12H-T performance Build (2 Viewers)

[mudgudgeon]

Gbentick, interesting read mate.

Curious, what is the purpose of the back cut turbine blades? I am assuming it is less restrictive?
How does this affect spooling and boost at low RPM?
Is wastegate operational?

 

[gbentink]

Clipping the tuirbine; what I have called "back cut" is for additional flow at higher rpms but may be good in the midrange.

These turbos use a fairly tight exhaust housing and are restrictive after ~2800rpm.

This is an experiment I wanted to try. Some people say "never clip a turbine, blah blah....but when many turbines ship from Garrett clipped already, what do you think is correct?

Basically, clipping the turbine reduces the work the turbine can do but decreases the restriction through the turbine.

I postulated that back cutting the turbine would see a similar rpm for initial spool, but bring on boost with rpm more gradually over std and see increased performance up top. I havent done before and after measurements, so impossible to state conclusively. Also, my exhaust is so retsrictive up top that until I change it, it is unlikely I will see much benefit. What I can say though, is that so far the negatives with the auto are minimal.

All the mods are a balancing act. Too big a compressor wheel = loose bottom end, too small = loose top end. The turbine side is the same and is something i have not toyed with before. If for example an engine uses a small exhaust housing that causes the compressor to hit surge down low and logically would also choke it in the higher rpm, clipping the turbine does the job of reducing the surge tendency and increasing flow.........all good in that application. Ours is close to that application.

I plan to fit a larger compressor wheel (which I have, balanced ready to go in), boost controller set for ~ 19psi (waiting for it to arrive), intercooler and free flowing exhaust in the next month or so. It would seem to me that ~200 flywheel hp is EASY and 240hp MAY be possible with only the mods referenced. I am sure there is more there, but not at the boost and hardware I am playing with.

Already it drives "strong" and gets to 100km/h quickly, I am hoping for sub 10 seconds to 100km/h or 64MPH as a benchmark! Probably takes 12-13 now.

 

[gbentink]

It may be interesting to note with turbos is that as you move from the center of the efficiency island towards surge, you loose efficiency. This is Ok you may think, I have an intercooler so the extra heated air can be cooled and I have my boost; so whats the problem??

The problem is that you need more exhaust energy to drive the turbine and this comes at a cost - backpressure. Backpressure robs power through turbine drive losses and reduced volumetric efficiency.

So by clipping the turbine or fitting a slightly larger A/R exhaust housing; you might loose a few psi down low, but proportionally a smaller loss in torque. Why? Because as you reduce the torque to the compressor (that would otherwise surge or near surge) at the low revs it moves the compressor to a more efficient spot on the compressor MAP, so you limit your losses to an extent and *may* gain better fuel economy. By better I mean, *might* be measurable on a long drive.....

 

[Dougal]

All the mods are a balancing act. Too big a compressor wheel = loose bottom end, too small = loose top end.

I think you've got that backwards.
One of the main indicators for a compressor is tip-speed. A bigger wheel gives a higher tip speed for the same turbine rpm. Sure it'll be heavier and take a fraction longer to hit the same rpm. But it does more for the same rpm.

But a bigger compressor wheel will choke the turbine more. Hence it's not as good for the high end.

Have you timed it to 100 yet? How's the axle tramp with leaf springs and that much torque?

I still don't understand why you persist soo much with the CT26's.

 

[Dougal]

It may be interesting to note with turbos is that as you move from the center of the efficiency island towards surge, you loose efficiency. This is Ok you may think, I have an intercooler so the extra heated air can be cooled and I have my boost; so whats the problem??

The problem is that you need more exhaust energy to drive the turbine and this comes at a cost - backpressure. Backpressure robs power through turbine drive losses and reduced volumetric efficiency.

So by clipping the turbine or fitting a slightly larger A/R exhaust housing; you might loose a few psi down low, but proportionally a smaller loss in torque. Why? Because as you reduce the torque to the compressor (that would otherwise surge or near surge) at the low revs it moves the compressor to a more efficient spot on the compressor MAP, so you limit your losses to an extent and *may* gain better fuel economy. By better I mean, *might* be measurable on a long drive.....

