2.7L rebuild suggestions...

[Chain_rxn]

first, i'm a total newbie to auto mechanics. this is my first car project. the background - the car is a 1975 911S that i am backdating to 911R appearance with all fiberglass parts [including roof]. goal is lightweight [less than 2k?] street/track car. striped interior. rollbar/simple cage. coilover suspension.

current state of car:



my 2.7L looked pretty bad...















for as dirty as the engine was [oil leak on cylinder bank 4-6?], it had zero broken head studs. and was running [110k on the odometer] before i dropped it from the car.

so, the PLAN [help me out here] is a 6 plug street engine, carbureted. i guess i'm wanting a 2.7 RS or RS high compression engine, per waynes book. unless someone with more knowledge than me has a better idea... hoping 180-220hp.

my next step is the machine shop. so i want to accumulate parts that i need to take to the machine shop so they can do their magic. so that means buying stuff...

case mods - oil bypass, case savers, case mods needed for newer oil pump?

LN engineering cylinders/pistons combo. i ASSUME 9.5 compression as i don't have much urge to dual plug [simpler is key here]. 90mm versus 92mm? BTW, why are my friends, who built chevy v8s, saying they are running 10-11 compression?

should i keep my original rods or use LNs 'improved ones'. they are in the budget. the titanium rods would be more fun...

carbs - what size?

heads - do i need them ported?

exhaust - planning on headers. guess i need a hot air block off plate?

i have mechanical chain tensioners already. should i replace with hydraulic?

let me know what yah think!

[Flat6pac]

You ll be far better off doing a 3.0, 9.3CR engine
The horse power is available with CIS and exhaust
Residual value for the base 3.0 is way higher than a rebuilt 2.7 because its too expensive to do it right...
Bruce

[burtm5]

heads on a 75 911 S should be 35 Intake 35 exhaust should be ok. You need to get intake manifolds from an early 2 liter S (35) or get pmo (36mm) 40 mm webers or pmo carbs, 9.5 JE pistons, SSI or early exhaust and early muffler. E or solex cams would be best unless you want all top end of an early S cam. If you review the books there is a point where if you increase compression ratio it does not increase hp very much. point of diminishing returns around 10 to one. so I wonder about the wisdom vs cost of twin plug. since chevie are water cooled iron blocks with different head flow they will not detonate at 10 or 11 to one. P cars are different. best I can tell an sc or later aluminum block is at least 33 lbs heavier than a mag case. studs pull on alum cases also. on light weight cars 9.5 CR made for high lift cams make fun motors IMO. best Henry

[tharbert]

You will need a 4 rib oil pump to go along with the oil bypass mod. I think you can still use the three rib pump but with the 4 rib, the pressure side is larger and the scavenging return side is smaller to take advantage of the modification.

Mag cases have a few annoying issues. One is, they tend to warp a bit once split. So, you will need to have it decked and line bored back to standard along with the other mods like case savers. You may want to measure your crank journals before you send off the case. If the journals are worn beyond spec, you'll want to get your hands on a good crank. Oversized bearings alone cost $700 versus $100 for STD. Getting a crank ground -1 is very costly and requires rehardening of the bearing surfaces and R&R of the oil galleys: $pendy!!! A good machine shop will evaluate your case and then discuss with you what it needs but you need to have a good crank in hand for that discussion. The reason why I suggest this is, I measured my crank after the case was done. It was worn way beyond specification. I had a very stressful month of shopping for a good crank. They are getting increasingly hard to come by and the prices are going up.

[tharbert]

And... Chain tensioners have been discussed at length here. I upgraded my old pressure tensioners with the Carrera type pressure fed tensioners. The OEM ones had failed. I debated simply rebuilding the OEMs but opted for the Carrera units after reading as much as I could find about them in this forum. There are some folks who prefer the solid tensioners. Since you already have them, maybe someone will chime in on why you should keep them. What you have is totally serviceable but they come with a price. I always thought they were associated with race engines and as such, would receive regular adjustment or replacement on a race engine maintenance schedule. I'd love to see a discussion about the pros and cons of the solid tensioners you have, maybe an argument to keep them.

