Thanks for any help guys. Here is my setup and problem:

355 cid, vortec heads, ~9.75 cr, performer intake, holley 650dp, 1.5 rr, 1 5/8" hookers, 2 1/2" dual chambered, voodoo 268 (60103), stock stall/TH350 , 3.70 posi.

Problem: I tuned using a vacuum gage and ended up with 17" at idle. Park/neutral idle is 1200rpm, drive is 700rpm. Any changes I made to carb or timing decreased rpm and vacuum so I thought I was good.

The vette is an absolute dog until ~2800rpm then it feels like a turbo kicks in and it takes off - a huge difference. *Also, it shifts at 3500 instead of 5500.

Do I have a timing problem? Could the carb need different jets? Is this just the cams power band - I would say it feels like only ~100tq until ~2800rpm then ~300tq.

 

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When you get a peak vacuum reading you adjust the idle down, 1200 rpm idle sounds high. Before I did mine my car idled at 900-800 and then I hooked up the vacuum gauge to the Manifold, where the powerbrakes get its vac. I turned the dist. until I got a peak of around 17" and the car was idling at around 1800 by time I got the peak value. I lowered the idle back down turning the idle adjust screw back to 850-900 and turned my dist. until I got another peak. I didnt need to mess with my advance springs because a dyno shop had already done it for me. I worked good for me. BTW the Dist. needs to be disconnected from the vacuum. Also make sure you have no vacuum leaks else where or it can throw off your readings. I had all my vacuum ports capped exept what I was using to tune with. Was your vacuum advance to the distributor hooked up to ported vac or manifold vac?   

I'm using ported vacuum for the dist but I also had all vacuum lines unconnected and capped. I'm running soft springs in the dist. My setup was great with the 260H (204 @.50) cam that was in. I'm sure I have a tuning problem, just not sure where?

Any clue why the th350 shift points dropped to 3500?

I'll work on retuning today.

The ported outlet on the carb is designed not to have vac. until the throttle blades are opened, because you don't want vac. advance until the throttle is applyed, I don't understand how you had vac. at that port at idle, like Tumarr recomended hook to the intake manifold to get direct vac.. this also eliminate's any vac. leaks down line possibley in headlite-WW systems, make sure all your vac lines are hooked up correctley, try timing with a timing light, vac adv.line disconnected and plugged, 2 degrees over stock at recomended idle ,reconnect the vac advance and see what happens.

I run my dist on ported vacuum, but I had all lines capped while checking vacuum from a manifold vacuum source -nothing was hooked to a vacuum port except the gauge.

I retuned and my vacuum is ~17", RPM in Park is 900, RPM in drive is 600. Any lower timing decreases vacuum and going richer or leaner on the carb decreases vacuum. 

Is this cam just too big? Should I advance it 4 degrees or try fast bleed lifers?

Thx guys!

Looks like I misunderstood your original post, from your latest post it sounds like your in the ballpark, check to see if the vac. adv. is working, blow on the hose if you can blow through it has a hole in the diaphram, pull the cap and rotor and make sure the weights and springs are not sticking on the adv.plate, if they are pay close attention how they come apart, clean and lube,reassemble makeing sure the parts go back where they came from.

You have a tuning issue.  The cams power band is 1800to 6200 so it will feel like it really comes on at the 2000 rpm point, but it should not be a dog down low.  The first cam you had was a power band of 1000 to 5500.  So there is not much difference.

Not sure why your tranny would be shifting at a different point, but the cam should not have affected this at all.  A 2400 stall converter is recommended with this cam to get the most benefit out of it.

 

I suspect the tranny shifting is a result of a misadjusted cable in a 350, or vacuum modulator failure in a 350 or 400.  Not related directly to the cam change.

 

I feel like it's a tuning issue too. I've tried two different timing lights and they must be inaccurate because the motor runs badly when the timing is below 25 initial per timing light - and below that with the vacuum gauge I only pull 15". Per timing light at 25-28deg the vacuum is at its highest of 17" idle.

Can you tune total mech advance by vacuum? How about setting the idle at 3000RPM then changing out advance springs until highest vacuum is achieved? My only clue right now is maybe too much total too early since I'm using very light springs.

I agree the engine response is a tuning issue.  But the shift point may be an adjustment, combined with tuning.  Take another look at Ben's method.

this example is with an MSD dist.

set INITIAL timing to the minimum required to get peak MANIFOLD vacuum.  you can turn your initial up further without vacuum increasing...  dont do this. turn it back down until it drops from peak..  then back up to barely reach peak.

this gives you the BEST off idle response.  the timing light figure from this will vary based on a number of factors.  lets just use mine as an example. 15 deg at idle.

then i usually take the second weakest springs and second smallest limit bushing and install them in the distributor. I drive the car..  i let it warm up..  and then drive it up hill with it floored..  if I get detonation early but it clears up..  i use the next stronger springs..  if i get detonation and it doesnt clear up i use a larger limit bushing.

i keep doing this until i get no detonation..  on my 427 i am using the third weakest spring combo and the second smallest limit bushing..

I have great off idle response.. and great accleration through the power band. 

so to summarize..  I set the IDLE timing and lock it down with the dist adjustment bolt..  then adjust wieghts/springs/bushings from there..

the way you are describing it is to set your timing to be correct at 3000 rpm...  and live with the consequences of what it will do to your idle timing.

I say adjust your initial timing first..  then use weights/springs for adjust your high rpm timing.

 So the answer to your question is yes, you can change the springs and go from there.  You will probably change them again, but it is all a balancing act.  If you once get closer, you can fine tune from there.