Realistic power and redline

[DannyP]

Hey everyone,

I have posted here a little but have mainly been lurking and absorbing.

I am in the process of building a motor, basically finishing a project of a dear and departed friend. So now is time to put it together. All I need to complete the motor is bearings, seals, head studs, rod bolts/nuts and some sealant. Plus a lot of time and careful assembly Yes, Wayne, I have your book, read through it a few times already.

What I would like, if you have a good idea, is realistic redline and guess as to power output of this 2.7 combo:

7R mag case, shuffle pinned, time-certed, and boat-tailed mains, oil pump mod, all done by Ollies Machine
Original NOS 2.7l Mahle Nicasil cylinders, moon cut
JE pistons, 10.5:1 CR
OE crank, polished
Rebuilt OE rods
Dual plug heads, port-matched to intake/throttle bodies
Rebuilt MFI throttle bodies, bored to RS spec
Rebuilt MFI pump, "S" space-cam
Webcam S cams
Bosch recurved dizzy with machined alu top for 12 port cap and rotor by Jerry Woods
New oil cooler
Carrera pressure-fed chain tensioners
Possibly shelving the dizzy for Megajolt crank-fired ignition( I already have this on my 550 Spyder rep., type1 powered and absolutely love this system!)

I would think it is somewhere between an RS and RSR spec, due to the dual-plugs, higher CR, but not 2.8 displacement. Can you all guess as to powerband/torque curve also. I am thinking 250hp at the crank or so.

This is all going into a '72 T coupe body, which is getting a few nice touches, 15" 7-8 Fuchs, 4 pot Brembos and drilled/vented rotors, Bilsteins all around, alum. bananas, alum. front crossmember/rack mount, larger torsions(have to measure, unsure of size I have), and all the usual stuff. Yes, this will be just another RS rep. Maybe we should call it JARSR. It will be Bahia red, original color, with black interior/trim and black/anodized Fuchs. SC steel flares are welded, battery boxes eliminated, and all problem steel areas have been cut out and replaced. I still have to buy a headliner/carpets/door panels and fenders/front bumper. But I have a lot to work with and a great start to a project.

It will be a great tribute to a great friend of mine Hope he's looking down and smiling.

[Eagledriver]

I had a similar engine but with 8.5 pistons and single plug. I'd estimate it had about 230 HP with a race exhaust. I ran it for several years with "solex" cams and then changed to "s" cams. I was hoping for more power with the "s" cams but based on lap times I think it was faster with the solex cams. I reved it to 7200 with stock valve springs.

With your set-up I'd use solex cams or "mod-s" cams or GE-40 cams. The "s" cams just give up too much torque and don't really add much top end power over the solex. With race valve springs and/or retainers you could rev to 7500 RPM. Thats all you can safely do without better rods. This will be an excellent motor and I bet you can get close to your HP goal.

-Andy

[BURN-BROS]

+1 with what Andy said.

Ditch the S cams and run a Mod-S and 7300 is more than you need. + running a 2.7 above 7500 tends to spit the flywheels off of the crank.

[Walt Fricke]

Here is a dyno run from my race 2.7. Mahle nominal 10.3:1 pistons, TP2.7 heads with 38mm ports and Electromotive ignition, Bursch 1 5/8 headers, Elgin 315 cam, Weber 46s. The best run actually showed 220 RWHP, but the shape of the torque curve didn't change. Whistle testing CR later showed less than 10:1 actual CR.



Until I dynoed the motor I routinely shifted at 8,000 rpm. Knock on wood, but the stock rods have not been a problem. Using the torque curve and my gearing, 7,600 was the optimum shift point (plus less stress).

Flywheel bolts backing out (damaging crank and flywheel mating surfaces from friction heating metal transfer) were a problem until Bruce Anderson told me how to deal with it: careful application of a little red Loctite, and torque them to 150 lbs/ft. No issues since. I would do this on any 6 bolt crank motor, just to be safe. No downside I can see.

I used Elgin (not same as Dema the cam maker, I believe) springs, but had issues with them breaking - inners one time, outers another, luckily never both together. Don't think I had them shimmed wrong, but wierd. Aasco's on next motor.