[Lapkritis]

Originally Posted by Chain_rxn

first, i'm a total newbie to auto mechanics. this is my first car project. the background - the car is a 1975 911S that i am backdating to 911R appearance with all fiberglass parts [including roof]. goal is lightweight [less than 2k?] street/track car. striped interior. rollbar/simple cage. coilover suspension.

current state of car:

my 2.7L looked pretty bad...
for as dirty as the engine was [oil leak on cylinder bank 4-6?], it had zero broken head studs. and was running [110k on the odometer] before i dropped it from the car.

so, the PLAN [help me out here] is a 6 plug street engine, carbureted. i guess i'm wanting a 2.7 RS or RS high compression engine, per waynes book. unless someone with more knowledge than me has a better idea... hoping 180-220hp.

my next step is the machine shop. so i want to accumulate parts that i need to take to the machine shop so they can do their magic. so that means buying stuff...

case mods - oil bypass, case savers, case mods needed for newer oil pump?

LN engineering cylinders/pistons combo. i ASSUME 9.5 compression as i don't have much urge to dual plug [simpler is key here]. 90mm versus 92mm? BTW, why are my friends, who built chevy v8s, saying they are running 10-11 compression?

should i keep my original rods or use LNs 'improved ones'. they are in the budget. the titanium rods would be more fun...

carbs - what size?

heads - do i need them ported?

exhaust - planning on headers. guess i need a hot air block off plate?

i have mechanical chain tensioners already. should i replace with hydraulic?

let me know what yah think!

I'd say you're doing very well for a newb. Keep at it. Bruce Anderson has given a nice roadmap for this type of build in his book as well.

Rods - stock

Pistons/Cylinders - Mahle RS spec Nikasil 8.5:1 90mm

Carbs - 40MM IDA-3C, 34mm venturi, F3 emulsion tubes, 135main jets, 145 air correction... tweak to your environment.

Heads - port to RS Spec 36mm intake, 35mm exhaust.

Exhaust - backdate to SSI.

Dansk muff works well, stainless if you can swing it.

Cut your baffle tin before painting/coating for increased cylinder cooling. This is the tin between the cylinders held in place with the metal strips from above; if you search you will see the instructions for how to trim.

Cams - you can go a bit wilder here. Webcam 464/465 would be my recommendation.

Other considerations:
Valve covers - turbo lowers or hargett billet with updated gaskets.

RS rocker shaft seals to stop oil leaks.

Clutch disc - spring upgrade from rubber center.

Ignition distributor - re-curve for carbs/mechanical advance. Maybe add MSD 6AL / 6AL/2 ignition box to prevent over rev on the track.

Fan - swap up to 11 blade

Headstuds - choose Supertec, ARP, Raceware, etc.

There are other configuration options to be had. For my mag case, I have the RS bits already but elect to use an iron cylinder instead due to the thermal expansion forces we're aware of and the fatigue on the case. I use the parts listed above but with 9.5:1 JE pistons. I added heat sinks and milspec black anodize coating to the hargett covers to help cool things down with great results. It's a fantastic drive on the street and my mind is more at ease than it would be with aluminum cylinders tugging on the old magnesium.

[The Watson]

Glad you finally posted! Your body and engine are cleaner than mine were, so you have a good start - compared to me anyway. A couple of points about the rebuild to consider:

- stock rods are good rods. You can always lighten them rather than going to after-market.

- I've seen some good counter-points to going to the 11-blade fan. My car had a smog-pump, thermal reactors, a/c, no fender oil cooler and a 5 blade fan when stock. I am changing everything BUT the fan and completely expect this to be plenty. It can always be changed later if necessary. Consider that racers use the 5-blade fans due to less HP drain. Pulley ratios can also be swapped to alter fan speed.

Keep listening to good advice but I write off the folks who say "you have to do what I did" when it comes to various alternatives. Make it yours!

[Chain_rxn]

great info guys! how do you know size of cylinders? 89mm vs 90mm... do i need to measure my current ones and just keep things the same?

i've never heard of those webcam cams. where do i find more info about those?

i initially won't be running any accessories off the engine, so i'll stick with the 5 blade fan. though, i wont have external oil coolers either. i'll see how it runs and the modify as needed.

[The Watson]

I would say first determine, if stock, whether you have alusil or nickasil p&c's. Conventional wisdom says reuse nickasil and recoat or replace alusil. Nickasil cylinders can be bored out I believe (to some extent). Lots of info on pelican and in Wayne's rebuild book. If replacing both, the nickies/JE option is a nice one in almost any configuration.