syntrix

The dyno has to be more than third party!

Dyno's do LIE!!!!

A tech has to put in humidity and one or two other variables.

If you are in the car.. or a tech is in the car, what's to say he's not in 4th instead of 5th? What's to say the A/C is not switched on for the baseline?

What's to say that 11,001 monkeys are not near the back of the car blowing on the top of the wheels to accel faster? LOL

Is 5th better? It's probably more near 1:1 which would bypass the gears in the gearbox all together. If there's a gear difference, that could throw everything, and you would never know looking at the results!

Just trying to open your eyes a bit about dyno testing. But most manu's will do halo infested runs on a 3rd party dyno anyway

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If it's cold here in Vegas, I could run to a shop and get a baseline.

10 mins later on a fairly warm engine, I could have 20whp without touching the car or affecting the tech's inputs on the variables!
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Like I said, HALO's everywhere, but it is easy to trick a dyno, and to even get varying results between HALO'd dyno runs.

I'll be the first to try a mod and put it agains LAP TIMES on a well known ROAD COURSE. That's how I judge my mods. (I will dyno for some average numbers though, but I won't rely on them until my lap times decrease!)

bureau13

I can't speak for everyone else, but for me...when I said "3rd party dyno" I meant someone other than the manufacturer performing the dyno run independently, on their own, etc etc...not that the manufacturer take the stuff to a dyno they don't own.

jds

canzoomer

Yes, but more pound of carbon result from incomplete combustion.

I have NOT done a direct comparison test, but I doubt much will be gained when the car is mistuned to start with.

OTOH, with proper tune it should gain some.

Time will tell.

Boozehound

Alright, it’s been a while since I’ve posted, but here comes the “bigger exhaust diameter makes no difference” topic again, so maybe this will help. Everybody wants an engine that’s able to “breathe” better, but how do you quantify “breathing?” I would guess that it’s referring to having increased mass flow rate through the engine in so far as air is concerned.

So what dictates the mass flow rate? If we assume that the gas is ideal, the mass flow is a function of density, cross sectional area, and the velocity of the fluid, or Mdot=(rho)(A)(V). Assuming the density is constant in the exhaust system (just easier for flow analysis), if you increase the area, the mass flow rate increases. Forget velocities and pressures for now (both ends of the cycle are at two fixed pressures anyway), and just think of a big drum of water. Put a 2 inch line at the bottom of a 10 foot high tank and you get incredible velocity but awful flow rate. Add a 12” line in the same spot and you drain the tank MUCH faster, but at a lower velocity.

I’m still kicking around the nozzle/diffuser part of the argument (how an increased exhaust tip *might* help), but that one’s for another time.

Gord96BRG

There's the major flaw in your assumptions. You're also ignoring any effect from resonance of the exhaust pulses, which have been proven many times over to be very significant. You can't just use constant flow calculations and assume that those are valid for exhaust system design.

Regards,
Gordon

canzoomer

Exactly. The classic example of this are small displacement two stroke engines.

I once owned a Yamaha DT250 ( OK, a LONG time ago).
With the stock pipe it made 18HP
With an expansion chamber exhasut it made 29HP.

islandsoon

We have become a cynical bunch. Sure, some mfging folks have 'fibbed about their dyno claims, but others seem to have a pretty good rep. Examples are Banks Power, Holeshot Performance, and closer to home for RX8 guys, based on feedback from several folks on this forum, it would appear the boys at Rotart Extreme have been pretty straight.
My hands on experience with Dynos has been limited to 4 stroke motorcycles. I have found significant power in aftermarket exhausts (97 hp stock bike gaining 9 to 13 hp depending on the can) and some gains in power from mods to stock intake (3 hp but required a jet change) and 6 hp gains with a K N filter set up (again required a jet change). So, as Ronald Reagan always said, "Trust but verify".

Boozehound

Alright, if you do have to account for resonance in the system (which amounts to what? Nodal pressures that impede flow based on wave superposition?), that isn't to say that increasing your exhaust diameter won't do anything for you. You're essentially saying that pipe diameter doesn't matter in pipe flow.

Even if resonance is a huge issue (and I'm not sure there's been a good explanation of its effect on pulsed flow), you simply take that into account when designing a new exhaust system. But to simply discount nominal diameter and the effects of nozzles or diffusers on pipe flow is rediculous.