Thank you and '71T dyno results

[dho]

First, I would like to express my sincere appreciation for this forum and all who so generously share their knowledge and expertise. I have been a long time member. Although I rarely post, I frequently read and study the issues, solutions and commentary provided by others. I am a hobbyist, and the rebuild I just completed would have been extraordinarily difficult without the resources available here. Thank you.

I recently completed the build of my ’71 911T, 2.2. The machine work was performed by JB Racing in Tavares, FL, and Wednesday I spent the day there with the completed engine running on the dyno. I can’t sing high enough praises for Jim Higgs and Dennis at JB Racing-they are professional, efficient, and their knowledge seems limitless. I recommend them highly. I am very pleased with the dyno results.

The engine: numbers matching ’71 911T, with the following performance mods:

Cylinders bored 1 mm to 85 mm; JE pistons with a measured ratio of 9.4:1
Cams: Solex grind by Webcam
Ignition: MSD Streetfire; stock Marelli distributor, with points
Intake: Zenith 40 TIN carbs, with 32 mm venturies; 145 main jets; 170 air corrector jets; 55 idle jets; stock emulsion tubes and stock idle air bleeds; fuel pressure 3.5 lbs
Exhaust: SSI heat exchangers, with Bischoff muffler

Results, (the complete table for the final run is in my post on the bird, engine building): Horsepower, 173.3 at 6300 rpm (compared to stock of 125 @ 5800 rpm; and stock S at 180 @ 6500 rpm); 155 ft lbs torque at 5300 rpm (compared to stock of 130 @ 4200; and stock S of 147 @ 5200). The torque figures are somewhat misleading because this engine pulled over 150 ft lbs from 4100 rpm all the way through 5800 rpm.

Thank you again for all of the help!
dho

[Jim Breazeale]

Very well done. Who said Marelli distributors and Zenith Carbs need to be replaced?

[Scott A]

Those are some nice numbers

[30westrob]

Basically more compression and more cam, and you have a 35+% increase in power with what looks like a very drivable engine. Nice job and thanks for sharing. Rob

[PrairieDriver]

Thanks for sharing this information, dho. As a fellow owner of a '71T, I find it helpful to shape my plans. Howard

[PatHidden]

Great numbers. Did you just do cylinders/pistons and the top end or was this a full rebuild?

[lkadams]

What's the expert consensus on the power at the crank vs. the wheels on a 911? What % loss from engine to wheels is typical? One day I'll get my car on the dyno, but it will be a wheel dyno.

[rgupta250]

Dho,

Those are impressive numbers.

I have a few questions:
- what crankshaft did you use?
- did you rebuild your heads? If so, any mods?
- was the Marelli distributor original to the car?

Thanks,
Ravi

[dho]

Howard, good luck with your build. I don’t think I would do anything different for my intended use, which is spirited street and occasional autocross.

Pat, it was a complete rebuild, with the recommended reliability mods, in addition to the performance mods.

Ravi, original 911T crank; the heads were rebuilt, but no mods; and yes, the Marelli is original to the car-it was rebuilt by Kurt at Partsklassik.

dho

[Bert]

Excellent results on your rebuilt engine.

It looks like you got the best of both worlds with that rich torque.

Thanks for sharing.