BigBlueDodge

Okay guys, getting some opinions from different diesel boards. I've been hearing alot lately that adding an after market air intake and high flow exhaust can actually make you LOSE hp and torque on an otherwise stock truck. From what I am understanding, is that diesels depend on some of the back pressure from the exhaust to help them achieve their torque. I've also heard that PCM will start defueling to compensate for the increased air flow.

Is this a myth or reality?

hilclmr

Reality

BigBlueDodge

how much are we talking? What is the exact cause of this ?

halerazor

how do you put backpressure on a turbo charged vehicle. backpressure would just slow the speed of the turbo even with a straight piped truck if your blowing smoke 5ft out the pipe its being restricted but no backpressure the turbo controls that. if i can crush a box style filter from the vacuum of my turbo how would it hurt performance to put a bigger filter on that allows more air

pullin hard

i think that when adding an air filter kit, or better flowing air filter, the turbo will spool up quicker as it gets more air from the better flow, more cfm's
adding an exhaust would help it get rid of the air, which in turn should work together.
but i think with out adding the extra fuel and such, it chokes it with too much air and flow, and can't use it to full .
i have tried this therory out on my last gas truck, and just the air filter worked good, but then adding exhaust, made it a bit slower, add a power programmer, made it wake right up.
don't really make sense, but........

PourinDiesel

Some back pressure will help turbo spool up on a stock truck in certain circumstances.
It goes both ways.
Think of it this way, you could use the largest exhaust housing known to man and your spool up would be terrible and you would lose power.
It works the same when you start making your manifold larger, take away the muffler and cat.
You have bring those pressures back up to get the turbo up to speed.
Now with a modified truck you will fill that pressure gap faster and also need the free flow to get the extra exhaust gases you have created.

I know this all sounds funny and back ward.

But I lost hp on the dyno running with my boxes off and intake and straight pipe vs. stock with stock filter and muffler, but I did gain torque with the intake and muffler gone.

*I didnt have the turbo and manifold listed on my signature installed yet.

There is a reason for stock truck turbo's having a small exhaust housing: Spool-up, low end power, emissions etc.

RockRover

Yea, my jaw droped when I first read on this forum (and over on TDR) about the HP drop.

I had just ordered my AFE, TT and Magnaflow thinking more HP (along with lower egt's, miliage, etc). Funny to. I already knew about back-pressure and hp/torque with stock fuel deliveries on gasser engines, but not this time....Must have been the heavy Rottella smell in my cab clouding my judgement!

Wonder why very few manufactures will back-up their "30hp! GAIN" comments? Yea maybe on a bombed rig pushing a ton of fuel! Not usually stockers.

I justified my purchases anyway in the knowledge that I would eventually buy a box for my rig. I did and know I can have fun knowing my truck breaths better.

-D

Scotty

Joe D over on tdr did a lot of testing on the dyno with air intakes and exhausts.

Nobody lost power nor did they gain any. In fact he did a run with no air intake and that netted some power.

I did my own testing too. Never have claimed a power gain and never have seen a power loss. Real world testing is a better judge of what a product does overall compared to a dyno.
I don't drive on the dyno everyday.

I did see an increase in throttle response especially on the 3rd gen Rams. I have a theory for that...the sensor sees more air and sees a lean condition. Therefore it adjusts the mix by increasing fuel parameters.

I also suggest not to use my air intake unless you are adding some power on the 2nd gens.
On the early 3rd gens [03/04] a stock truck will benefit from my air intake for egt reduction and reports are faster cooldown and throttle response. The 04.5-05's have a different turbo and bigger intake so it takes adding some power and not much to quickly outgrow the stock set up. Towing is where an intake and exhaust really helps these trucks.

Scotty

AK RAM

Some of you may remember this….It was either Jannety Racing or Precision Diesel that did some tests last year on the effects of just intake and exhaust and had a little discussion about the results on the forum. I believe it was a Van Aaken thread where they were testing the new VA box (back when it was new). They did baseline dynos totally stock, then with just intake and exhaust. The net effect was a loss of roughly 10hp and a little torque (if I remember right), which isn't much in the big scheme of things, but a loss no less. The comparative dyno graphs they posted links to showed the loss was pretty consistent over many runs and if I remember right, was in the upper RPMs, well above 2K. They also showed that the addition of a boost fooler (no additional fuel), which they used a VA C3.2 in the off position, was all it took to not only do away with the HP drop, but allowed the small gains to be clearly seen that are normally claimed by intake/exhaust manufacturers. Their results at the time clearly showed there is a drop on a stock truck, although somewhat small and probably not detectable via the butt dyno, and is it tied somehow to how the truck sees and reacts to boost. Good 'ol electronics for ya. Their test vehicle was an 04 HO (305) if I remember correctly.

Someone handy with the search feature could probably find that thread.

What did you do to your truck Scotty ? Blow something up ?

hilclmr

I remember that post but I couldn't remember who did it ,thanks for clearing it up AK

PourinDiesel

I have ran both ways.
I lost hp with the I and E added about 15. But, I gained about 10lbs of peak torque..go figure.

Scotty

Nope still waiting for the new bumpers.
A kid cut across the intersection with a mini van...totalled it, 12K damage to the truck. Its all done just waiting for the Road Armor bumpers...apparently in transit now.
Air brushed flames and many other things have happened to this truck over the past 5 wks.

Scotty

Haulin_in_Dixie

Scotty I ran your early Scotty II on my truck completely stock with a straight pipe. There was no noticable difference in power but while towing there was a slight increase in economy and "I think" some hill power gain at heavy loads. I do know that as I added small mods to the truck the towing power continued to increase, the power faster than the economy. The first genuine economy increase came with the EZ and 275's. In that time there was a period that the economy would increase until I used the power heavily such as a heavy load going north on I-81, all up hill, the economy fell through the floor, worst I ever had but much more power. I saw some 9 and 9 1/2 in that time. This did not recover until I started getting into the commercial cam setup. Even the first one brought the economy up major. Not too much economy difference in good conditions but a large increase when really using the power steadily. The full ISB275 engine or RV275, same thing, made a good increase in both power and economy in all situations. Now my lowest is near 11 and the highest is 13 or better with loads.

To sum up, while pulling heavy, I never saw a drop in anything with open stock exhaust and the ScottyII. I did both at about the same time. Larger injectors and EZ gave more power and economy as long as I did not use it hard, worse if I was heavy on the throttle.

Also bear in mind that the commercial cams are not race oriented, more power, better economy, not as fast light to light.

cheff

From what I have read and learned since I got my diesel I believe this affects gas trucks more than diesel. And it affects non turbo charged gas more than a turbo charged gas engine.

I have not dynoed the truck, but I know for a fact that I lost HP but gained Torque, with my new exhaust and intake hoses. On my 1500 4.7 I lost both torque and HP when I did the intake and exhaust. It just turned in to a slug!

BigBlueDodge

this is interesting. I posted this on a Ford diesel forum, and pretty much everyone called it a myth. I'm assuming this is something that is only experienced with the Dodges. Maybe the PCM programming ?