I am about to begin a small mod on a 2000 4.3 volvo motor. The mod will be simple and cheap. maybe 700. I had intended to use a comp cam: CS XM 270HR-12

Hydraulic roller tappet
Basic Operating RPM Range: 1,200-5,200
Intake Duration at 050 inch Lift: 218
Exhaust Duration at 050 inch Lift: 224
Duration at 050 inch Lift: 218 int./224 exh.
Advertised Intake Duration: 270
Advertised Exhaust Duration: 276
Advertised Duration: 270 int./276 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.495 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.503 in.
Valve Lift with Factory Rocker Arm Ratio: 0.495 int./0.503 exh. lift
Lobe Separation (degrees): 112
Intake Valve Lash: 0.000 in.
Exhaust Valve Lash: 0.000 in.
Computer-Controlled Compatible: No
Grind Number: CS XM 270HR-12


That is have that ground to a v6 type


The question is does that cam have enough overlap to create reversion in a 4.3 with stock exhaust. I was under the impression it would work with a 350 but i have been told by a few marine mechs that it would create significant reversion in a 4.3...

I dont pretend to be informed on this and can find little if any practical real world info on this other than this site. What is puzzling is the bore and stroke along with the vortec heads are the same in both engines...compression is 9.41.1 I was under the impression the smaller the motor the less chance of reversion...aka vacum . for the lack of a better term

I know this is not a engine you guys typically work with...and i also know the 350 route. The hull wasnt built for 400 hp and i will probably yeild 275-300 with the cam and lift....thats about 70-90 hp for 600.00 and some fun showing the kids how to work on a engine.

I guess i should also say i am trying to stay with factory exhasut...I dont need a phone call from the kids due to the noise police and there out in force in my area..

I know this post may seem absurd but need a bit a clarity on this 350 it is ok and a 4.3 is a no-no..

Thank you for any input.

I would not install anthing other than a stock cam with stock exhaust. Exhaust should be your first upgrade. But get out your wallet because $700 will not cover it. I had a 4.3 V6 in my 2nd boat it was a good boat for what it was intended to do. When I decided to go faster I bought a boat with a BBC. Just my 2 cents. Good Luck!!

I can extend the drop on the water back 12". that is not a problem. I really do not believe you can build a exhasut that benefit's the 4.3..aka i will be limiting the WOT to 5500. Beside Ive never heard a 4.3 open exhasut that wasnt a bit funny sounding...high speed bumble bee.

i just dont know this revesion thing to well..51 dergrees is going to cause that much of draw???

Is it EFI or Carb? If it is Carb and it's 2-barrel change it to a 4-barrel Carb and let it go.

EMI makes them. You need the exhaust for reversion issues. Long risers are required for bigger than stock cams. Water enters the exhaust further away from the engine. You would also need through hull exhaust. Or you could install a 350 with a stock cam or get a bigger boat with a bigger engine already in it. I would opt for the bigger boat with bigger engine.

The induction system is TBi running a mefi-3 comp...and i know this...i need no lessons on a carbed unit...remapping timing and injector pusles is not the question.

This is a simple question of overlap and is the above cam out of line.....I have read post's from some very intuitve people here....and i am asking some very basic question's.

Why could a 4.3 suffer greater reversion issue's than a 350. It's about fundamentals not feelings.....Hint 5500redline ...there is no free flowing exhaust that would aid HP...not even.

if your exhaust exits threw the prop,id be leary.i think you will have reversion problems.also,i don,t think you will see the hp gains that you are looking for.if you change to a better threw hull exhaust,and some head work&the cam change,i think you,d be pleased.

I believe I was mistaken on EMI making exhaust for the 4.3L engine. Seems as though somone makes them. I am not a engine builder your best advice on cams would be Bob RMbuilder. He is a tru expert on camshaft design. He will most likley tell you the same thing about aftermarket cams and stock exhaust.

If needed i can build my own exhaust...That is not the issue. I m just stuck on the fact that the cam can be run on a 350 safely but not on a 4.3...Its the same dam motor less two pistons.

Amount of exhaust pulses and time inbetween them. Yeh, prob some other things, but this is the biggest when comparing to the same motor + 2 cylinders.

As example: making a y pipe and then entering water after the Y would work much better than duals or enetering water before the Y.

A 10 cylinder with same firing order would be better than it's 8 counterpart. A 12 cylinder even better.

Thus, why increasing idle speed has a big effect also. Time !!!

BTW: Yes, this is CFM from the other site. LOL.