OK, for this next post, let's refer to this document here, specifically the dyno sheet on pg 2.:

http://www.htturbo.com/OldSchool.pdf

It's the ad copy of David Dunbar's truck and his well-publicized switch from twins back to a single turbo. Open it to refer to as you read this post.

This dyno sheet is very useful, because it shows the stock charger, twins, and the HTT single all on one sheet.

The stock charger (blue line) peaks the tq at 2200rpm and the HP peaks slowly after that because tq is dropping faster than revs are climbing.

Then twins were installed (pink line). Notice how the dyno curve for the twins never crosses the stock charger's run. At every point, the twins far exceed the stock turbo. From 1400-2100rpm in particular, the power increase of the twins over stock is huge.

Finally, we have the HTT single turbo runs (green and grey lines). As indicated in the ad copy, the curves shift to the right about 200rpm relative to the stock charger. But that 200rpm can be huge. With the stock charger going down the hwy at 2000rpm, you'd have 100hp MORE available to you with the stock charger than with the HTT unit. The twins would be 200hp more than the HTT unit at 2000rpm, right smack in the middle of your rpm range.

Only at 2300rpm does the HTT unit finally surpass the stock turbo for power output. In other words, at all point lower that 2300rpm, the stocker makes more power and at all RPM after 2300, the HTT makes more power. A couple hundred rpm later, the HTT begins outpulling even the twins setup.

Once it does pass the stock turbo, the HTT unit ends up making an impressive 60hp more than the stock with the same fueling (475 vs 415).

But if you look at 2k rpm, the stocker is making over 100hp more than the HTT unit.

So one way to look at this is that we gained 60hp. Another way to look at this is that we robbed Peter to pay Paul, only someone took some interest off the payment-- we "paid" 100hp and picked up 60hp.

Oddly enough, the dyno runs for the stocker and for the twins start under 1600rpm, while the runs for the bigger single start after 1800rpm. I suspect that the operating range of the bigger single starts around 1800rpm.

The dyno runs extend well past 3000rpm. (to almost 3400). Good for reference, but I don't consider anything past 3K to be useable power, and anything between 2800 and 3K isn't much better. I'm sure others would laugh at this because they are kissing 4K or higher.

So in my world (a scary place, for sure), bolting on this HTT turbo would give me more power than stock for all of 500rpm. Worse yet is the loss of bottom end tq-- I've gone from about 820lb-ft at 2K rpm to as little as 550.


The dyno curves shown are quite similar to what somone might see when a larger camshaft is installed in a gas engine with no other changes made. `You don't really gain much power, you just move it from one place in the RPM band to another and the "power" increase only results from the tq being made at higher rpm-- the actual tq production is usually a modest increase (if increased at all) and the RPM of peak tq production will usually climb higher and closer to the peak HP rpm.

Comparing this turbo to twins, the twins hit 800lb-ft just after 1600rpm. The htt single hits 800-lb-ft just before 2200rpm. The stocker hits 800 just under 2K.

Still the dyno sheets make the HTT single look pretty darn good. For one thing, notice that the angle of ascent on the dyno curves when tq is building. The tq climbs as fast with the HTT as it does with the stocker-- meaning it spools "as hard" as the stocker. Notice how the curve with the twins starts pretty high, but the ascent isn't as steep as either of the two single chargers. In this case, the twins wouldn't "hit" as hard (proportionally).

While the newer single turbos are better than ever, they still lose a lot of "area under the curve" compared to a set of twins, but area under the curve depends heavily on where the lines are drawn. If you look at area from 2K rpm to 3200rpm, the HTT is better than the stocker but a little worse than twins.

The lower inthe RPM range you draw the lines, the worse it looks for the single. These are all important considerations for a given application, because if a person is used to higher rpm (4.10 gears, short tires, etc) it might be ideal to have the powerband occur farther up. But a truck with an auto trans, taller gears or big tires might want to reconsider and have the powerband occur a little earlier in rpm range.

While the 62mm turbos are considered a "mild" upgrade turbo, they are actually a pretty substantial increase in size over the stock 54mm inducer most of us have.


A couple final notes-- the dyno doesn't tell the full story at all. There's no way to know EGTs but the drastically reduced drive pressure of the HTT single should help a lot with this.

