Exhaust options, yes again.

G'day.

I'm gonna risk the can of worm's.
I've been reading the post by FlyinOBrian2
17-2-2011.

Why do Formula 1 racers using O-200's use straight out stubs if it robs them of grunt ?

I have an RV4, ( an since I've owned it l don't need Viagra any more, an I'm 70)
l have considered replacing all the exhaust spaghetti with short stack slash cut 45? backward facing pipes.

Why?

Lighter weight, a bloody lot less heat in engine room, slightly aft shift of C of G,
(an that should give a coupla knots extra speed)

l don't give a dead dingo's donga
Fer all that exhaust technology, I'm not interested in every fraction of extra speed.

I'd rather have less heat, less spaghetti, more room in the engine room, an better air flow around the sump.

Nobody involved in those posts mentioned less exhaust valve temperature with
shorty' s

I'm real keen on knowin ( without Goin into too much detail) what I'm gunna loose OR gain running an io-320 at 2400 rpm.

Thank's.
An by the way,,,, I reckon Don's doin a good job, he'll get in again fer sure an when he's finished there send him over to us, we can give him a job, an pay him too.

I don?t really know a lick about airplane exhaust. But I do know a lot about back pressure vs performance. No back pressure will help make more HP, but you will lose bottom end grunt and torque production. My guess is to help the engine make power where it needs to make power, the exhaust is tuned specifically for it. And since airplane motors are run at such low rpm, I would guess that they would not benefit as much from a free flowing exhaust. Just a guess. I know some serious engine gurus will chime in with the correct answer soon!!

Thank's Pete.
So if I'm running at 2350-2400 rpm with a
4 separate pipe system with 3 and a half bends in each pipe with 4 cross overs behind the throttle body, l must have back pressure and no scavenging effect.

Add to that lots of heat.

If anyone is familiar with the Dehavilland Dove's exhaust / cabin heat system, or can get a view of it I'm interested to know if this system could be converted to a high pressure exhaust extraction system.

Cold ram air intake shroud flowing over short stack, backward facing exhaust.

The shroud would be ten inches longer at the end for a constant extraction effect.

I'm just an old busted arsed heavy equipment operator not a mechanical engineer, just wondering if it's feasible.

Maybe l should ask Myth Busters.

Thunda Down Under said:

G'day.

I'm gonna risk the can of worm's.
I've been reading the post by FlyinOBrian2
17-2-2011.

Why do Formula 1 racers using O-200's use straight out stubs if it robs them of grunt ?

I have an RV4, ( an since I've owned it l don't need Viagra any more, an I'm 70)
l have considered replacing all the exhaust spaghetti with short stack slash cut 45° backward facing pipes.

Why?

Lighter weight, a bloody lot less heat in engine room, slightly aft shift of C of G,
(an that should give a coupla knots extra speed)

l don't give a dead dingo's donga
Fer all that exhaust technology, I'm not interested in every fraction of extra speed.

I'd rather have less heat, less spaghetti, more room in the engine room, an better air flow around the sump.

Nobody involved in those posts mentioned less exhaust valve temperature with
shorty' s

I'm real keen on knowin ( without Goin into too much detail) what I'm gunna loose OR gain running an io-320 at 2400 rpm.

Thank's.
An by the way,,,, I reckon Don's doin a good job, he'll get in again fer sure an when he's finished there send him over to us, we can give him a job, an pay him too.

Click to expand...

performance engine tuning is a holistic process. Longer tubes in a properly designed header can create scavenging energy to pull more air fuel in during the valve overlap, while short straight tubes reduce backpressure. However, the same effect that scavenging provides can be had by using a cam with more overlap built into it, usually providing greater performance with lower fuel efficiency. In this case, reduced backpressure increases power and the combination of increased overlap and reduced backpressure maximizes power output at the expense of efficiency and this is why race engines may use it. Unless you share all of the custom designed engine parts from a tuned, race engine, it is not wise to use one or two parts that you see them use. Instead, trust vetterman that has designed his exhaust for best performance on stock lycoming engines. Turbo engines almost universally see performance increases with the least amount of backpressure.

Heat is heat. It would seem that keeping hot gas in a semi-insulating tube until clear of the cowl would net much lower cowl temperatures than dumping 1400* air directly into the enclosed cowl.

Larry