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Which Vetterman exhaust?

Desert Rat

Well Known Member
Hey guys- Clint at Vetterman indicated to me that the RV7 with IO390 can use either the crossover or the 4 pipe exhaust and the price is the same for either.

Would anybody care to comment on the pros/cons of each?

Thanks,

Terry
 
Hey guys- Clint at Vetterman indicated to me that the RV7 with IO390 can use either the crossover or the 4 pipe exhaust and the price is the same for either.

Would anybody care to comment on the pros/cons of each?

Thanks,

Terry

Years ago, it was reported that crossover exhausts on RVs will make the most power but 4 straight pipes will be the most efficient. Not sure I am a good enough pilot that I would be able to tell the difference on same airframe with the same engine. Boils down to what the person likes better.
 
Cabin heat

Years ago, it was reported that crossover exhausts on RVs will make the most power but 4 straight pipes will be the most efficient. Not sure I am a good enough pilot that I would be able to tell the difference on same airframe with the same engine. Boils down to what the person likes better.

I think you also need to consider the cabin heat muff. Maybe there is a difference there that would force a decision??
 
I have a never installed 4-pipe Vetterman if you’re interested. Came with my RV-8 project, but I’m not going to use it.

Not sure if the 390/RV-7 uses the same components, though.

Chris
 
What cowl are you planning on using? The cross-over comes really close to the sam james cowl, close enough that I had to send it back to vetterman for some tweaking. The 4 pipe is probably easier to make fit.
 
I have a 4 pipe on my 8. The bottom cowl pins are pain to get in & out. I’ll be changing them out for Camlocs someday. Otherwise the 4 pipes are fine. Lots of cabin heat with heat muff over 2 pipes.
 
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Thanks for all the replies guys-

Planing for the standard cowl, so no worries there. Any other issues with interference with accessories etc?

Thanks
 
... Clint at Vetterman indicated to me that the RV7 with IO390 can use either the crossover or the 4 pipe exhaust and the price is the same for either.

Would anybody care to comment on the pros/cons of each?
Terry, did Clint have any idea about the pros and cons of each? From what I understand, exhaust systems are very complex and sensitive to even minor changes, so I would guess that there must be a performance difference between these two designs.

The exhaust style that has the two left and two right cylinder exhaust ports connected seems like it might be subject to cracking due to the relative movement of the cylinders. This is why engine baffles are in multiple pieces - there's a lot of movement.

There was even a product that bound the two cylinders together to try to reduce this motion, but I have not seen one in real life, and I have no idea if it's a good idea.
 
In my initial email to Clint I asked for a recommendation re; which one of their products would be best for my configuration and the response was that either the crossover or the 4 pipe could be used.

He offered up his phone number if I had further questions, but I'm sure he's as busy as the rest of us, so I threw it out here before following up with him.
 
Cross overs are like headers on a performance car. They can increase flow during the In/Ex overlap and help pull more air fuel into the chamber, displacing more exhaust, thus creating more power. However, how effective they are is all about the length from valve to junction and cam overlap and it would seem unlikely that the Vettermans are tuned (pipe lengths changed to reach max torque) on a dyno, like performance headers are. The space limitations likely dictate where the junctions are.

I believe that Larry Vetterman tested these years ago when he developed them and reported a performance gain, but don't remember the numbers. probably still on his website, as it used to be there.

Straight pipes can be more efficient at a lower power level. Pulling more air into the cylinder and displacing more exhaust during overlap does increase power, but also allows or can allow more of the air fuel to leak out the exhaust port due to the extra flow. In the performance world, the only way to get a full air fuel volume in the cyl is to bleed a decent amount of waste into the exhaust. When dealing with efficiency or emissions, designers find other ways to increase power that are not as inefficient.

we're likely dealing with small differences here.

Larry
 
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I used a standard, two pipe cross over on the RV-8A. On the RV-8 I used the four pipe. Both were from Vetterman.

The four pipe has a slight edge on the “coolness” scale. Performance is very good, not sure if I could measure the difference between them however. If I had to do it over again I’d still go with the four pipe.

Carl
 
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