1968 engine conversion

[mv1439]

Can anyone tell me if I will encounter any challenges putting a 2.7 with a 915 trans in a 1968 911T. Thanks

[Oh Haha]

Yes, you will.

[Grady Clay]

mv1439,
First,
Welcome to the 911 Technical Forum
You will find a lot of help here.



A relatively easy conversion is to swap some of your 2.0 parts onto the 2.7 and simply do a proper rebuild on your 901/902 transmission.


First, what is the current condition of everything? What is the condition of the car – Rust? Previous crash damage repair? Wear & tare? How well does it drive?

Is the 2.0 running properly? Have you inspected the sump plate? Does the transmission work, and shift properly? Any noise? Have you inspected the transmission oil and magnetic drain plug?

What year 2.7? What exhaust? What is the condition of the 2.7? Is it running? What is its rebuild, service, tuning and running history. Have you inspected the sump plate? What is the cranking compression and cylinder leak test measurements? Have you checked for loose or broken cylinder head nuts/studs?


The Weber carburetors from your 2.0 will work well on the 2.7 – probably without modification, only cleaning and adjusting. You will want to add insulators between the intake manifolds and the cylinder heads (requires longer studs).

The 2.7 fan shroud provides better air flow to the engine oil cooler. Paint the shroud black. You may want to improve the air sealing to the intake manifolds. The fan housing (with coil mount) will fit this shroud. Use the alternator wiring harness from the 2.0.

What fan is on the 2.7? If 5-blade, you will need to swap the fan hub to the 11-blade fan from the 2.0.

You will need to use the voltage regulator appropriate for the 2.7 alternator to replace the Bosch voltage regulator on your electric panel.

You will need to use the long engine oil-out hose/pipe from the 2.0. You will need to use the engine oil cooler from the 2.0 to replace the 2.7 cooler. Be sure it is professionally cleaned. Use new oil cooler seals.

Use the oil temperature sensor from the 2.0 on the 2.7. Check to confirm the oil pressure senders are the same VDO part numbers.

You need to use the entire 215 mm push-type clutch-flywheel assembly from the 2.0 on the 2.7. Use this opportunity to replace the crankshaft flywheel seal and bring the clutch to new. The flywheel bolts must be replaced – be sure to use the 2.0 version and not the shorter 2.2/2.4/2.7 version. Note to not confuse the flywheel washers.

Regardless of age or history, replace the six chain ramps with new. Now is the time to rebuild (my choice) the existing chain tensioners or update to the pressure version.

If the 2.7 has the ’74 exhaust (2-in, 1-out), good. Otherwise use the 2.0 exhaust (same as ’74) if in good condition. If neither are acceptable, go for a pair of SSI. Use the 2.0 muffler as the 2.7 tail pipe doesn’t fit the quarter-bumper cut-out properly.

Of all the engine tin, use the best, simplest and most appropriate. The piece at the front (flywheel) end, use the 2.0 parts only. If there are A/C brackets on the 2.7, remove them.

When you replace the breather gasket with new, use the 2.0 crankcase breather as it is simpler. Remember to replace the thermostat O-ring with new.

Use the 3-pin Bosch CDI (or equivalent) from the 2.7. Your 2.0 did not originally have a CDI so it probably has an aftermarket unit. I recommend you install new points (or other) in the 2.7 distributor and have it run-in on a distributor machine (remember to set the engine to TDC compression on #1 cylinder).

You will want to start with all new tune-up parts: cap rotor, wires, plug connectors, sparkplugs, air filter, oil filter, fuel filter, oil and fresh high-octane gasoline.

Be sure to remove your oil tank for cleaning. You will need new gaskets for the oil level sender and the oil filter console.


There are at least two systems you may want to upgrade. The 2.0 fuel pump was originally located at the electric panel in the engine compartment. It is very desirable to relocate the pump and filter to the front suspension cross member and insulate the fuel hose from the tunnel to the carburetor inlets. Even better is to install a circulating fuel system.

A 2.7 generates a lot more heat. A front oil cooler system is absolutely necessary if you drive in warm weather. Elephant Racing makes the parts to adapt the 911SC parts to your early oil tank and hose fittings.

When dealing with your engine fan, be sure and end up with the 1.82:1 fan ratio.



That is the simple-but-proper engine swap.
Installing CIS in a SWB 911 (’65-’68) is about the same but you must additionally deal with the much higher fuel pressure circulating fuel system and swap the fuel tank.

