szabon

Any updates on this?

blade7

Yep Tim's giving me all the best bits off it, he just doesn't know about it yet .

Diver944

I'd heard on the grapevine that something went wrong and the engine is no more. Please say this isn't so

blade7

The last time I spoke to Tim he was waiting for some new parts and it will be going into his car.

333pg333

Be good to get an update on where Tim is at with this motor.

blade7

I'm fairly sure there will be less revs and boost involved in the future...

Dougs951

Had a failure?

blade7

I think Tim pushed it on the dyno to see what it would do, running 500+ bhp on the road was unlikely.

URG8RB8

Sid and Shawn's route appears to be the way to go on these big HP motors for the street.

Chris White

Wow, I missed this back in spring - good to see people doing the 16v thing the right way!!

blade7

Was it worth sacrificing 300cc for the rod ratio in your opinion ?

Chris White

depends on the goal. You can run higher RPM with the shorter stroke - but I don't know if the raised rpms make up for the lower displacement.

BTW - running higher RPM with less displacement is better for head gasket / head lifting issues. more firing events but less peak pressure in each event.

67King

I'm going to throw my thoughts in here on this, as well. To answer Chris' "does it make up" question, displacement was a secondary question to me relative to valve area. A few examples of produciton engines when I was at Ford were the 4.6L and 5.4L engines. They made very, very close to the same power with the same heads, be they 2V, 3V, or 4V. The differences could be accounted for with induction and exhaust losses, for the most part.

But it all boils down to somethign called "Z-Factor" which is similar to the average port velocity during an entire intake event divded by the speed of sound. And the port doesn't care what is below it. One of the first rules of thumb I'd use is 1#/min of airflow is equal to 10 horsepower. That's rough. More clarity is ISAC - indicated specific air consumption. Again, units are pounds of airflow (per horsepower-hour).

So what that all means is that you have roughly the same horsepower potential with a 3.0L as a 2.7L with the same head. It just happens at a different RPM point. This is very rough, there are a great many other factors that come into play - cam events, intake and exhaust tuning, and internal friction.

I am not a fan of oversquare engines, unless it is a 2V chamber. On our engines, you've got GOBS of potential for valve area. In this case, a 968 head may be a better choice, as the 37mm intakes are probably best sized for a 2.5L, whereas the 39's are best for a 3.0L, for the RPM ranges mentioned in the initial parts of the thread. Well, with a 104mm bore, you've got room for even bigger valves.

What it boils down to in my mind is that with a smaller bore, you are going to be more robust to detonation, and can run a higher compression ratio. Yes, your friction will go up a little, but in my mind it is a worthwhile tradeoff.

So if I had my druthers, moving from a 2.5L to a 3.0L, in this specific case, I'd rather do it ALL with stroke (or a 2.7/2.8 if doing one, but not the other). You need the same valve area to do it, regardless. But in doing it with bore, you are going to run into mechanical issues trying to hit an RPM point before you run out of airflow. I'd rather run out of airflow before oiling capability of valve float.

Agree with Chris on the cylinder pressure, but countering that is the dwell. Again, when you get the piston further from TDC more quickly, you'll be less likely to detonate. You have a more favorable (i.e. smaller) surface area/volume ratio.

URG8RB8

Harry:

As always, pleasure to read your insight!

refresh951

BTW, fundamentally Duke's new race motor is a Hybrid Stroker