Why isn't my Dakota R/T faster?

[dakrt2000]

Here is the list of my mods: Mopar Headers down to full 3" exhaust single out, custom intake, ported throttle body, 1.7 roller rockers, mopar PCM, autolite 3923s, msd ignition wires, 180 t-stat, 20" r/t wheels. Ok my 1/4 mile time is 15.1 @90mph. what gives, I ran the same time less the rockers and throttle body. So I cant understand it. Its a club cab but still I should be running high 14s with these mods. Any feedback or tips would be helpfull. Thanks guys.

Nick

[T.j.]

Have you dynoed it since these mods? do you run the 20's on the 1/4? Not sure if 20s will mess up your time.

[razman131]

Here is the list of my mods: Mopar Headers down to full 3" exhaust single out, custom intake, ported throttle body, 1.7 roller rockers, mopar PCM, autolite 3923s, msd ignition wires, 180 t-stat, 20" r/t wheels. Ok my 1/4 mile time is 15.1 @90mph. what gives, I ran the same time less the rockers and throttle body. So I cant understand it. Its a club cab but still I should be running high 14s with these mods. Any feedback or tips would be helpfull. Thanks guys.

Nick

well for one it appears you still have the stock beer barrel intake. that hurts your top end. runnin the 20`s adds a LOT of WEIGHT as well.

grab a M-1 intake, slicks and do some weight reduction.

ya got some great bolt ons there, and in the righ combo should get you high 14`s.

if ya wanna go faster, heads, cam and send your ECM to B&G or Mike Leach. dont get me wrong, the MOPAR ECM is good, there is better out there.

[realdeal7369]

Here is the list of my mods: Mopar Headers down to full 3" exhaust single out, custom intake, ported throttle body, 1.7 roller rockers, mopar PCM, autolite 3923s, msd ignition wires, 180 t-stat, 20" r/t wheels. Ok my 1/4 mile time is 15.1 @90mph. what gives, I ran the same time less the rockers and throttle body. So I cant understand it. Its a club cab but still I should be running high 14s with these mods. Any feedback or tips would be helpfull. Thanks guys.

Nick

a wheel change to someting lighter will get you a 14.8osomthing. the 17's i have with tires weight in at 60lbs each...check out prime wheels for there sets they have for the dak, i know i am, once my 318 stroker is done... :banana2:

[N56629]

You don't say what size tires you are running. If they are taller than original and you are running stock gears along with a ported throttle body, you probably have some low-end issues. How does it feel on launch vs. top end? What is your 60' time?

[dakrt2000]

I have been told that the M-1 will help me with my mods. My tires are 275/45/20 however I ran the same time with the same tires but without the roller rockers and throttle body. So you think I would have run a faster time. I dont have my timeslips so I dont have my 60 times.

[DirtyR/T]

yeah your 20's are hurting you. Get you the M-1 2bbl like everybody has said I would also get a 52mm F&B TB. I assume you ported a stock TB . Also get a 2800 converter.

[realdeal7369]

yeah your 20's are hurting you. Get you the M-1 2bbl like everybody has said I would also get a 52mm F&B TB. I assume you ported a stock TB . Also get a 2800 converter.

2800 is a little high in my opinion for the mods he has. if he had a supercharger...maybe, i would look at protorque or something like that for a billet converter in the 2200-2400 stall range. stock is 1200-1400 i think isnt it?

jim

[Brandon00RT]

Im at 14.67@93mph with my mods so far. This is with my bed cover, tailgate, full tank of gas, 20" R/T's up front with stock 17's out back on Kumho's. I havent went back with the weight reduction and drag radials yet, but you need to mod alittle more and lose weight :biggthump

[WicKed R/T]

Definately lose some weight. Also, what were your 60ft times? A good 2.0-1.9 60ft will get you a much better time

[RLG]

I lost .5 sec on 20s just by adding AuburnGear LSD and 4.10s. Gears would probably help you a lot.

[dakrt2000]

Thanks for all the input. But how much more weight can I loose? My rear bumper is gone and no spare tire, but what else could I do?

