Dilemma

[Bigtoe32067]

Ok I have a dilemma and looking for some opinions.
I have a 3.0 engine and a 2.7 mag engine and they both need rebuilding and I’m doing them myself.
I’m trying to figure out which one to keep for a 916GT I’m building.

The givens:
ITBs and EFI
Coil on plugs
Crank triggered
ARP head studs and rod bolts


So do I build the 2.7 into a 2.8 or the 3.0 into a 3.?

I’m leaning towards single plug and 9.5 but I have a twin plug 10.5 motor in my 911 that screams and it sure is fun but I don’t know if I need the extra umph.

If you had a reasonable wish list which one would you build for yourself and how would you build it.

Whichever one I don’t build for me I will rebuild basically to sell.

Thanks in advance
Tony

[stownsen914]

The 3.0 is a much more robust platform. Between those two options, I’d certainly consider that in making a decision. Do you have any autoX or racing classes in mind for the car? Displacement can be a deciding factor.

[Bigtoe32067]

No just a fun street car

[Bill Douglas]

The 3.0 made into a 3.2 with the 98mm's.

Sounds like fun whichever you choose.

[RSBob]

3 to a 3.2 short stroke?

[Bigtoe32067]

Can I bore and replate the existing cylinders and just get new 98mm pistons?

[Danimal16]

Originally Posted by RSBob

3 to a 3.2 short stroke?

This

[Bigtoe32067]

How does a 3.0 make a 3.2ss?

[Bigtoe32067]

And should I go 10.5 twin lug or 9.5 single plug? How much hp difference is there approx between the two?

[Bill Douglas]

Originally Posted by Bigtoe32067

How does a 3.0 make a 3.2ss?

Originally Posted by Bill Douglas

The 3.0 made into a 3.2 with the 98mm's.

The 98mm pistons make it into a 3.2 ss,

[Bigtoe32067]

I get it now
Because the 3.0 rods are shorter than the 3.2 rods.
I think that’s my plan so the next step is 9.5 or 10.5, single or twin plug?
Does it add much hp for the money? Pistons are the same price (almost) but the twin plug adds machine shop expense and 6 more coils expense. Is it worth it?
Tony

[dannobee]

3.0 rods are 127.8mm long. "Regular" 3.2 rods are 127.0mm center to center. Be mindful of the piston pin size, too. 3.0 are 22mm. 3.2 and 3.3 are 23mm.

Sell the 2.7 as a core. It'll likely need a lot of machine work once it gets torn down. See if the crank spins freely before you tear it down. If it doesn't, for SURE it'll need machine work.

Your call on twin plugging it. Pro: better combustion, less timing advance, more resistant to detonation "might" make a tiny bit more power. Con: cost, more complex wiring, more plugs to change on tune-up.

[spuggy]

Here's a contrary view; I've never driven one myself, but many have said that the free-revving 2.7 motors are a lot of fun in a light car.

Which a 916GT would be, no?

[Bigtoe32067]

I’ve heard the same about 2.7s which is why I bought it but I have a twin plug hot rod 3.0 SC that revs like a sport bike so a similar engine in a lighter car will be even more fun.
It’ll also be much more able to handle the extra stresses over the mag case 2.7.
I have full fg front and rear fenders with the flares built in along with fg front and rear bumpers so weight savings are important.
Tony

[kent olsen]

Years ago I had a 2.7 in my 72 and wanted more power. The cost to modify the 2.7 was what pushed me to a 3.0. I found an 83, small valves, and with the help of Mike Bruns in florida went to work on it. The 3.0 was a couple lbs heavier but much stouter. I wanted something I could run the daylights out of and then drive home and change the oil adjust the valves and that's all.

What I came up with, with Mike's advise and help was 9.5:1 pistons, twin plug, 40mm webers (later opened up to 42mm), ARP rods/bolts and the crank modified to turn 8000 rpm. I had a custom cam cut that lowered the peak torque (217 ft/lbs) to 4500 rpm while making peak power (245 hp) at 6900 rpm. I wanted a lower peak torque because that's what pulls you out of the corners. My 915 trans is geared to where each shift drops to 4000 rpm.

I don't do many track days anymore but the 22,000 miles on this engine have included lots of tracks when I lived in Florida and now on the west coast. With the weight I've removed from my car, now 2200 lbs, it gives me a 9:1 power to weight. She has been bullet proof which is what Mike and I built her to be.