mark kibort

Of course they are, as far as their own components go. after all, thats how dynos measure hp. rate of change of KE. ... it's not really any complicated programming, its just a basic equation. As you probably know, 400hp can be a big drum large diameter accelerated over 2 seconds. 300,000 Joules /sec or a small diameter drum accelerated over only 1 second. (still being 300,000 Joules /sec) (300,000 J/s = 400hp)

The point is, if you accelerate twice as fast for the same HP reading, the effect of the component inertia of the car being tested is much higher. Again, its one of the same reasons 3rd gear readings are lower than 4th gear readings.

As far as what Speedtoys said, that gives me an idea to get the dyno done for classing in 3rd gear, (and use the smaller roller dynos) it will always read lower and most racing clubs and dyno operators dont get or care about this fact.

mark kibort

For those playing along here. If you ONLY look at the wheels and tires being 100lbs, the KE at 800rpm to 1800rpm over 4 seconds is 10hp (ave) if done over 8 seconds, it would be 5hp (ave)
* assuming each wheel is 50lbs, 24" diameter and starting wheel RPM is 800 and final RPM is 1800. KE change is 30,000J = 37,000J ending RPM -7000J starting speed

So, if you accelerate the drums faster, the inertia has more of an effect. And the inertia of just the wheels and tires is only part of it. Everything else spinning has an effect too (before the gear box) . so , in the above example, if you are comparing two dynos, one with rollers half the inertia of the other, you could be measuring between 5-10hp less by only changing dynos.

BTW.. when you half the weight of the rollers, as we do in this comparison, the Inertia is halved. But if we also reduce the diameter by half, you quarter the inertia. So, in the end, cutting both in half, and you end up with 1/10th the inertia. this is why they can be accelerated much faster even reading near the same HP.

Still think there is no difference after knowing these facts, between a small roller and large roller dyno??

JWise

If I were looking for a Dynojet, I might go the the Dynojet.com website and use their locator. But that's just me...

http://www.dynojet.com/dynocenters/d...o-centers.aspx

mark kibort

I wonder if they track the transfer of title of all the dynos that seem to change hands between shops. This one dyno ive been using was used by the devek folks way back in the 90s!
Ill check that out.. thanks!
edit : the 2 out of 4 listed in my area are not available, but one looks like a possibility in the area near me. thanks again for the tip!
Mk

justaguy

If you're using an inertia dyno with no brake I see the point of the large diameter roller vs a small diameter. But most modern dyno's have eddy current brakes so the engine can be properly loaded in a way an inertia dyno cant. If I do two runs on our dyno back to back. one with the brake on and one with the brake off I get two completely different numbers. Go figure.

Mark , what are you trying to establish with the dyno any ways?

I would suggest using the same dyno for all your runs , no two dynos are going to yield the same results and you're going to end up chasing your tail.
That's my 2Cents

mark kibort

Generally, brake dynos are for tuning specific RPM. (using a brake dyno). i like to dyno in the way the engine is actually being used. Im not using it for specific RPM/ load /mixture/timing tuning, which is why i use the inertial dynos . All dynos with the same drum mass and size will register the same HP levels. Ive done hundreds of runs. very seldom am i surprised by the results and it has allowed me to do some optimization tuning as far as a air fuel ratios and cam timing. Generally, its just a yearly check up for the engine. I also need to use the dyno to prove performance for classification for NASA ST2 and PorscheOwners club racing.

when you are talking about "brake on and brake off" and getting two different values, are you talking about the dual function dynos? (both act like a brake and one acting line a inertial dyno)

keep in mind, there are very few variables based on the inertial dyno, as it measures how fast the drum can be spun up. you spin it up, the hp it takes, is what it makes. (ignoring all the correction factors)... with a brake dyno, you are doing things more statically (and conversions of the BEMF that the brake creates to stop acceleration equated to negative force. (or hydraulic versions) the engine and engine management systems might act differently, along with more heat being produced during the test.

I've run the back to back inertial vs brake dyno, (within days) Generally, the brake dyno was less by about 10hp . All my dyno runs (inertial) fell in a very narrow range over many years with no engine changes.

mark kibort

Yes, i think anyone would want HP to climb, anyway that it can! it's kind of a loaded question. are you asking is it better to have a HP curve that climbs or one that is flat for the same HP? the HP needs to be broad enough to match the gear spacing. so, in the 928's case, its better to have a flat HP curve (like the porsche GT4 cayman), but if you cant have that, its best to just make as much HP as possible. However, with our cars and limits of strength in the stock gear box, it would be more reasonable to want a climbing HP curve, so that the torque is lower in the mid RPM range and could lighten the load on the transmission.