[Alex]

You could still lose lots, only put enough gas in the tank to get you down the strip and back, take the tailgate off, same with the tonneau, stuff like that, weight it your worst enemy..not to mention those 20's are definiltly hurting the worst...it's a known thing apporx, that for every 100lbs,= a tenth of your et..

[MoPaR DaK]

Were you getting decent traction? Any clue of even remembering what the 60' was?

[360 xrt]

Just curios are you turning off your overdrive,also weather has a lot to do with 1/4 mile times.

[JethroStyles]

Are you running the Stock 3.90 gears?

With big Ol dubs on there, I'd run either 4.10s or 4.56s (if you wanna be fast in the 1/4 atleast) I would personally run out and buy a set of "Unique" 589 lookalikes... They are basic 15x8 Aluminum 8 hole wheels, they still look nice, and with 245/60R15s weight less than my stock 15x7 with 235/75s. It made a NIGHT AND DAY difference in acceleration, I never ran it at the track, cause it wasn't open... Unsprung weight is BAD... 20's look cool, but take em off at the track!... The front's be aight to run, but small wheels all around will help ya more than you think!

[realdeal7369]

i would get these...

http://primewheel.com/

model 231 in the truck/suv rear wheel drive section of the aftermarket wheel catagory. im getting a set for the track only...

and they do come in 6 lug too. just ask them....

jim

[N56629]

I have been told that the M-1 will help me with my mods. My tires are 275/45/20 however I ran the same time with the same tires but without the roller rockers and throttle body. So you think I would have run a faster time. I dont have my timeslips so I dont have my 60 times.

That tire/wheel combo is dropping you about one set of gears. 3.55's would be like 3.35 and 3.90's would be just a bit over 3.55. As far as I'm concerned, an M1 and larger TB isn't going to gain you anything on the bottom end. To make use of them you will need headers and gears. 4.56 gears would give you an effective gear ration of 4.3. That's where I would put my money first.

[mopar rt]

Here is the list of my mods: Mopar Headers down to full 3" exhaust single out, custom intake, ported throttle body, 1.7 roller rockers, mopar PCM, autolite 3923s, msd ignition wires, 180 t-stat, 20" r/t wheels. Ok my 1/4 mile time is 15.1 @90mph. what gives, I ran the same time less the rockers and throttle body. So I cant understand it. Its a club cab but still I should be running high 14s with these mods. Any feedback or tips would be helpfull. Thanks guys.

Nick

You listed a custom intake. What was done to it? Depending on the intake and how much you opened up the T/B you may be running too lean and not fully burning the air/fuel mixture. Opening up a stock T/B can take it past 1000 CFM and that is more then enough to accommodate 800 HP and above.

Again depending on the intake and T/B I would make two simple changes. One, drop the Autolites and go with a set of the NGKs in one heat range colder. Second, install a capacitive discharge system a MSD would be fine. If the intake and T/B have not been taken too far these two changes should get you the time that you are looking for.

The one clue that makes me think that your running too lean is the fact that you installed a set of the 1:7 rollers and never saw any improvements. If the mixture is too lean by adding the 1:7s all you are doing is allowing more of that lean mixture into the combustion chambers. If you cannot burn it then you will loose HP and torque.

[N56629]

You listed a custom intake. What was done to it? Depending on the intake and how much you opened up the T/B you may be running too lean and not fully burning the air/fuel mixture. Opening up a stock T/B can take it past 1000 CFM and that is more then enough to accommodate 800 HP and above.

No way are you going to get 1000cfm out of a modified factory TB. Not only that, but when did the TB start regulating the A/F? The PCM pretty much takes care of maintainig a constant A/F mixture, especially in closed loop.

Custom intake? That always throws me too. These days a custom (air) intake refers to some sewer pipe with an air cleaner attached to the end of it. It's not like the old days when you actually designed and built something like an intake manifold. It's custom air intake and that also has nothing to do with how rich or lean it runs.

[WicKed R/T]

The only real way to change the air/fuel ratio is to upgrade the injectors, flash the pcm with a different fuel curve, or relocating the IAT to the intake tube to make the pcm think the ambient air temp is actually cooler therefore the pcm dumps in more fuel.

