Swapping carbs from rochester to holley

[Synister]

Hi All!

This is my first post and enjoy the knowledge here on iboats.

I am going from a 2 barrel Rochester carb to a 4barrell Holley. Does anyone know what parts i will need to convert the linkage over ?

The boat is a 91 Thompson 4.3L/Alpha Outdrive.

Thanks!

 

[ENSIGN]

Re: Swapping carbs from rochester to holley

Your just waisting your time & money it's going to be to much carb and not enough engine.The rochester/mercarb is all you really need.

 

[Bondo]

Re: Swapping carbs from rochester to holley

Ayuh,... That's a Tough Swap,... Merc never used Holley carbs...

 

[zbnutcase]

Re: Swapping carbs from rochester to holley

Your just waisting your time & money it's going to be to much carb and not enough engine.The rochester/mercarb is all you really need.

There is plenty of engine there for a 4bbl and since he did not say what size of carb he is using how do you know it is too much carb?

 

[zbnutcase]

Re: Swapping carbs from rochester to holley

Go to summitracing.com and look up part # SUM-G1419, linkage plate.

 

[billy4hp]

Re: Swapping carbs from rochester to holley

Hi All!

This is my first post and enjoy the knowledge here on iboats.

I am going from a 2 barrel Rochester carb to a 4barrell Holley. Does anyone know what parts i will need to convert the linkage over ?

The boat is a 91 Thompson 4.3L/Alpha Outdrive.

Thanks!

What exactly are you trying to gain by going from a 2bbl to a Holley 4bbl? Unless your 2bbl is just plain worn out I personally don't see the need to change unless your boating ego just can't live with the fact that your boat only has a 2bbl carb...

At the most you will gain 20hp @ WOT and that is being generous... A 20 hp increase in more may gain you 1 to 2 mph... Which you could possibly achieve by going to a optimized stainless prop which would be much cheaper than doing your 2bbl to 4bbl conversion...

The summit linkage stuff works, CP Performance and Keith Eickert also sell nicer stuff if you are looking for bling factor..

If your current fuel pump is on the weak side, going to a 4bbl could possibly reveal this so you might need need to replace / upgrade your fuel pump...

JMHO..

 

[full stringer]

Re: Swapping carbs from rochester to holley

There is plenty of engine there for a 4bbl and since he did not say what size of carb he is using how do you know it is too much carb?

i agree totally and from experience he will probably need a adapter plate 26 bucks fuel milage will increase w/ a 4 barrel believe it cuz its true with vacume secondaries it's a good set up probably a 600 cfm would be purrrfect!!!

 

[mkast]

Re: Swapping carbs from rochester to holley

Ayuh,... That's a Tough Swap,... Merc never used Holley carbs...

http://www.mercruiserparts.com/Show...g&inbr=1582&bnbr=70&bdesc=CARBURETOR+ASSEMBLY

Just one of several Holley carburetors used on Mercruiser engines.

Holley part number 717-7 for the fitting to attach the throttle cable to the carburetor.

 

[Synister]

Re: Swapping carbs from rochester to holley

Your just waisting your time & money it's going to be to much carb and not enough engine.The rochester/mercarb is all you really need.

This is not even an answer to the original question... You know nothing about my engine combination...and apparently nothing about the offerings or sizes of 4 barrell Holley Carbs..

 

[Synister]

Re: Swapping carbs from rochester to holley

What exactly are you trying to gain by going from a 2bbl to a Holley 4bbl? Unless your 2bbl is just plain worn out I personally don't see the need to change unless your boating ego just can't live with the fact that your boat only has a 2bbl carb...

At the most you will gain 20hp @ WOT and that is being generous... A 20 hp increase in more may gain you 1 to 2 mph... Which you could possibly achieve by going to a optimized stainless prop which would be much cheaper than doing your 2bbl to 4bbl conversion...

The summit linkage stuff works, CP Performance and Keith Eickert also sell nicer stuff if you are looking for bling factor..

If your current fuel pump is on the weak side, going to a 4bbl could possibly reveal this so you might need need to replace / upgrade your fuel pump...

JMHO..

Yes the 2 barrel was worn out and I did repalce the fuel pump with a 6psi, 110 gph pump. I am aware of the offerings of automotive throttle linkage plates and brackets but was more concerned with the shift cable for the outdrive? Most automotive Detent cables are slightly different.

 

[Synister]

Re: Swapping carbs from rochester to holley

i agree totally and from experience he will probably need a adapter plate 26 bucks fuel milage will increase w/ a 4 barrel believe it cuz its true with vacume secondaries it's a good set up probably a 600 cfm would be purrrfect!!!

I replaced my 2 barrel intake with a 4 barrel.

 

[Synister]

Re: Swapping carbs from rochester to holley

http://www.mercruiserparts.com/Show...g&inbr=1582&bnbr=70&bdesc=CARBURETOR+ASSEMBLY

Just one of several Holley carburetors used on Mercruiser engines.

Holley part number 717-7 for the fitting to attach the throttle cable to the carburetor.

