Rebuilding 2.7 engine

[911s]

I'm going to rebuild a 2.7 engine. I want to use 40 IDA webers on it. What type of cams should I use with this, so as to get the most pleasure out of it. I use my car only on the street, so I want it to be as driver-friendly as possible, and still have good acceleration. Guess what I'm really after is bottom-end torque and good acceleration to 6k.

Also, I'd like to stay with the CIS pistons, so as to keep the cost of the rebuild down. Is this possible, and still be able to use a cam that is compatable with the carburetors and 2.7 block?

If I'm missing anything here, please shed some light on the subject for me. I'm a first-timer to rebuilding a Porsche engine, and can use all the tips that are available. I did recently purchase Wayne's book, and hope that it helps to guide me through the difficult parts.

Thanks for the help.

Bob (911s)

[Wayne 962]

Bob, the book will help explain a bunch of stuff, so I won't repeat it here. Basically, if you are buying new pistons, you might as well buy an 'RS' set and make it an RS-spec engine. In lieu of that, you can have your pistons machined (for pockets), and run an 'S' cam (the same cam that was used in the RS). With the 'S' cams, you probably won't get as much low-end as you would out of a 3.0L, but it will still be very fast. Alternatively, I would use the 964 cams and the CIS injection. If you're using the Webers, you should go with a hotter cam, but that will require compatible pistons - it's a tradeoff...

-Wayne

[Chas911]

I agree with Wayne if you keep CIS pistons the 964 cams should work well. However, if you do go with RS pistons you might consider the E cams. They tend to have more torque than the S cams in the RPM range where most daily street driving is done and they feel pretty strong. If you want to make real power though, go with the S cams.

[Wayne 962]

Right about 2.7 is where you still get a little peakiness. As I mention in the book, the 'S' cams feel much milder in the larger displacement cars...

-Wayne

[911s]

Thanks for the responses! This BB is invaluable, especially for people like me who have relatively little experience in putting together a performance Porsche engine.

I've heard that solex cams have a good, broad torque range, with plenty enough top end performance. How would this cam work in a 2.7? Again, I want to reiterate that I would like to not have to buy new pistons. Notching pistons would be a viable option for me, if it's not too costly to do. Seems that this would be necessary to do, regardless of which cam I go with. Does anyone know how much a shop would charge to notch pistons?

Wayne, what do you mean when you say 'peakiness'? Does it run out of 'pull' at a relatively low rpm? I'm thinking that the 'S' cams may kick in at a little higher rpm than I'm going to be operating in most of the time. Then again, I have no experience with them, so I'll rely on your knowledge in this area. I'd like something that has good pull from 3-6k. If it kicks in earlier, better yet. That's why I ask about the 'solex' cam. Do you think it would be suitable for my purpose? I have the Webers and a set of 1 5/8"Bursch headers that I plan on using on this engine, so I'm kind of leaning away from the 964 cams.

I do have the 2.7 engine that's currently in my car. It has CIS, and is stock, except for a pop-off and early heat exchangers. Perhaps once I get the engine I'm working on in the car, I can rebuild the other and use the 964 cams. Will those cams work with unmodified CIS pistons?

Thanks for the help guys!

Bob.

[Bobboloo]

A set of JE pistons is about $1,000. To spend the amount of money it will cost to rebuild your 2.7 only to short change yourself on pistons doesn't make sense to me. The machine work alone will cost alot $$$. You might as well get some pistons that will allow to run the cams you want and still get a decent CR. I can't see it costing less than $200 bucks to cut valve reliefs in some used low compression CIS pistons. Spend another $800. You won't regret it.

By peaky, Wayne means more peak HP as opposed to broader torque curve like on the E cams.

The Solex cam is somewhere between an E cam and an S cam. I believe it's a favorite for a 2.7 carburetted street motor according to Bruce Anderson.

