Tjabo

Hey guys, this may be stupid, and I'm sure whether it truly is or not, someone on here will adamantly say it is! Heh heh. . .

Anyway, I've noticed that when looking at dyno results, I often look at the engine displacement, and the RPM at which the horsepower line crosses the 200HP line. From that I get a basic idea of the "Spool" characteristics of a given turbo. Clearly displacement makes a difference in the RPM at which a turbo spools up, but since none of the normal engines on here make 200HP naturally aspirated other than at very high RPM, I think this looks like a fairly valuable datapoint.

Case in point, if you look at this dyno plot alleging to be a GT30r, you see the HP line crosses 200HP at about 4,700 RPM:



If you look at this one from another thread on the sc6262, you see that with an 84mm LS vetc (~1.9L?) this one crosses the line at about 4,900-5,000:



Of course, that is probably a bit of a displacement difference, but it's also a significantly larger journal bearing turbo.

Anyone find any merit to this type of analysis for a basic idea of power vs. spool out of a given turbo?

boosted91crx

you can also use a turbos compressor map and plot it to get a idea, but from dyno graphs i just look at where the HP starts to ramp up, that is where boost is starting to take affect.

Tjabo

Exactly!

I just thought that looking at a specific point helps to make things a little more definite/objective. I guess that's why I started looking at the 200HP line.

96 GSR-T

I think compressor maps are can be misleading.

I always look at the 5252rpm Hp/Tq crossover as a sign of inital spool up and power output, most people cross over into VTEC in this region + or - and if a car isnt making more than 200/200 at 5252rpm its pretty laggy IMO.

That 1st graph looks more like a 35R than a 30R to me, 30R's come on harder than that from what I have seen.

Here is my 81.5x87 8.2:1 Graph with GSR Cams and a 67ho, comes on decently.

Tjabo

Hmmmm. . . That makes good sense, sounds like a pretty good way to judge things.

And taking a good look at your dyno there, that t3/67ho is pretty impressive.

Thanks for posting!

LightningTeg

Full boost is where the torque flatens out or peaks.

96 GSR-T

VTEC was set at 4200rpm so I think that helped alot with the spool, most of the 67ho graphs I see are 500-1000rpm later than mine and/or under 200/200 at the crossover.

Tjabo

I guess "full boost" doesn't seem like that good of a comparative measure to me because it varies so much from setup to setup. I'm kind of looking more for an indicator of where the turbo is really lighting up. After going back and looking at a few more dyno results, both of the other approaches listed here seem pretty good.

turbociv910

Im trying to see a b16 w/ 42r graph-

Tony the Tiger

Full boost and full torque doesn't always come hand in hand... You can have a car that develops very early boost, but the engine could still be inefficient at those lower RPM's. Cars with roller rockers (VTEC killers) or very aggressive cams with smaller turbos could behave that way; although boost is there, the torque won't develop yet until the RPM's get there.

As always, spool HP/TQ on a dyno graph doesn't say much about boost response. When you drive the car on the streets or on a roadcourse, you'd rarely allow a car to make a full 4th gear pull starting at 2500RPM and go through the entire rev range in a span of 20 secs. Turbos build boost based on exhaust energy and time, so the more time you spend pegging the engine/turbo at XXXX amount of RPM, the turbo will gradually develop more torque the more time you are under WOT. Usually about 5-7 secs later the turbine will reach its highest speed under those specific RPM's and no torque is further made, but you would rarely drive like that on the road (like sticking it in 4th gear at 60 km/h and hammer the throttle for like 5 secs, trying to experience the "torque" illustated on a dyno sheet...lol)

On a street car, response is often what you look for. You can do simple tests, such has keeping the engine at say 4000RPM (a frequent driving zone) under light throttle, and then watch the HP and torque output about 2-3 seconds right after you go WOT on the dyno. This is a true measure of useful spool that you'd use on the road. You'd realize that some turbos make awesome spool on a dyno sheet, but fails to build any useful torque and has no response whatsoever. The other test is to see how long it takes the turbo to build full max torque/HP under spool range (how soon it makes max power). It can be done by holding engine RPM at say 6500RPM, and then go WOT and watch the dyno and see how long it takes to achieve that full torque and HP. Or else, you can run into a "grand daddy turbo" that looks good on a dyno sheet, but keeps falling out of boost between shifts and takes a lot of time to "wind itself" back up to high boost regions.

This is where the GT turbo vs old technology turbos come into play. You'd realize that a common T3/T4 50-trim can build very good torque on a dyno, but has slow response compared to any other similar sized GT turbos. This is also where common misinformation about dual BB turbos originate. On the dyno, ballbearing makes minimal difference, but response on the street or roadcourse will make you a true believer in BB turbos.

Tjabo

Wow, good explanation, thanks! ! !

ahobbs

good thread

LightningTeg

Tony I know exactly what your saying. When I dynoed my 18g it seemed to come on real slowly yet on the street it was very responsive.

turbociv910

vtec killers, 9 psi on a b16.. to show that it spooled up around 6, but didnt have peak tq till around 8500