Cam Advice For 25/30..

[psi]

i think that they have the same compressor.. different turbines..??

[Dale FZ1]

^^ GT30 is comp flow limited not turbine

hence a GT35 has a large comp wheel and relatively the same rear (from my understanding) and hence the 100hp difference in rating

Not straying from the question posted, but the key difference between GT3082 and GT3582 is the rotor size in the turbine. 60mm vs 65mm OD at the inducer. The actual housing is basically the same but with some differences internally to deal with the larger rotor. It means that when you look at the rear of an assembled GT3582 vs GT3082 it will have a bigger hole to vent through. Bigger hole = bigger mass flow capacity as you would see from the flow maps available from Garrett.

So for a given A/R eg. 1.06, the GT30 turbine will show a lower mass flow and efficiency than for a GT35 configured the same way. That is where your difference in "rated" power comes from.

Depending on the overall goals and mechanical spec, it may be a better bet to go either with a GT3582 or a GT3076.

[Dale FZ1]

I'd rather not spend $_$ on new cams unless I can really, really justify it..

I've had a mechanical engineer tell me to use the 20DET cams over the 25DE.. not sure on the justification though.

Back to the original question posted, after deviating

You may have been advised to go with a cam spec that was selected by the factory to work in a forced aspiration environment. Obviously that's with fuel consumption and emissions as big factors in the equation.

Depending on your own requirements, changed overlap and ramp rates could be beneficial to power production/delivery especially when using a far more flow-efficient exhaust manifold and turbine setup.

It would be interesting to check back-to-back the differences with a 20DET vs 25DE cam specs, but you may find the only real difference is fuel consumption due to blow-through of the inlet charge. Running the cam specs through the cam doctor program may be a big help to clarify likely outcomes and eliminate guesswork.

However if you know what that head/cam setup has been capable of in another previous engine build, why deviate from the known?

[bubba]

Back to the original question posted, after deviating

You may have been advised to go with a cam spec that was selected by the factory to work in a forced aspiration environment. Obviously that's with fuel consumption and emissions as big factors in the equation.

Depending on your own requirements, changed overlap and ramp rates could be beneficial to power production/delivery especially when using a far more flow-efficient exhaust manifold and turbine setup.

It would be interesting to check back-to-back the differences with a 20DET vs 25DE cam specs, but you may find the only real difference is fuel consumption due to blow-through of the inlet charge. Running the cam specs through the cam doctor program may be a big help to clarify likely outcomes and eliminate guesswork.

However if you know what that head/cam setup has been capable of in another previous engine build, why deviate from the known?

Thanks heaps Dale

I would like to do a back to back with the 20DET vs 25DE but probably won't happen

The impression I got was that using the 25DE cams would be costing me a little bit of power when compared with the 20DET cams. I'm not looking to squeeze every little poofteenth out but if I can make the same power with slightly less boost or a little more efficiently, then why not? particularly while the engine is apart!

The big thing that had me stumped was the opening times, the two cam specs have similar duration and lift with the 25DE having greater overlap.. but what would the earlier opening do?

I'm struggling to get my head around the more advanced aspects of cam timing still!