Inertia takes over once it's up to speed. When accelerating as on a typical chassis dyno run, it would register. On a naturally aspirated rotary, the biggest single performance gain you can get aside from a good exhaust is a lightweight flywheel. Everything else is miniscule in performace gained by comparison. That means it does in fact free up quite a bit of energy. At a steady speed where there is no acceleration, of course you won't see much of a difference.

If you think it probably wouldn't register, I have to ask and please don't get offended, have you ever even driven a car with a lightweight flywheel?

 

Maybe if you read your own things you will see

"If we measured the power output of an engine first with light flywheel and then again with the standard part on an engine dyno, no change in power will be seen to occur. "

So either you are posting up crappy documentation of a lightweight flywheel and contradicting it with good dyno information, or you are putting up good documentation of a lightweight flywheel and backing it up with a dyno graph that doesn't match.

Rotarygod,
If gtorx7 says that his time for pull will not change from a 600hp car or 900hp car, the dyno does not care how fast the car pulled. (This is the only dyno I have experiance with)

Let me ask you this, at constant rpm (say 6000rpm), does the lightweight flywheel make any effect on power?

 

"come up on the pipe"?

on collector size, does 80% come close?
and I am surprised you did not go bigger than 2.5" after collector, very interesting.

what kind of muffers you are using that give you good mufflering and good flow?

thanks

nice to have in-house dyno hey?

 

80% on collector size? As in its 80% close to perfect? Or 80% of the size? The length is what made the largest difference so must be spot on. I had a 3" exhaust after the collector for a really long time, but it was after the header was in the correct zone that the 2.5" exhaust complimented, and made more power. I am using two borla Xr-1 mufflers in the rear, on top of each other, and one borla xr-1 in the center. Under cruise its very quiet, wot is great not too loud at all. Much quieter than my original 3" exhaust. And makes more horsepower. Ironic in the n/a world. And yes in house dyno is priceless.

 

This is what I have been telling shm##### for a looong time now...but he refused to believe me. Granted my evidence was 'I feel like a 2 1/2 will be better' and my schooling is in computers not mechanical stuff.

 

That is mostly my fault. After I hit 206rwhp, with a 3" exhaust I told Seth 3" seemed to work great. Now I know differently, lol.

 

Not sure what you're trying to ask about the 600 to 900hp question, but I'll take you up on the 6000rpm at a constant (Provided we're talking on chassis dyno), then yes at that specific rpm the engine will still make more power at the wheels with the lighter one.

There's an old racing saying, for every 1lb you take off the drive terrain, it feels the same as shedding 100lb off the car. And no its not by taking the weight off its just by the power that is provided to the wheels.

 

if you still think a lightened flywheel makes no difference to power numbers, then please answer this. Why is wheel horsepower different from base/flywheel horsepower (Power being transfered to the ground not being transfered to the flywheel.).

 

There's no way you got 13 hp from just the weight of the flywheel alone. You probably increased your turbo spool up and boost from using the lighter flywheel thus making more power. Let's see how you launch from a dead stop with an alluminum flywheel vs a stock one. Which one do you think would be better for drag racing? Choosing the correct flywheel for your application and powerband is what is most important, the power made is insignificant.

 

And Flywheels continue...... lol

 

If you read my sig you would of realized I'm NA and i'm just running ITB's. As far as for drag racing I know that a heavier one is more suited but this isn't about what it suits best. And my personal best time at the drag strip (I've only been there twice in my life) was 14.6. I kept up neck to neck with one of those new v8 mustang for the first half.

 

guys please do tell why 2.5" works better than 3" in here.

I meant, 80% of total area of the primary tubes as the collector size,

I understand that you are doing this for a living, I appreciated any insights you can share with us.

thank you

maybe RotaryGod or Speedturn can share some knowledge here too...

LOL, yeah the flywheel continues.....

 

Yeah I heard 'Logan makes more power with a 3" ' all the time. I understand...it is hard to argue with someone who made 206whp n/a with a 3".

 

Everyone agrees on this point. The ENGINE still makes the same power. The dyno sheets are from a CHASSIS dyno. A CHASSIS dyno shows drivetrain loss. Less drivetrain loss means more WHEEL horsepower which is what really matters as that is what's usable.