If you're spending enough time in surge to affect your fuel economy then you've got a turbo selected by a muppet.

A turbo should only run near the surge line for breif moments of acceleration. As soon as it starts to build boost the air-consumption curve is headed right across the map away from the surge line.

Of course this brings us back to the biggest problem with a CT26. There are no compressor maps, so until someone makes us one (temp measurements on a turbo dyno) then it's just guessing where the surge line, choke line and efficiency islands lie.

 

[gbentink]

Quote " I think you've got that backwards."

I am referring to Trim, not diamater of exducer. Larger exducer requires more torque and on a given turbine, within some limits, can produce a higher pressure ratio.

Quote " CT26 persistence"

Reliable turbo, cheap to rebuild (easy also), cheap to high flow, bolts up to stock manifold, bigger exhaust side than GT25 series that can give > 200rwhp, different exhaust housing options available.....

I am playing with this engine since I will likely sell it within 6 months, so why not use what I have and learn? If I dont know what a modded stock setup can do, I am hardly in a position to know where the non stock items make a difference.

I will post a 0-100 time shortly. I have only driven it 50 miles since I rebuilt it.......

I guarrantee it will be a fairly impressive time, all things considered.

 

[Dougal]

Quote " I think you've got that backwards."

I am referring to Trim, not diamater of exducer. Larger exducer requires more torque and on a given turbine, within some limits, can produce a higher pressure ratio.

Oh right. It's worth stating trim to save confusion. After all different trim wheels (but same diameter) are often machined from exactly the same casting.

Did you know that a simple one plate adapter can let you bolt up any of the garrett T2/T25/T28 series to a CT26 manifold?

 

[gbentink]

I have seen them on eBay and may use one, one day. But if I am going to bolt on a Garrett, it will be the GT25 VNT that I have (direct bolt on) or the GT37.......... I may try the latter just for fun on the 4 litre.

I am going back and checking the casting on the 1HDT Auto (a friend has one, same as my old one). I am thing it may have a smaller AR than what is fitted to the 12HT.

This coming weekend I will do a 0-100 time and get one of my kids to video the whole thing from inside the cabin! Maybe I should put it on You Tube.....

 

[Dougal]

I have seen them on eBay and may use one, one day. But if I am going to bolt on a Garrett, it will be the GT25 VNT that I have (direct bolt on) or the GT37.......... I may try the latter just for fun on the 4 litre.

I am going back and checking the casting on the 1HDT Auto (a friend has one, same as my old one). I am thing it may have a smaller AR than what is fitted to the 12HT.

This coming weekend I will do a 0-100 time and get one of my kids to video the whole thing from inside the cabin! Maybe I should put it on You Tube.....

Forget Ebay, I have plans for all the common adapters. CT26 & CT20 round ports to T2, T25, T28, T3 to T25 etc. Any steel gas cutter can do the outline for you. Finish it off with a die-grinder and drill then you're good to go.

The GT37 is way too big for a usable diesel this size. Sure it'll give you a high power dyno queen, but drivability will be poor. The turbine map doesn't even start until 21 lb/min of exhaust flow. That's 4000rpm on a 4 litre engine.
http://www.turbobygarrett.com/turbobygarrett/catelog/Turbochargers/GT37/GT3776_452159_1.htm

Video will be cool.

 

[Tapage]

Forget Ebay, I have plans for all the common adapters. CT26 & CT20 round ports to T2, T25, T28, T3 to T25 etc. Any steel gas cutter can do the outline for you. Finish it off with a die-grinder and drill then you're good to go.

The GT37 is way too big for a usable diesel this size. Sure it'll give you a high power dyno queen, but drivability will be poor. The turbine map doesn't even start until 21 lb/min of exhaust flow. That's 4000rpm on a 4 litre engine.
TurboByGarrett.com - Catalog

Video will be cool.

thought a GT35 will be the max usage for a DD diesel aplication ..

 

[mudgudgeon]

which CT 26 housings and compressor wheel are you using?

I am currently rebuilding my 1HD-T after turbo disintegrated. I have std 1HD-T turbine housing and will probably combine it with Supra core and compressor wheel and housing.