[dakrt2000]

Ok maybe this will help clear some things up Originally I had 17 r/t wheels and ran a 15.1 1/4mile with headers intake 180 t-stat and Mopar PCM. Then I added 20's and ran the same time 15.1 similar weather conditions. After, I added 1.7 roller rockers and added a modified stock TB that flows close to the F&B 50mm (so the guy says that did it for me) and did a full 3" single exhaust set up with flowmaster 40 series. And still ran the same time. That Is what confused me about the whole thing. The truck felt stronger after the final three mods but didnt see an improvment at the track. Tractions seems good. I guess I will find some smaller wheels and go back to see what happens.

[T.j.]

Thats odd...whats your driving style at the track? OD on or off? what do you do for a launch. Your mods and times are peculiar(sp?)

[supradakotaman]

hmm i just find it weird that u ran the same times on the stock 17s and the 20s having the same mods each time? Unless when u were on the 17s u didn't get a good run and on the 20s u really got a good run? haha not sure. At any rate u shouldn't be in the 15s still with those mods now...try again with the oem wheels and see what happens!

[dakrt2000]

I leave the O/D on. Hold the brake pedal and give it a little rev.

[mopar rt]

No way are you going to get 1000cfm out of a modified factory TB. Not only that, but when did the TB start regulating the A/F? The PCM pretty much takes care of maintainig a constant A/F mixture, especially in closed loop.

Custom intake? That always throws me too. These days a custom (air) intake refers to some sewer pipe with an air cleaner attached to the end of it. It's not like the old days when you actually designed and built something like an intake manifold. It's custom air intake and that also has nothing to do with how rich or lean it runs.


First I can tell you that a stock T/B opened up can exceed 1000 CFM. Been there done it. The set back is that you loose too much metal and the shaft is too easy to bend. I did not say that the T/B regulated the air fuel mixture.

It stands to reason that the more air that enters into the intake thus finding it’s way to the combustion chambers will produce a lean condition. Nothing in the PCM controls air intake. The T/B is nothing more then a controlled vacuum leak and if you push past the design limits you will lean out the mixture and decrease vacuum. The internal combustion engine is really nothing more then a very large vacuum generator. Too much air in and vacuum decreases too much air out and the vacuum decreases. You want a controlled condition that is balanced.

I still say that if he installed the MSD he would see noticeable improvements in his times.

[dakrt2000]

I will look into an MSD setup. What will it do to correct what you are saying?

[MoPaR DaK]

A ported throttle body is not going to make it run lean... lol

I'm with N56629 110% on this one.

[T.j.]

I thought I read somewhere that running with the OD off is the best thing, am I wrong on this one?

[WicKed R/T]

OD should be turned off when racing at the track. Reason being is you risk the chance of burning it up.

[mopar rt]

A lean mixture is harder to burn then a rich mixture this is even more so at lower RPMs. The MSD with it’s multiple sparks and hotter sparks will help burn the fuel mixture. A more complete burn means more HP.

Too large of a T/B will also slow down the velocity of air entering into the intake manifold thus robbing power in the low end. A great tool to have in your box is a vacuum gauge.

The ideal air-to-fuel ratio is called the Stoichiometric Ratio. This ratio describes the ideal thermo chemical process, where all of the air and all of the fuel is consumed during the combustion cycle. Also realize that all internal combustion engines control the amount of power by controlling the amount of air that is ingested in the engine, then supplying enough fuel to burn efficiently. The ideal combustion ratio is 14.7:1.

[N56629]

First I can tell you that a stock T/B opened up can exceed 1000 CFM. Been there done it. The set back is that you loose too much metal and the shaft is too easy to bend. I did not say that the T/B regulated the air fuel mixture.

It stands to reason that the more air that enters into the intake thus finding it’s way to the combustion chambers will produce a lean condition. Nothing in the PCM controls air intake. The T/B is nothing more then a controlled vacuum leak and if you push past the design limits you will lean out the mixture and decrease vacuum. The internal combustion engine is really nothing more then a very large vacuum generator. Too much air in and vacuum decreases too much air out and the vacuum decreases. You want a controlled condition that is balanced.

I still say that if he installed the MSD he would see noticeable improvements in his times.

