Is it worth swaping a 4.3 MPI for a 5L ?

ric · **Posted:** Sun Feb 15, 2015 3:47 pm

deafwish wrote:

Your 5.0L may not pull the RPM to warrant going to a 4BBL & may just use more fuel than pump more air!

http://forums.iboats.com/forum/engine-r ... -gl-vortec

RPM range for a marine v8 engine is 1500-5000 and cruise is around 3000-3500rpm. You can very much benefit from a 4bbl with vacuum secondaries. You can just as easily murder horsepower and fuel economy if you get a mechanical secondary carb. DO NOT GET ONE OF THOSE.

A proper camshaft and intake combo will put best efficiency and torque around 3500rpms, cruise RPM.

But, I gotta say with a proper prop installed, my 220hp 5.0 vortec puts 8 full sized adults on plane without effort on my 215 ssi. Doesn't need more power.

deafwish · **Posted:** Sun Feb 15, 2015 4:51 pm

I really don't think a 4BBL will be warranted for anything <5000 RPM, as the CFM requirement just isn't there...
If this was a flat bottom race boat, sure go the 4BBL.
A social/ ski boat, the 500CFM, 2300 will be a cracker of a carb, with awesome metering and torque.

ric · **Posted:** Sun Feb 15, 2015 5:26 pm

500cfm 4bbl with vac secondaries will get way better fuel economy

deafwish · **Posted:** Sun Feb 15, 2015 5:53 pm

Not if the secondaries are open!

Who makes a 500CFM 4BBL?
I trust you know that the scaling of a 2BBL and 4BBL are different?
A 500CFM 2BBL will flow LESS than a 500CFM 4BBL. :wink:

ric · **Posted:** Sun Feb 15, 2015 8:08 pm

Holley sells a marine 500cfm 4bbl with vac sec

deafwish · **Posted:** Sun Feb 15, 2015 8:23 pm

Which one?

https://www.holley.com/products/fuel_sy ... rburetors/

Jdpber · **Posted:** Mon Feb 16, 2015 9:45 am

jus put a carbed 572 in her and call it a day

LouC · **Posted:** Mon Feb 16, 2015 11:45 am

If so deaf why did OMC and others offer the 4.3 with both a2bbl and a 4bbl?
2bbl was rated @ 175, 4bbl @ 205 hp. You definitely feel it when the secondaries open on the Q-Jet.
The small primaries allow it to be pretty economical.

deafwish · **Posted:** Mon Feb 16, 2015 3:03 pm

Torque is needed on a social boat, not top end HP.
While I'm certain the 4BBL will deliver another 20 odd HP, this will be difficult to notice on a boat, in real world gains.
All I'm saying, is if it has a Holley 2300, leave it be. :wink:

p.s. Did anyone read the link I previously supplied?!

meinmelb · **Posted:** Mon Feb 16, 2015 3:34 pm

Thanks Mate. That post was very interesting with all his experimenting. Just swapping out from a 2 to 4 bbl gained him nothing however adding the new intake manifolds and roller rockers seemed to net him about 30+ hp. This was measured unscientifically and mainly at WOT with some gains in acceleration. Not bad, but his was a Volvo and the parts were an easy swap. Mercs not so easy with linkages hoses etc.

I am still waiting for the Mercury tech to call me back and will take it from there. If there is no immediate difference between the 2 motors then it might not be worth it as upgrades seem to be a very grey area and I don't want to swap motors hoping the upgrades will make a difference?

Winter Sux · **Posted:** Mon Feb 16, 2015 4:55 pm

ric wrote:

500cfm 4bbl with vac secondaries will get way better fuel economy

500 CFM with vacuum secondaries or mechanical secondaries is still 500 CFM. The fuel economy wouldn't even be noticed between vacuum or mechanical in a marine engine.

ric · **Posted:** Mon Feb 16, 2015 7:06 pm

Winter Sux wrote:

ric wrote:

500cfm 4bbl with vac secondaries will get way better fuel economy

500 CFM with vacuum secondaries or mechanical secondaries is still 500 CFM. The fuel economy wouldn't even be noticed between vacuum or mechanical in a marine engine.

At cruise? No. But you'll notice a shit ton more power getting on plane with vacuum secondaries.

meinmelb · **Posted:** Tue Feb 17, 2015 2:24 am

So I spoke to the Mercury engineer today and his opinion was that it was not worth it even if it was a free swap. In his opinion the power and torque figures between the 4.3MPI and the 5L carb are not enough to overcome the additional weight, the fuel, and the reliability differences. Any slight increase in torque from the 5L would be low in the rev range and unlikely to be felt by me in that boat. I would however feel the fuel difference as the carb fed 5L would use noticeably more fuel.

He was however very excited about the new 4.5V6 that is supposed to be as good as the 5L MPI on power and performance but lite on fuel like the 4.3MPI, and with the lower weight that power is very noticeable....and I quote "It goes like a dog shot in the arse" :shock:

... but at the price they are asking it is not worth it for me.

Like everyone else I have spoken to, the real upgrade would be to the 5.7 V8... If only I could find a good used motor under AU$5K... not likely as they are in huge demand and as rare as rocking horse sh!t down under. Plenty new ones at AU$16k and above...

Oh well time to fix the 4.3MPI and move on.

deafwish · **Posted:** Tue Feb 17, 2015 3:24 am

Just throwing the concept out there, but...

Did you expect the Mercury Engineer to really sell the concept of carburetted technology when all their marketing dollars now go in to EFI?
There is never a replacement for displacement - especially in a boat.

I say do it. Your boat will have better re-sale, too.

schoolsOut · **Posted:** Tue Feb 17, 2015 3:14 pm

deafwish wrote:

Just throwing the concept out there, but...

Did you expect the Mercury Engineer to really sell the concept of carburetted technology when all their marketing dollars now go in to EFI?
There is never a replacement for displacement - especially in a boat.

I say do it. Your boat will have better re-sale, too.

+1

www.iFourWinns.com

Is it worth swaping a 4.3 MPI for a 5L ?

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