Matt H

They have a little more displacement and make a "few" more revs.
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mark944turbo

Yes , but I thought that the k-26 would become inefficient once it started spinning a certain speed or got to a certain temperature. This is what everyone has said, and that has nothing to do with displacement or engine speed, it just has to do with how much air the turbo can move. Where it is going is irrelevent, by my thinking.

dand86951

Stop and think about the differences . The K26/6 does make 300 brake HP in the 2.5 litre two valve single overhead cam with non sequential engine management. The 300 BHP mark is relatively easy to get to even in our stock engines with stock valves, exhaust and intake restrictions. They didn't say what size exhaust turbine they use but since the peak torque is at 5000 then my guess is large and high flowing.

On the 962 each turbo is only required to feed 1.5 litres of four valve double overhead cam engine with probably lots better head flow, exhaust and intake flow not to mention the more sophisticated engine management. A K26 turbo is just an air pump, but the entire engine system determines how much horsepower can be achieved with a given turbo. You have to believe Porsche and Dauer picked the best turbo to match the engine.

mark944turbo

Thats the explaination I needed, thanks! I bet it is the 2v vs 4v that made the most difference, I didnt consider the effects that that would have on airflow, effects that we can not easily reproduce on our 951s.

hosrom_951

Take off the K26 and slap on a pair of K27's, watch what happends......

Danno

Mark, also consider that at high-RPMs, the 2V heads on our cars gets very, very restrictive. And the K26 has to force air for 2.5L displacement through 4 small intake-valves (625cc each). Each K26 in the 962 has to only feed 1.5L through 3 large intake-valves (500cc each). So there is less restriction to flow and the turbo can flow more CFM at a lower pressure-ratio (more efficient, heats up air less).

Most of the tuners I've talked that have flowbenched the heads seems to indicate that the 4v heads will flow close to double the 2v ones at high-RPM. The best comparison I've been able to find is with PowerHaus's 3.0L 968 engines at 19psi using K29 turbos. One has a 2V head and the other a 4V head:



Notice that mid-range peak-torque on both cars is about the same at 450 lb*ft TQ. This would indicate that at their most efficient VE/RPM-range (1400rpm higher on 4V), they both have roughly the same combustion-chamber pressures. However, as RPMs increase the VE decreases, the 4V head drops later than the 2V. High-RPM torque, even though it's the same value, results in more HP. So the 4V head gets you 450hp while the 2V head is 380hp, both from the same turbo.
I guess not for a Canadian, eh?

Here's the car I want: Derek Smith's 962. Although technically being the tube-frame model, it's probably more correct to call it a 956 (except for the 962 wheelbase). Anyway, check out the Photos page, the parts he makes are incredible!