This is true, more so in a turbo application where you need to worry about boost falling off between shifts, etc. But seeing as all we're discussing is N/A cars...

And not everyone likes going fast in a straight line

 

Drrr...I totally missed the engine dyno part in that explanation.

 

Was anything else changed when you went to 2.5"? What is the diameter of the collector exit? This is interesting since australians are seeing increase from megaphoning their bridge ports out to ~4" after the collector and stock port ITS cars are running 3". How was your step to 3"?

This car falls pretty much exactly in line with what I would want in a daily driver. Do you have any video of this car?

 

Chew on this.

A straight pipe of a given length will have less backpressure (at the exhaust port) than your system with no Y-pipe.

It's not about "pressure" per se it is about using the exhaust's inertia to your benefit.

 

On an inertial dyno, a lightweight flywheel will show gain because inertial dynos measure acceleration and calculate power/torque.

On a steady state dyno, it will not show gain because you're measuring torque output and calculating HP from that. (Please don't tell me "dynos measure HP and calculate torque" - our steady state dyno certainly measures torque, it's basically just a lever pushing on an electronic scale, and a computer controlled water brake to hold the engine at a given RPM)

If you mean the difference between flywheel HP and wheel HP... this is very basic stuff. Gears and other driveline parts have power losses associated with them, some of them are constant with respect to RPM (lube splash, seal drag) and others vary depending on the torque load (gear losses, bearing losses) so as a general rule of thumb, for the power levels WE are concerned with, there's a roughly 15% power loss through the driveline. At higher power levels this percentage goes down.

PS - The guys here loved your "exhaust backpressure closes exhaust valves" comment...

 

That doesn't even matter, all that matters is how the car accelerates.

HP is only a portion of that.

 

I think its due to increased velocity and slight pressure increase a 2.5" exhaust created. Note that I mean more pressure pre- collector, not post. It was about a 6 ft-lb and 10rwhp gain if I recall correctly from just the change to 2.5". Collector size currently is a good amount smaller than 80% of the two primary tubes.


Yes, I have been changing the entire exhaust around to get the 30+hp gain. It definitely was not from just a 2.5" system. The collector size is smaller than 2.5" and of course has a small megaphone on the end of it. When I ran a 3" system there was a 5" long mega-phone going to it. A bridge port has a MUCH different need than what I am running, so after the collector its pretty common to see a nice long mega-phone going out to 4". Racing beat has been doing this since the 80's. However the racing guys running 3" on stock ports, I personally cant see a need. Not saying they may not make more power. For me the power increase with 2.5" ONLY occured AFTER the header finally was made to the correct size and length. So in short, if using a 2.5" exhaust on a poor header, you can easily make less power than a 3". This is why I got confused before, and you can see how. Its the best daily driver I've ever built. SOOO much fun. Video will be coming soon!

 

It sucks that these guys is messing your thread with this flywheel argument. Anyways, I really would love to make that much power in my n/a especially on a street port. How does the car idle, and how is the low end? And do you think that a 6 port would be able to make similar power while still using the actuaters?

 

Well this is what I get for only ever wanting an rx7 and only ever modifying a rx7 and being a member on an rx7 forum and never wanting to put an ls1 or any other piston engine in my rx7 and only just now (a week ago-ish) started looking into a z31/z32 car for the wife and still haven't gotten to read up on how the piston engines work in detail. Hell 6 months ago I found out that the piston moves up and down from the *bottom side* =p I know enough to get by, and far more than most of my friends, but sometimes those details....

Since i've been post whoring anyways... why can't a piston engine run without headers? feel free to move this to pm's if you want to keep the rest of the discussion cleaner.. (There's already like 3 topics. here...)

 

It idles at 1k, with a nice little lope. Low end feels great, and it will cruise along at 1200rpms in 5th gear all day long nice and smooth. If you check the dyno charts at the beginning, you can see a direct comparison of low end torque vs. low end torque king, the GSL-SE. I dont think a 6 port with actuators will be easy at all to get these numbers, but nothing worth while is easy. Maybe with some work/research you will be one who can!

 

It's sounds like your talking about a megaphone and reverse cone after the collector? If so you should see the one I'm currently fabing from scratch for my 20b.

 

I know your setup is a daily driver and you want a quiet exhaust but did you ever try open header exhaust like what most all motor drag car racers use to see what kind of power you can make?