How reliable is a built 2.7L?

[JeffW]

I'm still debating rebuilding my 2.7 liter or doing the 3.6 liter swap. The 3.6 liter looks to be better just because it has more power, larger displacement, and aready has the good stuff like twin plug ignition. But then again I already have a 2.7 liter that has all the upgrades but is leaking everywhere. Has been rebuilt with the caseserts, 11 blade fan, turbo valve covers, carrera tentioners, all that stuff. About what does it cost for a hi-performance parts kit to rebuilt a 2.7? And if I were to do the swap to 3.6L what kind of price would my 2.7 be worth? I want the most reliable and with most power I can get.

Thanks,
Jeff

[thrown_hammer]

Jeff,
I have been debating this as well. I have seen a few people on this board have suped up 2.7's I was thinking 2.9 P/C's, PMO carbs and some agressive cams. I will be interested to see some responses from people that have already gone down this road.

[Early_S_Man]

An RS 2.7 engine is exactly as reliable as any 2.4 MFI engine ... and the RS 2.7 piston & cylinder sets are currently the most economical Mahle sets on the market, and the best quality, to boot! It kind of depends on the personality you want for your car ... your 915 transaxle would need work to be satisfactory for a high-revving engine like an RS or similar 2.8 or 2.9 engine.

There are also other considerations that have costs, too ... such as your oil-cooling system, which is likely to be unsatisfactory for ANY upgrade you have mentioned! There are NO simple answers to your question!

[makaio]

How built are you talking?

RonninLB from this board has a mild 2.7 that he built, and it's a great runner.

If you want to just fix the leaks, you could do it pretty cheap if you do the labor yourself.

I'm guessing your 2.7 would fetch $2000 if you cleaned it up, and had proof of re-build. Less if you have no proof of re-build.

[pwd72s]

I'm with Warren on the 2.7 RS..It's a respected track engine..My rebuilt 2.7 has another purpose than track..It does come down to what you want. I suggest forged pistons and the 8.5c.r. for street use. The 3.6 is more powerful on the track,, no question about that..but when I offered a cross country/full circle event between any of the quick 3.6s around here against my humble 2.7 with simple rules such as a solo driver and no outside mechanical help, I was unable to find anyone who would step foreward with their powerful 911...go figure.
...but back to the subject..the machine work is just as important as the new parts...RoninLB

[JeffW]

The main problem I have with the 3.6L is the $10,000 for one with all the parts. I may be better off to getting a 3.0L or 3.2L that is rebuilt. I need basic reliability and speed would be a plus but I don't need speed without reliablity..

[Wayne 962]

JeffW, you are thinking smartly here - it is all about cost. Without a doubt, a 3.6L engine will give you more power and probably greater engine life. It also should hold its value well.

However, the 3.6 conversions are very costly (engines are the biggest cost), and other than Dr. Steve, there isn't a lot of information out there about this conversion (there's some, but no real conversion guides, etc.).

The 2.7 liter engine is a great, quick responding engine. The 2.7 RS is great especially with higher compression pistons (what I tend to recommend for performance). It's still expensive to completely rebuild one (about $6K in parts and labor if you do it yourself).

See this thread:

Paul Weir

-Wayne

[CamB]

Originally posted by Early_S_Man
...the RS 2.7 piston & cylinder sets are currently the most economical Mahle sets on the market, and the best quality, to boot...

Warren - you got me worried (I just bought Mahle 98mm P&C) - how come the 2.7 are better quality (or more to the point - is there something wrong with the other Mahle P&C).

Thanks, Cam

[JeffW]

what kind of power does one of these 2.7 RS motors make? I may be interested in that. Will I have problems since My motor has already been rebuilt? It was a quality rebuild considering it has 105,000 miles on it now and only has oil leaks and low oil presure.

thanks

[Early_S_Man]

Cam,

No intent to say that the RS 2.7 sets are better than anything else sold ... just that they are Nikasil, and the pistons are forged! Many of the $3000 Mahle sets on the market aren't! Some others are both Nikasil and forged ... like the new offerings from Andial intended specifically for street applications, and offering 9.5:1 to 9.7:1 compression ratio range.

[CamB]

Well, here is hoping the 10.5:1 98mm for twin plug are both forged and "nikasiled" - given the cost...

Otherwise watch this space to see if I complain of a rebuild after only 150-200k miles.

