Timing - how far can I go?



Motor is six port 13b street ported and is used for racing only.



Using a Racing Beat downdraft manifold with 51 IDA Weber carb running on 93 octane unleaded.



EGT will run to 2100 degrees F. during a race. When I see it getting that high I back off which is not good for racing.



A/F ratio is running around 12:1 to 13:1 and timing is 27 degrees BTDC when the EGT goes up.



I can't figure why I can't get the EGT down unless it is due to late timing. It seems to me that the timing cannot be late at 27 BTDC, but, I don't know what else to



try.



So, just how far can I advance the timing before I risk damaging the motor?



If you have any other suggestions to try, I would appreciate hearing them.



Thanks.

 

yeah 2100 is high...



cold air intake? if you cool the air into the engine, it'll be colder coming out....



27btdc is about right, i'd be looking for other things before running more timing. how is your timing split? if you're not running any between the L and T adding some might help



richening it up will help too, the motor will make best power around 12:1 at the low end leaning out to the mid 13's, but you cant always do that, due to egts



i noticed at the track they were all shooting for about 1750ish... and they were all running dual egt's

 

Keep the A/F in the 12sright through the range. Timing is fine, but 25 degrees would be fine as well. Shoot for 1600 degrees EGT and keep going richer until you can do it. Probably the float bowl is empty half way down the straightaway and the needle seat is then the only jet left metering fuel. There is a long list of mods that must be used to get the Weber to work so far above its designed operating range. The carb leans out when fuel supply cannot keep up with demand because the fuel level in the bowl drops too low. There are two accelerator pump wells in the bowl, but only one is used. If the second well is still in there, drill a 1/4" hole near the bottom and notch the top of the well wall, so that fuel in that well can add to the total fuel available. The biggest needle and seat available. Or a 350 or 400 Gross jet if you can find one. Paul Yaw may stock big ones. Set the float high enough to make the boosters drip, then lower it just a bit. Increase the fuel pressure until the boosters drip, and leave it there. (about 6 pounds). Drill out the hole that feeds the needle seat. Remove and discard the little filter above the needle seat. Mount the fuel pressure regulator within 12" of the carb. Insulate the fuel lines from heat, all the way back to the tank. Use 93 octane pump gas with no alcohol. If it has alcohol in it, it will run leaner yet.



It is possible that the pulley is not marked correctly, or has no marks at all beyond TDC. It may have no TDC mark and just one mark at 13 degrees. So you need to find actual TDC and mark that on the pulley. Then measure the pulley diameter to find circumference using C=3.1416 X diameter. Then divide the circumference by 360 to find degrees per inch. Measure from the TDC mark in the direction of rotation, and mark 20 and 25 or 27 degrees. File a notch in the pulley and add a drop of colored paint, to make timing easy. The keyway in the pulley should be pointing at the 9:00 oclock position when the pointer is over the TDC mark on the pulley.



Get me the choke size and I can suggest some jets.



Lynn E. Hanover

 

Thanks, j9fd3s.



I am using a Ben Beasely designed snorkel with the intake in the airstream outside of my roll bar.



I am using no split on the timing. When Daryl Drummond modified the motor to run in FM he took away the split.



I have always tried to get about 1650 degrees as do most FM guys.

 

Thanks for taking the time to try to help me once again, Lynn.



I need some time to digest all the info. I wanted to get back quickly, though, to tell you that I am running 44mm chokes. I would really appreciate your thoughts on jetting.



I hadn't even considered fuel pressure. It has been so long, I don't even know what I am running, but, I know it is what I ran as a FM (guessing at about 3 psi).



I am using a 300 needle valve.



As rpm increases above about 7k the mixture goes to 13:1, egt goes up, I ease up. Since I haven't really pushed it beyond 8k, I am guessing that as I approach 10k (where I would like to go) the lean condition would worsen.

I seem to have done no damage to my apex seals yet. I just checked them.

 

methinks mr hanover is correct



i'm sure you've noticed, but the weber is really easy to work on

 

Is that a Renisis engine in a Formula Mazda?



Lynn E. Hanover

 

My motor is the 13b as used in the 85 GSLE, I think. Anyway, not the Renesis.

 

yeah i have a weber on my motor right now b/c my holly suxed. man i was going to buy another motor and everything for the road course b/c i didn't think that my weber would hold up but after hearing all this i might just keep my weber setup and hit the road course up with it.

 

PROBLEM SOLVED, THANKS LYNN!!



I’ve now had a chance to get my car on the track since Lynn gave me his advice. My egt problem seems to have been cured.



In case anyone else has the same problem, here is what I did:

- bought a #300 ball fuel inlet valve from Gene Berg (that is the biggest I could find),

- reset the fuel level,

- opened up the inlet just before the valve,

- increased the fuel pressure to 6 psi, and,

- opened up the two fuel bowl vents slightly.



Evidently, as Lynn suggested, my fuel level at full throttle was going down causing a lean condition and elevated egt.



Thanks again, Lynn. This forum is great.