Lotus Elan

(v) Fast Road Car

PostPost by: 1owner69Elan » Fri May 04, 2018 7:19 pm

Out of curiosity what is the rod length that you end up using in the Frankentwincam?

How much weight savings have you done? I did some obvious things (several of these for other reasons than weight) that shave off about 60 pounds net (mag bell housing, alloy flywheel, aluminum radiator, no spare tire (don't have a spare 26r wheel that would work anyway), alternator, starter, ...).

BTW, I was little concerned about the light flywheel but have noticed no lack of drivability and the engine spins up more readily I suppose (but I don't remember enough to compare with stock). Also, no lack of smoothness at idle.


Frankentwincam looks like a nice build. Should give you plenty of power/torque for a road car.
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PostPost by: knockoffnut » Sat May 05, 2018 11:09 am

Thanks 1owner. I just checked with my buddy on his jetting, and the 45DCOEs on his 2.0L LTC are set up on 38mm chockes, which surprised me as that's quite large for a street engine. Would you by any chance know the jetting specs for your engine? It would be very helpful for a starting point on my engine when I get to that stage. On a properly balanced engine the flywheel acts purely as a flywheel, storing energy for moving from a stop without the engine bogging. These big(gish) engines in tiny cars don't need much of a flywheel effect, so everyone I have spoken with says alloy flywheels are fine for that. It is the high load on fasteners from the torque, that makes racers recommend steel flywheels, but severely lightened steel works very well. I have one of each to choose from. (next in line is a very light LTC Seven project) I expect to use 5.2" steel H beam rods, but I haven't finalized those calculations yet. I have all the other bits and I am just doing the rod calculation now. I need to check my figures against actual chamber volume, make sure I have enough meat in the pistons to cut the required dish to bring the CR down to 11:1 for 94 octane fuel, and then work backwards to rod length. I am told by the folks who have done it before that 5.2" is the right setup. I will post an update when I know the final setup.
The car has an alloy bellhousing, trans case, diff case (nose), wheels, brakes, radiator, lightweight body. I will likely add alloy door handles, and maybe the fueltank too. Some of this "added lightness" will be offset by the weight of the rollbar.
1964 S1
1965 S2
1967 S3 SE DHC
Frankentwincam
Seven S2 A
Seven S2 F
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PostPost by: 1owner69Elan » Sat May 05, 2018 4:59 pm

Here are my jetting specs along with some others for comparison:

lotus-twincam-weber-jetting.jpg and
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PostPost by: knockoffnut » Sat May 05, 2018 11:38 pm

Thank you very much for posting this 1owner. It is very much appreciated. Your curves start at 600RPM. Does your engine idle at 600? If so that is quite an accomplishment for a 181HP 1700cc engine. I expect that could be one benefit of the 40DCOEs and the 32 chokes. Must be great fun to drive!
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1967 S3 SE DHC
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Seven S2 F
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PostPost by: 1owner69Elan » Sun May 06, 2018 12:35 am

The 600 rpm data point is from Pertronix, not an idle point measured by me.

My car idles around 800 rpm, quite smoothly and quietly, cold or warm. In fact, I am a bit startled that the idle is so good.

It also starts easily from cold (not that cold here), no choke hooked up - not needed.

In the car's previous incarnation (Stromberg head, stock SE cams etc., but with emissions removed) it was about the same idle rpm but I don't recall it as quite this smooth and balanced. Perhaps the Stromberg head siamese intakes had something to do with that.

The car while cosmetically in stock form (except for 26r wheels and wide tires) is a very different experience now with all of the uprating throughout. Not that I didn't thoroughly enjoy my car before.
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