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Max revs for standard rods and crank

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I am working on a new 2.2 L 912 for my S1 Esprit. Built a lot of high rev competition Lotus twinks for my Elan but this will be first exercise on a non standard 9xx engine.

I need to decide what maximum revs I will build it to. The head with suitable valve springs and buckets should be good for 9000 rpm based on the components I use in my competition twin cams which appear to fit OK and run with much heavier valves and more extreme cam profiles than required in the 9xx.

Forged high compression pistons good for similar 9000 plus rpm limit and as I need new pistons the cost increment for forged ones not much.

I dont need to build a 9000 rpm engine as I would give away to much low end torque for intended use of road and tack days but interested in what is the standard crank and rods good for in the 912 2.2L block. I should be able to get around 220 to 230 hp at 7000 to 7500 rpm based on my computer simulations in a nice tractable engine with the sort of cam profile I am looking at but its nice to have some headroom above that knowing a missed change will not blow the motor.

I would like the crank and rods to go to 8000 rpm so I dont need to look at expensive custom replacements. Does anyone on the list have any real experience with high rev 9xx engines and know the limits on the standard crank and rods (using good quality ARP style rod bolts)? Any issues with 912 block stiffness or ancillaries at these revs also.

cheers

Rohan

Edited by Rohan

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88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

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LotusBits reckon they can get almost 220 bhp with gas-flowed heads, new cams and valves and high-compression pistons. They also mention that 270bhp is possible without turbocharging or nitrous. The web page is here. You could contact them to see what they have found.


S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE

 

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Hi Trevor

I have talked to LotusBits already (it is where I got the 2.2L engine from for rebuilding). They wanted around 1000GBP for their CNC machined gas flowed head modifications - very nice but I think I can do the equivalent here at substantially lower cost. I have a couple of heads to work on and the needed ultrasonic thickness measurement tools and die grinding equipment to port the head without going into water jackets and can get access to a flow bench to test the results

I set my target 220 to 230 horsepower at 7000 to 7500 rpm based on what they have achieved and matched both a standard engine and their modified engine in my engine dyno simulation program so pretty confident it will work.

cheers

Rohan

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Hi Rohan,

If you're prepared to do the head yourself, you'll obviously save a lot of money. If you want another stateside option, talk to Richard Reyman ([email protected]) with West Coast Cylinder Heads, never mind about the SBC stuff on the website, Richard is well-known in the Jensen community and does excellent porting and head assembly work, and has built a 270 hp 907 of his own (though I think it was modded to a 2.4!). Good luck.

^_^

Eric

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Rohan,

Block flex in these motors is an issue, as is rotating mass and the crank is quite long, 2" longer than a BD crank for example.

The rods are plenty strong, but they weigh over 900g! My recommendation is go for the lightest rods you can afford. Crower is a decent source, and cheaper than Carillo and others. A decade ago, the 4340 rods were 680g or so; they make much lighter ones now (probably a result of FEA). I went with Ti, which are about 150g lighter than steel, but over twice the price as well.

The Mahle forged pistons are fine, but the pins have unnecessarily thick walls, in addition to being 25.4mm when 20mm would have sufficed. You can save about 45g per wrist pin going to a thinner wall quality material. I bought mine from a company called Western Wrist Pin, who doesn't seem to be around any more, but Crower should be able to refer you to someone. They steered me to Crower.

Knife edging the crank is also a good idea; I would suggest getting it nitrided as well. Garry will tell you he doesn't do much with the stock cranks. While I've haven't heard much about them failing, not too many folks seem intent on revving to 8000 rpm either. That's probably right at the limit.

Hope this helps.

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Thanks for the advice - Lighter rods and pistons seem to be a consistent recommendation. I agree the orginal rods are certainly heavy. JAE do a JE piston 11:1 forged piston and SAENZ rod combination that looks good being strong, light and a reasonable price. I will explore these and other options. Do you know anyone doing lightweight flywheels?

regards

Rohan

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I haven't been able to find anyone in the States doing flywheels. I have a mate who was trying to get Fidanza to do one w/o much luck. Getting a ring gear is also a bit of a problem; the later turbo cars use steel flywheels w/ integral ring gears.

Try Conversion Components in NZ. http://www.conversioncomp.co.nz/productinfo.php. They do alloy flywheels for Jensen Healeys. While I can't speak to their flywheels, the cast a one off bellhousing for me and did a pretty good job. Check w/ Colin Dray. If you're not already aware the standard Lotus bolt pattern (at least on my S3) is the same as the 240mm AP tuning clutch covers, giving you plenty of options for robust clutch covers and discs.

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FYI, Fidanza did a batch for the NA cars a few years ago - made a custom one for me and a year or two later several came up "on clearance" suggesting that they made a few after mine then unloaded them. Problem was, thought that they (probably all) had to be re-drilled for the crank dowels as they just made them radially symmetrical and thus the flywheels wouldn't fit. Nice work when all done, though, at 8.5 lbs. May be worth a call if they still have the pattern, they're now more into making and stocking more mass market stuff, tho'.

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