Thank you and '71T dyno results
 

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 yesterday 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, (see table below for the final run): 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!



http://forums.pelicanparts.com/uploa...1714063706.jpg

What makes it outpower a 911E, and at higher revs,, despite having much smaller ports?

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Rob, maybe some of the experts will chime in, but my understanding is:
1. The port sizes for the T and E are the same-32 for intake and exhaust; the S is larger-36 for intake and 35 for exhaust; the valves are the same size for all 3.
2. my mods include slightly larger bore: 85 v. 84;
3. my compression is slightly higher: 9.4 v. 9.1;
4. the SSIs and Bischoff muffler may create better exhaust flow; and
5. the most significant change is the Solex cam profile which is a good match for this combination.

The E has MFI v. my Zeniths, but I don't have any framework to compare those 2 systems.

Thanks for the question.

dho

Those are remarkable numbers. 173 at the wheels is around 200hp at the crank. Out of a single-plug 2.3 with 32mm ports. My 2.2 is very similar (T heads, S p/c's, mod-solex cams) and it's definitely not putting down 173 at the wheels.

Black 993, not at the wheels-it was an engine dyno. Since everything had been replaced, repaired or modified, I wanted to test everything out before installing in the car.

dho

Ahhhh, ok that makes sense.

You will be very happy with those torque characteristics in a street car.

The E has MFI v. my Zeniths, but I don't have any framework to compare those 2 systems.

I would think the MFI should be better than carbs as there are less restrictions (no venturi). I built a couple small engines with both MFI and Zeniths recently, here are the dyno results at the wheels. Larger ports did not hurt power or torque in my case.

https://forums.pelicanparts.com/porsche-911-technical-forum/1151593-dyno-summary-testing-early-2-4l-2-5l.html

John

Thanks. I think T has 30mm, E 32 and S 36mm. Maybe you have ported heads.

MFI should have better fuel atomisation.

I wonder if the JE pistons have better squish than E pistons.

I guess all the different bits add up. I need to choose cams for my 2.2 engine, but I have E heads and MFI. Likely going JE pistons but maybe higher compression than you.

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Engine or chassis dyno??

Jeff, it was an engine dyno-numbers are at the flywheel.

Rob, according to Bruce Anderson's book, the port sizes are as I stated above: 32/32 for the T and E; and 36/35 for the S. I went with the Solex cam because it was recommended by JB Racing and because I found some dyno numbers that showed a high, flat torque curve, which I wanted for a street engine. I am completely satisfied with the outcome, but two others you may want to consider for a similar application are the mod s (DC-40) and the mod Solex (DC-30).

dho

I don't know which is true as I have no T ports on hand to measure but I've had multiple people tell me Brucey's book contains typo's and inaccuracies and on this thread it appears to claim 30mm ports on the T: https://www.early911sregistry.org/forums/showthread.php?42132-2-2-T-heads-similar-to-2-2-S-and-others

I do have a 911T so maybe one day I'll have a chance to measure them and find out for sure. Either way, I'm glad your engine gave you a good outcome.

Rob, I agree there is a lot of inaccurate info floating around. The engine is back together, so I can’t measure, however, according to the factory manual, page SE 35, 1st Revision, December 1970, the port sizes are the same as stated in Bruce’s book.

dho

I am pretty sure the intake port sizes are 32 mm, 34 mm, and 36 mm for the T, E, and S respectively. My 2.8 was ported to 38.5 mm intake and 38 mm exhaust.

Nope.

I have a 1970 2.2E in bits at the moment and the heads have the MFI and 32mm ports.

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doswald , I suspect you are comparing DIN horsepower ratings and SAE horsepower ratings . 173 SAE
is at most 160 DIN . I think your engine is as expected , stronger than an E because of the Solex
camshafts .

Good point about the ratings, Richey. Were the factory ratings DIN? I don't know what rating the JB Racing dyno uses. In any event, it will be a significant bump over a stock T. I'm looking forward to getting the engine installed this weekend!

dho

173.3HP SAE equals 170.9Hp DIN. Conversion factor is 1.0139. Not that much of a difference.

The Porsche technical specifications book for '72 - '73 911's lists the 911E 's horsepower as 165 DIN and 185 SAE . Someones math is incorrect , but I'm more likely to believe the Porsche spec book .