2.2E Mild Upgrade. Short stroke or long? Opinions Please!

[wagonboy]

Hi Scott, Great advice and thanks.

Starting with your question about CR, I understand the free HP argument to go with an S comp. set up but I guess I just figured that with a higher CR I would be moving the powerband up the rpm range and getting away from the one trait that the E engines trump the S. Okay, there are more variables including valve size and cam lift/duration. Maybe comp. has less to do with the difference between power and rpm than I first thought? Stupid now that I think about wanting an S cam, valve train as these changes probably have more effect on moving the power up the rpm range than does a simple lift to CR.

Increasing displacement only via increasing bore has the effect of decreasing compression (all else being equal) which can be brought back up by changing piston height/dome (?wording) but I wondered just how much could be regained by installing larger domed pistons without worrying about the piston coming into contact with the valves. I thought I should still be safe if I kept CR as close to the original E set up of 9.1 and maybe I shouldn’t push it higher. But then again as the head of an E is the same as the S in terms of cc size and the S has a higher lift cam with valves that are slightly larger, I need not worry about this. [Wondering out loud] If increased CR is simply just free HP, why don’t more guys who rebuild their 2.4S and 2.7RS spec engines increase their comp from 8.5 to 9.8 – the threshold deemed okay for 91 pump gas and a single spark plug? If a stock RS engine gets 210hp with 8.5:1 comp wouldn’t a bump to 9.8:1 give them much more? I imagine some people do go this route but I’ve rarely read about it. If you want 240-250HP it seems most just go with something north of 3 litres to get the desired result.

At first my motivation with this upgrade was to find about 20-25hp over a stock 2.2E. Going the SS method I get to maintain the engine’s willingness to spin up more quickly than later long strokers. I like the idea of something between an E and an S engine. I’ve heard about solex cams which have lift/durations between E & S. This sounded promising but I have read that these are only available with a carb setup.

After thinking it over, maybe maintaining the stock E cam and valve train, boring it out to 89-90mm and bumping the CR to something closer to an S 9.8:1 is the way to go… would a set up like this work? What would be wrong with this?

Lastly, the case… I’ll look into a 7R. Am I just asking for trouble going for more power while keeping a stock 1 or 3R?

I know I’ve raised a whole bunch more questions. Feel free to ignore my ramblings as this could go on forever. Thanks again Scott for your insights and input.

[wagonboy]

Hi Scott, Great advice and thanks.

Starting with your question about CR, I understand the free HP argument to go with an S CR set up but I guess I just figured that with a higher CR I would be moving the powerband up the rpm range and getting away from the one trait where the E engines trump the S. Okay, there are more variables including valve size and cam lift/duration. Maybe comp. has less to do with the difference between power and rpm than I first thought? It’s stupid for me to have thought going with S cams and valve train wouldn’t affect the power/rpm balance as much as bumping the CR.

Oh and to answer your question about “Cam to suit S spec engine”, I was thinking of going whole hog with an S setup. The way I figured, the price of this route still results in spending less than 15% of the total restoration on engine work. Perhaps though, the money would be better spent on other ways to develop more performance and to do it reliably.

Increasing displacement only via increasing bore has the effect of decreasing CR (all else being equal) which can be brought back up by changing piston height/dome (?wording) but I wondered just how much could be regained by installing larger domed pistons without worrying about the piston coming into contact with the valves. I thought I should still be safe if I kept CR as close to the original E set up of 9.1 and maybe I shouldn’t push it higher. I knew that the E and S head cc size was the same so I should have clued in that what ever worked for an S would still work for an E set up so I need not worry about raising the CR.

If increased CR is simply just free HP, why don’t more guys who rebuild their 2.4S and 2.7RS spec engines increase their comp from 8.5 to 9.8 – the threshold deemed okay for 91 pump gas and a single spark plug? If a stock RS engine gives out 210hp with 8.5:1 CR wouldn’t a bump to 9.8:1 give them much more? I imagine some people do go this route but I don’t recall reading about it. If you want 240-250HP it seems most just go with something north of 3 litres to get the desired result.

At first my first motivation with this upgrade was to find about 20-25hp over a stock 2.2E. Going the SS method I get to maintain the engine’s willingness to spin up more quickly than later long strokers. I like the idea of something between an E and an S engine. I’ve heard about solex cams which have lift/durations between E & S. This sounded promising but I have read that these are only available with a carb setup.

After thinking it over, maybe maintaining the stock E cam and valve train, adding 89mm pistons/cylinders and bumping the CR to something closer to an S 9.8:1 is the way to go… would a set up like this work? What would be wrong with this?

Lastly, the case… I’ll look into a 7R. Am I just asking for trouble going for more power while keeping the stock 3R?

I know I’ve raised a whole bunch more questions. Feel free to ignore my ramblings as this could go on forever. Thanks again Scott for your input.