Installing a 915 in a SWB is possible but there is interference between the transmission and the body at the rear seats. This can be modified but is a major deal. There is also a difficult issue adapting the axle CV joints to the transmission axle flanges.

With care, a well built type 901 will survive a 2.7 just fine. Many (most?) feel that a type 901 is far better shifting than a type 915 transmission. On the other hand, the 915 is a larger (and heavier) transmission, designed for larger displacement, torque and power engines. The 915 also allows the use of the larger 225 mm pull-type clutch.

I hope this helps.

I see you FS some mid-911 parts.
What else do you have?
Some, but not everything, may be suitable for your ’68.

Best,
Grady

[gsjohnson]

Originally Posted by Oh Haha

Yes, you will.

Just trying to increase your post count?

[Oh Haha]

Originally Posted by gsjohnson

Just trying to increase your post count?

I don't need to increase my post count but thank you.


I was answering the poster's question. His question was rather vague, don't you think?


What did you contribute?

[mv1439]

Grady, thanks. The 68 is in good condition and had already been converted from a 2.0 w/sportamatic to a 2.2 w/901 5 sp but the engine is frozen. The body is in great shape with only a little surface rust in a couple areas. I have a 74S and I'm putting a Euro 3.2 in it so I have my newly rebuilt 2.7S motor that I thought I would put in the 68. The engine is set so I just want the best way to make the switch. I have a front oil system I am going to install to take care of the added heat issue. If I need to change the oil tank also I will as I want to stay with the 2.7 oil cooler. I already have the 11 blade fan on the 2.7. I plan to keep the CIS system. I would like to use a 915 from a 72 - 74 as it has the 7/31 ring and pinion but was not sure what mods would need to be done to make it work. That wourl also allow me to use the later cluch set up. Can you be more specific on the mods needed to make the 915 work? Thanks

[mv1439]

Oh haha, I have a stock 68 sportomatic that at some time was converted to a 2.2 w/901 5 sp. I would like to put a fresh 2.7S motor in it and use a 915 trans if it is possible. I already know some mods will be required but not sure which one's. Can you be more specific as to what knowledge you may have on the conversion and challenges I may encounter. Thanks

[Oh Haha]

It appears Grady covered most of the issues you may encounter. Obviously, a problem may come up at installation that can be addressed at that time.

I found this thread that has some details on fitting a 915 box.
HELP please - putting a 915 into a SWB - axle set-up?

Here's another that has some great details that should help you.
Modifed SWB cars

[Grady Clay]

OK

First let’s discuss installing the 915 so you may see the wisdom of using the 901. We will talk about a type 911 later.

The big issue is the transmission interferes with the sheet metal between the rear seats.

You can either ‘heat & beat’ the metal to gain clearance. As I recall, about 3” or more are necessary. In the end you will need to modify the rear seat upholstery.

A ‘cleaner’ solution is to cut out the SWB rear seats and install the rear seat sheet metal from a ’72 and later salvage. This also allows you to use the ’72-> rear seat upholstery and carpet pieces.

If you go this route, you are getting farther away from the car ever being possible to be returned to original.

Easier is to adapt the 915 axle flanges to the small SWB CV joints and short axles. One issue is when Porsche introduced the LWB in ’69, they angled the axles to the rear. This was well and good as the dramatically lengthened the axles and enlarged the CV joints to handle the angular running.

In order to get longer axles, they changed two other parts. The trailing arm (banana) was changed to use the one-piece, dual-row ball bearing. This was much narrower than the SWB ball/needle bearing set up and allowed the outboard CV joint to be moved out.

On the inside, the distance between the two transmission axle flange surfaces was decreased. This moved the inboard CV joints in.

The combination allowed the much longer axles.
All is well and good.

Now comes the 915.
In order to reduce the angularity, the 915 differential centerline is moved toward the engine by 10 mm compared to the 901 and 911 differential centerline.

Sure enough, this reduced the angularity and allowed use of a thinner CV joint (starting in ’72).

All this effects you as the short (SWB) CV joints will see much more angularity because of the repositioned 915 differential centerline. Will it work? Sure but those small CV joints are already stressed by the much larger engine.


Typically, you fit the 915 to the SWB CV joints by making an adaptor between the inboard CV joint and the transmission axle flange. As I recall, it is about 30 mm thick.


I think the best solution is to use a ’70-’71 type 911 transmission. It fits the chassis without modification. It uses the 225 mm pull-type clutch (even though it uses the Rube Goldberg linkage). The differential centerline is in-line with the rear hub.

