t4m0 vs. j4j1???

I used the j4j1 as a base tune, but ive changed everything that made it a cobra tune, The main differences between the two is the injectors and the MAF curve, although the same MAF, the curve is a little different. There are other odds and ends like high speed fuel enrichment, ect.

the j4j1 is probly a good place to start for you tho.

Just get your timing and AFR down to whatca want on the dyno and your tune will be close, but to do all the other tuning such as idle tuning, injector stuff ect. the R/T version is a must.

The problem your going to run into, even with the dyno time, is that once the adaptive kicks in and starts doing its thing...is when you will be at a dissadvantage. You know this from what you posted. I just dont want you going into a dyno session and thinking your all around drivability is going to be knocked down...WOT probably so but you may end up with alittle hickup here and there non-WOT.

The kinda good thing is that atleast you can get the car to RUN with the base model. When you have more cash you can always buy the upgrade.

IIRC on the J4J1 there are some much deeper (deeper than the tweecer will go) programming changes over the t4m0. The theory is that Roush had a short time to get the eec setup and working. They are believed to have shut down some parts and changed the way some other are calculated. I dont know if the posts are still there but I remember someone who had the ability on eectuning to look DEEP at the code. I am also preaty sure the load is calc. diff./or a diff. kind of load. The breakpoint and slopes are kinda screwie as well from other eecs.

The changes are also thought to be the reason its a good base and more adaptive as far as how it reacts to tunes...so its kind of a mixed blessing being a "hack" job.

For na 302 h/c/i combos ... many t4m0 peeps have found the j4j1
to be a way to make most of their drivability issues go away with
nothing but a quick upload.

Most of those peeps got 24's or larger and after market meters
so
They are gonna get into their tune to perfect their drivability.

Why anyone would wanna move a bunch of that t4m0 stuff over
to the j4j1 they will end up changing much of it anyway
to work specifically for their combo

One thing I like about the j4j1 is it does less + or - to spark and fuel
with the act and ect and there are other things but that is the biggie

True ... the j1j4 does add fuel at 90mph but its a snap to null that out

Yes ... You need the RT unit for the best results

Yes ... I'd tell you to use the j4j1

Grady

Punisher302 said:

thanks, gentlemen. my reasoning (however basic, hehe) was that because i have a cobra engine, i should use the base cobra tune.

of course, all i kept from the t4m0 was the injector #'s as i'm still running the stock maf and stock injectors (19#ers, hopefully i'll get some 24's soon).

gonna borrow a laptop today so i can raise the idle on my #3 & #4 settings to where it needs to be and drive it around for a couple days and see how the car runs that way.

i appreciate the responses--thanks.

Click to expand...

J4J1 , stock idle is 672 up that to about 704 and it should be good

Paul

One thing that is very different between the two is in the area of the various
values that are associated with injectors.

Here are just the main ones

t4m0

high slope ..... value chosen
low slope ...... high slope value x 1.46
breakpoint .... value chosen
inj offset ....... 1.125@14 volts

j4j1

high slope ..... same value as low slope
low slope ...... same value as high slope
breakpoint .... na if high/low same value
inf offset ....... 0.5@14 volts

The 4 parameters form a relationship with each other

Notice the HUGE difference in the one and only offset I listed

The t4m0 uses an offset more than double the value of the j4j1

I spent a lot of time with those relationships and found you can obtain
a nice stable Closed Loop tune with just about any slope value within
reason such as:

high low same
low@ high x 1.1
low@ high x 1.2
etc

You can see the lower offset value is present in the file where the
slopes are the same

Here is where I saw a rule of thumb come into play with slope values
after all my hosing around with trying different values

The larger the offset used ... the larger the difference between the slopes
will end up needing to be

These days, EEC Analyzer can help with inj values tremendously

Another big difference between the two is the scalar ... load scaling switch

T4M0, U4P0, W4H0 use a value of 2
while
J4J1 uses a value of 0

Tons of info written about load scaling so I won't get into it but
I use the default value of 0 in my j4j1 based file

Grady

Punisher302 said:

thanks, Sniper. that's actually where i have my #1 and 2 settings at: 700-750rpm and it idles great.

Click to expand...

you are welcome I just did a chip for a guy that did an auto to manual conversion on a 95GT , I used the J4J1 tune to reference for changes I did to his , I cant remember everything I changed but I tweaked his timing in a little faster than the J4J1 in the upper load levels and the car runs as if it has a set of GT40 heads on it and its bone stock , he is looking to get some heads and stuff soon , so I will get more experience with these computers as he gets more money to mod his car , he could not believe the difference it made, I am hoping to get some track times soon , we are going to pull the chip and run it and then put the chip back in a run it again to get some comparisons