UNDERSTANDING how to "turn up" the power

[BPaulsen]

Coming from a bone stock truck and only moderately trying to improve performance a bit (without sacrificing too much fuel economy), I'm learning something on this board every day. Membership is not only worth the moderate admission; it's priceless!



I'm trying to UNDERSTAND what's going on when turning up the power. I want to KNOW what I'm doing and WHY I'm doing it, and my guess is other members are feeling the same way.



So here I go, and please chime in with your expert advise.



1) Although the 5. 9-liter Cummins engine is capable of much more power, ours has only 160hp at about 2500rpm because of factory settings which were based on primarily emission and warranty concerns. Right?



2) We get a better initial throttle and cold start response by turning the smoke screw on the IP in. The reason the factory didn't do this is, again, emissions concern. Right?



3) Max horsepower of 160hp comes at 2500 rmp although many stock trucks run out of steam at around 2400 rpm. What happens is that the "governator" spring inside the IP cuts off the fuel to the pump at that given rpm level. Changing the screw to a "better" one will allow fuel to flow beyond that rpm point and the Cummins is well capable of reving higher, up to a point of 3000+ rpm when valve float will occur, something that can be prevented by installing "better" exhaust valve springs. Right?



4) Now I'm getting a bit lost.

The power diagram of a stock engine reads that beyond 2500 rpm the power curve falls off rapidly. If the fuel is turned up, and if thanks to setting and governator spring the engine reves higher, will the power also climb up, i. e. , 160hp @2500 rpm will turn into 180hp @ 2900 rpm or what. Or not?



5) Spoolup.

I understand that a smaller turbo exhaust housing will allow pressure to build up faster, thus the turbo will spool up quicker, hold boost earlier, i. e. , lower in the rpm range, and--since there's no wastegate--run with somehow higher boost in full song. The 16cm2 housing is a great compromise since it allows spooling up quicker but will not allow the boost to climb to levels where it would potentially harm the engine.

Question A): with more boost coming in earlier, is the power output of a 16cm2 housing at, let's say 1700 rpm also higher than it is with a stock 18. 5 or 21cm2 housing?

Question B): All things being equal, except for a smaller housing. Since at 2500 rpm the smaller housed engine would make more boost, is there also more power?



6) Injectors

"Bigger" injectors flow more fuel. But if you install Bosch 190 or POD injectors, and left everything else untouched, wouldn't they NEED more fuel to begin with? HOW can they make 40hp or more power?

 

[cerberusiam]

1) Although the 5. 9-liter Cummins engine is capable of much more power, ours has only 160hp at about 2500rpm because of factory settings which were based on primarily emission and warranty concerns. Right?



Yep





2) We get a better initial throttle and cold start response by turning the smoke screw on the IP in. The reason the factory didn't do this is, again, emissions concern. Right?



IIRC in will lean the mixture and out richens it. NOT: the only thing I could ever get the smoke crew to do is clean up the idle. I have seen no noticeable gains in start or throttle response. May very depending on tune.





3) Max horsepower of 160hp comes at 2500 rmp although many stock trucks run out of steam at around 2400 rpm.



IIRC factory specs are start defuel at 2600 and all in by 2900. In my experience the high idle screw and linkage is responsible for most of the lack of throttle and shutting down at 2400. Changing the gov spring OR changing the gov weights will allow higher revs. If one expects to run much over 3000 then valve springs are a really good idea. This engine is an interference engine so valves and piston will meet.



4) Now I'm getting a bit lost.



HP is a function of rpm. The higher you can rev the HP will be read so if you have the fuel to feed the higher rpm's the HP will rise.



5) Spoolup.

I understand that a smaller turbo exhaust housing will allow pressure to build up faster, thus the turbo will spool up quicker, hold boost earlier, i. e. , lower in the rpm range, and--since there's no wastegate--run with somehow higher boost in full song. The 16cm2 housing is a great compromise since it allows spooling up quicker but will not allow the boost to climb to levels where it would potentially harm the engine.

Question A): with more boost coming in earlier, is the power output of a 16cm2 housing at, let's say 1700 rpm also higher than it is with a stock 18. 5 or 21cm2 housing?



A lot is dependent on the compressor and fuel curve for power at certain levels, but, changing nothing else will probably only result in nominal changes of power.





Question B): All things being equal, except for a smaller housing. Since at 2500 rpm the smaller housed engine would make more boost, is there also more power?



Once again this is more related to fuel and compressor map than it is housing size. If you have more air (boost) than the you have fuel exhaust flow drops which drops boost back into line with avaialble fuel for rpms.



6) Injectors

"Bigger" injectors flow more fuel. But if you install Bosch 190 or POD injectors, and left everything else untouched, wouldn't they NEED more fuel to begin with? HOW can they make 40hp or more power?



It is only possible to shove so much thru a fixed orfice at a certain pressure. Increasing the size of the orfice increase the amount of fuel that will flow at a certain pressure for a certain time period. Bigger injectors allow more fuel at lower or the same pressures while not taxing the pump.

 

[JLEONARD]

5) Spoolup. ally harm the engine. 

Question A): with more boost coming in earlier, is the power output of a 16cm2 housing at, let's say 1700 rpm also higher than it is with a stock 18. 5 or 21cm2 housing?



A lot is dependent on the compressor and fuel curve for power at certain levels, but, changing nothing else will probably only result in nominal changes of power.

With only a 16 cm housing and a K&N filter, I made 160 hp at the rear wheels. So if you work that back to ENGINE hp (assuming drive train losses) I would say that it is a significant improvement. Plus lowering engine rpm by about 400 when the boost started to come in.

 

[dpuckett]

I agree- changing exhaust housings will change your torque curve, and may give you power sooner, thus giving the FEELING of more power. However, it takes fuel to make power, so the gains will likely be in the lower RPM range.



Jay- did you get a syno reading BEFORE the housing swap? Many of the nonIc engines made ~200hp and ~500lbft off the assembly line. Not sure why, but they did.



To answer a few other questions-



(2) To improve low end throttle response, you need to take off the AFC cover, and turn the starwheel (gear- like thingie) counter clockwise to lessen tension on the AFC spring. You can also rotate your tapered pin to where the deep part of the taper is facing the front of the pump. I agree with cerberusiam, the smoke screw has done little in my experience, even with a new pump.



(4). Not necessarily so, but it is possible. It takes fuel to make power, and takes fuel to make RPM, so you just because you have more RPM doesnt mean ipso facto you have more power. Your power curve can also flatten out til the governed speed, or it can even fall off.



Daniel

 

[cerberusiam]

With only a 16 cm housing and a K&N filter, I made 160 hp at the rear wheels. So if you work that back to ENGINE hp (assuming drive train losses) I would say that it is a significant improvement. Plus lowering engine rpm by about 400 when the boost started to come in.

I have noticed a lot of the 5 speed trucks will dyno right at the rated power with only the addition of a good air filter. Any numbers on the before changes?