Also, this is a mobile DynoJet if I'm remember correctly what David's dyno is. That means that the larger single already has a strike against it compared to street testing. An inertial dyno tends to exaggerate a loss of spoolup on the bottom with larger turbos compared to what a butt-meter might tell you.

I'd be honored if David could chime in here with the "rest of the story" on his HTT turbo. I'd suspect that in the real world, his HTT performs better than the dyno sheet would suggest-- he says as much in his .pdf file on the HTT site.


Justin

 

^^^ What did you mean to say here? ^^^

... good analogy comparing bigger singles to larger cams on a gasser and how they effect the powerband - that's how I view it as well.

Why don't you consider RPM in excess of 3K to be useable power?

 

Newer SINGLES.

As for the 3K powerband not being useable, it's because it's so far out of the "design spec" for the CTD app as installed in a Dodge.

True, the old Marine 12Vs would rev to 3700 all the time. But making the higher RPMs truly useful on a Dodge application not only needs some kind of software trickery (drag comp, Smarty, TST comp, redline box, whatever), but also needs stronger valve springs and a different cam.

The factory cam on the 24V is dialed in at 2K rpm (as verified by this being the lowest BSFC in factory trim). BSFC past 2700rpm is getting worse pretty fast-- it actually starts getting worse past 2K, but the rate of increase picks up the higher you go in RPM.

If a person installed some beefier springs and an appropriate camshaft, then the useful rpm range can probably extend to 3500 or so.

I think I remember someone posting on TDR a long time ago that Cummins says that rotating assembly is pretty good until 4K rpm-- so really we only have to worry about the valvetrain and the fuel delivery (inj pump) to get closer to 4K.


With a Smarty/TST stack and an H2 cam and matching springs, I'd feel pretty comfortable extending my definition of "useful"power.

But if I picture myself yanking a trailer up a large grade and ask myself how high on the tach I'm comfortable running it, the answer is right at the "rated" power of 2700rpm. I'm sure it's safe to 3200, but the engine isn't really pulling well at that speed.

Then again, if I had an HTT turbo, the pull would be there for sure, and 3200 would "feel" a lot better.

Justin

 

Great post Justin you really get a guy thinking......

 

I have a 3gsk but just dont feel comfortable pulling the 12,500 5ver at more than about 2500 rpms. But thats just me.

 

Also, there's quite a difference in the powerband between VP trucks and the HPCRs... With aftermarket fueling, plenty of power still there at 3500, especially with cam & springs. The CTD in the '05 works a lot harder blasting down the quarter than it does pulling the sled WOT at 3500 RPM.

Additionally, lots more area under the dyno curve on a common rail - most of max torque is in at 1600 RPM, and it stays almost flat to just past 3K. (stock fuel map)

 

how did you figure this out??? dragging a sled seems like it would be WAAAAAY harder on a truck in all ways then a drag strip run

 

we didn't rob peter to pay paul, we just have to operate the truck at a higher RPM

 

If I wanted to do that, I'd buy a gasser...I like torque, so twins for me.

If course, I'm also a hypocrite, since I have 4500RPM fueling with the cam, headwork, and turbo to help support it too

Chris

 

Well, you either see it or you don't, I guess.

As for the difference between a HPCR truck and a VP truck, all I can do is shyly acknowledge that the VP trucks are not as good as P-pumps or HPCRs.

The HPCR is a far superior fueling technology in every way that I've toyed with trading my truck on one that just a year newer to get a common rail. Then I realize that I love my truck and it's perfectly adequate for what I want to do.

The injector setup on the HPCR allows for a much higher tq output and more control over fueling. I personally believe that we are headed in the direction of "charge shaping" where the computer is determining the exact pressure and temperature in the cylinder a couple hundred times a seconds by injection manipulation.

The Siemens piezo 6.4L Ford injectors are a bellweather of things to come, imo.

Anyway, that all relates to turbos a lot, because the HPCR setup can spool a much larger single turbo with acceptable response.

JMO

 

It certainly is in some ways - here's my observations as left-seat pilot...

EGTS are much higher in the quarter (especially with no-lift shifting from the tree to the traps) and there's lots more banging about due to gear changes, but the sled is what tears up the driveline more - 1st 25' eats up the soft parts, last 25' spits out the hard parts. The engine just hums along at 3500 RPM.