Engine/Transmission (1994 - 1998) p-pump tuning

[AH64ID]

Pre temps are not really changed with modification on older engines, but newer ones are. As you increase timing from the OEM retarded profile the max safe EGT drops, and the variance between pre and post changes too.

Also what modifications do you do that allow the piston to get hotter? That's really what we are after isn't in, not melting a piston.

With varying turbine efficiency you get different temperature drops across the turbine, and thus post is not a constant. Even thou pre does not tell you the piston temp it's a more constant indicator of conditions.

Why does ISSPRO make a post gauge? That's easy. . people buy it, and that doesn't make it the best way. Yes it's better than nothing, and on a 100% stock motor it's fine but as you effect flow thru the turbine thru modifications the reliability of the post measurement changes. So yes 1000° post is 1000°, but is it 1200° (safe) or 1450° (unsafe) pre? You won't ever know if you only watch post, and with modifications that assumed 300° differential can easily get you in trouble.

What about the difference pre and post when the WG opens and closes? Now the air isn't getting a temperature drop across a turbine and your post temp will climb and you will remove fuel to keep the EGT's cool, that removes power unnecessarily.

There is one time a post is a better temp, and that's when monitoring EGT's for shutdown.

Is post EGT or TOT?

No 1301° won't cause a failure, but if you use 1000 and its a 370° (possibly on a B series) difference and you sustain that temp then yes you can have a failure, even at your safe post temp.

The bottom line is that you are guessing with post temps, and you don't have to with pre.

 

[hsmith]

Not sure if this makes any difference, but I can tow with my #10 plate, enhanced air mods, timing, and stock sticks and not worry a lot about egt's. If they start to get a tad high, I control them with the right foot. When I ran the 75 hp sticks, it was a completely different story. Leaving soon for a 6-7k vacation and am not concerned about not being able to control the temps. Also have a cooling mist system for backup, seldom used though.

 

[Bob4x4]

The 10 plate was designed for the 215 pump and defuels at the rpm it should with stock injectors. The 100 plate does not. Even with the 10 plate it is in the fringe of too much with a stock turbo and will benefit from a larger turbine housing. Add injectors and you need more air unless of course you don't mind driving staring at your gauges

 

[Cosmo]

With the injectors, I figure I was seeing about 600 degrees difference pre/post after however long it takes to get from 0-60.

If I get home at a reasonable hour tomorrow I'll check to see if the wastegate is actually opening.

When I get some time, I'll tinker more with everything and figure it out.

 

[SRay]

Cosmo: my truck did at one time have a seized open wastegate. For some reason I never noticed it happened until I pulled the manifold out to replace the gaskets. Looking into the turbine housing it was open a little and wasn't moving from there. I unseized it, closed it, and removed the hose. It's now seized again but in the closed position. I think the truck was a bit more peppier but smoked the same and pulled the same.



The ddp 50 injectors smoked less than my factory injectors but runs hotter.



I've got a bae turbo kit for my hx35 that I'm gonna install and maybe either the 18 or the lagmaster 21cm turbine housings to help lower egt's while still trying to look as factory as possible.



Bschwarzli's 1990 1st gen truck made 285 hp over my 283 on the dyno and his runs cooler egt's using a hx35 turbo with a 18cm turbine housing. I think he sees 1,250°f towing and 1,400°f wot. I'll have to ask him again, not sure. But it's better than my setup. I just installed the ddp50 so I now have more power than Bschwarzli but pushing 1,600°f max.



While he did beat me on hp. My truck puts a lot more torque down. So something different with the pumps.

 

[hsmith]

I agree Bob and I do have a Super B setup. I spool pretty quickly and tow well. My CM gauge sits in the dash next to the spill holder. It's bright red digital temps are easy to read at a glance also.

 

[Cosmo]

You can tow all day long at those temps. As far as the high boost numbers, it sounds like your waste gate is not working, maybe a hole in the diaphragm or sized up? I think a #16 turbine housing would help and is a cheap mod.



Nick

Bingo.



THANK YOU. I hadn't even considered that the wastegate wasn't working. I put air to the hose and it just comes blowing right out the shaft.



Now to get that fixed...

 

[cerberusiam]

Now watch the temps go ballistic when the WG opens. That will limit boost which limit the air available and there go the EGT's.

 

[Cosmo]

Which is kind of why I posted this thread, to get tips on how to fine tune everything in the AFC...

But honestly, is limiting boost really going to cause the EGTs to go much higher than super-heated over-compressed air?

And again, limiting the boost was my main concern. The EGTs after 10+ seconds of WOT are something I'm not going to hit nearly as often.

 

[cerberusiam]

EGT's at WOT throttle are not as important as EGT's at part throttle and 70% load towing a grade. At WOT, less boost, same fuel, it will be hotter. Even if the turbo is out of its map it is still providing usable air in the form of boost even though the charge is not as dense and cool as it could be. Performance at lower boost pressures that do not involve the WG are the key.

The test will be maintaing acceptable speed on grades when loaded. If you can maintain an acceptable speed on a long grade with EGT's in an acceptable range, the problem is solved. Example; 45 mph with EGT's at 1300 degrees while keeping the engine temp from hitting the peg. Someone else may say I want that speed at 65 mph with the same results. It is going to be relative to what you deem accpetable.

 

[Cosmo]

Ok so here's an update.

I ordered an AFE wastegate actuator and it showed up the other day. Of course, the service writer didn't bother to tell me that it showed up in the 6 hours it sat next to his desk before he went home, so I didn't get it until yesterday when I checked the shipping status and saw it was already delivered.

Today I went to swap it out, and the #$(U% actuator rod was about 2" too long with the end threaded all the way in.

So I did some measuring and figured I could cut about an inch off both ends. It worked. Truck doesn't go a tick over 40 (which is still a little higher than I would like) and I haven't seen over 1350 under extended WOT acceleration up a decent grade.

If I tow a trailer will I want to keep an eye on EGTs? Yeah, but I would anyway.