"Sleeper" hotrod - homebuild 2.7CIS to high comp 2.7 MFI

[gav p]

Thanks for the interest chaps And great to hear others' thoughts - there are always options out there which are not immediately apparent - i.e. EFI had never crossed my mind, but I see the advantages...

The main issues for me around EFI are complexity and cost - I don't have the time to really shake down an EFI system, and certainly have no electronics experience to help with the process. I already own the whole MFI kit and have rebuilt the throttle bodies etc, so it would be a shame not to use it.

Why not go EFI rather than mess around with your E engine especially as you recon it has never worked perfectly?

- good point Jason However, as the Check, Measure, Adjust MFI bible states, the engine will never run properly with MFI unless the underlying mechanical condition is not 100%. I seem to remember one of the first items on the 10 point checklist is a compression test, and if the leakdown numbers are over 10% they don't even recommend you bother with any of the other steps....

Anyway, my point is that I suspect there's nothing much wrong with my MFI system - it is the tired engine it sits on which is the problem. We'll see anyway. I plan to get the pump looked at again during this project, and re-test the injectors for spray characteristics.

It is never going to beat EFI on efficiency and flexibility, and like James I would love to have more control over the full range of running conditions, but as with most MFI nerds I love the sportsbike-like throttle response and the amazing sound it makes

Aiming for the same ride height and rubber combo as the green loveliness?

That would be fantastic - I'm not sure I would go much lower with my own car, but the rubber choice on the green car is spot on in terms of looks. It is actually running 7R's on the rear, which if I were to use it would probably be a set of the Group Four repros (not seen a set myself though). Full spec of the green car is here:

http://forums.pelicanparts.com/porsche- ... od-41.html

....a useful thread there for anyone interested in hotrods. From gorgeous to horrible, and everything in between - there is certainly something for everyone

A related question: how do you mount an MFI pump on a cis case? Are the pump mount studs still there on a cis case?

Yes, Tim is right - the case still has the same three studs that the MFI engines use, so it is a simple bolt-on job.

[Mick Cliff]

The main issues for me around EFI are complexity....

There are 'plug and play' solutions - search Clewett (uses PMO throttle bodies) and D-Zug (Triumph triple ITB's) and Jenvies with an Emerald ECU. None are cheap, but have you costed refurbishing MFI throttle bodies and injector pumps for comparison - you're looking at £2k+!?
Difficult time for you making decisions at this stage, as what you decide to do may have a bearing on the basic rebuild....

[gav p]

An interesting day in the garage today - it started with removal of the timing chain covers and rocker covers -



All very clean internally, although the righ hand cam has clearly been the victim of an earlier ham-fisted "mechanic"..


I guess they didn't bother with these the last time around -


- these are the pre '79 cam tools which I picked up from ImpactBumpers a couple of months ago. They made removal of the cam nuts pretty easy.


Nothing untoward in the cam carrier areas - once again, very grotty on the outside but clean on the inside. I guess the lack of oil deposits indicates use of synthetic oil?

Anyway, all went fairly smoothly with the stripdown - chain tensioners, cam nuts, then chain cases on both sides. No major dramas. Then it was on to the cylinder head nuts, all of which required pretty minimal torque to slacken. With the nuts off, the complete head and cam assemblies on each side were loosened and it should be possible to simply lift them off of the studs. However, on this engine the surface corrosion of the head alloy in the headstud areas meant that quite a lot of tapping and jiggling was required.... eventually they came off OK, but a classic case of being far harder than the manual suggests. The temptation to hit things ever harder when they are sticking is strong, but with delecate alloy components and castings this is the last thing you should do.

So, with the heads off, this is what I found - quite a bit of water in a couple of the bores along with lots of discintegrated paper towel material (which had been stuffed in the inlet ports at purchase), and also an M8 washer (!).... just as well it was always destined for full rebuild





On the plus side, once the gunk and water was cleaned up, the conditon of all items was remarkably good. The plugs were fairly clean, the cylinder bores are unscored and the heads don't show any major evidence of leakage at the barrel sealing surface. The complete head/cam carrier unit from each side of the engine are now sitting on my workbench, ready for stripdown later.

