 |
PM |  | |
Quote | | |
Reply | | |
Full Topic | |
| Joined: | 04-07-2022 |
| Location: | Oregon USA |
| Posts: | 130 |
| Status: |
Offline
|
Vance,
Reconnecting the battery after I finished restoration was how I burned up my wiring harness so I'd be nervous too. Mine was caused by a short in the cigar lighter, I had to replace the harness. I'd consider a battery ground cutoff switch or at least when that ground goes onto the battery terminal I'd standby and be ready to pull it immediately.
If you've changing timing duration to a configuration that hasn't been done before I'd be nervous too. I'm not sure what the goal is by going off script are you expecting to find an additional 20hp that no one knew was there? The 907 started life as a racing engine that was detuned for street use. During it's production life in a number of different cars it was improved, modified, upgraded and evolved to it's final iteration the 912 Turbo in the Esprit. My point is do you think there's anything that hasn't been tried already during development including what you're doing? I get it you want to experiment but what I learned a while ago was doing your own engineering can get really expensive really quick do to it's trial and error nature with no guarantee of satisfactory results.
Delta sells a very nice exhaust system that most guys use it's HD and nicely finished with polished S/S exhaust tips.
Thanks for the suggestions, I will respond to them in order.
I have read about others that have had issues with the cigarette lighter causing shorts and big time wiring problems (letting out the Lucas smoke, as it were). Because of this forum, I ground the tip off the lighter connection, used a 90o lug to make the connection, and added an in line fuse for the lighter in the center console. This was done because I could see how the lighter would make my nice neat wiring job go 'poof'. This is one reason I hang out on this forum - for tips from owners who "have been there and done that".
Yes, I am in unexplored territory as far as engine tuning goes. When the Lotus motor was built, symmetric cam lobes (intake and exhaust) and tight lobe centers (110o in our case) was how one made power. Power continues to increase all the way down to about 106o but emissions increase, fuel economy drops and idle gets rougher the tighter the lobe centers get. Economy and emissions demands made manufacturers look for other ways to get power without destroying economy and emissions. There are many things that have changed since the 70s in this regard, but the two that are of interest here are lobe centers (MOPs) and duration. Modern cams generate power by opening the exhaust valve earlier (by increasing exhaust duration) and spreading the lobe centers. By opening the exhaust valve earlier, two things happen - there is a small power loss because the power stroke is shortened but it happens as the piston approaches BDC when there is little leverage (the connecting rod is nearly vertical) and the chamber pressure has dropped almost as low as it can go. Because of this, the power loss is very small. Second, the early valve event allows the exhaust gasses to use the remaining combustion pressure to bleed off before the piston begins its upward stroke. Because the exhaust gasses have started to bleed off the engine needs to do less work pushing the gasses out during the exhaust stroke - which frees power to move the car. The gain due to reduced exhaust stroke work more than offsets the loss in power due to opening the exhaust valve early. The wider lobe centers improve fuel economy and torque and reduces emissions. All modern cam designs go this route to make power, increase economy, and reduce emissions - even 16 valve designs. The emissions reduction occurs because there is less valve overlap, and therefore less time for the incoming air/fuel charge to escape through the exhaust valve. Longer exhaust duration also allows one to make a bit more power as well. And yes, the Lotus motor may not respond well to the changes I have made - but I have a spare cam and so can restore the original configuration should I not be happy.
Thanks for the suggestion on the Delta exhaust system. I will check it out. I would like to hear from others as to how happy they are with it. Some systems don't fit, some don't muffle, and others drone on and on and on. I want it all; tone, fitment, and a subdued volume level. Wish me luck.
Vance