[Matt Holcomb]

Originally posted by JeffW
what kind of power does one of these 2.7 RS motors make? I may be interested in that. Will I have problems since My motor has already been rebuilt? It was a quality rebuild considering it has 105,000 miles on it now and only has oil leaks and low oil presure.

thanks

Jeff,

With the standard CR (8.5:1), these engines develop 210bhp at 6,800rpm. This is good enough to propel a 1080kg car to 60mph in under 6 seconds.

However, if you decide to increase the CR to, say, 11.3:1 (like mine), you can expect close to 240bhp with a standard exhaust and intake system. Add another 20-30bhp if you ditch the air box and add a 2-in-2-out muffler. But, with a CR that high, you're gonna need access to 98-octane fuel if you want to keep the single-plug heads.

Irrespective of the type of fuel you have access to, you will need to upgrade to a radiator-style oil cooler.


Matt Holcomb
MFIWDP
1974 911 Carrera 2.7 RoW
1975 Mercedes-Benz 280SE
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[JeffW]

Is it costly to upgrade to dual plug heads and will these options work with the CIS fuel injection?

[CamB]

Yes and yes. Upgrade to dual plug requires either an electromotive crank fired setup, a distributor with a 12 wire cap or a 964 dual distributor. The first one is the cheapest (I think). I am not sure whether a 964 distributor can be converted more cheaply, but I doubt it (you need two CD boxes, 2 coils, etc).

You only need twin plug beyond a certain compression. A man who has written much on this (and knows way more than I) has a good summary here:

http://www.rennsportsystems.com/~porsche/2a.html
http://www.rennsportsystems.com/~porsche/2f.html
http://www.rennsportsystems.com/~porsche/engines%202.7-3.2.html

Alternatively, Wayne has probably written a bunch of stuff for his new book and could let you know ahead of time

(edit) And you have to have the heads machined for the second set of plugs, the lower valve covers need holes for the wire connectors and you need another set of plug wires.

[Wayne 962]

You have twisted my arm:

Twin Plug Ignition

Twin plugging or twin-ignition is an upgrade that is usually best installed along with an increase in the compression ratio. Typically, to reduce cylinder head temperatures and reduce detonation at higher RPM, I recommend that a twin-plug ignition system be installed if your compression ratio is higher than 10:1. In addition, twin-plug ignition systems should probably be installed on engines with piston diameters greater than or equal to 98mm. The piston diameters at this range are so large that it takes too long for the ignition flame front to propagate across the combustion chamber. Usually minor horsepower gains can be expected from engines with less than a 10:1 compression ratio. Engines with compression ratios higher than 10:1 stand to gain the most from the twin-plugging, increasing the overall power, while reducing power-robbing detonation. The 911 cylinder head does not lend itself to ideal, uniform ignition.

The two valves in the center of the head take up the majority of the room, forcing the spark plug to be located off to the side. The ideal place for the spark plug would be directly in the center of the cylinder head. When the spark is fired and the mixture is ignited, the flame front expands across the combustion chamber. Installing two plugs per cylinder increases the efficiency of combustion, and reduces the time it takes for complete combustion to occur. Having this ideal combustion also means that the ignition timing advance can be reduced, because the spark can be fired closer to the top dead center. Engines that typically would see a temperature increase due to the load of running a high compression, can sometimes see this increased temperature reduced due to the added benefits of reducing the ignition timing advance. Most twin-plug engines will achieve their peak horsepower output at about 23-24 degrees of total advance, compared with the typical 30-35 degrees required for single plugged engines.

With respect to the 911 engine, the high-domed pistons that are typically used to increase compression ratio have the unfortunate side effect of splitting the combustion chamber in half. On a typical single-plug head, the flame front will start from one side of the combustion chamber and travel across the center of the head to the opposite side. This delay in complete combustion means that the ignition timing on the engine must be advanced so that complete combustion can occur by the time the piston has reached TDC.

Installing two plugs per cylinder means that the combustion process is initiated on both sides of the cylinder head. This accelerates the entire ignition process and allows you to retard the ignition timing by 10 degrees or more at higher RPMs. The most efficient operation of any engine occurs when the combustion process exerts force on the piston right after the cylinder has past TDC. A pressure increase that occurs before the cylinder has reached TDC can push back on the cylinder as it’s compressing the mixture – decreasing the engine’s overall performance and possibly causing pinging and knocking in the engine. The accelerated ignition sequence from twin-plugging gives a net power increase because there is less energy wasted on pushing back on the cylinder while it’s approaching TDC. The gasses in the combustion chamber expand later in the ignition cycle, and allow all of the pressure that is built up to act upon the cylinder during it’s downward stroke.