Next job is to remove the cylinder barrels and their tinware, then the pistons. Hopefully I'll get some time this week to crack on

[Lightweight_911]

Good progress Gav & encouraging not to find nasty surprises ...

[gav p]

I have a 2.7E engine in my 72 car...
Bob Watson build ( and tune...)
No need for twin plug heads...was his opinion.
It is pretty powerful, with 219bhp on Bob's Rollers and torque above an RS spec engine.
Make sure your rev limiter is in good order and it gets there very quickly in 2 and 3 gear...
Be interesting to see your engine come together

Good to hear about this similar spec, and also Steve's 2.7 on PMOs - gives me confidence that the basic idea is going to deliver the goods Also made me wonder why the factory didn't try this sort of CR for street engines once the 2.2s had finished production.

Does anyone know why the stock 8.5:1 CR was set so low for the 2.4-2.7 MFI cars?

[Cortina]

Low CR ... to easily (safely) run on 2 star fuel ?

[gav p]

Managed to get a bit of time in the garage to remove the barrels and pistons earlier, and started by getting some pictures to remind me how the cylinder tinware will fit back in place when it comes to the rebuild -



Then followed some careful wiggling of the barrels away from the case seating surface. Interesting to start getting glimpses of the internal case condition - as you can see, the barrel skirts look brand new! -



Then it was straightforward to remove the barrels altogether, followed by the pistons. All looks to be in great condition, and once again at first glance the pistons look almost as good as new! Too bad that they are likely to become paperweights now that high comp pistons are on the menu...



Really interesting to see the further EFI discussions above, by the way. I am still keen on retaining the MFI system since I have already invested some capital in it - rebuilt TB's a few years ago, new injectors etc. I have also spent many hours getting to know exactly how every component works, and I view the system almost as a glorified GCSE Physics excercise what with all its thermo-switches, barometers, bi-metalic discs and more balljoints than you can count on two pairs of hands....

I see where Mick is coming from though - all these things mount up, and once you get into pump-refurb territory it gets expensive quickly! My gut feeling is to stick with MFI now I have invested in new and refurbed parts. If this expenditure hadn't happened though I am confident I would find a lot to love about EFI...

More research needed though on my part I feel - its not too late to change tack!

[gav p]

Managed to get out into the garage again over the weekend. The barrels and pistons have cleaned up really well, and certainly show no real signs of a hard life.

Moving back to the case, it was time to remove a few more components in preparation for splitting it. With barrels and pistons removed it looked like this - starting to get some interesting glimpses inside:



Next to be removed was the sump strainer plate, which was a good opportunity to take a closer look at the magnetic sump plug. Some debris is attached to the magnet, but as suggested by the apparently good condition of the steel parts so far seen during the strip-down, I am guessing this level of build-up is not too serious? Of course, anything non-ferrous would not be caught by the magnet though...

[gav p]

Then it was on to the exciting bit - splitting the case. None of the fasteners gave any major issues, although more signs of a previous rebuild are seen: the large nut buried deep inside the timing-chain area of the case shows evidence of mistreatment - not sure how someone managed to make this much of a mess of it -

[gav p]

Anyway, with all of the nuts out of the way, it was time to tap the case apart. It took quite a while to work the two halves away from each other, but in the end the left half was free and could be lifted off. One thing which was immediately noticeable was just how lightweight the case halves are - they really are a finely engineered work of art. This is amazing considering that, not only do they stand up to the internal stresses of the engine when running, but they also form a structure which supports the weight of the entire engine and gearbox assembly when bolted into the car.

Internally, the engine once again looked far better than it did on the outside - a thing of beauty indeed! -



Everything seems to be more or less as it should be. The main bearing shells don't show any real wear, and have "STD" stamped on the back which thankfully indicates that the crank has not been re-ground. One of the bearings shows some scratches on the bearing face somehow inflicted by the previous engine builder -



Interesting to see the marks left on the engine by previous mechanics - each tell a story. Some fairly poor practice revealed by these details, but it's just as well that no serious damage has been found so far.

Next task is to extract the crank and remove the rods, to reveal the condition of the big-end bearings.

