Here's a question for you dyno gurus. Say I have my car dyno tuned with my current setup SMIC, RB exhaust, resonated mp, etc....and a couple months down the road, say I want to switch to a FMIC, or a different exhaust or whatnot. Does that mean I have to get my car retuned on the dyno as well or will it be safe? Of course I realize that if I change my turbos or port my motor I will need a retune session, but what if it's just a normal bolt on?

 

Anything that changes the flow (basically, anything the intake or exhaust air flows through) has the potential to change your mixture for a given set of conditions (RPM, boost) with a given fuel map. If the new part flows about the same as the old part, the difference might not be enough to warrant additional tuning. The ECU will account for changes in intake temp, but not for changes in flow. Get a wideband to see if/how much the mixture changes. You can also do your own tuning with it.

-Max

 

Heres my question. When u guys are saying ur dyno figures are u using dynojet dynos? Cos here in aus we use dyno dynamics dynos which show roughly 30% driveline loss while dynojet use ~15%. I was always wondering how u guys were getting such high figures. Does that mean say at my mechanics the 488rwhp the guys car gets with the GT3540 should have ~12-15% added to be the same standard used as u guys?

 

Different dyno types read different figures.

Some operators do not apply (atmospheric and alttitude) corrections and hence if you dyno on a realy cold day you will get an over inflated number. Conversly if you dyno on a realy high pressure day your figure can be higher. Same applies to people testing at altitude on hot days for the other extreme, if the figures are not corrected to proper standars you will not a get "bench mark result" that will allow you to compare figures.

So first check is to make sure the figures are corrected for these atmosheric variances.

Secondly make sure the figures is what was measured at the roller, i.e RAW FIGURE no factors added to it to account for losses.

Then you can look @ differences in dyno types. For manual trans cars in the power levels averaged by single turbo guys a ROUGH GUIDE for you is the following, to convert RWHP to rough engine power.

Dyno Dynamics multiply by 1.3 to get engine power
Dyno Jet multiply by 1.15 to get engine power
Dynapack multiply by 1.17 to get engine power

As the power levels go up the power lost in the trans etc gets lower and the ratios tend to be less, this should help you do some comparisons though.

Just keep in mind dynos do vary a hell of a lot too, it should realy be a double check to another reference either on raod, or say maybe another dyno to double check the result if in doubt. If you do a search there is more info on this topic about comparing different dyno systems/correction factors etc etc.

 

But the factor of 1.15, 1.3, 1.17 if for figuring engine power right? So does that mean that they still read the same for the rw power?

STEPHEN

 

I had my car dyno tuned on a dyno dynamics and I was told that the rwhp is 15 pct less than what a dyno jet or mustang dyno will show.

 

If you have the engine power, you divide by the conversion for the respective dyno. Given the same engine number, dividing it by either 1.15, 1.17, or 1.30 will all produce different numbers.

Ex.200 engine hp/1.30(for dyno dynamics)=~153.8 rwhp

200 engine hp/1.15(for dynojet)=~173.9 rwhp

kyle

 

thanks for the interesting info everybody...

my dyno appointment at XS is on monday, anyone have any last minute advice??

 

MAKE SURE they have big *** fans, you need 2 fans (and not those ***** 30 inch home depot fans), one pointed at your intercooler and the other at your Intake.

 

If you have a stock IC, then I'd redyno with major IC change. The stock and PFC basic temp corrections throw a lot of xtra gas in at high temps expected with stock worthless IC. I can see going from 12.5 to 13.5 just changing to a real IC. See this thread:

https://www.rx7club.com/forum/showth...hreadid=137398

 

Assuming temp corrected and near sealevel, the main difference is the dynamic dyno uses 8.5" dia roller pair, vs dynojet with 48" or 24" drum. Dynamic has much more tire flex friction, and dual rollers increase effective weight on tire to make friction worse. That 1.3 correction may be ok for near stock hp, but likely way high for much higher than stock power.

Coast down tests on dynojets give somewhat accurate non-power based losses. Coast down on non-inertial dynos requires 2 runs at different brake loads, if not the operator is using fudge factor for system inertia.

The 13% (1.15 factor) total loss is good for stock FDs on dynojets, based on many published runs. The factor drops with major hp increases, mabe 1.12 at 350 rwhp.

I don't understand why the dynopack would have a larger factor vs dynojet, since dynopack runs directly of wheel hubs ... no tire losses. Otherwise agree with Rice Racing.

Note if at high altitude, the SAE elevation correction will be wrong on turbos, if comparing with same boost at sea level.

 

What equasion do you use to "correct" HP ratings?

 

For FD on dynojet, assuming about 50% of loss is power dependent:

eng hp = 18 + 1.07 x (rwhp)

so a bit less than 1.15 factor at high hp, say 400 rwhp:

400x1.15=460 eng hp, more accurate is 18+1.07x400=446 eng hp.

 

But if I dyno my car at say 30 deg at 1000 ft altitude, what temp and elevation do they correct it to and how. I would asume they use mean sea level, but what temp? I dynoed outside at about 30 deg and the guy told me I had 286 corrected rwhp. I assume I made more than that because it was so cold out.

 

The sae ambient temp correction is likely ok, but ambient pressure correction is for non-turbos. So, to find out what the real corrected rear wheel (not flywheel) hp is, multiply the 286 by:

k = [Pt(B+14.7)] / [14.7*(B+Pt)]

B = boost pressure off gauge at max hp.
Pt = ambient pressure during test, psi

so if local pressure at 1000 ft was 14.0 psi, and boost at 286 hp was 12 psi, then k = .98

in this example, 280 rwhp would be expected at standard sae temperature (60 or 70F?) and 12 psi boost, at sea level.

If u test at 7000 ft, the turbo correction k can be .90 or less.