selfproclaimedv8buff

before i ask my question, what is the difference in the #8 and #6 hotside?! the #8 of course is larger which creates a big more lag but does it put more power out then the #6 hotside? i think its minimal. my reasoning .... if the compressor wheel is the same then the same amount of power should be exerted from both hotside's but its more a matter of when the power comes into the rpm band? correct? this sparked interest was a result of 'sparkys' (no pun intended) results on the dyno this saturday. Does A/R only a measure of the compressor side or can it be a measure of the turbine side too?! What is the different A/R numbers for a #8 and a #6? thanks all.

TurboJew

cause I'd definately take it

Mihnea

You are almost right wrt power from both hot sides, however, the larger hot side will be able to produce more power than the smaller one, at the expense of some low-end torque, but basically the larger the hot side, the lower the exhaust back-pressure at the same boost levels.

The problem is that past a certain point (that is pretty much different on all engines/turbo combinations/exhaust systems), the more you increase boost, the more you increase exhaust backpressure, so you're starting to lose power.

So, IMHO, when I know a #8 hot side with 50 trim cold side can run 26 psi at the redline (and still have lots of efficiency with an FMIC), I would never try to run so much boost on a #6 hot side, because back pressure before the turbine is going to be very high.

High back pressure means more heat stays inside the combustion chambers instead of being rejected through the exhaust, which means you have to dump more fuel in to keep things cool, and retard timing because of hot spots that may appear.

If you lower back pressure by using a larger hot side, you can lean out the mixture to bring EGTs up, and advance the timing to take advantage of the cooler combustion chambers, without getting more detonation than before.

Higher cylinder peak pressures, less fuel being spent means higher efficiency and more power.


HTH,


Mihnea

fusilier

The #8 is .8 A/R the #6 is .6 A/R Measure the exducer and the rest can be obtained from the A/R

And you're right about flow through the turbine. The #6 sweetspot is sooner than the #8.
IMO, it'll be a bit more "torquey" like the RS2 which is also a #6 but will show signs of flow restriction at higher RPMS. Its a very good size for the street.

Mihnea

No matter what Corky Bell says in his book (duh, can't remember if he actually says what you're quoting), a KKK#8 hot side IS NOT a .8 A/R, nor is a #6 a .6 A/R.

#6 and #8 stand for the hot side's scroll volume in cubic centimeters, thus 6 and 8 cm^3 scroll volume, but these measurements have nothing to do with Garrett's A/R ratings.


Just my 0.02,


Mihnea

Mihnea

the A/R is the ratio of the scroll area divided by its radius, KKK's #s are just scroll volume.

A ratio can't be equal to a volume, or just because you're very lucky then...

fusilier

6 cubic centimeters is very small. that's 6 ccs. Are you sure?

For instance then... A K27 #7 is much larger than a K26 #8. That doesn't seem to match the cubic centimeter thing, unless its a small.And a K27 #9 is much larger than both of them. I'd think by more than just two cubic centimeters.

edit: what part of the scroll comprises the volume?

Mihnea

I have this information from several KKK engineers whom I've discussed with, and Ned has also posted this sort of information on the lists.

Now a Turbonetics K26#8 isn't really a #8, a real KKK 26#8 hot side has a 56mm exducer bore. The turbonetics one is 63mm.

But the scroll volume (yes, ccm=cm^3 or cubic centimeter) has nothing to do with the exducer bore, and some exducers can be larger than some others although the scroll volume is smaller...


Cheers,

Mihnea

fusilier

I'm going to have to start measuring some volumes to see what they're trying to convey with that system of measure. Ive got a K26 6 and 8 and k27 7 and 9.

I for the life of me thought the numbers expressed mathematical aspect ratios of the housings to the exducers.

So.. If what your saying is true, a #6 K26 has 1 cubic cm less than my #7 K27 in the scroll volume. I personally find this hard to believe cause the K27 is almost twice the weight of the K26. But I'll check it out. The exact extent of the scroll is what I'm curious about. The #8 K26 has 50mm inlet, yet 1 cm3 more volume whereas the #7 K27 has a 55mm inlet and only 1 cm3 more volume than a #6 K26 which is back to the 50mm inlet. The Exducers between the also make the volume thing seem funny because the Exducer size on the K27 is larger.

selfproclaimedv8buff

learn da thermodynamics and j00 gonna be smart boy!