Birdbrain

I cant find an answer to this, so lets find out what ya'll think

I did my ISR mod the other day, and my engine RPM dropped ~300.

I went from a little under 3grand doing 60 to a hair above 2500.

I have GREAT throttle response now and it seems like there is more umph than before.

But, i just cant figure out why my rpms dropped... im not really worried as it seems like i barely have to give it any gas to stay doing 60, and im pretty sure my tach didnt magically get skewed somehow since my idle stayed the same on the tach, but whenever im driving, it ~300 lower for the most part.

Ideas?

3.0 auto, 4.88 with stock 31x10.5 tire size

Elton

ain't working so hard to pump air now ? could pull the efi fuse so it reset the computer

Birdbrain

I was just kind of thinking that general idea Elton... I'm not complaining! shes running great! just kind of wondering WHY it happened lol

kiyobrown

Just like we discussed earlier. I thought speed and rpm's are speed and rpm's. I wouldn't think your rpm's would change, just that you could get to 60mph using less throttle. I would think the way for you alter what rpm you would have at 60mph on the speedo would be diff gears or diff size tires. But you have an auto, so maybe it changed your shift points of the auto tranny? Not quite sure how to explain it.

Glad it worked out for you though, I know your other intake hose was ripped. Lol

Jay351

Theres no way the ISR mod lowered your gearing..

I bet your tach is reading off. Try cleaning the ground/mount.

kiyobrown

The 3.0 is slowly lulling you sleep and then it's gonna steal your wallet.

rebelrunner

the engine isnt having to work as hard to keep you at those speeds because of better air flow

abecedarian

Theoretically- not possible unless the mod changed your gearing. Even if the mod increased engine efficiency 100%, the wheels still turn the same distance per revolution, the driveshaft still turns the same number of times per wheel revolution, the transmission still has the same ratios internally, and thus the engine has to turn the same number of revolutions to make everything move the same as it did. So increasing efficiency would only mean that you burn less fuel. Basically, whether you put a 454, Briggs & Stratton or even some turbine engine in the truck, the output shaft would have to turn the same RPM's to move your truck the same speed.

Edit-
In retrospect, there may be the odd chance that the transmission fluid isn't heating up as much as it used to, for whatever reason. This could cause a drop in engine RPM to maintain speed due to the fluid being cooler and thus more viscous which in turn means less torque converter slippage (which in turn means less heating of the fluid). However, I don't see 300 RPM's difference resulting from this.

Birdbrain

Where do i get access to the ground/mount?

Could i have bumped something while installing the mod? Hmm....

Jay351

The ground for the Tach (that will eff with it if its dirty, mine sure did) is on the ignitor.. Or coil, I can never remember which are which. It grounds where it mounts to the inner fender.

But its easy to spot, as there is another wire using it as a ground.