You can remove the entire shaft and throttle plates, open it up to 52mm and still not flow 1000cfm. The trottle shaft bearing limit the maximum diameter on stock throttle bodies. To do what you suggest, you would have to remove the bearings, plug and relocate them. Then you would have to plug weld part of the IAC cavity. Alternately, you could do what I do and that is to remove the center section, use a half throttle shaft, .035 throttle plates and even then you would be hard pressed to get to 1000 cfm.

Even if you some how manage to reach that stage you would then have to modify the manifold to flow that much air. Those two ports on top of the manifold act like a restrictor plate unless altered.

Of course the PCM doesn't control air intake, it controls how much your injectors flow by controlling pulse width. There is a point beyond which the PCM can not compensate, but I doubt that you will reach it modifying stock parts.

There's nothing wrong with installing an MSD ignition, but it wouldn't help if a lean condition did occur.

[MoPaR DaK]

But as mentioned above, the PCM will give an adequate ammount of fuel and make the proper mixture. You're not going to run lean from a air intake and bigger throttle body.

[dakrt2000]

Who here turns there O/D off when racing? I messed up my O/D by turning it off back when my R/T was still under warranty. I would like to know a bit more about this. It started leaking trans fluid out where the drive shaft connects to the tranny. and O/D had to be replaced so I never turn it off anymore. I would like some more input on this topic though.

[MoPaR DaK]

I turn it off, no problems.

[N56629]

Who here turns there O/D off when racing? I messed up my O/D by turning it off back when my R/T was still under warranty. I would like to know a bit more about this. It started leaking trans fluid out where the drive shaft connects to the tranny. and O/D had to be replaced so I never turn it off anymore. I would like some more input on this topic though.

Coincidence. What you described sounds like a rear seal. I don't understand the part about replacing the OD. It makes no sense that your OD should be affected by turning it off. You won't even come close to redlining in Drive.

[dakrt2000]

The dealer told me they replaced the OD unit. But maybe it was the seal too. It was a while ago.

[MoparDrvn]

I turn OD off ... even sometimes when I'm driving in townbut when racing it is off all of the time..the OD wants to kick in every chance it gets.. & IMO if you are on the gas hard it will cut on & off thus causing more ware...

[Five9Dak]

Anytime you are driving the truck hard you should have OD off, because it is meant for cruising not beating on it. I will go in and out like the previous poster said. Id say I drive with OD off about 40% of the time, cause hunkering down in OD is just gay IMO, why wiat for a downshift when you can already be in the right gear?

Your tranny failure is unrelated to OD being on of off.

An important thing we are leaving out in this discussion, What were weather conditions and 60 foots for each of the days in question? IMO the mods you have done, would not show up if you had a great run in great weather w/o the mods, and poor conditions and 60 foot in the modded runs. Because in identical conditions, I think you would gain .2-.3 from EVERYthing you listed.

Oh, how much do YOU weigh? (if your heavy it makes it hard to compare to other drivers, on the converse, im like 130lbs so my truck turns a lil faster time then it would if a larger adult was driving.) I think you were prolly running too much gas in the tank on the latter modded runs.

I dont think stalling the stock converter is helping you any, if anything it is hurting consistancy and making your comparisons harder.

[dakrt2000]

Lots of good info guys thanks. The next time I will go to the track I will turn OD off and get som 15" rims with slicks instead of 20's and give it a go. Hopefully i will have an M1 by then too.

[360 xrt]

truth be told about your rims(20s) your truck won't know the difference between 15s or 20s its all about tire diameter,so if your WHEELS are the same height 17 verses 20 with tires theres no difference.as far as engine mods go i knew right away you run with OD on because your adding parts for higher rpm horsepower and its shifting into OD before making full power in 3rd gear.

[supradakotaman]

well i think for the rims...it's the matter of added mass of the 20"ers versus the 15"ers rather than overall diameter, since it is true what u said that the height of tire + wheel if unchanged won't do a thing.

[N56629]

truth be told about your rims(20s) your truck won't know the difference between 15s or 20s its all about tire diameter,so if your WHEELS are the same height 17 verses 20 with tires theres no difference.as far as engine mods go i knew right away you run with OD on because your adding parts for higher rpm horsepower and its shifting into OD before making full power in 3rd gear.