[gav p]

Right - a couple of weeks with no updates... but things have been progressing. I have now driven a 911 with two engines...

OK, so actually not quite as strange as it sounds. I made the trip up to Brackley the other day, to drop off the main engine components for machining. it was great to meet Nick, and was also a good excuse to use the 2.4E again before the old engine is removed The weather wasn't great, and I had to be careful on the roundabouts approaching Nick's workshop as there was the 2.7 crankcase sitting in a tub in the back of the car behind me! But the journey was fun, and driving it again after a couple of months off offered a nice reminder of why these cars are worth the effort and expense.



Oil slick on the ground under the back of the car not pictured.....

Anyway, I'll post some details later, but suffice to say that Nick has given some fantastic input into the proposed engine specification. And on assessing the condition of the 2.7 components he came up with some interesting findings. Details to follow if I get some time to post this evening...

[gav p]

With the engine components unloaded, Nick set about checking the condition - starting with the crank.



Thankfully the crank turned out to be straight and also free of cracks. Furthermore it had not been reground during previous rebuilds and is still well within tolerance for use with standard bearings

[gav p]

Next the cylinder barrels were investigated.



Having taken a good look at the bores, Nick came to the conclusion that not only were they showing very little wear, but that they were not the "Alusil" version which the '74 CIS would have originally been equiped with. Rather, they are Nikasil Mahle replacements, and are in fact the very same cylinders as used on the 2.7 RS engines. Apparently these, paired up with standard CIS pistons, were a standard rebuild replacement for worn CIS engines because Alusil was discontinued by Mahle at some point.

This is great news - it avoids the expense of replating the 2.7 cylinder bores or purchasing of new cylinders

[gav p]

The rest of the components also checked out pretty well. The case shows no damage, with no sign of any pulled head studs although they will all be replaced and the case strengthened before new studs are fitted.

One item Nick found some wear on was the intermediate shaft gear -



Some pitting and a bit of deformation on the drive side of the teeth can be seen. Apparently this is not particularly serious and can be re-used. The main downside is the potential for a little bit more noise at idle due to gear-chatter. I understand that the alternatives are either a new gear and shaft assembly for ?£800++, or to hunt down a good used one. I don't see this as a priority on a non-concourse engine, but if anyone does happen to have a good one then do get in touch.

[gav p]

Regarding the rebuild spec, my overall plan of building an original-looking E-cammed motor "on steroids" is still very achieveable using the CIS base engine.
However, assuming we stick with the E-cams, Nick's suggention is to keep things simple -

- Don't twin-plug it: the main benefits of twin-plug are felt at high RPM, but with the E-profile giving more power at midrange RPM the ultimate top-end performance is not a priority
- Don't bother with Boat-tailing the case/cylinders: once again, has minimal impact below 7500rpm and with E-cams these sort of revs are not where the engine is naturally needing to be. As also mentioned by James earlier I think.
- Don't lighten the flywheel if it's likely to see lots of everyday/street use (apparently they are already quite light anyway).
- High compression pistons, aim for 10:1 - apparently the main consideration here is fuel type, since this CR would require routine use of 97-98RON unleaded.
- E MFI pump recalibrated for 2.7 fueling

This spec would give a motor with mega-torque, and around ~210-215ish BHP apparently.

Thanks to the visit to Redtek, I now also understand a little more as to why there would be so much torque - apart from the cam choice, it's a lot to do with airflow speed through the inlet ports: a smaller port size increases airspeed which improves torque, but at the expense of top-end BHP (due to restricting the volume of air the engine can suck in at high RPM). The E port size is 32mm diameter (as are the US-spec '74 2.7CIS ports on donor engine heads). I seem to remember the S -heads are 36mm? Apparently the 2.4TE is just 28mm. Please shout if this sounds incorrect!

If I keep with the E-sized inlet ports, throttle bodies and MFI trumpets, then the port size is smaller than the S/RS version and therefore gives more torque but less top end BHP than an equivalent S-sized ported engine. Increasing the CR will give it's own power improvements though, which goes a good way to making up for losses due to the restricted airflow.