[Wayne 962]

The best suggestion I have is to drive someone else's car that has the combination that you are thinking about. That is really the only way to learn how it feels...

-Wayne

[911s]

Wish I could drive someone's car, with a setup similar to what I hope to achieve. Problem is, I don't know anyone with one. The only guys I know all have stock cars, and have no intention of changing it.

Now, if by peaky it is meant that it has more peak hp, then wouldn't S cams be even 'peakier', by that definition? Afterall, S cams are supposed to have more peak horsepower than E cams to begin with. I can't see how the E cams are going to generate more 'peak hp', and the S cams are going to actually get mellower (torque band move nearer to street driving range). Would seem more logical to me that, if a cam that is revvy in a smaller engine becomes less so in a larger engine, then a cam that kicks in at a lower rpm range would have a power band that kicked in very early, and then ran itself out at the higher rpms. But that's just the way that I would see it, and since I have NO experience in this area, I do welcome the input of others. Does anyone else have an opinion, that either supports or disputes this claim? Better yet, is anyone currently running a carbureted 2.7, with either S, E, or Solex cams, that can give me feedback on how their cars' run, and what rpm range their engines operate well in?

I'd love to buy a set of pistons for this motor. If I come across an extra $800 between now and the time I'm ready to to the rebuild, then I'll buy them (but honestly, I know I won't. I'm just trying to have a little fun here. Sure more compression would make the intake charge more 'ignitable', but for the price, I'm willing to forgo it. My situation is such that, I got the parts dirt cheap from a guy that was getting out of the 'scene', and I just want to get this motor together, using the basics that would be required to get it running right. If pistons are only another $800, then ported heads is only another $500, new valves is only xxx, carrera tensioners is only yyy, a lightened flywheel and aluminum PP is only zzz. It's endless. I want to draw the line at a rebuilt engine with cams adequate for me to run the webers on. Fact of the matter is I'm happily married, have 2 children, have plans to send both of them to college - as my wife and I have, and plan on having a fruitful retirement at an age where I can still enjoy it. I'v seen too many guys throw all that away because they become 'obsessed' with their cars. Like I said, I'm just trying to have a little fun in my middle age without having to sacrifice ANYTHING in order to do it. Besides, I bought the car for only $5500, so it wouldn't make any sense to spend double that in order to put a engine into it, especially when it already has one that runs just fine.)

Sorry, started rambling there. Anyway, am interested in any feedback, either from people who have this type of set up, or who knows of someone with it, that can shed some light as to how the engine performs for weekend street driving. As always, Wayne, your feedback is always valued. I've had other cars with syncronized webers before, so I expect that I'll be losing some drivability over the current CIS set up. That's fine with me, because that's what I want. I don't want a sports car that drives like my daily driver. I just don't want one that can't do the 'stop-n-go traffic' thing without gurgling the carburetors everytime I try to throttle it out of the hole, either.

[911pcars]

Bob (911s) and Wayne,
I wasn't aware one could remove any measureable amount from the top of a CIS piston for added valve clearance due to an early cam. How much material can be safely removed?

I'd double check with an experienced Porsche-based machine shop as well (German Precision, Competition Engineering, Biekers, EBS, etc.).

A long duration cam (S-type or beyond) will act less "peaky" as the displacement increases. The added torque from increased bore and/or stroke (compression ratio as well) compensates for any camshaft-induced torque reduction at low/mid engine speeds.

MHO,
Sherwood Lee
http://members.rennlist.org/911pcars

[911s]

Sherwood,
I like the explaination on the S cams. Can you explain why the E cams become more 'peaky'? Also, good idea on the pistons. I know with other types of engines, one checks piston to valve clearance by placing clay on the piston top, then assembling the engine and rotating the crankshaft to allow the valve to compress into the clay, then pulling off the head and measuring the amount of relief there is between the valve and the piston. Is there another way to check this clearance? How does one go about determining how much relief the piston needs in order to clear the valves?

