2.1L longstroke revisited

[tadd]

Ok, so after thinking about this build option some more, I think this is the way I want to go.

SO... since I will be using 'light weight' 80mm JE pistons I was thinking of doing a poor mans Ti rod by using the 2.0 rods on the 70.4mm crank as they are ~550g (for the light group) vs ~660g for the 2.4 rods. Now I realize that there is a 2.2 mm difference in center-to-center distance... can I make that up by turning the cylinder base spiggots 2.2mm? I have no idea if this will 'slack the chains' too much.

I also read in waynes book about offset boring of the piston pin bushing. How much could I save there?

Thoughts?

Tadd

[davidppp]

Hello, Tadd.

Sorry, but the 2.0L journal is too big to fit the 71mm crankpin.

JE's in the 80 mm size are not at all light, BTW..they are substantially heavier than the stock, 1960's mahle pistons...

A poor reflection on JE IMHO.

kind regards
David

[tadd]

David:
Whoops! Holy moley how in the hell did I miss that tidbit. Thanks for correcting me. Guess I was blinded by the idea...

tadd

[kenikh]

Supposedly Jeff Gamroth built a 2.1 long stroke and it is freaking torque monster on the track. Not sure of the spec, as I merely overheard a conversation regarding this motor. Does anyone know any more on this motor?

[Steve@Rennsport]

We built a whole run (8-9) of 2.1's for Brumos' vintage racing program several years ago and they really do well.

Depending on who they were built for, these engines varied a bit in camshaft and compression ratio but that combination really pulls hard out of corners,...

[tadd]

I was wanting to use the C6 (906) cam but the RSR cam is interesting too. Would you be willing to share which you liked best? The heads are 73.5T - DIY twin plugged (take the advice and use the wax!) and have been opened up to 38/38.

I wanted to keep the free reving nature of the 66 crank, and found out today that Ollies does the 906 crank drilling mods (I was going to try it, but couldn't figure out how to fit on the mill ). The missing mass should also help with longevity, me thinks.

I've got a really nice 2.2S MFI pump. I assume I should be able to get it close. (or maybe I need a 2.0S pump instead? MFI is supposed to run rich?)

I figure with the extra .6 point CR bump I can use a shallower piston dome and still be get 906 sized CR for better detoniation control.

The last piece of the puzzle are rods. The 2.4 rods just seem like mass overkill and I just need to decide if I want to throw money to the wind and go with titanium loosing another ~100g of mass off each big end. It would be complete overkill, but what the hell... other wise it would just be an RSR gas tank. Now those are hard to find.

tadd

[Steve@Rennsport]

Hi Tadd:

Everyone has their favorite cam choices so all I can offer is mine.

The Factory race profiles: 906 & RSR are pretty old technology now and there are better choices for both power & MUCH improved drivability. Small displacement engines become pretty cantankerous when one makes the wrong selection,........

For this series of 2.1's, we mostly used either GE-60, GE-80, depending on the customer's driving skills and the car's gearing. A few of them received a custom profile of ours but that demanded a lot of the driver and a real well-spaced gearbox to keep it on the boil.

All of these particular engines were carbureted to comply with the HSR rules for 914/6 cars. Some had 40's and some received 46's, depending on camshaft selection and headwork.

All of these engines received Carrillo rods, too. No stock rods used here for 8500 RPM usage. Titanium rods are life limited so we do not use them unless one has the budget for regular replacement.

Hope this helps,

[kenikh]

I assume you built these on aluminum cases with revs that high?

[tadd]

Steve:
Thanks for the info. It is much appreciated when I get advise from one of the 'big guys'.

I had been looking at the older porsche cams for that 'old skool' feel. This will be a street motor going into a 67 SWB. My mind isn't made up yet, but I may stick with the stock chrome steels with a 185/65 for that 'extra fun quotient'. I will take a second look at the GE-60 though.

