coppercutlass

Ok i have been putting this off way too long and plan on doing this in the near future. My current curve seems good not exactly where most would want it but it worked good and i had no reason to mess wit it. Now im on quest to get maximum hp. and i know i have to do this to get where i want to . My only issue is the charts for curving they give you a graph and show you where your mechanical advance would be based on rpm with certain springs. You add that to your intial and that would give you your total right? But on these charts it also shows where it would stop pulling max advance. for example if i use the gold springs the moroso chart tells me it would give total 24 degrees at 5k rpm and with the medium springs it would be 22 degrees at 7k rpm . im confused most people say you would want your total timing coming in by 3200 rpm appx. i think correct me if im wrong again please i still dont understand this fully. if my initial timing is 14 degrees and i use the gold springs ill have 30 degree at 3k rpm but the chart shows it will still keep advancing is this right? or do those graphs just show if your distributor stops advancing at 3k rpm thats will be your total timing 14+16 at 3k rpm would be 30 degrees total ? im so confused i read stuff all day and still dont get it .my current set up had 28 degrees total in around 2800-3000 rpm i think . also what would be a desiarable total timing to have and where to have it all in.

bigD

28 degrees does seem a bit conservative but i'd say having it all in around 2800 to 3000 rpms is good. i'm sure that there is a built in limit to the amount of advance, but i don't know what that number would be.i know that there are bushings available to limit the advance. are you running a vacuum advance?

coppercutlass

yes i have vacuum advance but i know that it plays no role to wot only to crusing where it's good for fuel economy i know that has a role too mianly for street crusing . i got this distributror i have had lying around and i got a mallory 6al ignition for free from a freind of mine so i figured id mess with the spare unit and leave the good one alone.

MDchanic

Well, the instructions do say that it hits 30° at 4,000 crankshaft RPM and 24° at 3,000, with the lightest springs. If you figure 6° initial, that's 30° at 3,000, which is about right.
The instructions I'm looking at make no mention of variable advance limiter bushings, but I would say you would need to install them to keep it from going past 24° (or whatever you need).

- Eric

coppercutlass

im currently running 14 degrees initial so im guessing im close with my current set up ? My only issue is starting it with 14 degrees intial is when the temps go up it struggles abit to start . Cruving it would be the way to go since i could lower my intial timing and bump my mechanical does that sound right?

TripDeuces

http://msdignition.com/uploadedFiles...structions.pdf

I used the MSD instructions as an example. Go to box 'F' in the lower right corner. Let's say you used the silver advance bushing and the light silver springs. The silver advance bushing gives you 25* distributor degrees (does not include initial). So that means you'd need 11* initial to get to 36* total, 25 + 11 = 36. I assume you're using a stock distributor so you're going to need to know how much timing is built into it.

By using the light silver springs the advance starts just above idle and is all in by roughly 2200 rpm. The lighter the spring the quicker the advance comes in up to the max built into the distributor.

The springs control the rate at which the advance comes in. Not the total advance built into the distributor. I hope this helps. You're right in thinking that you want all the advance in by roughly 3000-3500 rpm.

MDchanic

Yup, that sounds right.

- Eric

coppercutlass

my current distributor went into my dads and is a proform unit . i got the procomp hei he had that has the usual parts found in summit brand, proform etc. I also have a stock unit. I also have a curve kit i never used it has the weights and springs and bushing . I will be using the stock unit to upgrade as the procomp unit is very close to the proforms performance. Spark is a bit weaker but for 55 bucks it worked good i just wanted to test it on my dads car as mine had a dead starter .

MDchanic

Are you sure you mean distributor degrees, and not crankshaft degrees (the instructions don't seem to say)?

- Eric

coppercutlass

Btw thanks guys now i have a good idea of what to do. I have never curved a distributor and the instructions are unclear and everywhere i looked didn't make sense.

TripDeuces

Yes I mean distributor degrees. I know three types, initial, distributor and total.

Initial + distributor = total That's how I was taught. Call them what you want but what I'm reading off the crankshaft (timing mark) is either initial at idle or a combination of initial and distributor depending on the rpm up to and including total.

Copper is working with an HEI which I'm not as familiar with. It's my understanding that the HEI timing kits allow different amounts of advance (distributor) depending on which weights you use. Rate is still controlled by the springs. Lighter brings it in quicker and heavier later.

droldsmorland

350/400/455 or ??? More engine specs, compression, heads, cam... It must be specifically taylored to your junk and driving style. What fuel are you running?

General giude lines for a street driven W30ish spec 400/455 will be something like this with an HEI....
Base timing 12 (+/- 2 or 3*). Add another 10*(+/- 2) with a adjustable travel (not rate) vac can and have the rest all in at 2800-3000. For a total of 36-42* total. You can mix and match springs to attain this. You can do this with a set-back timing light. First use a vac gauge to attain max vac reading with carb then go at the timing. Re-adjust vac when your done with the dist.
If all this is more than you want to deal with I highly recommend that you send it out to someone who curves distributors. It $100 around where I live. Best 100 you'll spend.
Give it as much ignition timimg as it will take before spark knock.

MDchanic

Better make that five:

1. Initial
2. Distributor (or mechanical, or centrifugal)
3. Total

AND, separately:

4. Crankshaft (as measured by a timing light on the crank) and
5. Distributor (as measured at the distributor itself, such as on a distributor machine).

Though we usually talk about crankshaft degrees, many distributor specifications are expressed in distributor degrees, which are ½ of crankshaft degrees because the distributor turns at ½ the speed pf the crank.

- Eric

coppercutlass

i think if i went with lighter springs and brought my timing back a bit id be perfect with the distributor i had ., But as a mentioned its in dads car now which also has my old engine so im gonna go ahead and rebuild the stocker hei i have lying around . i have a good idea of what to do now so ithik im up for the challange id rather mess with it for few hours than pay some one 100 to do it . I can also buy all the proform components individually for my stocker and build the stock one to the same specs as the proform as they have the same whieghts and springs as most curve kits come with and start with that for a base line and go from there . If all else fails i have a procomp thats untouched.

yankees

Copper Cutlass keep us informed on how things turn out and the details on what you actually do. Where are you running your distributor vacuum to? I assume you are running a holley carb that has a vacuum port on the front metering block that you're running to your distributor is that correct?

let me know what you change your initial to.



Thanks

coppercutlass

I always run vacuum so it onlt advances under acceleration I can never get good idle in drive with the vac port that pulls in idle . I forgot if its ported or un ported I think its ported. I just make sure if pulls no vac during idle

RetroRanger

mark71 and my experiences w recurving an HEI in a SBO 350

https://classicoldsmobile.com/forums...-hei-help.html

coppercutlass

Yeah I seen that thread before. I'm just worried about the curve . I just neede some clear thoughts as to wtf the charts meant. Now I have a good idea time to play with it. But that won't be for another month or so . I'm busy finishing up my dads resto I would like to tsee that thing on the street next spring