This still has the axle length issue to deal with. I would inquire of Sway-Away about a pair of custom axles. You could use the large 108 mm CV joint on the inboard end and either standard ’68 CV joints on the outboard end or modify the SWB stub axle to fit the 108 CV.

You can’t do jackrabbit starts with a 901/911 as the 1st gear is cantilevered. (Not so with a 915.) With a well rebuilt type 911 and reasonably not abusing it, a type 911 works well with a 2.7.

I successfully use a type 911 with my 2.8S MFI and SCCA 2.6R, both double the output of a CIS 2.7.

Best,
Grady

Next, engine

[Grady Clay]

Oh Haha,

Thanks for posting the links.

Here is an image from:
HELP please - putting a 915 into a SWB - axle set-up?






This is a highly modified car but it is worth looking at the issues.
Most of these techniques are not suitable for a normal street SWB.

First note the clearance between the SWB stub axle modified to attach to a 108 mm CV joint (green arrow).
This is after the shock has been repositioned to the outboard of the chassis and on the outboard
side of the trailing arm, (red arrows). You can’t do this on a street 911. You can’t leave the
shock as original as it will interfere with the 108 mm CV joint. You can’t move the CV joint inboard
as that would exacerbate the axle length problem.

Note this car has modified the frame (yellow) to gain clearance for the CV joint on ‘bump’ with a
low car. Also, the inboard mount for the trailing arm (banana) has been repositioned (teal arrow).
This may have re-positioned the stub axle centerlint to match the differential centerline.
Of course this would change the wheelbase.

I can’t see the rear seats but many racers remove the seat sheet metal and have a removable panel for
ease of service.

Note the front brake rotor and aluminum front ‘S’ caliper.

Nothing like a street SWB.


Using the small ’68 CV joint is the easy solution.

We should investigate using the 100 mm 911SC (type 923, 912E) CV joint.

Critical to this whole issue are angularity and distance between CV joint centers (axle length).

For example, the RS Spyder has the inboard CV joint inside the ‘differential’. This is possible because
it is a ‘spool’ and no differential parts. This allows very long axles (almost touching in the
middle of the spool) to reduce angularity.

Best,
Grady

[gsjohnson]

Originally Posted by Oh Haha

I don't need to increase my post count but thank you.


I was answering the poster's question. His question was rather vague, don't you think?


What did you contribute?

The question didn't appear vague to me. Grady was able to answer it in detail.

I own a 68 911 and I dropped in on this thread to see if I could learn a little something. But then I encounter a wise guy response which I thought was uncalled for to this new member.

Although, I see my response got you off of your duff to actually contribute.
And I thank you for that...

I just thought it was a rude response. That's all.

I apologize if I offended you.

[mv1439]

Thanks Grady and Wayne. After reading all the data I think I will take your advice for now and stay with the 901 for now. If I am right using the 901 the conversion is basically an engine change. I am confident the 901 will handle the 175hp of the 2.7S motor. I assume that since it currently has a 71 901 w/2.2 motor that the Axle hookup will be correct and I can just connect the 2.7 up and go. I'm I correct?

[Oh Haha]

No offense taken.

It WAS a wisea$$ response.

Good day, Sir.

[gsjohnson]

Peace Brother.
Take Care...

[James Brown]

I was going to say that Wayne but you beat me to it! There is a lot of new (to Porsche) people who don't do there homework. I love to answer questions but the "meaning of life" ones or " help needed in re manufacturing my unibody" are a little vague. Good intentions but there are good manuals out there that go a long way to answering the majority of questions. I like the beyond-the-book questions or fabricating something from nothing. But hey, everyone has to start somewhere.

[Grady Clay]

Is the engine original ‘74S USA configuration?

The most important issues are around the CIS fuel system. The safety issue is the ’68 Weber carburetors use ~3 psi fuel pressure. These came with ‘compression cones’ at the ends of fuel hoses. They didn’t even use hose clamps. They used fabric covered 7 mm low-pressure fuel hoses.

CIS can run above 75 psi (4.9 bar) !

As CIS progressed, every fuel connection was a screw-together high pressure fitting. Even the supposedly low pressure return was screwed together high pressure capable. Converting the ‘69 to CIS, it is wise to use the best of the Porsche example.

Starting at the front, you need a late CIS fuel tank. Not only will this have the screw fittings but it has the necessary ‘swirl pot’ air fuel separator and no=air fuel pick-up. CIS won’t work properly below about ½ fuel level without this tank.

Unless you find a ’73.5 911T tank (unlikely), you will need a collapsible spare and air pump.