Why do you say that Ti rods have a lifetime? The materials chemist in me is curious? So long as the forces don't exceed the plastic region of the material then the lifetime should be infinte - unless you are saying that Ti work hardens with repeated stress cycles. (like why copper is not used for hydraulic lines). I have heard about the small end going out of round, but that sounds like a design problem (much like the early 1980s aluminum motorcycle frames that were built like they were steel and broke - then someone got smart and designed to Als strengths, hence the large beams nowdays).

tadd

[Steve@Rennsport]

Tadd:

Glad that helped,...

The GE-60's are still drivable (kinda like a super S cam) for street use, but you'll need close-ratio gears to take advantage of what they do. Exhaust configuration is VERY critical on these engines and the wrong one kills the low & mid-range torque.

I've used Ti rods since my 935 days and lost a few engines with these things from extended use. Porsche considers them a replacement item in the GT-3R engines due to extreme RPM's over time and given the consequences of a failure, I'll not take any chances with a customer engine. I'm not a metallurgist by any stretch, however I have some experience with these things so all I can do is report my observations over the past 25+ years.

IMHO, something happens to the metal whether its accumulated stresses or heat and I'd have a hard time using them on an indefinite basis. Don't forget, 911 motors have a finite amount of space inside the case for the big end of the rods; perhaps they work better in something with more room for a larger part,..


Kenikh:

Most were built on modified early sand-cast cases, but a few were done with 914/6 1R-2R ones. Needless to say, all of these were shuffle-pinned, line bored and machined back to standard. Other mods were done for improved oiling.

[davidppp]

Ti rods are prone to creep.

ie they literally stretch in use, and the big ends go out of round.

This may be why Steve lost some engines..the rod failure may have been initiated by losing oil clearance.

Kind regards
David

[tadd]

Steve:
The fact that you have been doing this for 25 years is why I am pleased to hear you chime in. Observation is the best, ok, only science. I have a bunch of theorists I have to keep in line at work .

The reason I was curious about rod design is that the Acura people don't seem to have any problems (at least as far as I have read) and they have a bit of time on their cars at this point. Maybe it was the alloy chosen or maybe just the fact that the Porsche rods just had a much harder life. I know I wouldn't want to come back as a 935 rod (enron excs perhaps? :eek.

Dave:
Guess I will need to do some more reading... do you know if that is material creep or fatigue creep?

tadd

[kenikh]

Originally posted by Steve@Rennsport
Tadd:

Glad that helped,...

The GE-60's are still drivable (kinda like a super S cam) for street use, but you'll need close-ratio gears to take advantage of what they do. Exhaust configuration is VERY critical on these engines and the wrong one kills the low & mid-range torque.

Thanks Steve! For a GE60 on a small motor, what exhaust would be best?

Headers into megaphones being a "10" and a stock 2 liter exhaust being a "1" in terms of back pressure? I am merely wondering what criteria make a good exhaust for a street driven, twin plug small bore on a GE60.

[tadd]

MFI!

tadd

[kenikh]

Reversion resistant induction was assumed (by me). I should have been specific.

[Steve@Rennsport]

Originally posted by kenikh
Thanks Steve! For a GE60 on a small motor, what exhaust would be best?

Headers into megaphones being a "10" and a stock 2 liter exhaust being a "1" in terms of back pressure? I am merely wondering what criteria make a good exhaust for a street driven, twin plug small bore on a GE60.

Kenikh:

Tadd brought up a good point; camshaft choices in MFI motors must be matched to the space cam in the pump so you'll need to talk with Gus AT PFI to see if he can match the pump to your camshaft of choice.

We use a custom-made header for these small displacement, high RPM engines combined with a Flowmaster Series 80 muffler. These incorporate a crossover in the single muffler (its a dual-in/dual-out) that is SO critical to these engines.

Megaphones are only good for engines that live at 7K & up. They really kill the low & mid-range drivability which is very important with these things. The operative word here is "street-driven" and that truly frames what you do,....

FWIW,....exhaust systems have a huge influence on intake reversion issues when using any of these long duration, narrow lobe center cams. BTDT,...sooo many times,.......