[edmayo]

Actually it's the other way around, all other specs being equal, increasing the bore increases the C/R. You are shoving a greater volume (increased swept volume) into the same size combustion chamber thus increasing the C/R. As to why more builders don't increase the C/R more when building 2.4 or 2.7 spec engines (or any engine) is that the piston dome has the greatest influence on the C/R. Trying to get a 9.5 (or so) C/R from a 8.5 C/R ratio piston is not easy on our engines. It's not just a simple matter of cutting the head to get it closer to the piston dome as say on a Chevy V-8. When you move the head closer you also affect chain length, then you need spacers to move the cam housings back out, and/or different size idler chain wheels. In addition, I would NEVER do any mixing and matching of engine piston/cam pieces without checking for piston/head and piston/ valve interference. There's nothing wrong with what you're wanting to do, you just need to make sure it all fits!

[wagonboy]

Thanks Ed. Okay think I see what you are talking about w.r.t. increasing bore size leading to a higher CR. While the volume of the head stays the same and the volume of displacement increases how this would obviously lead to more CR.

Concerning the comment about why don’t builders of 2.4/2.7 engines just up their CR from 8.5 to something more actually I was thinking not about shaving the head but about changing out the pistons with a higher dome thus leading to a reduction in combustion chamber that way. I figured that builders who go the twin plug route and up their CR above 10 must have replaced pistons, never thinking about machining the head to reduce the size of the combustion chamber was wrong.

The adage: “Just enough knowledge to be dangerous” certainly applies with me. I apologize if some of my comments or “conclusions” seem stupid. I’m learning. Thanks for all the comments as they’ve been a great help. I have some good and knowledgeable people working on the engine (I wouldn’t dare try tackling this myself). What I hoped to gain from this exercise is to better understand what the various options are, what works, what doesn’t and most importantly the why and how. This allows me to ask the right questions with the people working on my car so that at the end of the project, I’m happy knowing what I have and in the future I can work on this car and maintain it myself with the knowledge that I know exactly what I have.

I envy the guys on this board who have the ability to be able to work on and rebuild these cars yourselves. I’d like to get there some day. I like to think that I have a fairly good understanding of cause and effect when dealing with mechanics but it’s the little details that would kill me if I took on a project such as this alone.

Thanks all.

[Scott Clarke]

Marc-

Increasing the CR actually increases torque, so you loose nothing except the ability to use bad gas. Just about anyone rebuilding a motor with JE pistons will bump up the CR. JE has pistons off the shelf that will result in a 9.7:1 ratio with your SS configuration. On the other hand, Mahle pistons are hard to come by and expensive, and limited in CR choices. For years there was the exception of the 8.5:1 RS pistons, which were plentiful and well priced, and of course, of unsurpassed quality. I think this explains a lot of rebuilt motors with this CR. No good for SS, though, as you'd end up around 7.5:1. Also, I'd be thinking about 90mm and not 89. 90mm is the standard 2.7 bore, so used cylinders, which can be resurfaced, are plentiful. 89mm cylinders were generated to comply with racing regulations that limited displacement to 2.5.

You should probably go through the rather depressing job of tallying up all of the stuff you need to rebuild a motor. All of the little stuff kills you, like rod bolts, flywheel bolts, gaskets, rocker shafts, the list goes on and on. Wayne Dempsey's book about 911 engines is a great tool for this, as it enumerates all of this stuff and has good photos of what everything looks like. If you built a S spec 2.5SS and it was 15% of your restoration cost, you'd have a very, very expensive restoration. If you get a really good handle on the complete cost of everything you will be in a better position to evaluate some of these choices, and do what we call, in my profession, "value engineering."

[YTNUKLR]

I don't think you really have enough tire to warrant a big motor, 2.8L+, or the transmission for that matter. So don't even go there unless you want to fall down the slippery slope of death...

You do have some options and you've mentioned them.

A 2.7 hotrod can have pretty fantastic performance ( S cams or more ) with high CR (9.8:1). At the limits of your gearbox and not completely "in character" although definitely not a "truck motor".

A 2.5 Solex is a sweetheart. If I was in your shoes, I would do this. 90mm cylinders, 66mm crankshaft, 2.52L. Fun, fun, fun, and well-matched to your car. I would use a spare engine case from a 2.7L for this job. Webers/PMOs are going to be the most reasonable. Twin Plug is preferable.

A 2.2 E is great. I would do this if you are going to *use* your original engine case. If you are just going to set your original case on a shelf, see above: 2.5 Solex.

I love the 2.2E, my favorite for a 2.7 is an S (=RS). A 2.5 Solex is kind of right in-between, most of the way to the 2.7 in terms of displacement/HP, the torque/feel of an E, and the revability and fun factor of the 2.2.