So 250 at the crank doesn't seem out of reach, depending on how all your parts work together. Dyno the engine so you can figure out your shift point before worrying about redline.

Just one thing out of whack can kill that top power. I dynoed my just rebuilt stock 3.0 SC with what I thought was a really clever exhaust: the '74 with crossed cherry bomb mufflers (pretty blown out, too) at the rear. Results well below other similar engines. Then pulled the mufflers and put on a straight pipe with just Supertrapp difusers on the end. Now results were where they should be. Which is not to suggest that is an especially good exhaust system, but to emphasize that the cherry bomb system stank without me realizing it.

Walt Fricke

[BURN-BROS]

Originally Posted by Walt Fricke

No downside I can see.

Ah! those harmonics do not limit themselves to the flywheel alone. Extreme cases are outright crank failures. The 150 ft/lbs torque fix only got the racing community thru the hard times untill the 9 bolt came out.

The 2.7 performs very well below the 7500 rpm mark as Walt's dyno shows. Healthy motor BTW.

[DannyP]

Thanks for the replies, guys. I appreciate the cam tip. Exhaust hasn't been decided yet. Intake and exhaust ports measure 36mm, valves 45 and 40mm. I don't think anything bigger than 1.5" exhaust will help as 36mm is approx. 1.4". I am unsure who rebuilt/modded the heads so I don't know spring brand. I also like the tip on the flywheel bolts, thanks.

I have built many engines but this will be my first 911. I am lucky to have a couple local friends who will be there to help at the right time.

[joetiii]

Walt,

How does the Elgin 315 compare to other cams?

I know Dema's Mod S cam is around 292 duration seat to seat. I could never figure out how these numbers corelate but the 315 might be like a GE60 or GE80 no?

[Walt Fricke]

Joe

I like the 315, but don't really have a basis for comparing it with something else. Hence the torque graph. I fussed around for a while at first getting the Weber 46 jetting right, which greatly reduced the flat spot I think is kind of common around 4,000 rpm. Comes out of corners fine now. I used an Elgin 310 in my 2.3 (85x66) motor with Weber 44s, but never completely got that motor to pick up promptly exiting certain corners. It threw a rod before I got that in hand.

One oddity of the 315 is that Elgin specs the lash at 0.008". Double what one normally sees.

I now also have a 2.8 long stroke Weber 46 with a GE80. It seems to drive about like the 2.7, but (I hope) maybe a little stronger. When I get that motor to a Dynojet I may have some basis for comparison. Its intake port is 40mm instead of 38 on the 2.7, but otherwise the motors are the same in most important categories.

When I finally get the 2.8 SS built, I will have yet another engine to compare, though I haven't settled on a cam, thinking I will first get flow numbers from the heads when they are done. I want peak HP somewhere around 7,5-600 so my optimum shift point (which is going to be about the same for all gears in my box) will be 8,000.

Walt

Elgin has some specs on its website, but I have trouble knowing what is an apple and what is an orange compared with the GE 80 specs one finds.

[J P Stein]

My purpose (home) built autocross motor makes 190 ft/lbs@ 3800-5300, & 198 hp @ 6400 on a chassis dyno. 10.5:1 Mahles (race gas), Solex cams, 36mm int., 35mm exh.& Weber 40s.
This would also make an excellent street motor if twin plugged. The rev limiter is set at 7100 in the interest of longevity (194 hp @ 6800). Is there more peak power to be had?
I would expect so but one becomes addicted to torque when you want/need it.
Tuning issues are practically non-existent with the mild cams.....once you hit the combo. 40ish years back I learned the frustration of an over cammed/carbed motor in a street car. Now days I'll give up bragging rights for tractability every time.

[BURN-BROS]

Name.........Seat timing...0.04.......0.05..............lift........ ...Lobe centers
ELGIN
315int..........315............285.........277.... .........0.501...........100
300exh........300............273..........266..... ........0.474..........100


Here is some info on the difference in duration @ different lift.