gruhsy

Is the super 65 a T4 or KKK hot housing?

I have the T4 with my Super75. Can't remember if it's a .58 or .68 T4 with low back pressure.

refresh951

I believe the PTrim is T4

refresh951

Amazing what a 16V head does! So much less stress on the turbo and the inter-cooler. So much less heat. I do not think we will be going much over 18 psi. We will go back to the dyno and run over 550 rwhp at 18 psi, pretty sure of this. We will also look a lot at the VarioCam switch points and optimize the tune for the street. I am concerned about head lift. 24 psi would be something like 30+ psi on an 8V in terms of cylinder pressure. The tune for pump fuel will need to be very conservative, probably running no more than 13 psi.

gruhsy

I thought that the 16V head was less prone to detonation...from posts on here. Interesting you are calculating 13psi for pump gas. I run 94 octane at 17-18 with my M-tune.......well will be again when I get the rod mod done.

P-trim with the Super75 was not dependent on hot housing I'm pretty sure. Super75/10 or a Super75 T4 with .58 or .68

My original P-trim was a Super75/10 4 bolt KKK hot housing with 4 bolt down-pipe. I ended up switching to a V-band with T4 housing instead. I would have to speak with Mike/Dave to verify but if my memory serves me correct this is what I did and I am sure both options were P-trim.

refresh951

Was your car an 8V? Keep in mind 17 psi on an 8V vs 17 psi on a 16V are two totally different things. Cylinder pressure is a matter of flow. The 16V head flows A LOT more therefor cylinder pressures are much higher with the 16V head than the 8V head at the same boost pressure. You cannot compare boost pressure between the two.

13 psi on an 16V would be like 18-19 psi on an 8V. Would you run higher than 18 psi on pump fuel on an 8V. If so the timing better not be aggressive.

Assuming no knock which has pretty much been the case running E85, head lift is an concern.

gruhsy

Ahhh. That makes sense. Ya mine is an 8V with larger cam.

I'm gettin it....you have crammed way more air into it, and more easily, due to the 16V which then affects cylinder pressure....putting it simply.

Thanks

refresh951

Exactly! Most just look at the boost pressure which cannot be translated from the 8V to the 16V.

When an 8V and a 16V have the same power output, the flow is comparable. One way to think about it is that flow is a function of pressure and resistance (restriction). The 16V head greatly reduces the resistance.

gruhsy

I should send you my Super75/T4 Turbo and 5 inch exhaust to test out with Jon's car

refresh951

No thanks! Jon's car is near completion and I have to get back to work on the Super Beetle.

gruhsy

I guess I will just have to buy Duke's intake if available and a 16V head from Michael

Voith

Shawn, what thickness head gasket did you use with this engine and what is the piston bowl size in cc?

I'd love to get to 8.0 CR but as it stands according to online calculator I can only get to 8.04 CR with .120" Cometic which is one thick gasket. One step thinner is .075'' which bumps CR to 8.7.. :/


I think your cyl. pressure explanation is spot on, but how would you comment on this:

Seems to me you two are both good in engine planing/tuning yet completely on opposing sides over this.

refresh951

We are using custom pistons in which we moved the pin height. I do think our CR was a bit higher than 8:1 IIRC. I will have to go back and look but I think 8.2:1.

I would respond to the use of higher CR with this read:

http://www.modularfords.com/threads/...boost-pressure

ptuomov

I think the link has a sensible approach to compression ratio and boost.

The way I think about this is that there are some constraints and you maximize your objective within those constraints. The main constraints that I have are knock frequency limit (approximately the limit on frequency of exceeding the maximum unburned end gas temperature, which I can't measure), maximum peak cylinder pressure limit (I have a sensor and data acquisition system for that, but it's not hooked up yet and I don't know what the maximum cylinder pressure limit is), and the maximum exhaust gas temperature limit (my EGT sensor is too slow for dyno pulls, have to fix that). Finally, unlike with your motors, I have the largest turbos that physically fit in my engine bay without chassis modifications (928), which gives me the compressor mass flow limit. The question then is what do you want to maximize within that envelope?

Here's my question to you: Given that I very much agree with you on how one should think about these things, what's your approach to squish in the combustion chamber? Did you leave in the squish pads to the head unmodified (they are small in the 968 head)? Also, what kind of squish zone clearance are you using between the piston and the head? Are you shooting for fast or slow combustion with this motor? Fast giving more power but also higher peak cylinder pressures and the associated problems.

refresh951

We did not optimize for squish on this motor as we were running the pistons a bit down in the hole (about 0.03" IIRC, 0.07" deck clearance including 0.04" gasket). I have built several E85 motors running the pistons down in the hole (sometime large amounts) without much ill effect. Squish pads on the head were untouched.

refresh951

The more I look at the numbers and the results on this motor, the more convinced I am that running lower CR is far better. The cylinders fill up so efficiently with the 16V head, it just does not make sense to give up the volume.

To go from 8.2:1 to 9.2:1 I give up about 3% cylinder volume and gain about 3% in thermal conversion efficiency. Now given the weakness of the head due to bore size, it just does not make sense in my view.