Chuck Schreiber

Awesome!!

jcorenman

Yes, Greg's Carbon/Carbon clutch and original TT rebuilt a couple of years ago with Constantine's bearings.

the flyin' scotsman

^^^ thx Jim, so essentially a new drive train....may have to make that trip to see it in the flesh again

UpFixenDerPorsche

My apologies Jim, but I'm puzzled re your rationale in reconciling the disparity between readings of two different dyno results, on what seems to me as being produced by the same car.

A difference of a couple of HP here and there would be easily be a comfortable margin of difference in instrument readings, but 10+ stuff ... arrhhh gee mate ... not so sure.

Chuck Schreiber

Jim,
Maybe I missed it..
Do you have the Doc Brown brown exhaust as well?

jcorenman

The two sets of curves on that graph were the same car, same dyno, same operator, different engine config. My confidence is high that those are valid before/after comparisons.

My point was simply that different dyno's produce different numbers, but that was not the case here.

jcorenman

No, the exhaust was built by Louie Ott for the previous owner, Devek L2 headers into a Louie-style crossover with dual 2.5" pipes. There is a Bullet brand muffler on either side of the tranny (where the factory resonators go), no rear muffler. I added cats about a year ago.

Bullet mufflers got bought out by Magnaflow some years ago and those mufflers are no longer available, but do a nice job. It's too bad, they seem to flow well and are reasonably sedate when idling and cruising around town (and appropriately non-sedate with the throttle opened up).

Chuck Schreiber

Roger that.

Really nice setup!! 👍🏼👍🏼

AO

What a very cool project and an awesome outcome! I'm sure it must be a blast to drive.

It's pretty amazing what kind of power you;re getting from the engine. Clearly the hardware has a lot to do with the results, but let;s not forget that Jim (and Sue) are MASTERs at tuning, and thing these cars. Jim probably has more hours with the sharktuner than anyone and get get a car into proper shape in just a couple hours or less. I guarantee there's more power there. Get some 93 octane gas, a little more tuning, and that car will make 400 WHP no problem.

Jim,
Regarding the tranny rebuild, did you or Greg touch the hardware side of the PSD? That the accumulator, but the actual clutch plates, etc on the tranny side? And if so, any difference?

mark kibort

actually, i havent found that to be the case. a dyno that is an inertia dyno, will always produce the same results. it has to...... the only difference is the car and how its "feeling". sometimes how its strapped down, air pressure in tires, and how you roll into the WOT run, can make a diff. you can see 10hp variance on the first couple of runs as temps stabilize, but after that they are mirror image, usually. then, if you could instantly beam the car to an other dyno and run it, it would be near the same. ive seen very little difference even going to a brake dyno.
again, if you run on two same dyno types and see different runs, its usually not the dyno.
the holbert car was run on every dyno from the bayarea to sacramento. (almost) and its runs were always 320rwhp +/- 1-2 hp. currently on the stroker, about 5 diff dynos and all are between 372 and 375rwhp. (not all 248e's either)

its simple..eitiher you accelerate the drums at the same rate or you dont. the dynos dont lie. correction factors can be off and played with , but just do an "actual " run and that is exactly what the car is doing.

mark kibort

what is your take on the trade offs? (besides the obvious... cost, method, availabliltiy)

jcorenman

I don't have as much data, but it only takes one data point to demonstrate that not all Dynojets read the same. But in this case it was the same dyno, so the point is moot and will not be mentioned further.

jcorenman

Thanks to everyone for the kind words. This really has been a fun project.

Here's some more pics, assembly this time. First, the obligatory "art" shot:



Rods, ready for assembly:



Cosmic crank, waiting...



Pistons and rods:



All together:



Combustion-side view. (Note the added valve reliefs for the 968 pistons, to accommodate both banks):



Valve train assembled and cams getting dialed in:



Final assembly on the test-stand:



Finishing up topside connections:



And underneath also:

FredR

Jim,

The motor looks newer than when it came out of the factory 26 years ago. Presumably the good Doctor has the castings chemically/ultrasonically cleaned?

I rather suspect you now own one of the 10 best n/a 928 motors in the world - many congrats.

Any guesses as to what your original motor might have run to had you not intervened at this stage? Other than possibly the [suspect?] thrust bearing everything else seems as though it was in pretty good nick.

Just goes to show what intent and some $$'s can do. Interesting choice on the crank.

Rgds

Fred

Tom in Austin

Spectacular! I remember hearing the Zyclamarot car run with it's new Greg Brown engine ... you could tell what a beautiful piece of machinery just by the sound as Dan revved it up ...