I tried to find if I had a pic of the tag, looked it up once and it's the smalleest option I believe, .85 or .95 comes to mind. Will check it out again this weekend.

My friends with big hp Dmax's claim it's just too small and is probably whats holding back on the revs. It started spooling up fairly quick once I increased injector size and opened up the intake flow. So guess I could try a little bigger wheel now and not suffer to much low end spool time. What you suggest for a step up trim?

I would love to go with twins, but keeping them small and in the Banks sidewinder config so it spools quickly and still has plenty of air up top. The best thing about being in a boat, I have plenty of room to flip the manifolds over and mount them outset, up front.

But that's another one for the winter project list

-K

 

it does sound like you are being choked up by the small exhaust housing. They come with a .85 .95 1.06 and 1.19 housing. if your goal is to spin 4000 rpms you just might have to end up with the 1.19 housing to keep from choking out.

you could go with compounds instead of a true twin turbo setup.

 

drive pressures will help you figure that part out

 

oh and heres a formula i came up with to figure out ammount of crank angle degrees the engine is rotating while fuel is injections.

.000006(RPM's)(Pulse width) = degrees of crank angle rotation.
its easy to remember because the number 6 is the sixth number after the decimal

 

What cam is in it?

Sent with a Droid RAZR in one hand and 14,000 volts in the other.

 

Will see if I can get that drive pressure reading tomorrow, if I can find a volunteer to set on the engine and take readings at 90mph

Maybe will just port it to the boost gauge in the dash for a single run, not as much fun..

On the camshaft, it's stock GM grind. If I recall when reading some specs, it's topped at 3600 also. But most guys say heck with cams, just blow more air.. Thoughts on that?

-K

 

That works with compound chargers and big boost numbers. You can make up for it that way. With single chargers tho the only way to make more power up high is with a different cam. That is considering everything else is there. To me the boost sounds low. I tune an lly pulling truck for a friend and he runs 50psi of boost with a 68mm charger and it shifts at 3800rpm. On the dyno his power fell off at 3600 bad even tho the boost was the same. As rpm increases above 3500 the window of time to get both fuel and air into the cylinder decreases very rapidly.

In short imo rpm and cams go hand in hand.

Sent with a Droid RAZR in one hand and 14,000 volts in the other.

 

ive made power with a stock turbo with stock cam well over 3600. one time i dynoed the truck it made 450hp a 4500rpms .

but yeah you have to increase das boost to get the air in.
keep it simple, for has can you get the air in, and how fast can you get the air out
what did you set the valve lash to?

 

i also agree with you HD that drive pressure is a very possible cause

 

Thanks for all the input guys.

Valve lash is probably right at factory clearance. Was set by my main helper, a young GM tech who does mostly Dmax work all day. Has set this one up 3 times, maybe 4.. I do have fly cut pistons in there now, expecting to cam it one day. What ya thinking, tighten them up a little to gain some duration??

I often think of this boat as a water dyno, ya can't BS about your numbers, and it sure likes to break stuff..

I just pulled up the Diesel Power article from when PPE laid this out years back. Take a peak and you get a better idea at their reasoning behind the charger selection. They also stated "makes approximately 650 hp and 1,300 lb-ft of torque at about 3,400 rpm and has a redline of 3,600 rpm." A bit of stretching on those power numbers IMO, but notice the redline figure?

All said and done, redline hasn't moved much since the first day I drove it 3 years back. Just gets there quicker on a little bigger prop than they ran back in 07. I've upgraded about everything but the CP3, cam, and charger. Relocated the intercooler away from the turbo heat, which also ditched those nasty looking [but nicely welded] U-bend tubes someone probably spent 10 hours on.

What I have gained thus far is spool time and low to mid-range power, she must be 850hp now... Seriously tho, mid-range is super strong now, to the point you would expect to see it smack 4500 with ease.

The other thing that hasn't changed much is EGT's, when ya climb above 3000 R's, EGT's are gaining on the tachometer. Which again leads me to that tight AR Garret. And yes I've always thought boost is a little lower than to be expected. Would love to try another charger, but it has to fit the custom exhaust and T4 pedestal. Both are water cooled, and not easy to modify or replicate quickly.

There is another guy out there I've spoken with who is running a very similar setup to mine, but using a bone stock LLY Dmax with EFI tuning only. He claims his EGT's are much lower than mine with a stock turbo. He just turns up the air pressures using EFI to drop the EGT's at high rev's. An option I don't currently have.

Will try to get those drive pressure numbers together so maybe we can lay this to rest and discuss the water cooled turbo options

-K