Baseline temps and boost

[DThibault]

I just finished (with the help of guys here) going through the injectors and turbo of my old 93. This thing started out an old fertilizer truck single wheel W350, rusted to death cuz of the chemicals but well serviced. I got a cab from New Mexico, front clip from Maryland, painted it, rebuilt the Getrag and transfer case and built a nice flatbed for the back. Good looking but a pig. I wanted to liven it up a little. Anyway, before I started I got some gauges in it and a brief test got me 15 psi and about 1000 degrees on the pyro. Does that sound about right for a stock machine? I then put some 190 injectors in it and a 16 cm turbo housing for starters and now can't test it because of snowy roads. Will these mods change much on the gauges (or seat of the pants) without touching the fueling? Should I go ahead and turn the pump a little to get a little more out of it? I don't want a short fused bomb, I just want a little stronger horse to pull the cattle trailer and provide some fun while driving around the countryside. Thanks

 

[JLEONARD]

You'll probably get a little increase from those mods but probably not enough to meet what you want.

If it were me I would turn up the pump a bit... at least one turn on the screw.

And make sure the fuel pin eccentric is on the steepest section (facing forward)... grind off half the plastic collar while your in there.

That should get you boost into the 20s and keep EGT in check.

 

[JGrefenstette]

the temp and egts sound about right for what youve described. i put gauges in my truck after taking off the muffler and making my exhaust 4inch past the cab and turning out behind the rear wheel. and i took the air box off my intake. on flat ground i can hit 14psi ok, on a good grade ive hit 18psi. temps will stay pretty low unless you lug it or floor it at low rpms. for example, in 5th @ 60mph, 600-700 is a good temp. bost will stay at about 5psi @ 60mph.

 

[PToombs]

Jim, word of advice, don't lug it! If you lug it much you'll be putting a trans in it. Empty is more forgiving than loaded, but still not good. Loaded not below 1900, 2000 rpms.

 

[JLEONARD]

I am in 4th at 40 mph on a flat road (1400 rpm?), unloaded. On a hill, I wait until I am going 45... more if I am into it and accelerating fairly hard.

IMO there is a certain gratification in hitting 5th at 45 and rolling into the fuel..... give a nice smoke trail that will fill an intersection:-laf:-laf.

I try to limit boost when "lugging" so as to save the gutbag... but if she goes, she goes.

 

[JGrefenstette]

Jim, word of advice, don't lug it! If you lug it much you'll be putting a trans in it. Empty is more forgiving than loaded, but still not good. Loaded not below 1900, 2000 rpms.

hahha, shucks pete i never said "I" lug it. i said temps will rise if 'you' lug it, or 'you' floor it at low rpms ! :-laf dont worry im not scared to drop down a gear when pulling the hills if necesary, but honestly i rarely have a load and have never needed to down shift, im im much over 60mph the boost climbs at up we go.



ok i lugged it once. was down off rt. 81 in Christiansburg VA, on some back road through the mountains, in the Blueridge on an agressive grade to say the least. was talkin to my brother and not payin any attention to the gauges (very unusual of me) an i notice the motor is sounding week. look over, 1500rpms 1100degrees 55mph 5th gear grabbed 4th and wound the poor girl back up. i promised her it wouldnt happen again. it hasnt. so there you have it. my one confession

 

[JGrefenstette]

IMO there is a certain gratification in hitting 5th at 45 and rolling into the fuel..... give a nice smoke trail that will fill an intersection:-laf:-laf.

.

i find gratification in almost every aspect of driving the getrag

2nd gear is a favorite. get it to about 1800rpms then hammerdown. it bout stands up on you. love feeling the whole truck raise like that. 3rd is a great gear in general. still has enough to feel the truck torque-up on ya and can get you up to some good speed. 4th is a screemer. the boost i have found is best with 4th. i hit 18psi+ in 4th on a grade. thats pretty good for my setup, from what i hear. i rarely hit a high gear and smoke it out tho. i can blow some good smoke if i hold her down from say 1500-2500rpms. once i get past 2200rpms, watch out if your on my right

 

[JLEONARD]

I can hit 30+ psi at about 1500 rpm in 4th or 5th... . then it's a nice trail with gradual clearing:-laf

 

[JGrefenstette]

30psi?!?! thats pretty sick. what all have you done to hit numbers like that? does not having an intercooler allow you to get hight boost?

 

[Tippin Spotted Cow]

In theory, your intercooler should give you more boost, provided it doesn't leak. If its the original, it probably leaks a little. Cooler air takes up less space than warmer air, thus more pounds per square inch are possible with less effort from the turbo. A bigger intercooler should provide slightly higher numbers, actually (see second gen intercooler install).



I'm at roughly 42psi if I goose it, whether rolling or stopped. Probably the biggest thing would be to turn in your fuel screw and a couple other 100% free modifications to the fuel pump. More fuel = more exhaust = more pressure in the exhaust manifold = faster turbine = more pressure on the compressor side of the turbo.

 

[JGrefenstette]

i understand the chemistry of cooler denser air vs. hotter expanded air. i was just wondering if having that tiny distance from the turbo directly into the manifold would create any more initial boost. ya no, if it would have more potential... but i understand what your saying.

 

[dpuckett]

The intercooler increases air MASS going into the engine, but not necessarily pressure.



PV=nrT, with



n being the mass of air,

r being the universal gas constant,

T being temp,

V being volume, and

P being pressure.



Siince we are comparing trends, and not actual numbers, we will ignore "r" and "n". If "P" increases, so will "T", all else being equal. If you decrease "T", "P" will decrease, too. So, in theory, adding an intercooler can decrease your boost, but should also decrease your temps.



I could peg my 40psi gauge on my nonIC 91 with stock injectors, and 120cc fuel. My current truck has a similar turbo, intercooler, and stock IC injectors, and mid 30s is all I can get (and not NEAR as hot). Did I mention an extra 40cc fuel in the 92? FWIW, if I get much over 25-28psi boost, or over 3200rpm, my lift pump pressure plummets. Seat of the Pants says they are within 30hp of one another- similar acceleration and pulling ability, only the 92 is a LOT cooler doing so.



I agree with you, Tippin- the stock, original intercoolers probably leak by now. I got one from a 96 that had been tested to 50psi, and put it in.



That is today's physics lesson.



Daniel

 

[Tippin Spotted Cow]

Yeah, I guess I didn't neccessarily have my head on straight for that one... My theory would work if there was a way to cool the air before it got to the turbo, because air would take up less space, and more mass would move through the turbo, then warm up after being forced through and create higher psi. But I guess I bombed that one, cuz, as you said, if air is cooled AFTER the turbo, yeah, it could created a slight pressure drop.



What you could try, if you're a little ambitious, and have money to spare, is a water cooled intercooler. It bolts right on top where your intake plenum is right now, so the tube from the turbo goes right over the motor, just like on non-ic, and into the water cooled intercooler. They were provided on B5. 9 engines for other applications, so it must be somewhat a bolt-up job... kinda.



Or you could go for a real fun idea and go from your intercooler, into a water cooled one, and be the coolest kid in town... . no pun intended.

 

[PToombs]

Wow perfessor! Why are you working in the BBQ factory? :-laf

42 psi? :-laf That's about where I'm at, sometimes, and the clouds still rollin! :-laf

 

[Tippin Spotted Cow]

Yeah, for the first time since I put the spring in I decided to put my big boy pants back on and punch it off the line to see what it would do... 47psi... and high enough egts to cook thanksgiving dinner in about 3 minutes.

 

[PToombs]

Which turkey would your family rather see, the one under the hood cooking or the one behind the wheel? :-laf