Feedback from people that have installed the streetmaxr 65.5 turbo and 37" tires.

peont · Feb 7, 2017

Feedback from people that have installed the streetmaxr 65.5 turbo and 37" tires.

I am looking for feedback from people that have installed the streetmaxr 65.5 turbo and are running 37' tires on their truck. When driving around 50 to 55mph area does your truck shift into 6th gear? If so does the rpms stay high enough when you give the truck very light throttle to accelerate when going down the road that the turbo builds boost and exhaust manifold doesn't climb high enough causing compressor surge? The reason I am asking this is my truck will stay in 5th gear until around the 65mph area with the tune I am running again for this turbo because of the turbo making the noise in the tune that shifted earlier. The tune I tried that shifted earlier because I didn't like how long the truck would stay in 5th gear before shifting would shift into 6th gear around 50 to 55mph. Then if I tried giving a little more throttle the rpms would be too low and the exhaust manifold pressure would go high but barely build boost causing the turbo to start making a noise like it is in compressor surge. I was told that with the streetmaxr you don't really want to see under 1450rpms for this turbo when cruising and trying to build boost. So after finding this out about the streetmaxr I am definitely going to be looking into regearing my truck because I have the 3.55 gears with the 37" tires to get my rpms up to around stock or a little higher than stock in 6th gear. Has any one regeared their truck running 37" tires and the streetmaxr? What gear setup did you go with? Thank you for taking the time and reading my post.

bpan · Feb 7, 2017

I have a StreetmaxR with 37s. I my truck shifts to 6th around 55mph as well. But as soon as I give it any throttle it downshifts to 5th. This is very annoying when in and out of traffic so often I manually lock it out of 6th. I have 3.31 gears.

1800bigk · Feb 8, 2017

Smr 65.5, 37s with 3.73 gearing. Truck also shifts into 6th around 55 with my tune and will quickly downshift if I give slightest throttle input which like bpan mentioned can get old when you're not hotdogging. I have found switching to tow/haul mode will prevent that instant downshift if you don't want it. I have only experienced compressor surge once or twice and that was when I was using cruise control going up steep grade. The cruise control was trying to maintain mph but hill was steep and it just never got into the throttle enough to downshift. When I sense the cruise is not giving enough gas pedal now going up steep hills I just give it a nudge to drop into next lower gear to prevent the surge. This barely happens like maybe twice in 15k miles with the turbo.

doo dah · Feb 9, 2017

Streetmax is VGT right? I have non VGT 64mm from Industrial and when I was on 37s it was far from optimal. I had issues like you where shifts were funky up top and seemed to go from 4th to 6th skipping 5th altogether at times. I had 37/13.50/20s and 3:55s, now I am stock with factory wheels/tire size and no longer have the issue. I highly recommend regearing if you are going to stay with 37s or taller. My truck will hold 6th while towing my 42' fifth wheel even up slight grades and rarely has to shift below 5th. the whole shifting strategy just seems better than when I had the taller tires nd lift. I'd recommend at least 4:30s if you can find them or 4:88s if you are going to be towing.

dsmracing1 · Feb 9, 2017

I'm running just under a 36" tire and got sick of the lugging and shifting into higher gears too early with the 65.5. Really simple fix there fellas is to run a non VGT Trans file. My truck doesn't even think of shifting til 6th until 62-63 mph thanks to Morgans trans tuning...

bpan · Feb 9, 2017

I've wanted to try Morgan's tunes, not that I'm unhappy with mine I just like having options. What does he charge for a tune?

dsmracing1 · Feb 10, 2017

bpan said:
I've wanted to try Morgan's tunes, not that I'm unhappy with mine I just like having options. What does he charge for a tune?

I can't even remember now what he charged for tunes. You could always talk to your current tuner as well to see what he can do for you as well for an updated trans file.

peont · Feb 10, 2017

This tune I am running now won't shift into 6th until around 68/70 mph area for my truck and when you get around 63mph area it drops back down to 5th gear. This tune for sure keeps this turbo out of compressor surge, the truck from shifting gears early, and very responsive. Another reason for me looking back into regearing the truck besides running 37" tires is before I put a muffler on the 5" exhaust it was so loud in the cab staying in gears so long and being in 5th gear all the time doing the 55mph speed limits here in Louisiana got really annoying. So I made a spreadsheet that I attached calculating the rpms trying to the rpms close or just a little higher to what the stock setup was for my truck. I didn't put 3.73 gears on the spreadsheet because it was still under what stock the rpms were for my truck. It looks like 4.11 gears maybe the gears I am going to go with to get close to stock rpms. Anyone running 4.11 or 4.30 gears with 37" tires and streetmaxr? I want some input of anyone running them gears before I pull the trigger.

Morgan@Midwest Diesel & Auto · Feb 17, 2017

Whenever you run a tall tire like that without a gear swap, a trans tune that holds the gears longer is needed no matter what turbo you have.

Remember, your speedometer cannot even be corrected to that extent. So 60 mph your probably actually going 65 or so. At cruising speeds you do not want it to lock into 6th and lug the engine down to 1500 or less. You cannot pull the truck back up to speed when passing from that rpm without a downshift.

For guys with taller lifted trucks and have not re-geared to get back to the proper ratio, proper tuning can bridge the gap.

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