View Single Post
Peter Guldan Peter Guldan is offline
Peter Guldan's Avatar
Join Date: Apr 2004
Location: Memphis
Posts: 130
Howdy Chaps,

Long winded one here, bear with me....

ITB flexibility…or any modern engine mgmt equipped air cooled flat 6 for that matter.

In a word, ITB’s are fantastic when coupled with modern engine mgt designed to exploit their benefits and can be more Mr Hyde or Dr Jeckyl when called for than any single throttle body setup. The original 2.6’s maiden voyage was a spin around the block from the shop with the owner aboard as pictured here. That white Explorer is turning out of TN State Highway Patrol office one driveway over from the shop For a machine capable of this level of angst under power, it cruised casually past without raising any eyebrows – as an old schooler, I’ve yet to come to grips with power/docile nature but more on that in a moment. On a short schedule before Sebring it was driven on the street to identify any minute detail that might need addressing and as a commuter spent many a night in Pat’s driveway at home alongside the family car. The GT 1 was no different. These machines are driven around the shop grounds, on/off trailers, in the pits with no drama. But, to refine this system to such a degree of utility requires some vary careful tuning on a load varying dyno like this one to work through every transition possible, an inertia dyno is not adequate. As you can get an indication here, rather than just continual single pulls, they’ll spend lots of time fully exploring many sites on these high resolution maps. He just spent 3 hours in the cell last night on only the initial setup for the new PMO ITB PWR EFI NA system. But once a base is established, it’s relatively quick after that.

I’ve recently begun sifting through years of PWR’s/customer in car race videos, doing summaries and uploading them to youtube, here’s what’s out there on Pat Williams Race Videos currently. As they let the camera run continually, what’s not on here is hours of footage I’ve trimmed that applies directly to this drivability discussion. So, I’ve taken a piece from a typical Saturday, this being Putnam, click here. After 15 minutes at up to 7,500 (for a good heat soak), the clip starts as he rolls into the pits for tire temps. Though the tach only runs down to 2k, this is about 1k idle. Once complete, it rolls off barely touching the throttle on a 3 disc Tilton, idles at pit out and then runs through 3 gears to 7k plus before turn one. It’s tuned speed/density on an open map and in lieu of an idle motor/air slide, cold idle is completely controlled with ignition. GT 1 runs in the same groups as the latest 4litre, sequential shift, ABS, SC extremely refined factory machines which unlike ALMS/GrandAM run unlimited in PCA at over 500hp. Competing against these with a 14 old torsion bar based chassis long BH 4 spd without even a brake booster is utterly hopeless if your motor is not there for you at all times – there are no flat spots.

Now, 935’s (sigh) and modern painless drivability. As an old schooler (a rabid IMSA race enthusiast and recent 22 year old college grad with a 911, I was there for the 935 hay day in 78-79) I am seemingly forever programmed by these beasts to correlate performance with a raucous nature and some drivability issues. They were anything but tractable, idling - if you wanted to call it that - at high rpm, belching black smoke from richness, that cadence of locked fully advanced distributor in concert with the cams, it sometimes took all the crew to maneuver one out of the garages as a very high active first in conjunction with a locked spool meant they generally only wanted to turn when in reverse. Off boost, they had no power, you could hear the cylinder pressure build (along with the sound) as they reached a rather narrow explosive power band. But as everyone was equally hindered, it didn't really matter. They got a little better with the switch to Kugelfisher from Bosch later on but were still hairy. Parts were readily available, were of superb quality and the Whittingtons/Pauls/Fields did not hesitate to use their stuff up (ruin it, actually), these being qualifying and twin 30 minute sprint races of an afternoon, the former would put an engine in for each sprint for their 2-3 cars if excessive boost & ambient heat had taken its toll. Have a picture (slide, if anyone remembers those) of the trash can outside the main Road Atlanta garage next to the Goodyear garage full: pair of headers, a turbo, 3 heads and a ruined crank. When they got too hot the factory blew more air on them with a flat fan, they cinched exhaust valves so elaborate oil galleys were run out to the guides, suffered from tremendous blow by so they networked the crankcase vent through the cage, etc… Surely, I thought when it was announced that this 3.4L twin turbo would be built that unlike the 2.L TT, the 2 2.6L TT ’s and the 3.0L TT that the good old 935 days would have to come back. How could you make that kind off power without all the baggage of a Hollywood starlet? I was quite disappointed – initially - though this machine sounds every bit as deafening and purposeful as any 935 under load, engine mgmt is so accurate it needs none of those band aids. The worst part, there’s no hint of the menace within at idle, my most favorite part, but I guess time marches on….


1950 Vincent Rapide - A Red Rapide Experience -
Old 12-29-2009, 12:09 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #53 (permalink)