I would like to speak directly with someone who has used either an s, E, or Solex cam in a 2.7. Is it possible to get away with using the CIS pistons? Is the engine suitable for use in a street-driven vehicle? Any other insights into problems encountered, and how to correct them, would be appreciated.

Thanks

Bob.

[911pcars]

Bob,
Compared with E cams, S cams are more "peaky". A "peaky" cam is usually described as one having longer duration, increased overlap cam timing (both valves open at TDC exhaust/intake) . This results in the intake and exhaust gases mixing at idle/low speed and an engine that has a characteristic loping idle, relatively little torque at low-to-mid engine speeds and poor fuel mileage. However, at higher engine speeds, the longer-opening valves increase the volumetric efficiency allowing more air/fuel to fill the cylinder and more time for exhaust to leave the cylinder.

A mild-to-more-peaky cam progression would be T, E, S, to 906 cam timing. See the cam timing chart put together by John (jleutjen) in the "3.0 CIS cam" thread in this forum.

Sherwood

[J P Stein]

I have Solex cams in my 2.7L, Webers, and 9.7:1 Shasta pistons.
The motor makes excellent power. I haven't had it dynoed and am content to say that it has in excess of 200 hp. The cams come
on with a bang around 4K and pulls hard to redilne.....7100 or 7300 (depending on the chip)if I need that extra 30 feet at AX, the 7300 goes in.

It took me some time to get it tuned.....I'm a bit of a slow leak, I guess. The problems I had were ignition related....trying to get it to run properly on the idle circuit (below 3500 rpms). Since most of ones street driving is on the idle circuit this was something I need to get right (or good enuff).

The final set-up was:
RS spec dizzy with Pertronix
MSD 6AL & hi-vibration coil
Magnecore wires
NGK BP7es plugs gapped to .045

To run E, S, or Solex cams, you really need to swap out the P/Cs.

Here's a pic of the motor....note that it's facing the right direction
The key is to come up with a set of Nikasil cylinders. RS spec
P/C s are available (new) for around 1500 bucks if you shop carefully. The C/R is 8.5:1....which didn't thrill me.

Then one needs to learn to tune Webers....no small chore...for me, at least.

Feel free to PM me for any Qs. Here's a pic. You'll note that the motor is facing the right direction. ......

[Wayne 962]

Sherwood, on page 174 of the Engine Rebuild book, is my info on cutting pistons.

Basically, you can shave at least 1mm from every piston. In general, you don't want the piston to be thinner than 5mm in any location. This goes for CIS/Motronic or regular pistons...

-Wayne

[sammyg2]

J P, isn't that engine backwards?

[911s]

Wayne,
You said that the E cam gets peaky as the displacement increases (consistent with what you've said in the book). Now, the S cam, which operates in higher rpms in smaller engines, has a tendency to soften up in larger engines (supposedly because the larger engine produces more low end torque because of it's displacement - as Sherwood has said). So, can you explain to me what happens when the E cam is placed in a larger engine (basically, describe what 'peakiness' is, in laymans terms)? I'm not trying to get technical here, I just want to understand exactly how the cam is supposed to react in a larger engine.

Now, it appears that I'm going to have to get a set of pistons if I'm going to make this whole thing work. I didn't want to go this route, but if it's necessary, then it's necessary. First, I will need to determine what type of cylinders I have, right? The book says that if it says 'Mahle' on it, there's a 50/50 chance that it's Nikasil. Is there some other means that will assure me that I have this type of cylinders (the last thing I need is to buy a set of pistons, that I have been trying to avoid buying, only to end up with a set that is incompatable with the cylinders I have - and which would probably be non-returnable because they are custom)? I'm assuming that I will have to tell the manufacturer of the pistons what type of cylinders I have - afterall, if the cylinders are hard then the pistons have to be soft, and vise-versa. Any info (part no.s, markings, particular colors that identify the type of cylinder it is?