You mention an "auto" 1HD-T turbine housing, as far as I can tell, from info on the net, 1HD-T all had the same turbine housings?

 

[gbentink]

From experience, I can say you are wrong

I also have video of it, engine mount ripping torque between 2000-2200!

 

[gbentink]

CT26 from 7MGTE.

I understood that the manual 1HDT had a larger housing. I could be wrong on this because I has since discovered the 12HT has the same housing on both auoto and manual.

I have been lead to believe that the 1HDFT had a bigger AR exhaust housing. After driving it, I believe it.

 

[Dougal]

From experience, I can say you are wrong

I also have video of it, engine mount ripping torque between 2000-2200!

You're talking about the GT37 on a 4 litre diesel?
Do you have a model number for this turbo, because the maps for the GT37's on garretts website show that's not going to happen at 2000rpm.
If you ran an extremely dirty tune (high EGT's, lots of smoke) you could get it to spool sooner. But that's not drivability.

How much torque exactly is "engine mount ripping? Given that most engine mounts resist prop-shaft torque of several thousand Nm I don't think it's a useful description.

 

[gbentink]

Tapage, I have a question for you.

The 12HT is a noiseier engine than the 1HDT that came in the 80 series, however the NVH levels in the 80 series are MUCH improved over the 60 series. I was wondering how noisey the 12HT is over the old 3F inside the car and also whether the 12HT is fairly quiet with the bonnet down in the 80?

 

[gbentink]

Dougal, it is a VNT 52 trim 82mm

 

[gbentink]

Actually it was on a 4.16 litre, not 3.98 litre, but we are talking 100rpm difference between the two.

It was my Brothers car and I got him the turbo and setup a rudimentary electronic control for it.

From a very smokey start (he didn’t care) it went to a haze at 1800rpm to zero at 2000rpm when all hell broke loose, spinning the 35" tyres between first and second changes.

Don’t know what it boosted to, but the needle accelerated past 20psi (gauge limit) fast at approx 1800-2000rpm.

On my spreadhseet, it matches following the surge line. I would only put it on my 12HT for fun. I intend to use it seriously with the 4.93 litre stroker.

He did not keep going with it because he was concerned about the life of the motor with such unknown high boost but for the most part he built the pump (VE) himself and it was out of fuel after 2500rpm. He used the wrong bits off a lower revving diesel.

 

[gbentink]

OK, it was in the 700-800nm range I am guessing, probably the higher end. It had the biggest of the bPWR barrel intercoolers and a 4" straign through exhaust, turbo back.

The gear shift severely lent over and it "felt" like it was trying to twist the chassis. Pump was 140cc and it was smokeless under boost.

Doesnt your little 3 litre do that?

 

[gbentink]

Shows no problem hitting 30psi by 2200rpm on my spreadhseet

 

[Dougal]

OK, it was in the 700-800nm range I am guessing, probably the higher end. It had the biggest of the bPWR barrel intercoolers and a 4" straign through exhaust, turbo back.

The gear shift severely lent over and it "felt" like it was trying to twist the chassis. Pump was 140cc and it was smokeless under boost.

Doesnt your little 3 litre do that?

My little 3.9 is full-time 4wd. With just over 500Nm it can break traction on dry tarmac in second, in wet tarmac or cornering hard on dry tarmac in third.

I use a man-made viaduct of known slope to calculate power and torque. I know I've got 75kw at the ground at 2000rpm. If you allow 35% drivetrain loss then that's 535Nm.
It burns clean below 1000m altitude. 20psi with no intercooler.

It doesn't take 700-800Nm to break traction in a 2wd leaf sprung vehicle. Have you verified torque or power figures or just guessing?
Of course with a 4.2 and VE pump, your brothers truck sounds like an 80 rather than a 60. Full-time 4wd and auto or manual?

How do you predict 30psi with your spreadsheet? It is very difficult to predict spoolup times for fixed geometry turbos unless you have a baseline (i.e. same turbo on different engine or only slightly different turbo on the same engine). It is nigh on impossible to predict behaviour of a VNT on a diesel with a spreadsheet.

To burn 140cc/shot of diesel cleanly (AF ratio 20) in a 1HD requires 60psi of boost. Colour me sceptical.