ignition advance curves?

[67resto-coupe]

i have the msd pro-billet ready to run dizzy. is anyone familiar with changing to a faster or slower advance curve? in the instructions that shipped with it, it shows that it shipped with a "factory curve"....where the advance goes to a max of 20 deg at 4000rpm...

but then there are 6 other combos that can be made with a combo of springs and stop bushings. all 6 optional curves hit a max of 30 deg starting at 5500rpm, 4750rpm (w/linear adv from 1700-4750), 4750rpm (w/a slight adv bump at 2500rpm to 15deg), 3750rpm, 3100rpm or 2700rpm...

has anyone experimented with any of these other curves? pros/cons? just leave it at the factory setting?

625 demon, jetted down
rpm airgap intake, tri-y headers
e303 cam, 1.7rr
initial timing set at 16deg...

looking to see if i've got any add'l power anywhere or if i can get max hp to kick in a bit sooner.
thanks.

 

[Starfury]

I'm not a roller cam guy, so I'm not sure how quick you want the advance to rack up, but usually you want to shoot for about 32* total advance (initial + mechanical) @ 3000rpm. I imagine with the roller cam you don't want to start out with too much advance for fear of knocking (roller cams have less valve overlap than flat tappets, creating more cylinder pressure at lower rpms). If it were me, I'd try starting with 8-10* initial, then have it kick up until it hits ~32* @ 3k rpm. That means you need a bushing that limits you to about 22* mechanical advance, along with the appropriate springs that get you to that point quick enough.

Keep in mind, the curve chart is approximate. Test it out first, and then test it again a month or two down the road. My springs loosened up quite a bit, giving too much advance too soon.

 

[tarafied1]

how do you like the E303 cam? is it strong or mild?
:nta

 

[67resto-coupe]

i like it. but i have to admit, i had a rough time getting this motor to "settle in", meaning it was hard to get a stable tune. after my ignition and carb issues, i think i have it down. it idles pretty lumpy and sounds awesome from mid-high rpm. i'll upload a video this weekend. it sounds great with my 2.5 spintech exhaust. i have read many other posts that would lead me to believe that this cam does not like to idle. since my only comparison is the orig 289 and stock cam, this is night and day. i couldn't break the peg-leg tire loose with the orig motor, but this new roller/e303 can virtually do it at will.

 

[tarafied1]

cool, thanks. That's the cam I have in my motor going in the drag car.

 

[65-408]

i like it. but i have to admit, i had a rough time getting this motor to "settle in", meaning it was hard to get a stable tune. after my ignition and carb issues, i think i have it down. it idles pretty lumpy and sounds awesome from mid-high rpm. i'll upload a video this weekend. it sounds great with my 2.5 spintech exhaust. i have read many other posts that would lead me to believe that this cam does not like to idle. since my only comparison is the orig 289 and stock cam, this is night and day. i couldn't break the peg-leg tire loose with the orig motor, but this new roller/e303 can virtually do it at will.

I am thinking spintech also, how do you like it? mainly cause they are supposed to be better for drone, how are yours? will be looking for your video...

 

[67resto-coupe]

the spintechs are pretty sweet. warning though: i had them dumped out just before the rear axle. the dumps were clocked at about 45 deg to the sides of the car, not straight down. with no interior and no sound deadener, it was really droney and i only lasted 2 wks. i had tailpipes installed to the rear valance w/slashcut ends and the drone is almost completely gone. if you have a full interior, it may not be that bad. maybe potentially droney on the fwy, but again, i don't have any interior. just sheetmetal and 2 front seats. i'll be sure to post some vids this wknd.

 

[garner67]

I am thinking spintech also, how do you like it? mainly cause they are supposed to be better for drone, how are yours? will be looking for your video...

I have a set of SpinTech sportsman 2.5" mufflers with 2.5" pipe from engine all the way out the rear, and even with a full interior and sound deadening, I have a hell of a drone between 2100 & 2200 rpm. Basically, they're generally pretty damn loud.

I also bought a second set of mufflers to quiet it down a bit. I went with a set of DynoMax Ultra Flo's (JohbPro's suggestion). However, I did weld some stainless v-band clamps on both sets of mufflers and exhaust pipes, so it's easy to change the mufflers, just takes 15-20 minutes to do the swap.

For every day or long trip driving the DynoMax mufflers are more preferred, but for track weekends and short local crusing I do like the deep meaty sound of the SpinTechs... that's when i'm not in the "drone rmp range".

Here's a link to v-band clamps (they're a bit pricey, but great quality)... V-Band Clamps