supercharged 308 dyno results

Well, I finally drove my supercharged 77 308GTB after working on it for almost 2 years and it flies! Now it feels like it breathes! It better, the air is being crammed down it's throat!

Wednesday night I trailered the car to HP Works in Colonial Beach, Virginia to have the Electromotive TEC3r engine management system set up on the dyno, spent the night at a motel in town and was at the front door at HP at 8:00 AM on Thursday. Unfortunately we had a bunch of teething problems to sort out. The engine had been starting fine back in New Jersey but, of course, in Virginia it wouldn't start. It was running so rich on the unsorted fuel map that the plugs were totally fouled.

Another problem was the fan on the Ford high out-put alternator destroying itself on the dyno. Everything, including alternator, AC compressor and supercharger, run on the same serpentine belt (the water pumps are electric) and I thought that perhaps the load had moved the alternator on its mounts enough to allow the fan to touch the alternator mounting bracket. Not so. It turned out that centrifugal force at high RPM was flexing the fan allowing it to strike the mounting bracket and an idler pulley destroying itself. We damaged two different Ford fans and also unsuccessfully tried fitting a Motorola fan before straightening and severely trimming the second Ford fan allowed us to continue.

The idle stayed at 3,000 RPM after the first dyno run with both throttles closed. We knew the engine had to be getting extra air from somewhere but where was that? The bypass valve return hose had been collapsing under vacuum before I reinforced it with a spring inside so that was the first thing I checked for, a leak, but the hose was good. We finally decided the IAC (idle air control) valve must be getting sucked open by the supercharger. I removed the right throttle body and we plugged the idle air passage, which is about 3/4" (19mm) in diameter, and installed a threaded restrictor with a 1/4" (6mm) hole in the passage after threading it. This did the trick.

Anyway, we had a few other minor problems and Thursday ended without a good dyno run. Another car was scheduled for the next morning but we started early, the next customer, with a 1940 Willys drag racer sporting a blown Hemi, was a little late and was patient with us when he did show up so we managed some good dyno runs and tuning and wound up with the following at the rear wheels: max torque 231.3, max power 307.0 before we had to get out of his way. Boost was at around 10 PSI but I have not been able to decipher the data logging disk I was given. I'll get help on Monday. I have a dyno sheet but it doesn't scan very well. Hopefully I can get an electronic version on Monday.

The guys at HP Works figured on a 30% drivetrain loss and figured we had about 399 HP at the crankshaft. I talked to Mark Eberhardt and he thinks the drivetrain loss is more like 18% in which case I would have about 362 HP at the crankshaft. Which ever the figure, this car really flies now! I drove the car around the back roads of Virginia and was not disappointed. This car moves like no 308 I've ever driven and smooth too! At some point the car will be back on the dyno for more tuning but for now I'm pleased with it.

I still have a few issues to sort out. The main electric water pump, which is supposed to be controlled by the ECU, runs continuously so I never got the coolant temp up without blocking the radiator with cardboard. I have no tach and no speedo functions. The brakes need some tuning. The car has a Tilton tandem brake master cylinder set-up and think I need to go down a size. The alternator fan, which in desperation I trimmed with tin snips, needs to be replaced with something similar but slightly better balanced.

This coming week will be busy. If the weather holds out I'd like to take it on a run being organized in North Jersey next Sunday.

Wil
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Yeah, this really woke the car up! Thanks for the in-put but please, somebody lie to me and tell me the 30% number is the right one

 

Thanks Mark!

 

Thank you.

 

Thanks. I see Tillman just posted the link to those pictures (Thank you Tillman because I wasn't sure where to find them). It looks a little different now but only in minor details. The long duct accross the left (front) cylinder head has been replaced with an oval tube to allow some hot air to escape from below and the brake calipers no longer have Porsche scripts for example. I'll take some new pictures tomorrow if I get the chance.

 

Fresh pictures.

You can see the belt is slack (the wrench is still on the belt tensioner) so I can machine the alternator fan round after trimming it with tin snips at the dyno shop.

The view into the right wheel well shows one of two air filter housings (one on each side of the car) with fiberglass ducts to the stock air inlet on the right side of the car and the former oil cooler air intake on the left side. The oil cooler was replaced with a Setrab water/oil unit on the lower fire wall. The guy in Australia who complained about the Porsche logos on the calipers should feel better now.

The front trunk doesn't look very 308 does it? There's a picture of the two Meziere electric coolant pumps, one for the engine and one for the intercooler. Both circulate non H2O Evans coolant. The radiator is a Griffon Ford NASCAR type modified to fit. Not seen on either side of the radiator, below the headlights are two intercooler heat exchangers (Ford AC evaporators), each with it's own Flexalite electric fan. The radiator fan is also a Flexalite unit.

I bought the steering wheel used off a vendor at Lime Rock in September. The red looks bright in the picture but it's a very close match to the seats. The only flaws are two tiny paint chips inthe MOMO Corse script. It's otherwise perfect. The radical off-set really gives good leg room and also improves the sight line to the gauges for me as long as it's pointing relatively straight.

Behind the steering wheel are AutoMeter boost and coolant temp gauges. The switch at the top right of the temp gauge toggles between engine and intercooler coolant temp. Below the steering wheel, to the left is the brake bias control. I've got Ultimate pedal pads on the brake and clutch pedals but not the accelerator or foot rest. I'm over 6' tall and need all the leg room I can get!
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Thank you. The air comes in from both sides, yes. My thinking was that since I have no idea how effective the air scoops in the side of the car are and since the left intake on the SC wanted a short run to the left air scoop, why no use both? Yes, the extra turns in the duct from the right will slow the air but a little extra air at high speed is better than no extra air. The metal duct is not really not too restrictive where you see it get narrow. I changed the shape to allow air to circulate past it from below. It's hammer formed from two panels and the cross section of the oval shape has the same area as the 3" round ends. The system uses two 5.0 Mustang throttle bodies only because I was unsure about how efficiently I could get air to the SC knowing that demands would be higher than with a set of carburetors.

The system uses one MAP sensor which happens to be mounted on the right air filter housing but it gets it's vacuum/boost signal via a hose connected to the plenum below the intercooler below the SC.

 

I forgot. How much did I pay you to write that first paragraph?

I knew some people would hate the red steering wheel but I like it. The red is not as bright as the pictures suggest. It's an almost perfect match with the muted red on the seats. Anyway, lilke my wife says, I've probably been hanging around Lamborghinis too long.

 

Thank you.

 

Thanks

 

Thanks