I theory, you are right, but in reality you are looking what is available for tires in those sizes. You can't get a descent drag tire for 20" rims, actually, I don't know of any over 17". A 15" steel rim and a good set of tires will outperform anything you can put together on a 20" rim.

[realdeal7369]

Who here turns there O/D off when racing? I messed up my O/D by turning it off back when my R/T was still under warranty. I would like to know a bit more about this. It started leaking trans fluid out where the drive shaft connects to the tranny. and O/D had to be replaced so I never turn it off anymore. I would like some more input on this topic though.

i turn mine on and off whenever i feel like it, had no problems. what you are supposed to do, (and what the dealer dont tell you), if you are driving in the city, and or in traffic, turn the od off. this keeps the trans from searching through too many gears, and helps to keep the heat down in it too. the more it rows through the rgears the more heat builds up in it.

O/D is mainly for the highway use, and is not meant for a towing gear or climbing up big hills or mountains ranges. if your towing, keep it off.

jim

[dakrt2000]

It all makes sense now :biggthump

[DaPurpleRT]

Get DRs/ET Streets, add an M1, turn the OD off and you will be capable of low to mid 14s.

[tweetybyrdrt]

I got over 400 1/4 mile runs with the overdrive turned off, no problems. it's the 400 runs that killed my stock tranny. my mods are M1, pph headers, mopar pcm. I leave the tounou (sp), tailgate and spare on. run Hoosier Quick time pro's on the back and averaged 14.70's to 14.90's in shitty Hawaii conditions. here at LACR (High desert, LA county REALLY shitty conditions) I have a really hard time hitting the 14's at all. ie... track conditions, track prep, weather, elevation, wind, and how pissed the wife is that your at the track all effect your time's. Just go back over and over again, learn your truck (at the track) and your times will improve.

[Li'lBlackTruck]

I'm curious what your reaction time is.
Headers will lean out an engine. When I put headers on my Barracuda I did some research and the rule of thumb for a carburated motor is to go up 1 or 2 jet sizes after adding headers.

[WicKed R/T]

I'm curious what your reaction time is.
Headers will lean out an engine. When I put headers on my Barracuda I did some research and the rule of thumb for a carburated motor is to go up 1 or 2 jet sizes after adding headers.

Your r.t. has nothing to do with your e.t. It only matters when you're racing another person. As far as headers leaning out an engine, these are FI engines in which the pcm is constantly adjusting itself to keep the a/f ratio the same. Have you ever looked at an a/f ratio on a FI car or truck, the thing never stays still unless of course you get a wideband. A wideband is the most accurate way of determining your a/f ratio.

[Five9Dak]

Increasing the airflow of a speed density motor will lean it out at WOT. This is because the ecu beasically dumps fuel in open loop mode. Your stoich cruise AFR will remian the same.

[03Dak]

Would be nice if the aftermarket would provide us an affordable way to reflash our PCM's rather than force us to stand alone units or generic flashes for stock vehicles.

As Black stated:

Increasing the airflow of a speed density motor will lean it out at WOT. This is because the ecu beasically dumps fuel in open loop mode. Your stoich cruise AFR will remian the same.

In SD open loop, the PCM relies solely on the data in the VE table and a stored LTFT, used as a multiplier, for fueling.

In SD closed loop, the PCM is constantly chasing it's tail, adjusting the LTFT's, to reach the commanded AFR.

Opening the intake and exauhst systems creates a lean condition, that, under closed loop operation, is accomodated for in the LTFT's. Positive LTFT's indicate a lean condition the PCM added additional fuel for. Negative LTFT's indicate a rich condition the PCM as trimed, removed, fuel for.

If your LTFT's are positive under closed loop operation, when you go to WOT, the LTFT of the Fuel Trim Cell you were previously in, is used as a power enrichment multiplier creating, more than likely, a rich condition. If your LTFT was negative, then you more than likely will run WOT in a lean condition.

So, to the guy that started this post, get a program like AutoTap, log your LTFT's and O2 sensor inputs under closed loop and WOT and you should be able to tell if you are running rich or lean.

Also, ditch the 20's for racing. IIRC, 1 lb of un-sprung weight is equivalent to 4 lbs of sprung weight.