Turbo upgrade

[ChevyMan19036]

I am looking to upgrade my GM4 turbo. What does anyone recommend?

Matt
1995 chevy k2500 6.5 td

[Robyn]

You could use the "GM8"

The big issue is, "What are you looking to accomplish" ??

Unless you add an aftercooler you are still limited to about 12-13 PSI MAX Boost.

Boost simply for boost's sake will do little for you.

Once you reach the "HEAT THRESHOLD" of about 14 PSI and the EGT's start heading into the Ozones its all over.

Going higher on the boost pressure requires a charge cooler of some sort. From here you can go higher on the boost.

Now the issue is the 21.5 compression pistons need to be swapped out for some 18:1 slugs so that the extra boost can be used without melting things.

You can quickly reach another "Point of no return" and that the limits of the head gaskets.

The head gaskets, bolts and such on the 6.5 were not designed to handle HIGH boost pressures.

GM designed these engines to operate around 8 PSI and do so over the long haul.

12-13 wont bother them much, but beyond this things can and do start to go away.

Basically there are 5 bolts per cylinder spaced around the diameter of the hole.

There is not enough clamping force to hold really high boost.

Now lets head down into the basement, the 6.5 has a cast iron crankshaft thats not designed to handle BIG power.

Now if you start with a P400 engine (latest incarnation built by AMG) with a newly redesigned block and a main girdle along with a forged steel crank, you can do a lot more.

The new heads are better than the old GM stuff but the design still has limits.

A P400 with proper cooling mods, an after cooler and such should be able to handle 325 HP and live (this is long term use) and this is with a driver who understands when to get the boot off the Loud Pedal



The GM8 does flow a tad better but the overall picture is still the same.

The 6.5 is best set to run at around 13 PSI max boost and at a HP level of around 275-300 with maximum EGT's of 1000F pre turbo.


To conclude, unless you plan on spending some serious $$$$$ on exhaust system, cooling system mods, a power chip and other items, the addition of a different turbo is going to net you next to nothing.

I have installed a Banks exhaust and a Heath chip along with the turbo master and the results are some very good useable power.
I am still using the GM4 turbo.

The boost is set to 13 PSI max and the EGT runs at around 1000F pre turbo


Missy

[More Power]

I am looking to upgrade my GM4 turbo. What does anyone recommend?

Matt
1995 chevy k2500 6.5 td

As Robyn indicated, knowing what your performance goals are would help define the turbo selection.

The GM 6.5L TD can handle 1250 degrees F (pre-turbo) for the time it takes to pull the longest Interstate grade at the GCVWR rating. "Pre-turbo" means your exhaust temperature pyrometer/thermocouple is located somewhere between the exhaust port(s) on the head(s) and the turbocharger. I prefer locating the pyrometer in the exhaust crossover pipe a few inches down from the driver's side exhaust manifold. Drilling the ex man can work too.

Jim

[arveetek]

Along the same line, I also have a GM-4 turbo on my 6.5L, but have a GM-8 in my possession that I can swap on. Will I actually gain anything on a Tahoe that only tows periodically? I love the Turbomaster on my GM-4, and I would have to buy a new for the different style 8. If there isn't a huge difference between the two, I won't bother with swapping.

Casey

[HH]

The GM-8 made a large difference from my GM-3 with my 18:1 engine. Boost over 15psi, with Turbomaster. Tows much better.

[Kennedy]

The difference between the GM4 and GM8 is quite miniscule. It's simply the eblow being more relaxed on the GM 5 and GM8.

In my experience, the HX 35 helps, but is too small. The HX40 is a better match, but out of the box a bit lazy. RJ has a nice blueprint for the HX40 that he offers and through testing, it has been found that ECT yes I said C is greatly reduced to a point where it is no longer a concern. EGT also no concern any more.