Dyno vs Actual Exhaust
 

Since the complete rebuild of my 468 two years ago I have not been able to get much over 5000 RPM out of the engine in the boat. Had no problem on the dyno. Made great torque 700+ Ft. Lbs and up to 642 HP @ 5300 RPM.

The only difference between the set up in the dyno and the boat is the exhaust. The dyno used dry headers, the boat has Imco Powerflow Manifolds. Would the engine flow that much better with CMI or other headers vs the Imcos and could I lose that much HP with a wet exhaust vs dry?

My cam is the following:

Crane HR-214/325

[email protected] [email protected]
.059/104 Degree Intake
.034/114 Degree Exhaust
Gross Lift .553 with 1.7 Ratio Rockers

I'm running a Procharger at 5 PSI.

Engine runs great, just can't get the RPMs that I need on the top end.

Re: Dyno vs Actual Exhaust
 

If you remember the last thread I started about the exhaust mufflers and there claims of no power loss there were some things I didn't specify depending on the exhaust your running you may be giving up up to 8 mph which sounds crazy out of exhaust but it's true I have a very old friend in the boat business that now works at the leading performance manufacturer in Miami I can't say the brand but they have tested there own boats and confirmed the speed lost also. One good way to know if the system is holding you back check the plugs and if they are darker then they were on the dyno take the mufflers off and hang on.

Re: Dyno vs Actual Exhaust
 

Laz, what if there are no mufflers?
I got a set of Stainless Marine manifolds instead of headers.
Didn't want the risk of headers cracking and like the 5yr warranty they offer. But i will not be running mufflers. So would this pertain to your findings?
I dont think pantera28-650 has mufflers.

Re: Dyno vs Actual Exhaust
 

Have you tried any prop pitch changes to confirm the rpm loss?

Re: Dyno vs Actual Exhaust
 

What fuel system are you using and is it the same as on the dyno?

Re: Dyno vs Actual Exhaust
 

Storm I guess thats why I'm not supose to assume . Of corse I automatically thought the fuel and system were the same because thats how I run it here and also on the mufflers because they are enforced up north . I had thought after I answered many other questions such as x dimension how many blade props what pitch and so on but again assuming some things are constant with the dyno test . I also thought that was alot of power for a small engine but given the blower and boost he may be right. I still think the plug reading should give him a good indication as to if the exhaust is part of his problem. Good Luck Laz Mesa

Re: Dyno vs Actual Exhaust
 

What cam is that. Can you give duration at .050? A Procharger engine that stops making hp at 5300 is a little odd. Usually they keep making more power as you spin them faster.

Re: Dyno vs Actual Exhaust
 

Pantera
"My cam is the following:

Crane HR-214/325

[email protected] [email protected]
.059/104 Degree Intake
.034/114 Degree Exhaust
Gross Lift .553 with 1.7 Ratio Rockers"
.................................................. ..........
That is the Crane master for the intake lobe for the 721 cam, not the part or grind #. It's 276* seat (.004") and 214* @ .050
The 325 is lobe lift
The .059"/.034" is the valve lift at TDC on a 109* LSA.
Bob

Re: Dyno vs Actual Exhaust
 

Sorry, but that cam belongs in a pickup, not a boat.

Re: Dyno vs Actual Exhaust
 

I suspected it was a 721 cam. The 731 seems like a better choice for a hot 454.