If you are cost-conscious, as we (mostly) all are, I would do the 2.5L like this, without expensive additions like MFI and Twin Plugs; these items add SIGNIFICANTLY to cost, like $3k each all said and done, so $6k more for a Twin-Plug MFI motor vs. a Single-Plug Carbureted motor:

-2.7L Engine case, machined/prepped
-66mm Crankshaft (a *balanced and prepped* 911T crank would be OK to 7600, and you probably won't go there often)
-Good oil pump; 911SC 3.0L is the sweet spot (fits, made of Alu instead of Mag, works well, doesn't cost a ton)
-90mm Nikasil cylinders; Used Mahle cheapest, New Mahle RS kit next, then LNE "Nickies" for big bucks ($3k / set of cylinders)
-JE pistons at 9.6:1 (don't use 2.7RS pistons...the motor will be a dog with ~7.5:1) . 10.3:1 with Twin Plugs.
-2.7 911S Heads, Stock
-Solex Cams
-Weber/PMO 40mm Carbs

Spend any money you *would have* spent on a more expensive combination on 1) Suspension, 2) Short Gears and 3) LSD...i.e, if you build it with Carbs and Single-Plug, spend your $6k here!

And just to clarify...Adding bore does not increase CR, because you are adding volume/displacement throughout the entire stroke. Compression *ratio* is the *ratio* of volume @ BDC vs. volume @ TDC.

Also...compression ratio has nothing to do with 'character' - you're confusing it with cams.

Everything is interrelated and it needs to be built as a system.

A "big" cam needs big ports and high compression; a "little" cam does not. You choose your cam based on the character and your planned use of the car, then you build out the ports and compression to suit. You are pushing the envelope for single plug, for example, by running E cams and S pistons - the 911S compression ratio for that E cam is a bit high. There is a reason Porsche ran 9.1:1 instead of 9.8:1, and it wasn't all about marketing and trying to make a less-powerful 911E...

You want all the compression you can get, of course, for the fuel & conditions you have (weather, altitude, etc.), but you always want to be able to advance the timing quite radically and not have detonation become an issue. Timing trumps your static CR ; rather build a motor with a little less CR and more timing, than its counterpart that is hamstrung in the timing department because you have too high of a CR...

[wagonboy]

Hi Scott K.
Still a little confused about the CR but I’m more of a visual thinker. If the volume of the cylinder increases but the head volume does not change I would have to think that the CR would go up. After all, any engine I’ve ever seen opened up, the piston at TDC rests just above or flush with the top of the block/case/sleeve and as such, the head volume would still be relatively the same regardless of the bore size. Am I missing a variable besides bore/stroke and head cc size needed to calculate CR? I’ll have to stand over an open engine on the stand again to really see what’s happening
in this area.

As appealing as a Solex cam sounds, I’m sticking with the MFI setup. As the MFI came with the 2.2 in the car, I’m not out of pocket for an upgrade. So it’s just a matter of calibrating it for the combo I finally decide on.

At the moment I’m leaning toward S Cams & Ports/valves with 90mm pistons/cylinders. Keeping any element of an E engine (be it the cam or cam & port/valves) for me might be compromise for the sake of compromise since I’m 90% committed to spend the $’s upgrading to S vales/ports which I know now won’t work with an E cam and if the cost is in machining the valves/ports then upgrading cams from E to S is a comparable drop in the bucket so what’s the sense of keeping the E cams after spending big $’s on the valves/head? I’ll keep the 66mm crank. I still have to decide on the case. I like Scott Clarke’s reasoning on this subject and I’ll really have to think about piston squirters. This sounds like a good investment in the
reliability department. That and the 7R case itself.

I always love it when people post pictures of their car. Although mine is still a ways from being finished I thought I'd post a picture anyways - the first on this board... This is the 1970E that the engine will eventually go into. I haven't named her yet... I think it's probably imprudent to christen it before it's road worthy...

[Reza]

is that ossi? looks fast already.

[YTNUKLR]

Marc-
Sounds good. Beautiful car! Ossi Blue? Early Gulf Blue?

Well. You are right the CR goes up with bigger bore or bigger stroke and the same head Volume, oops. However, you do want to bevel your heads for the increased bore, which technically adds a bit so you will actually have a bigger head volume . That and I can't imagine you will have exactly the same dome volume on the piston when you're done.

You don't have to spend big $'s on the heads . . .2.7 S heads are great for this. They already have 35/35mm ports which is very close to S spec.

Anyway, think about cams first, where you want the power to come on and how you will use the car. Then set the ports and CR based on that...

[Scott Clarke]

Marc-

Great looking car! S ports work really well with E cams. Also, E and S valves are the same. Remember that you'll
need to change the space cam in the injection pump if you go to an S cam. Also, you will likely need an external oil cooler, especially if you go with S spec.