wot is 4300 rpm and 44 mph and I’m trying to eek 50 from it if possible then cruise at 35 should be a little more efficient. Plus have that flat out speed if I want it.
I do not want to do heads as I’m going to v8 swap it down the road so intake and crab gains maybe rocker arms as I have them depending on if I feel like taking the exhaust off to gain 8-10 hp from it. I guess this motor is 180 hp some say the crate engine is 225 now maybe different cam I know the later better heads but seen 190 hp on that model so many hp numbers on a lot of the same parts so wondering how much of that is also in engine timing.
But anyone that did the swap and can tell me exactly the gains is much appreciated.
Thanks

 

[Rick Stephens]

Never see a big speed difference. You might gain a couple seconds on hole shot. Takes more torque to increase boat performance - mild - correction - VERY mild horsepower changes will not have much effect.

 

[Lt1z350]

Right now the holeshot is just about 3 seconds I don’t see it get any better then that. Lol it comes up so fast on this new hustler prop and lost no wot at all. But rpm is lower from 5000 rpm on the 3 blade rubex to now 4300 on this 4 blade. Same 44/45 mph depending on water conditions. So was thinking a little jump in hp will gain back some rpm which will equal mph also. This design intake seems to be a poor choice on this motor but maybe they know something I don’t on it.

 

[Rick Stephens]

I don't see the intake doing enough to matter. Definitely cheaper to swap prop to tune things to perfection. Might consider a little faster prop and venting it to get the hole shot.

 

[itsathepete]

Not saying you're wrong, but are you sure the manifold is a single plane or if so is it original. Boats typically use a dual plane manifold and if your holeshot is good, that's probably what it has. Doubt you'll see any performance increase from a manifold and carb change unless you're going 2bbl to 4bbl and vortec heads.

 

[Lt1z350]

Short runner single plane iron intake. It has a slight divider not very tall. But not a true dual plane long runner made for torque and lower rpm like this motor.
I called edelbrock they claim 18 hp from the tech department. Took a 180 hp 95 down 4.3 and made 202 I guess the original intake made 184 he wasn’t very clear on it.
But I don’t like the design of this at all. If it was to really pick up 15 hp or more I’m sure it comes at a more useable rpm also. I found one under 300 bucks so might just try it as know where boat stands right now. If it makes more torque it will cruise at a lower throttle /rpm make same mph for cruising around point to point.
I’ve seen a 4 hole version of this manifold also. Was on a Volvo penta 4.3 motor which was more of a dual plane longer runner design. I’ll try to find it again and post picture.

 

[Lt1z350]

Just says marine high rise but has egr which is Odd. It’s a lot taller then what’s on this boat but can see it’s dual plane.

 

[achris]

Making more power is a double edged sword..

Advantage- who doesn't want more power? But I'd be interested in the torque numbers, not the maximum power.

Disadvantage- when the engine makes more power you need to change the prop to keep the engine in the recommended revs range. That change is reflected throughout the entire range, not just at the top end, so you may end up with a boat with a higher top speed, but struggles more in the midrange (due to a taller prop)....

The decision you need to make should be based on torque not power...

 

[Rick Stephens]

The decision you need to make should be based on torque not power...

Zactly


Hard to get more torque without adding more cubic inches

 

[itsathepete]

Its definitely not marine. Probably from an 85 or 86 gm truck which are just about the only carbureted 4.3 applications.

 

[achris]

Zactly


Hard to get more torque without adding more cubic inches

Advancing the cam timing adds torque... (At the expense of peak power though. Always the compromise)

 

[jimmbo]

Advancing the cam timing adds torque... (At the expense of peak power though. Always the compromise)

If a bit more initial timing helps the Bottom End, then just change the advance curve of the Distributor to limit Centrifugal Advance. The OP's engine sounds old enough to have a Mechanical Advance Distributor. Heck, my 2002 Volvo 5.7 has one.

 

[Scott Danforth]

installing a carb spacer and increasing plenum volume increases low and midrange

BTW, Volvo Penta manifolds and Edelbrock manifolds both come out of the exact same casting boxes at Buddy Barr castings.

Not sure what your issue is with your motor, however I suspect tuning and potentially carb issues. cant swap manifolds and not tune the carb.

More air probably will lean it out there seem to run a little rich stock on this 4 bbl stock carb. I might do the 1409 at same time which I did find guys that

the motors with higher power have vortec heads

if I feel like taking the exhaust off to gain 8-10 hp from it. I guess this motor is 180 hp some say the crate engine is 225 now maybe different cam I know the later better heads but seen 190 hp on that model so many hp numbers on a lot of the same parts so wondering how much

what is is you are trying to do?

if you want a bit more power, swap to vortec heads and a vortec intake and properly tune the carb

if you want a go-fast boat, pull the V6 and install a V8

 

[jimmbo]

BTW, Volvo Penta manifolds and Edelbrock manifolds both come out of the exact same casting boxes at Buddy Barr castings.



if you want a go-fast boat, pull the V6 and install a V8

I certainly can't argue with last comment above.
I have the 4bbl intake on my 5.7 Volvo, and I will agree it looks very much like an Edelbrock, but I did see some difference

 

[Scott Danforth]

@jimmbo I had an opportunity to tour Barr when working on the Verado CAC. They make castings for Edelbrock, Volvo, PCM and many more. Lots of design commonality across various brands

 

[achris]

If a bit more initial timing helps the Bottom End, then just change the advance curve of the Distributor to limit Centrifugal Advance.

Didn't read my post properly did you? I said CAMSHAFT timing, not ignition timing....

Chris........

 

[itsathepete]

If a bit more initial timing helps the Bottom End, then just change the advance curve of the Distributor to limit Centrifugal Advance. The OP's engine sounds old enough to have a Mechanical Advance Distributor. Heck, my 2002 Volvo 5.7 has one.

achris is referring to cam timing not ignition timing. Cam timing changes valve event timing which can affect the way the cylinders fill at different rpms. Generally advancing cam timing improves low end torque and retarding it increases top end power

Edit didn't see previous response

 

[jimmbo]

Didn't read my post properly did you? I said CAMSHAFT timing, not ignition timing....

Chris........

oops me bad

 

[Lt1z350]

Making more power is a double edged sword..

Advantage- who doesn't want more power? But I'd be interested in the torque numbers, not the maximum power.

Disadvantage- when the engine makes more power you need to change the prop to keep the engine in the recommended revs range. That change is reflected throughout the entire range, not just at the top end, so you may end up with a boat with a higher top speed, but struggles more in the midrange (due to a taller prop)....

The decision you need to make should be based on torque not power...

That is one of the issues on upper rpm. I am on a hustler 4 blade 14/19 now 44 mph was only 4300 rpm where the old solis 3 blade 14/19 was 45 at 5000 rpm prop was beat up pretty bad so probably a little more slip then it should have been. Hole shot is excellent on this 4 blade was poor on the 3 blade I just am not crazy on the lower 4300 as seems like was working too hard and needed a little more rpm.

 

[Lt1z350]

Zactly


Hard to get more torque without adding more cubic inches

bottom end isnt the issue at all. It screams out of the hole I am actually impressed with how fast its up on plane. It struggles with higher rpm some. Changing to this 4 blade I lost 700 rpm and seems to struggle at 4300 trying to maintain top speed. To me thats something going on up top. My bottom end and mid range seems spot on where peak torque comes into play. This is why I looked at manifold choices. Typically a open plenum like the stock one is more for higher rpm like 5000-7000 when comes to cars and that application. No one would ever run an intake like this on a street car the dual plane is king on the street for power and dual purpose racing if still using a carb anyway.