As far as numbers that i would make with the greenbay stroker, i already know it. We make 380ish rear wheel HP.
as far as the stock manifold numbers.... i know i am HEAVILY restricted. there is good and bad with that. the engine doesnt work as hard , so it lasts longer, but also for some of the classes i want to run in , it doesnt help me to make any more HP (HP /weight ratio regulated classes for ST2 in NASA or GT2 with Porsche owners club POC)
However, with GT2 SCCA, i could use the extra HP and thats why i have STARTED the Aston Martin Intake project which i think is good for another 50hp when done. We all know that the Threshie intake (CF intake) on andersons and Fans cars made near 100hp more with no real tuning, so there are some big gains to be made with the intake that im investigating.

mark kibort

Swaybar, let me answer what was talked about with Greg brown and the carl engine and intake. ( I think this is the area you wanted me to see, right? https://rennlist.com/forums/928-foru...l#post14622860)

you and a few others are absolutely right. racing takes HP, and the average hp you can use is the potential for how fast the car will be on the track. and yes, anyone that races knows this and would NEVER use the car below 4500rpm unless they made a mistake in a selection of gear choice! greg talks about the "torque " at the lower rpm range for street driving and that is only for feel and comfort while driving around town or the highway. its nice to floor it at 3000 without a downshift and have more HP available than the next car in a lane next to you merge into traffic. cool for the street, no reason for it on the track.

Greg then goes on a rant forgetting that mark anderson and his 1:24 best time with his 928 , is slow by today's standards of technology (guys in cayman GT4s with 370rwhp are running in the 1:22s on DOTs ) He didnt win the "Porsche cup championship" running his 928, but running his GT3 cup car. Carls car could be a monster if set up right and mark or I could help him with that.
So, the point is, the HP that Carl made is AWESOME and woudl be very fast at the track with everything else dialed in from chassis to driver. the hp curve is great , giving huge hp and not breaking things at the lower RPM. we have to remember that the anderson FAN intake (CF intake) sacrificed much torque in the lower RPM vs the stock manifold but gained HUGE HP from 4500rpm to 7000rpm. this is where you want the HP to be , as thats where you would be racing it. you are dead nuts right.. if you are a racer, you use the engine where it makes HP, not where it makes torque. (as i often say, rear wheel torque ( or "HP") is what accelerates you faster than the next guy , not engine torque)

Im a huge fan of the intake , and have always said that the stock manifold, as great as it is for the street , is terrible for the track and for maximizing HP. thats why my Aston Martin intake project is so exciting for me. once i get the adapters from Hans, im going to get welding on it!

Mk

V2Rocket

Mark - why not just buy Carl's new high-rise manifold, already done and proven and production ready?
Sell the AM intake to offset the cost a little.

Imo000

I wondered the same thing.

mark kibort

i was looking at the thread.. its 59 pages long!!! ugggg,, why didnt someone start another topic?? anyway, i understand it might be what im looking for, but i do have some requirements.
i do need it to be able to bolt on without an aftermarket FI system or engine management system. i would like it to fit under the hood, for which the AM intake will as planned.
if this is what the product brings, I'm very interested!

maybe we need to start a thread based on that product offering if Carl is going to start making them.
Mk

Speedtoys

The duration of the power stroke of each cylinder is different, and the engine reacts differently.

Thats why_real_tuning is not done on a dyno,

Dynos are good for solving drivability issues, however, and compliance testing.

SwayBar

Mark, I think this is all excellent advice.

With the AM intake, you have LOTS of tricky fabrication work to do just to get it bolted onto the motor. Next, you need to fab an airbox, throttle linkage, etc., and then tune it properly. I'm thinking the first part will be much more difficult than you imagine.

If you get Carl's canted version-2 intake which will fit under the hood, there's no need to modify anything to get it bolted onto the engine. Plus, it's already optimised for use with a big stroker - just look at those PERFECT numbers.

The throttle body is located in the same general location as stock so the airbox may not be too difficult, and throttle linkage etc. all need to be done regardless of route chosen.

Let's see, an additional 150 chp will net you a grand total of approx 510 rwhp. Can you even believe it?!

Sure, it'll take some work, but it will be A LOT LESS work than going the AM intake route.

Finally, no more stroker tractor motors with Carl/Catorce's intake!