As always, everyone's input is appreciated. Anymore insights from people running carbureted 2.7s with any type of cam/piston combination is also desirable (I spoke with a couple guys previously that were running 2.7/weber combos. I was trying to get weber venturi and jet sizes for a 2.7 w/webers on a previous thread. One of the guys' was from Australia. Sure would like to hear from them).

Thanks,

Bob

[J P Stein]

The inner walls of Nikasil cylinders will atttract a magnet....a slight amount, but enough to feel.

[jgparker]

The last time I ran at Sebring (a cheep brag) I used my 2.7 with CIS pistons and cams and webers. It had good pull across the entire RPM range, but did not peak-up like my E-cam S-piston 2.2. It was nice not to have to shift so much, but I love the feel of a peaky cam. I have heard you really should ditch your CIS pistons if you want to go to an aggressive cam.

Peaky means poor torque at low RMPs with an abrupt surge of power over 3500 or 4000 RPM. A peaky motor is great fun on the track, but can be very annoying in stop-and-go traffic.

The engine I'm building now is a 2.9 9.8:1 with S cams and webers. It should be fun. I plan to drive it on the street too.

If you have 2.7 Mahle cylinders, I think it should be closer to an 80% chance of being Nikosil. KS made most of the Alusil ones.

[911s]

JP,
Does the webers on a CIS engine improve the performance of the engine over the stock injection? May be something to consider, but only if it yields 15% or better in hp, with comprable improvement in low end torque.

Now, the problem with CIS pistons, when used with any of the typical performance grinds (E, S, Solex, GE 40) is with possible piston to valve clearances, right? Perhaps I should look into a custom grind that keeps near original-CIS lift specs, while adjusting duration and lobe separation specs. I doubt anyone has worked with such a combination, but perhaps I should consult with a cam grinding facility to see if this is a viable option.

Anyway, I haven't ruled out purchasing new pistons, nor have I ruled out the possibility of relieving the CIS pistons. It just means I need to do a little more homework before making a decision.

All in all, this BB has been invaluable. It explained to me what possibilities are available, what problems I may encounter, some tried and true combinations, and resources available for me to research. Thanks to everyone who help shed some light on the subject, and if anyone has input to share, it is greatly appreciated.

Thanks, guys!

Bob.

PS: I've been hearing about this GE 40 grind. How is it, and would it be good for a 2.7 street engine (with appropriate pistons, of course)?

[jgparker]

I'm not a big fan of the CIS system. Webers are an improvement, but I don't know by how much. To really make a 2.7 engine come alive, you need to go with a more aggressive cam, but you can't use a very aggressive cam with the CIS induction system, or with CIS pistons.

[jluetjen]

Bob (911S)

You might want to check out this thread where I discuss the affects of different cams on different sized engines. The conclusions that you have drawn about "radical" cams in "big engines" I believe is accurate based on the data. The "Big engines mellow radical cams" myth has a degree of truth and a lot of urban legend to it. I've come to the conclusion that a more accurate conclusions is that an inefficient (ie off-cam and making maybe 60% of its peak torque) large engine is a lot easier to put up with an an inefficient (off-cam / 60% of peak torque) small engine.

Some of the other factors that come into play is the porting and valves sizes, and the cam timing. Nobody talks about 911 valve sizes much since they are generally more then adequate. So in a 911 motor, that leaves porting and cam timing. 2.7RS motors, the classic case that people point to when discussing the "mellowing" affect of larger motors actually have something else going on. The ports were never changed from the 2.4S when the capacity was increased. While the 2.4S intake ports were adequate for 2.2 and 2.4 S's, they were actually a little undersized (relatively speaking for 911's) in the 2.7RS. As a result the torque peak was shifted downwards a little and tailed off more at maximum rev's compared to the 2.4S.

So basically as you are spec'ing out your engine, you will need to consider all of these factors as well as a few others. But then you had already come to that conclusion.