[kenikh]

Ugh; I was hoping to build the best motor I can without changing space cams (Gus has gotten EXPENSIVE), thus I was looking at cams for 2.0 motors. Looks like I have a lot of thinking to do. Anyhow, enough of my semi-sidetracking; back to 2.1 long strokes...

[jluetjen]

Originally posted by tadd

I wanted to keep the free reving nature of the 66 crank, and found out today that Ollies does the 906 crank drilling mods (I was going to try it, but couldn't figure out how to fit on the mill ). The missing mass should also help with longevity, me thinks.

...

The last piece of the puzzle are rods. The 2.4 rods just seem like mass overkill and I just need to decide if I want to throw money to the wind and go with titanium loosing another ~100g of mass off each big end. It would be complete overkill, but what the hell... other wise it would just be an RSR gas tank. Now those are hard to find

Tadd;
I'm trying to follow your logic trail and to be honest I'm having a hard time.

1) Are you planning on using a 66 mm crank or a 70.4 mm crank??? It's not clear to me that in and of themselves that the engines with 66's rev any freer then engines with 70.4's. The 70.4's will have some vibration issues at engine speeds above 7500 RPM unless you take some steps to address them. I believe the issue would manifest itself in flywheel bolts vibrating loose or breaking. The engines built with 66 mm cranks by virtue of their shorter stroke will survive higher rev's better then longer stroke cranks. But this may be academic if you're not routinely working the engine at engine speeds above 7500 RPM.

2) Are you trying to "built a motor with the parts that you have" -- paraphrasing Don Rumsfeld -- or built to some sort of a spec? I thought that you were trying to build a motor with the parts that you have -- but then you start talking about Ti Rods. If you're going to blow the money on Ti rods, why not invest the money instead in a standard 66 mm 2.2 or 2.3 using 2.0 rods and 84 or 85 mm P&C's and something like GE40/60/80 cams depend on where you want your rev range. You'll most likely wind up with more performance per $ spent then any 2.1. Alternatively, if you're really married to the idea of a 70.4 mm crank, build a 2.4 or 2.5 liter version of those motors with the longer stroke. The extra capacity will most likely more then make up for the increase in rotational mass.

As I mentioned in your earlier post, the 2.1 idea really sounds like a solution to a problem that most people don't have. (Note, now if you're racing with a vintage race group that requires "original" motors, and you don't want to cut a 2.0 case to fit 84 or 85 mm P&C's, I could picture a 2.1 to be an ideal solution -- assuming the rules allow oversize motors.)

[tadd]

John:
There is no spec, ryme or reason to my maddness.

You are correct, I was looking at the 2.1 since the parts were close at hand and I think it has some interesting technial merits. Kenikh tries to keep me honest via off board email, and brought up vibration problems. So I start processing this and what might be done. Somewhere in the last week, I was reading about 906 motors and looking at pictures of crankshafts... then the wheels started turning (a truly dangerous thing) and my moron post about using 2.0 rods on a 70.4mm crank to save 60g per throw and the post about drilling the crank for another 70g. Those are pretty significant numbers according to my mal-informed opinion. So then I play a few F=MA numbers games with 935 Ti rod weights and I began to wonder if it was worth splurging on those (since the factory moded the flywheel and crank with holes). Then he gets back from Sonoma (after his absence puts me into a porsche coma ) and tells me good things about the 2.1 as a motor... fuel for the fire.

I don't have anything aganist 2.4s, 2.5s or even 2.7s. Boring out the case would be easy peasy compared to getting through the head fins.

I guess the 'build philophosy' I am chasing is motorcycle on 4 wheels (since the missus doesn't like me on the RZ anymore) and that entails keeping the motor small and snappy.

I could just drop back to plan A and use the 66T crank and rods I also have, but its not quite as interesting as the 2.1 according to my inner engineer.

I know none of this makes any sense... but I really do appreciate the advise given.

tadd