Hey guys, I'm in the process of recurving my dizzy. I did this many years ago with a recurve kit from H-O Racing still, lol, but want to recheck everything. I found the info below with the kit I bought, but not an expert and don't know exactly what it means. Can use your help with this. There are 3 different kinds of springs with the kit: Gold, Black and Silver. What does the below mean??
That makes sense, the heavier the spring the more centrifugal force it's going to take to expand.
Well if you bought the kit from HO Racing it might be meant for a race engine with very high cylinder pressures. One may not want to get full mechanical until higher rpm unlike a street/highway car that would want it all in in the early 3000 range.
I have mine set at 28 total, I had to make a lot of adjustments to get 28 total at 3200 and still have the mechanical start to come in at higher than idle rpm and have a good initial for starting and keeping a smooth, cool idle. Lot of trial and error involved.
Most engines will run great with a close to stock timing and advance, but once it's modified it takes some screwing around to get optimum setting. Chassis dynos help for this but cost big $$$
You recurving due to problems with detonation or power?
Thanks Al, the car is kinda dogy from a dead stop, I'll recheck the timing and curve next WE and report back. HO did sell racing and street application aftermarket parts, I'm sure I got the street, need to verify that as well....
If your engine wasn't a dog on launch before and it is now it could be the advance, could be air fuel delivery as well. If it's not a case of slowly getting worse it may be the above or gearing. You'll want to check to see if the mechanical advance is even functioning, they can get gummed up and stop moving, springs can break, weights can jam. Same with the Vacuum advance, they can stick or the vacuum can can get a leak.
That curve kit you bought come with a selection of cams and weights as well as springs? Different shaped cams and different weight weights will give you a range of total mechanical advance as well as the speed it comes on. The springs will also vary when advance starts and stops in the rpm range. The idea is to find out what timing and advance curve is going to be best for your engine, An initial of 18 BTDC and a total of 30 at 2800 RPM may be great for one engine and crap for the next. Only way to tell is testing , by driving the car or on a chassis dyno. I set mine on an engine dyno, worked great with the engine on the dyno but I had to test and adjust the curve once the engine got in the car.
There are places one can send a distributor to along with info on the car, gearing, transmission, weight, engine specs, type of driving etc. and the company will set the advance curve using the supplied info. Even then I think further real life testing on the car on the road is the only way to get the timing and the advance correctly set.
Thanks for your input. Not slowly getting worse, its just not as responsive as it was. Its the original untouched engine so with that compression ratio I'm thinking 34-36 total advance should be good. The kit came with 3 sets of springs, one busing and 1 set of weights. I rebuilt the dizzy 3 years ago and know the vac advance works and springs are good and lubed the weights, so nothing stuck and I took out the excessive play. I'll start from baseline and check timing next week, record initial, mechanical advance and total and go from there. Rocky Rotella wrote an article on Pontiac Engine timing and suggested to leave the original weights in place. Only use bushings and springs to get the timing right. I know I have the initial set at 12 believe I was able to get to 36, but don't remember the RPM. I'll record everything and post current settings on here. I think you're right that my curve is just not there cause once the car moves it goes with no problem. I can also hear a slight miss fire at idle and know its ignition related. More to come....
12 initial and 36 total is a common number for our engines, when the vacuum is added we can get close to 50-52 which will be great for cruise and fuel economy. Maybe all you need is to do is use some lighter springs to get more advance sooner. That may give you some more acceleration while keeping the initial and total the same.