Base map wanted Lotus 912

Post maps up for others to get them going in the right direction. DISCLAIMER: USE AT YOUR OWN RISK. CONFIRM VALUES!
Rob Stevens
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Re: Base map wanted Lotus 912

Post by Rob Stevens »

That looks great, great change from mk1/2 escort. With a period engine to top it off nicely, I'd imagine around 180+ bhp
annteak
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Distributor: Lotusbits

Re: Base map wanted Lotus 912

Post by annteak »

Here is the engine back in 2013 at the builders on Delortto 45 Carburettors and a dizzy before I converted it all to Jenvey throttle bodies / S40pro ECU etc; making 203bhp @ 6900 but strong numbers over most of the rev range, a big flat stop around 4000 - 4500. I hope to map out, in the car I expect a little reduction due to exhaust but wit the bodies I hope for a rebalance in those numbers.


https://www.youtube.com/watch?v=wt35Tl1rQm8
Screenshot 2020-10-15 at 01.11.38.png
rjwooll
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Re: Base map wanted Lotus 912

Post by rjwooll »

That looks a superb conversion! As I expect you know, there is common history between the Vauxhall slant 4 engines and the Lotus 9xx series. Lotus used the Vauxhall block initially for development and competition, and I'm pretty sure Lotus subsequently ran 907 testbeds in a VX 4/90 and a CF van! Then there were the early versions of the rally Chevette which used the Lotus head on the Vauxhall block.

Anyway, enough history! Send me your email address and I'll send you my map. My car was also set up by Northampton Motorsport. I'm using Jenvey 48mm TBs and (I think) Bosch 240cc/min injectors.

You may be interested to know that the standard Lotus airbox seems to give better dyno results than anything else. Someone with a Jensen Healey ran some comparative dyno tests showing this. Whether it will fit I don't know, but Lotusbits (Marton, near Leamington) may have a used one if you want to try it.

Cheers, Richard
annteak
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Re: Base map wanted Lotus 912

Post by annteak »

Just for your reading pleasure. The full story on the prototype is very long but a local chap to me owns the Viva HB GT used by lotus during the 907 development and also owns one of the development engines.

The EX Lotus owned HB GT now in the hands of a local chap to me:
https://www.annteak.com/lotus-viva-gt-history/

The prototype 907 engine unrestored
https://www.annteak.com/prototype-lotus-907/

The prototype 907 engine post restoration
https://www.annteak.com/lotus-907-prototype-update/

A close relative to the 907 but all of Vauxhalls work and 10 years before the HS / HSR
https://www.annteak.com/vauxhall-8-valv ... inal-part/

my email for the map is paul.bottomley@annteak.com
rjwooll
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Re: Base map wanted Lotus 912

Post by rjwooll »

Thanks Paul - map sent

Richard
annteak
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Re: Base map wanted Lotus 912

Post by annteak »

Got that thanks, feedback when I start everything literally!
annteak
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Distributor: Lotusbits

Re: Base map wanted Lotus 912

Post by annteak »

Well thanks to here, I had the car at Northampton Motorsport today, one issue with the rear axle at high speed has stopped us going above 100mph / 6000 rpm, so its now fully mapped to that point. Once I have found the source of the vibrations (many suggestions already received to last a lifetime so don't feel the need to add please) I will be back and finish off the mapping up to 7200rpm... (my imposed red line) .

On the engine dyno some years ago (on some old delorttos) it was seeing 203bhp @ 6900, today due to the rev limit we saw 188bhp (at flywheel) at 6000, so suspect its all going to be about the same but now on throttle bodies and the more spaghetti shaped exhaust manifold than the straight manifold use don the engine dyno.

We had a small fire at one point the manifold was glowing red hot under load at 5500 and it melted / set alight to a suspension bush, so some mods / heat shield is required there, was exciting to see my car on fire!!!

https://www.youtube.com/watch?v=hvJ6_Hfx-nE
Rob Stevens
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Re: Base map wanted Lotus 912

Post by Rob Stevens »

Hi Paul, shame you couldn't finish the mapping, but TBH the fuelling will probably stay the same over 6000 rpm, likewise the timing requirements, might be able to add a couple of degrees if lucky to get you over the 200 bhp
They probably could have checked the mapping in a lower gear?

Sure is going to be fun, can't weigh much more than my Elise.
annteak
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Distributor: Lotusbits

Re: Base map wanted Lotus 912

Post by annteak »

Troy at Northampton Motorsport finished off the mapping from 3500 to 6000 in 3rd gear, then did the final 6000 rpm and roll down to calculate the correct power numbers (on edge when that was done) but didn't want to push it harder than 6000 till the vibration was assessed in case it is actually a gearbox issue, not the prop or axle angle phasing etc. Wise idea is you ask me!

Number wise its looking very promising, the engine was dyno'd when built when on carbs and straight through exhaust, and the new numbers now its in the car match well, so I can infer at the rev rise it should correlate well (?). see screen grab below. Salmon was the engine dyno done a few years ago, and purple is the latest run at Northampton Motor sport.
Screenshot 2020-11-29 at 11.29.17.jpg
katana
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Re: Base map wanted Lotus 912

Post by katana »

If for no other reason, the infilling of the mid range hole and general smoothing of the curves, still gives the nod to EFI over an obviously good carb set up. You may not make more 'ultimate' power but how its made is so much more impressive.
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