You will need to address the lack of fuel vapor recovery system as a full tank will spill fuel on hard right turns with the ’68 overflow. The ’69-’73 vapor separator under the cowl will solve most of the spill issue.

It is desirable to keep as much of the fuel system as possible out of the engine compartment to avoid ‘heat soak’ after the engine is turned off hot.

Porsche eventually returned the electric fuel pump to the front cross member with later CIS. This cool location is very desirable. Use the latest CIS electric pump with a check valve. Even though Porsche never had it so, I would also locate the fuel filter on the cross member. I don’t know if it is possible to locate the accumulator there also. If you can install the accumulator in front, you must position the fittings ‘UP’.

A ’68 is the only SWB that you can install the aluminum cross member on without changing to the entire LWB front suspension. The aluminum cross member has more room for fuel system components.

(Installing the entire LWB front suspension is desirable. Another subject.)

Your chassis has only one fuel pipe in the tunnel. The CIS requires two. It is not reasonable to tear apart the tunnel to install a second pipe. A better solution is to install two new pipes alongside the tunnel on the passenger side. Best is high pressure 3/8” (0.375”, ~10 mm) stainless steel tube. To the ends you can silver solder modified metric fittings common to the CIS system. This allows everything else to be standard metric or Porsche parts. Remember to use the two different sizes for supply and return – same as the CIS.

The pipes go through three panels; the firewall at the rear torsion bar tube, the bulkhead behind the passenger floor board and the panel between the gas heater well (‘smuggler’s box’) and the steering rack. There should be a straight fitting at the rear and a 90° bend at the front. The only bends in the pipes are where the tunnel flares at the front and rear. Feed the pipe assemblies in from the front with the cross member removed.

Use large rubber grommets where the pipes go through the sheet metal bulkheads. Make them tight on both the fuel pipes and the chassis. Put the split down.

You should cover the pipes with 1-2 layers of heat-shrink tubing. Shrink over the center of the pipe first, slide un-shrunk tubing over that and then solder the last fitting. Finally position and shrink the remaining shrink tubing.

Make two hose assemblies with a 90° fitting under the rear torsion tube and a straight fitting at the engine. Use two insulating tubes, something like Aeroquip ‘Firesleeve’, between the fittings at the torsion tube and the engine. In hot weather there is VERY hot air wasted from the heater control flap valves.


With this scenario, I would use the electric panel from a CIS 911. This allows you to use the 14-pin engine connector common from ’70. You can adapt the SWB wires to the panel and hide the connections behind the panel. You can do this while leaving all the original wires and connectors as original. This also gives you proper mounting for the CDI.

With this, use the original 2.7 engine wiring. This lets you use the rear tin where the main red (B+) wires, etc go to the starter. You will need to zip-tie to not use the back-up light switch wires. You will need to tape up some wires. Use the existing SWB wires for the temperature sender and the oil pressure sender.

Look over your starter motors. Many 2.7 (almost all 2.4) use a Bosch 1.5 hp starter (’68 has 0.7 hp). Use the 1.5 hp on the 2.7. As an aside, the 2.7 chassis has a main starter cable size 25 mm. Your ’68 cable is 18 mm. I found no need for larger with my ’68.


The oil tanks are different ’68 to ’74. The two most significant differences art the oil hose fitting size and type. Obviously the hose between the tank and cooler is push-on with a hose clamp where ’71 and earlier are screw fittings. The size of the engine-out fitting is different.

The other is the filler neck and filter through a much larger opening through the inner fender.

You will need to make a bracket between the oil tank and the quarter bumper support.

If you have the opportunity, there are several ‘improvements’ that can be made to oil tanks.

The advantage of using a later oil tank is the ease of installing the front cooler system. I recommend you use the aftermarket hoses that go up over the tire inside the fender. You don’t have extra room inside the wheel as the later chassis has a formed pipe clearance there.

The crankcase breather hoses should bolt right up.

You will need to plug the evaporative emissions connections at the engine unless you run extra hoses to the front.

What did I forget?

Best,
Grady

PS; look under the ’68 and confirm it has the original 902/902 and not a type 911 transmission. Just to know for sure.

[BoxsterGT]

Thank you Grady, I am getting an education.

Every time I log on I look for your posts.

Len

[cnielsen]

Old post...I know.

Grady, you are a wealth of knowledge!

You mentioned using the 70/71 style transmission with the funky clutch linkage. What are your thoughts on the 69 transmission with a more traditional a clutch linkage?