so i have a 90 rex dex, d15b2 multiported, z6 manifold, gsr throttle body, si trans, lightweight flywheel, stage 2 clutch, header and full 2 1/4 exhaust....but the question is why does the car feel like it cracks vtec at 4k rpm to redline? it runs just fine, no cel or anything, its snappy but just pops at 4k and takes off, i wouldnt say it reallly bogs but just doesent have the go like it should until that certain point........any input?

 

Depending on which ECU you are running may effect lower RPM. Since you are running a MPFI d15b2 motor, the Si ECU will not be exactly correct for that motor, but it does suffice to run it efficiently.

If you want a better powerband you will need to have the car professionally tuned which will allow for max power output and fuel opimization where some places in the current map maybe running a bit leaner than other spots.

 

Timing good?

 

as far as i know timing is ok...it does have a slight backfire when shifting sometimes....dizzy timing?? idk.....and im running the pm6 ecu and a z6 map sensor

 

Backfire should be Spark PLugs/Wires/Ignition Timing, or maybe o2

 

if anything its probably the plugs if thats the backfireing problem

 

timing

 

double check on the timing.
friend had a crx similar to your problem. we checked the timing and found out that the timing was off by a tooth.

 

i had the same problem in my prelude, figured out the stuff inside that cat. converter melted and caused it to back fire like crazy at a certain point. check that too.

 

also you might want to consider using an obd0 map sensor. obd0 and obd1 maps ARE different. obd1 maps register about 1.5psi more than obd0. so for any given amount of vacuum (or boost) the voltage would be different between the two.

 

hmm...is there any obd1 map sensor thats close to the obd0 kind, cause im running a obd1 manifold and TB

 

how can u tell if its just one tooth off?

 

easy. on the crank pulley, line up the white mark that is approx 1" away from the three marks with the arrow on your lower timing belt cover (you ARE running it right? it's there for a reason). then look at where your cam gear marks are pointing. the two lines that are even with each other [the look like this, if this were your crank pully: (-*-)] should line up with the edge of your head.

 

Me too. Except i recently swapped the obd0 map sensor to a obd1 map sensor because i thought it looked cleaner. I didn't notice any difference in how the car drove.

If you want to swap it though, my obd1 intake manifold had an outlet near the right side (while looking into the engine bay), under the intake channels. You can run a vacuum line from this to the obdo sensor which bolts to the fire wall. Make sure you plug the hole where the obd1 map sensor would have been (or probably even just leave the obd1 map sensor there, just un plug it).

 

sounds to me like the TB is too big for the engine and the real light flywheel isn't helping

 

i was also thinking about the flywheel, could it be to light? its and 8lb. ??

 

and i've heard that before as well, but in the past people more knowledgeable than myself explained how they are different and that you shouldn't mix and match. now whether doing so actually affects your car to any appreciable degree, i can't say.

 

i used to have the gsr map on there and it ran like dog ****....ever since i put the z6 one on there it ran way better...maybe a b7 map ??

 

I guess i'll have to look into it then.