On an engine with a compression ratio less than 10:1, twin-plugging really doesn’t have too much of an effect, primarily because these motors are not running at unusually high compression. However, on a race or high-compression street motor, the twin-plug system can increase horsepower primarily in the high RPM range by creating more efficient and quicker combustion in conjunction with the increase in compression. In basic terms, twin-plugging is used to gain the maximum effect of increasing the compression ratio. Without the implementation of the twin-plug system, a high-compression motor may encounter significant detonation at higher RPMs. Adding the twin-plug system decreases detonation, decreases your cylinder head temperatures, and also will decrease the octane requirements of the higher compression engines. The addition of the twin-plug system is typically required to allow the car to fully utilize another set of engine modifications that increase the compression ratio.

There are three common implementations of the twin-plug system. One such implementation uses a 12-plug RSR / 917 distributor. While RSR distributors have long been in the ‘unobtainium’ class of parts, they can indeed sometimes be located for the right price. With prices ranging from $2000-$4000 each, they certainly require a certain breed of buyer. If you happen to come across one of these distributors, make sure that it will be applicable for your application. The engine pictured in Figure XX has a 12-plug distributor installed on it, however, this distributor is originally from a 935, and contains no centrifugal advance mechanism. The 935 race car operated in a narrow RPM band, and was tuned to this range. As a result, it didn’t need the addition of the centrifugal advance. Such a distributor would be difficult to use on a street engine that needs a broad power band across its entire RPM range.

In addition to the potential $4000 price tag for the bare distributor, the cost of a distributor cap typically runs about $700 each. Not for the faint of heart, it’s important to keep this in mind when you choose your method of twin-plugging.
An alternative to the genuine RSR/917 distributor is to have a standard distributor modified to accept the 12-plug RSR cap and rotor. The distributor is modified by mounting an adapter ring to the top of the distributor and cutting the center shaft to accept the larger RSR rotor. Andial of Santa Ana, CA sells an excellent quality 12-plug distributor that is converted in this manner. The entire process is difficult, as the cap and ring must be aligned properly, and the distributor advance curve needs to be modified to match your individual engine’s requirements. With a setup like this, its usually wise to convert or install a breaker-less system like the Pertronix Ignitor. This is often the preferred method of twin-plugging for the 911 Turbos because it is possible to keep the centrifugal boost retard timing that is required for smooth engine operation.

[Wayne 962]

A second alternative to the expensive RSR solution is to install a 964 distributor on your engine. Starting with the 1989 Carrera 4, the 911 engine used a dual distributor configuration that is connected with a small toothed timing belt. This distributor will fit unmodified into a 2.4L or later engine case. The distributor assembly needs to be matched to the appropriate crank gear. The 911SC 3.0L and 1978-89 Turbo engines ran the distributor counter-clockwise. For these engines, you will need to have the crankshaft distributor drive gear changed to the later-style gear from the 3.2L engine. Machining costs for using the 964 distributor are modest, yet the cost of the 964 distributor setup itself can be several hundred dollars. The major problem with using the 964 distributor is that you need to implement a method for adjusting the timing advance on the distributor. The 964 engine uses the Motronic Engine Management system which controls timing advance and retard using the fuel injection computer. Therefore no adjustability exists within the 964 distributor housing.

You also need to devise a pickup method for triggering the ignition system. The best solution that I have seen involves the removal of the internals from a 2.7L distributor for placement in the primary 964 distributor. You can then attach a Pertronix breakerless ignition system and trigger the spark electronically. Running this setup with an MSD unit that has an adjustable advance/retard curve eliminates the need for a vacuum canister or a mechanical centrifugal advance mechanism. You can also have the distributor modified to accept a 3.0L pickup mechanism.
Unfortunately, it is difficult to make this particular 964 distributor configuration work with the 911 Turbos because the turbo plumbing has a tendency to get in the path of the two distributors.

Depending upon your engine’s configuration, the 964 solution may also require a slightly modified oil cam line to bypass the larger distributor assembly. In addition, if you are twin-plugging a 911SC engine, you will have to replace your original crank gear with one from a 2.7L engine or a 964 engine (the 911SC and Turbo distributor turns in the opposite direction than all other distributors).

