2.7 Rebuild – To bore or not to bore and other questions

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Hi all, I’ve started to tear down a ’76 2.7 motor for a rebuild that’s going in my ’71T. This is my first engine rebuild.

My goal is to have a streetable hot rod motor with a target redline of about 7,200 RPM that can do some AX and track days here and there.
I’ve read the books and I’ve read the posts and now I need to pick a direction but I’m in need of some guidance...

Here’s my plan so far:

Reuse my cylinders and bore to 92mm
Pistons would be JE 9.5 to 1
Stock 2.7 cylinder heads
PMO 40mm carbs
DC40 camshafts
4 rib oil pump
Single plug
Casework by Ollies
1.5” European headers

Please chime in with any suggestions!

My biggest question right now is about the heads…will they need a chamfer with the 92mm pistons? Are the stock port sizes ok? Stock valve springs/retainers ok?

Here’s the beginning:



The exhaust came off without breaking any bolts. And, I was surprised to find 930 tensioners in here. I guess I will keep these and forgo the pressure fed tensioner upgrade…

[fanaudical]

Something not to overlook: Be sure to ask Ollies to check case twist and crank bore alignment. Many of these older 2.7 mag cases need to have mating faces shaved and then crank line bored back to round. Oversized bearings can sometimes be hard to find.

[911 SLANT]

I just finished the same build on my 1971 911T with a 2.7 mag case. Only difference I went with 46mm PMOs due to my larger Intake port. I bought the 92mm J&E 9:5.1 pistons and cylinders from EBS Racing . Car pulls like a Banchee after 3500 all the way to 6000 for now while I break in. Only have 50 miles on motor now. Having a little stumble from 2800 to 3400. Went to Richards at PMO yesterday to talk about the transition circuit. He recommended a little change in jetting. That what I'll be doing today. Nice build though I love how motor revs quick and pulls hard with MoD S cams. I do run aluminum flywheel and aluminum Pressure plate. No problem with stalling.

[Henry Schmidt]

Nice headers, who builds them?

[911 SLANT]

Henry, these are Brian's at M&K RSR headers

[draw]

Originally Posted by fanaudical

Something not to overlook: Be sure to ask Ollies to check case twist and crank bore alignment. Many of these older 2.7 mag cases need to have mating faces shaved and then crank line bored back to round. Oversized bearings can sometimes be hard to find.

This is on my list for sure...thanks for the advice!

[draw]

Originally Posted by Henry Schmidt

Nice headers, who builds them?

Henry, I'm wanting to use your Supertec head studs for this build...any other suggestions?

I've been to your shop by the way...you and I chatted while your dog chased rabbits or goats or something.

[draw]

Originally Posted by 911 SLANT

I just finished the same build on my 1971 911T with a 2.7 mag case. Only difference I went with 46mm PMOs due to my larger Intake port. I bought the 92mm J&E 9:5.1 pistons and cylinders from EBS Racing . Car pulls like a Banchee after 3500 all the way to 6000 for now while I break in. Only have 50 miles on motor now. Having a little stumble from 2800 to 3400. Went to Richards at PMO yesterday to talk about the transition circuit. He recommended a little change in jetting. That what I'll be doing today. Nice build though I love how motor revs quick and pulls hard with MoD S cams. I do run aluminum flywheel and aluminum Pressure plate. No problem with stalling.

Thanks for chiming in 911 SLANT...I love your build! I'm basically following your "recipe". If you don't mind me asking, did you chamfer the heads for the larger pistons? Thanks!

[911 SLANT]

No, didn't have to. The J&E pistons cleared just fine.

[Geneulm]

This is a fantastic combo. I’m figuring your ports are already 36mm?

I had the same combo and was a great engine.
However the bottom end did not hold up with your planned usage. The case was not dowel pinned. It’s replacement is (a 2.8) and has been a great runner. Maybe the first had some other issue undetected?

The experts can chime in on what the latest method is — I know there has been a bit of debate on whether or not and how to pin these cases now.

Alternatively you could build a short stroke which is a lot easier on these old cases.

I would also include a 4-bar oil pump and as much cooling as you can get.

[draw]

Originally Posted by 911 SLANT

No, didn't have to. The J&E pistons cleared just fine.

Perfect, those pics are worth a thousand words...thanks!

[draw]

Originally Posted by Geneulm

This is a fantastic combo. I’m figuring your ports are already 36mm?

I had the same combo and was a great engine.
However the bottom end did not hold up with your planned usage. The case was not dowel pinned. It’s replacement is (a 2.8) and has been a great runner. Maybe the first had some other issue undetected?

The experts can chime in on what the latest method is — I know there has been a bit of debate on whether or not and how to pin these cases now.

Alternatively you could build a short stroke which is a lot easier on these old cases.

I would also include a 4-bar oil pump and as much cooling as you can get.

Thanks for the advice!

Yes, the ports are 35mm (+/- 34.7mm measured). Interesting to hear your experience with the bottom end and dowel pins. I was going skip the dowel pins, but maybe it's a good $500 investment.

I did consider a short stroke, but decided the trade off in torque wasn't worth it.

An upgraded oil pump is definitely on the list.

[draw]

The tear down continues...

Here's where I'm at now. The chain housings (left is mag and the right is aluminum) are worse for the wear and will need to be replaced.





This rocker shaft looks like it walked out pretty far...hard to tell from the pic, but it's sticking out about a quarter inch.

[IndyAlex]

Ward, you seem to have a really good grasp on your rebuild. I'd recommend calling William Knight though to pick his brain about your build. I'm working with William right now on a similar 2.7 build for my 911 at the moment. Super knowledgeable guy and extremely helpful.

William Knight is a Superhero

Leave a message or send him an email.

[cmcfaul]

Will be a screamer that will want to run past 7200 RPM redline. Anything you can do to lighten the valvetrain is recommenced.

Chris
73 911 E 2.4 with 9.8 CR and DC 30's

[lvporschepilot]

Fab engine! Make sure the intake and exhaust ports are opened!

[Walt Fricke]

Rather than considering shuffle pins for the case halves, you ought to think of bushings - tubes around the through bolts. Like what Porsche does for the #1 main bearing. There is a trick which allows you to drill these holes larger one by one with the case otherwise bolted together, so the tubes line up perfectly. Cgarr can do it for you, as can other machinists. Pretty straight forward. A good idea for a race motor, whether tracked or not, and especially for a mag case.

[75 911s]

Myself and a friend just had our jugs sent out, he used millennium, I used US Chrome. Both sets (his a 3.0 and mine 3.2) had one bad cylinder returned with excessive pitting. I was able to source a set of jugs for free but it still cost me an additional $220 to get the 7th one bored and plated. Just a word of caution when considering new jugs vs boring existing.

[Evan Fullerton]

The pitting being from exposing porosity in the cylinder casting or a bad plating operation?

[draw]

Originally Posted by HelpfulNobody

Ward, you seem to have a really good grasp on your rebuild. I'd recommend calling William Knight though to pick his brain about your build. I'm working with William right now on a similar 2.7 build for my 911 at the moment. Super knowledgeable guy and extremely helpful.

William Knight is a Superhero

Leave a message or send him an email.

Great advice, I will do that!