Engine/Transmission (1998.5 - 2002) twins installed have questions?

[Wyatt 1]

I installed some twins, street twins from piers. They seem to spool real slow but that is compared to the stock turbo, so far only pushed it to 35lbs of boost, stock clutch didnt like it, I was on my way to the shop to install the new con fe. Also the egt is very throttle responsive I went up to 1200 easy but cools off quickly is this normal, I assumed the twins would be allot cooler when cruising right now they are running about 800 degrees with no load, should it be cooler and could this be because they are new?

 

[ThrottleJockey]

Those Jammer 3s MIGHT be a bit small to turn your big charger, more fuel and that set up will light off.



It sounds like your big charger is being kind of lazy. More fuel and you get more boost.

A set of twins will always spool slightly slower than the smallest turbo in the set.

 

[justinp20012500]

Cruising my twins are hotter then my single was.

 

[Hohn]

Cruising my twins are hotter then my single was.

This is probably a good thing for engine durability. A CTD running a constant 1100 degrees or so will last a long long time.



Hotter cruise, cooler peak-- both are good things IMO.

 

[justinp20012500]

This is probably a good thing for engine durability. A CTD running a constant 1100 degrees or so will last a long long time.



Hotter cruise, cooler peak-- both are good things IMO.

Is there any documentation that exists showing a CTD will last longer @ 1100* (pre) then 800*?





Wyatt 1,



When pulling a hill I can get to 1300*, when I notice it I just give it more fuel and the boost shoots to 55-60 and the pyro falls to 800*. Just use your foot as a guide.



Around town the truck runs cooler with the box on kill then when its off.





Justin

 

[jwilliams3]

Doubt it.

Cooler the better for longevity.

Easier on the rings, block (coolant), gaskets etc.



IMO

 

[Hohn]

Doubt it.

Cooler the better for longevity.

Easier on the rings, block (coolant), gaskets etc.



IMO

I'd encourage you to re-think your doubt. WHY exactly are lower temps easier on the block and rings? Gaskets, I will grant you.



But the engine is designed to SUSTAIN EGTs up to 1300 or so indefinitely. That means that piston clearance, ring gaps, etc are all spec'd with this temp in mind.



In most engines, cylinder bore wear goes DOWN as cylinder operating temperatures come up. I don't remember where I saw the graph. The reason is that the piston's expansion in the bore produces a tighter fit, equalling more piston stability and LONGER ring life.



Bore/cylinder/piston life gets longer as the cylinder temps gets hotter, RIGHT up to the point of seizure. Ever notice how many racers report that an engine has run it's absolute best JUST before it blew up? (think Nascar or Midgets, or Sprints).



Same thing with oiling systems. Higher operating temps burn off moisture, which reduces the formation of acids. Oil flows better when it's hot, allowing better lubrication. (Yes, this also breaks down the oil faster if running dino).



Cooling systems operate at their given temps because of the limitations of a water-based coolant and the small range between operating temp and boiling temp. A higher temp (if possible) INCREASES engine efficiency, as it results in less heat loss to the coolant.



That's my argument, what's yours?



jmo

 

[Hohn]

Is there any documentation that exists showing a CTD will last longer @ 1100* (pre) then 800*?





Justin

Well, the documentation I saw was bore operating temperature, not specifically EGT. I'd think that higher EGTs would mean hotter bore/cylinder/piston temps, though, wouldn't you? The documentation was also on a gasser, but again-- the same principle applies.



Is there any documentation that shows that a CTD will last longer at 800° than at 1100°?

 

[Forrest Nearing]

at 800* EGT, coolant temperature swings up and down... at a steady 1100*, coolant temp will probably sit more even at a more optimal operating temp.

 

[Hohn]

Agreed. Less stress on the t-stat because it's not cycling all the time.

 

[justinp20012500]

But the engine is designed to SUSTAIN EGTs up to 1300 or so indefinitely. That means that piston clearance, ring gaps, etc are all spec'd with this temp in mind.

Every thing I have seen that was published by Cummins says not to exceed 1000* sustained exhaust gas temp. (Now it did not say anything about pre or post so that temop can be up for debate)

Is there any documentation that shows that a CTD will last longer at 800° than at 1100°?

Dunno??? Just thought I'd ask. You talk about this subject like you have seen documentation.

 

[Forrest Nearing]

big trucks have traditionally run their pyro thermocouple post-turbo, so I've got to assume those are post-turbo numbers.



Forrest

 

[Hohn]

Yes, the 1000° figure from Cummins is POST turbo. The spec for PRE is 1350, I believe.



And yes, I HAVE seen researched documentation showing that cylinder life (bore, pistons, rings) increases with engine operating temp, right up to the point of failure.



Wish I could remember where I read it, though.

 

[Forrest Nearing]

it's true... that's why trucks that pull trailers all the time will go 500k-1mil miles and grocery getters are blowing oil out the road tube at 200-300k

 

[darkhorse]

it's true... that's why trucks that pull trailers all the time will go 500k-1mil miles and grocery getters are blowing oil out the road tube at 200-300k

Golly! Over the hill as I am & i'm still learning new stuff on this board.

 

[Wyatt 1]

Thanks for the reply everyone, kinda spun out of control but thanks, Throttlejockey what would be a good injector for this setup?



Also I got about 500 miles on the new set up and the new clutch installed and decided to try out 4 on the box it pulled hard boost got up to about 40 and it cut out in third and fourth gear so I got out of it, didnt look like anything blew apart but it would not boost above forty, I was busy watching the pyro and the boost could their or is their a rev limiter maybe the RPM was to high, that is the only thing I thought about after the fact, I retightened everything boost wise but did not test, any body have any opinions?

 

[ThrottleJockey]

Maybe step up one size to 4s at least. I'd go 5s or 6s IF they were still streetable. HOs run out of fuel at EDM 4s but you can still run a bigger stick, it just won't net you any more HP. It will help turn a set of twins, though.



Brian

 

[Wyatt 1]

Thanks Brian, any comments on the cutting out while getting on it in 3rd and 4th gear?