RS Distributor

matty74 · matty74's Garage

My planned engine rebuild

from 74 2.7 CIS 150 hp engine

to

webers
JE Pistons (maybe go to 2.8) 9.8:1
GE60 cams
74 exhaust (SSI) etc..

Now my question is would my configuration benefit from a RS Distributor what can I do with my current electricals dizzy points etc..

afterburn 549 · 10-30-2006, 06:40 PM

long and short, from a romantic nostalgic pt of view looks good. aside from that do some home work on "stand alone" systems ( much more flexibility )

911pcars · 10-30-2006, 09:22 PM

"Now my question is would my configuration benefit from a RS Distributor what can I do with my current electricals dizzy points etc.."

Short of buying a direct-replacement RS distributor, you can look for any '69 or earlier S distributor; about the same specs., or you can opt to recurve your distributor to S/RS specs.

Better yet, since your engine doesn't replicate a factory-spec build, after the engine is assembled and broken in, put it on a dyno (engine or chassis) and have the tech optimize the timing at 500 rpm intervals under load. You'll end up with an optimum timing curve specifically for your engine, then find someone to modify your distributor to replicate the curve (with some comfort cushion). See Steve at Rennsport in OR or your favorite distributor timing specialist.

Sherwood

Steve@Rennsport · 10-30-2006, 09:47 PM

Matt:

Just have it recurved appropriately, and you'll be very pleased.

304065 · 10-31-2006, 07:34 AM

Sherwood,

How would that work? Do you set the engine up on a dyno and use a crank-trigger with an electronic timing control to optimize the torque across the RPM range, then replicate as closely as possible an advance curve from that?

That seems logical but I wonder how it's actually done. Steve?

Steve@Rennsport · 10-31-2006, 09:16 AM

John:

Thats one way to do it, but sheer long-term experience allows one to choose the proper advance curve for these applications.

There are lots of variables at work here: fuel mixtures, octane levels, environmental conditions, final CR, ignition, and displacement all play major roles in how much timing a given engine can tolerate. This is NOT a one-size-fits-all proposition so one must allow for these since detonation thresholds change with outside air temps and cylinder head temps.

Engine Management timing maps, distributor advance values or crank-triggered stand-alone ignition systems are usually optimized on an engine dyno or load-type chassis dyno.

911pcars · 10-31-2006, 11:14 AM

The variables that Steve mentioned may make the difference between max. power and engine-damaging detonation. The cushion I mentioned is the difference between optimum spark advance and real-world timing that takes those variables into consideration so the engine doesn't approach detonation.

In the days before electronic ignition and laptop changes, the dyno operator would advance the distributor by hand (with mechanical weights locked in place) and chart the engine power with degrees of advance while monitoring EGT and A/F ratio. After all is said and done, an advance curve and max. advance is established for your engine for that day, including ambient temperature, humidity, fuel octane, altitude, etc. The actual distributor advance curve created follows that timing curve but retarded a few degrees from the actual numbers for safety.

Or something like that.
Sherwood

304065 · 10-31-2006, 12:17 PM

Sherwood,

That reminds me of the way they used to set the timing on the MGA's B-series engine at the factory: turn the distributor until the engine pings, then back it off slightly and tighten the clamp. I'm sure it works, although I suppose you would need a way of measuring TDC, but the dyno probably has that built in.

But wow, what a way to measure: stand next to a running engine howling against the dyno brake, inches from the moaning fan at 6000 rpm, then reach out and turn the distributor by hand, hoping you don't get electrocuted in the process.

The reason I'm wondering is that I believe the advance curve on my 901/05 will need to be reset following a rebuild to a mild street 2.4. Just curious as to how the recurving might work.

Steve@Rennsport · 10-31-2006, 10:57 PM

Quote:

[i]
wow, what a way to measure: stand next to a running engine howling against the dyno brake, inches from the moaning fan at 6000 rpm, then reach out and turn the distributor by hand, hoping you don't get electrocuted in the process.

LOL,....This is why we get the "big bucks" when we dyno an engine to optimize its performance,.....

This is done at several RPM points from idle to 5K.

rlane · 11-01-2006, 02:47 PM

I don't want to hijack your thread matty74 but you have gotten great advice from some real experts that I also have a question for. I have a RS spec'ed motor and acquired an extra distributor Bosch 231 184 006 (I think) and had it recurved/rebuilt as a spare. When I went to install it to dissaemble and clean the current dizzy I found that the refurbished one will not fit in to the case. When I calipered it I realized it is several MM larger diameter across the long portion of the dizzy case. I have heard these can be machined down, if so who do you guys recommend for this. Also what cases is the larger distributor designed for..Is there a site that gives the dimensions of all Bosch dizzys? .. I may want to sell it.

matty74 · matty74's Garage

richard not a problem