Thank you for such a simple answer to a simple question... So many people assuming.....

FYI I have a 91 4.3L non balance shaft, roller engine.......

I took a set of 97 Vortec heads and had a CNC program run on the bowls to take advantage of the 2.02/1.60 valves, clean up work done to the ports but did not effect the short flow runners, 4 barrell Mercruiser single plane intake with a spread bore to square bore adapter, custom ground camshaft and digital ignition system. With the increased compression, cam and heads (that were run on the flow bench to make sure they werent all jacked up because everyone swears you cant run 2.02/1.60 valves on a vortec head and out flow the OE sizes...) This engine will make 300 HP. If the outdrive lives great. If not it was a strange science experiment that was fun.

So many opinionated assumption related answers...

Simple questions, simple answer.

 

[mkast]

Re: Swapping carbs from rochester to holley

4 barrell Mercruiser single plane intake with a spread bore to square bore adapter
This engine will make 300 HP.

A Mercruiser SINGLE plane manifold?
Most times an adapter is used, flow is disrupted.
300 horsepower, out of a 4.3, at what RPM?

 

[Bondo]

Re: Swapping carbs from rochester to holley

http://www.mercruiserparts.com/Show...g&inbr=1582&bnbr=70&bdesc=CARBURETOR+ASSEMBLY

Just one of several Holley carburetors used on Mercruiser engines.

Holley part number 717-7 for the fitting to attach the throttle cable to the carburetor.

Ayuh,... Where's the applications,...
It was Never used on a 4.3l...
Maybe on some Old Fords in the 70s...

This engine will make 300 HP.

Now That's Funny...
I'd love to see the dyno sheet on that...

I am aware of the offerings of automotive throttle linkage plates and brackets but was more concerned with the shift cable for the outdrive? Most automotive Detent cables are slightly different.

Slightly Different,..??..??..??
The Throttle is completely independent from the Shift cable...
The ONLY place they interface is in the Controller...

 

[billy4hp]

Re: Swapping carbs from rochester to holley

Yes the 2 barrel was worn out and I did repalce the fuel pump with a 6psi, 110 gph pump. I am aware of the offerings of automotive throttle linkage plates and brackets but was more concerned with the shift cable for the outdrive? Most automotive Detent cables are slightly different.

That's why I directed you to Keith Eickert and CP Performance, both are go fast, marine parts suppliers / manufacturers... You could also try Hardin Marine...

 

[billy4hp]

Re: Swapping carbs from rochester to holley

A Mercruiser SINGLE plane manifold?
Most times an adapter is used, flow is disrupted.
300 horsepower, out of a 4.3, at what RPM?

He's only talking about 1.15 hp per cubic inch or so...

Pull the pin and spin her up to 6400 RPM and see what happens...

 

[Synister]

Re: Swapping carbs from rochester to holley

He's only talking about 1.15 hp per cubic inch or so...

Pull the pin and spin her up to 6400 RPM and see what happens...

Funny you seem to be the only one who gets it LOL

300 hp out of a 4.3L isnt hard at all, I will make between 290-300hp at somewhere between 5400-5800RPM, which is what the aftermarket ignition is for.

This is nothing more than a strange experiment that I picked up for a low low price and put a lot of work into, I have learned a lot about boats but building engines is my forte. This will be the 6th engine I built this year and the 3rd 4.3L in the last 5 years.

 

[Synister]

Re: Swapping carbs from rochester to holley

Ayuh,... Where's the applications,...
It was Never used on a 4.3l...
Maybe on some Old Fords in the 70s...



Now That's Funny...
I'd love to see the dyno sheet on that...


Slightly Different,..??..??..??
The Throttle is completely independent from the Shift cable...
The ONLY place they interface is in the Controller...

You are correct about the throttle, I am working with a basket case and finishing someone elses project and though they were off the same side. Glad I found a few mercruiser prints! If you dont think a 4.3L is capable of make 300hp I dont know what to tell you. Its not that hard with the right combination and my background.

 

[Synister]

Re: Swapping carbs from rochester to holley

In all seriousness this thread was started for a simple question that deserved a simple answer. I didnt ask any opinions for good reason.I dont care.

Thanks for the guys that actually answered the simple question with a simple answer. I may have jumped the gun and thought this forum was a great tool but it appears to be full of opnionated assuming people that are just typing in crap in an attempt to boost your post count.

I dont claim to know anything or everything, in fact i'm more of a jack of all trades and a master of nothing but I know how to build an engine to make reasonable power levels and in many instances make ridiculous power. I have done it for the past 15 years, I liked it so much it became my career.

Everyone have a safe and happy boating season!

 

[full stringer]

Re: Swapping carbs from rochester to holley

just do it bro!! put the holley 4 barrel 600 cfm marine carb on and your gonna love it. throttle response is great and watch the fuel milage increase as well as horsepower. i swear its true you will get better fuel milage and more horsepower with that 4 barrel than the two barrel dont forget to tell everyone after you do it the results im awaiting