The Motronic 3.2 engines can be specially adapted to use twin-plug ignition with the 964 distributor using a special splitter specifically designed for this purpose. This splitter is available from Andial, and the triggering for the ignition comes from the stock Motronic flywheel sensor. The 964 distributor merely distributes the spark to each cylinder, much as it does on the actual 964 engine. All that is required is a second ignition coil, and the lower spark plug wiring harness. This would be an expensive option to add to a stock Motronic 3.2 engine with minimal horsepower gains unless the compression ratio of the engine is increased.

Both of the above solutions can be used with complete, independent ignition firing systems. You can install a pair of OEM Bosch capacitive discharge units (CD Boxes), or run two aftermarket systems like the Permatune or the MSD 6AL units with Bosch blue coils.

The third solution is to install a crank-fire distributorless dual ignition system. Although complicated in nature, these aftermarket ignition systems can eliminate your distributor, and allow you to custom design your ignition advance to suit your specific application. Another advantage is that you don’t need to continually purchase a new cap, rotor or points. With the RSR solution, the distributor cap has the potential to cost more than the entire crank-fire system. The best known systems are the Electromotive HPV-1, TEC-II engine management systems, and the engine management systems from MoTec. The setup and installation of these systems is difficult and usually needs the help of an experienced installer. Clewett Engineering, located in Manhattan Beach, CA, is the foremost designer and installer of the Electromotive single and twin-plug ignition systems, and a good source for 911 engine-specific adapters and components.
Regardless of your choice of distributors, you will need to modify the heads for the second set of spark plugs. The best time to do this machine work, of course, is when the engine is out of the car and you are overhauling the top end, or rebuilding the entire engine. The addition of the second spark plug does not significantly weaken the heads, and the cost of the actual machining is not very much when compared to the cost of the additional ignition system.

In addition to the obvious machining to the heads (drill and tap holes for the spark plugs), you will also need to have clearance holes cut in the engine sheet metal so that the wires can pass through to the lower valve covers. The lower valve covers (Turbo valve covers recommended) need to be machined to have the clearance holes for the spark plugs. Like the upper valve covers, these holes are drilled in the dry areas of the lower cam tower so oil leaks are not a concern. It’s also common to install lower retaining brackets for the plug wires to reduce the chance that they will loosen with engine vibrations. In addition, the lower head stud mounting nuts have a tendency to interfere with the lower plug wires, connectors, and sometimes the plug socket used to install them. One solution to this problem is to use low-profile 10mm nuts with smaller outside diameters. Typical 10mm barrel nuts have an outside diameter of 18mm, and a height of 18mm as well. The low-profile aftermarket nuts from RaceWare or ARP have a 14mm outer diameter and a height of 11mm as well.

The conclusion on twin-plugging? Obviously, there is much more to the story than I can put into this section. The 964 distributor option is a bit less expensive than the RSR setup, and also reduces the requirement for expensive replacement distributor caps. The distributor-less solutions are a great solution if you are thinking of running an aftermarket ignition system, as the twin-plug crank-fire systems are only slightly more expensive than the single-plug systems. As stated previously, twin-plugging won’t necessarily buy you any performance increase on its own – to take full advantage, you need to combine it with an engine modification that increases the compression ratio.



Coming soon...

-Wayne

[JeffW]

The more I look at this, the more I push back to the 3.6L. If you were to upgrade to twin plug, buy all these extra go fast parts, you would probably be looking at close to the price of the 3.6L. To top it off there would be less hassle and tuning issues would be gone. I would be lost trying to build a 2.7l rs with twin plug ignition or what ever concoction I came up with. I think I'm going to break down and go with the best I can get currently which would be the 3.6l. Thanks for the help guys...

Jeff

[Jack Olsen]

From the standpoint of economy and reliability (especially if you're not building the engine yourself), the 3.6 is unbeatable.

I paid $5,000 for a 964 engine with 17,000 miles on it, and haven't had any mechanical issues with it at all, and I'm probably on about my 20th track day.

[JeffW]

You wouldn't happen to have a contact for getting such a motor would you?

[CamB]

Wayne

A twin plug distributor with an early style exhaust (either OEM, SSI, or I guess B&B) also needs a different air guide to clear the twin-plug distributor:

Hey Bill V (and anyone else who 964 distributor and SSI experience)

Alternative is a blanking plate (and no heat through left exchanger).

Do MSD make a standalone timing control? And then you need 2x CD boxes? I tried to figure out in my mind what would be required for advance control and gave up as it didn't matter (my engine is already getting MoTeC to control both ignition and fuel).

Here are a couple of pictures of the type of pistons Wayne is talking about - 98mm with 10.5:1 and deep valve pockets ---> I understand twin plug is pretty much mandatory.