I finished my head swap this weekend and wanted to share the experience and ask you other "vortec" experts some questions. First of all, I'm very pleased with the seat of the pants meter on these heads. I have not had a chance to tune yet, but my first impression was these heads have probably added 40 HP over the 75 CC heads that came on my 1971 LT-1 350. I also moved up to an RPM air gap over the Performer manifold on the old heads. I decided to leave the current cam alone for now - Lunati 10010 has .480 lift and 230 duration at .050. I'll make a trip to the track soon to confirm the gains. Car was running in high 13's on the last trip with drag radials.

I do have a slight hesitation on take off that was not there before the swap. I'm assuming my Edelbrock 1406 needs to be worked over for these new heads and increased compression. I raised compression from 9:1 to 10:1 with these heads, do I need to increase size on both primary and secondary jets?

I set the inital at 12 degrees for the first test drive. Performance was not great. Moved up to 18 degrees initial and holy cow! Much better performance and throttle response. I've got the mechanical advance set at 17 degrees all in by 3,000 RPM for a total of 35 degrees.
I installed a set of AC plugs for a 1996 Chevy truck and the gap was around .045 out of the box. I have an MSD 6A and an aftermarket coil, do I need to re-gap the plugs?

Finally, I had a tank full of 89 octane when I started the swap. I have had no problems with detonation so far graemlins/hurray.gif

You sure about the timing? My dish pistoned Vortec motor will not tolerate more than 30deg total even using 91oct. It runs best with 4deg initual and 30deg total in at 4000 rpm.

Yes, I'm sure about the timing figures. What cam are you running? The lunati grind I'm running seems to be taking away some cylinder pressure and that may be the difference?

I recently did the Vortec swap on our '79 Z28 and have been very pleased with em.

On the timing:
I beleive that the Vortec heads run best at 32 degrees max. total timing. Gary at GMPP has stated this and it was true with mine when I did the Vortec swap.

I'm running flat top hyper pistons. My compression is calulated at 10.3:1 and I also run 89 octane with no detonation. I'm running a Comp Cams 268H (.454 lift and .218 dur. at .050). I think the Vortec heads could use a little more cam but, I'm not going to change it at this point.

I'm still running the stock Q-Jet with the smog settings and I also have a slight bog when the secondaries open up. I really don't mind it too much as I love rolling along at about 20 mph then nailing the gas peddle, then after a split second, the front end raises up, the rear end squats and starts fishtailing as the rear tires start singing that wonderful song!

Dwayne

My vortec 350 will take up to 18* initial, but as soon as you hit the gas it tells you it dosen't like it. No more then 34* total, usually with 14* initial. I have the off idle hesitation with my vortec/ carter AFB combo also, as do alot of other people. I think its the carb, but can't get it to go away.

I have a Comp XE-256. Very mild cam at 600rpm idle it has 17 to 18 in of vacuum. I am not going to argue with you guys about timing but mine with the very slow timing curve has ripped the radiator support loose twice in a car with welded subframe connectors. The off idle hesitation may be the lack of any exhaust heat in the heads and manifold. The fuel will not stay vaporized until it reaches the combustion chamber. Mine is a pain in the posterior when the weather gets cold but a stock Q-jet works very well when it's 90deg out.

I have my 355 with Vortec heads set with 10* ini. timming, and 34 total. I have my vacuum advance to add 10* full manifold vacuum, giving 20 deg. ini. So when I hit the gas it drops back to 10*, and starts the cen. curve. I am running the little Edelbrock cam, 204/214 @50 with 420, and 443 lift. I have ran the best of 8.60 @ 85 mph in the eight with Pep Boy tires. I also have the Edelbrock 600 carb, a 2000 converter, and 3.08 posi. 16 mpg,and I can drive it anywhere.
Mark

Mike-

What's going on with your timing to cause the radiatior support problem? Guess I'm missing something??

My vortec 350 runs the stock vortec cam, like 202/204 @.050 or somthing around there. I also have the vaccum advance hooked up to ported, not manifold vaccum.

Now on my old 385 with vortec heads, I ran the stock HEI with a MSD 6a and blaster 2 coil hooked up to manifold vaccum with 10:1 compression and 91 octane no problems with around 10* initial with the vaccum un-hooked.

As for the hesitation- I don't think I have any fuel vaperization problems with the temps at 110* every day smile.gif Hope this helps someone...

I did the vortec head swap on the 355 in my '78 chevy truck about 5 years ago, and was shocked and amazed at the results. I started with a nothing special short block I built about 7 years ago...cast flat tops .040 in the hole, ported 882 heads, 266 crane energizer cam, headers, duals, stock convertor, and 3.08 gears. It ran a best of 16.06 and got 15mpg on the highway. I then swapped on the vortec heads (bumped compression from 8.4 to 9.4-1), a comp XE268 cam, swapped the old 8004 weiand for a vortec performer rpm, and a 2000 stall convertor. I reused the 1405 edelbrock carb, and immediately ran 15.20's and 8 mph faster, and still got 14.5mpg on the highway. My 1405 also gave me fits after the upgrades...it was perfect on the first configuration but had a nasty bog and would occasionally sneeze back thru the carb when the secondaries kicked in. I tried everything...jet/metering rod changes, timing and advance curve changes, accel pump adjustments...anything I could think of (edelbrocks tech support was NO help). I bet a set of bigger squirters would do the trick...my carb just had too lean of a secondary transition. I never did a squirter change...I ended up swapping on a 750 edelbrock and it did stop the sneezing and bogging, but I also lost some throttle response. I drove it this way for several years, then last year I made the best upgrades to this package yet. Since this is a 3.08 geared 4500 pound truck (that I tow with), I swapped on a vortec performer intake and a 650 holley spreadbore to try and gain some off idle torque and improve the fuel economy (I wanted to try this before swapping cams). The performer/650 spreadbore made all the difference in the world. Highway mileage is 16mpg, and the truck will melt the tires at a 20mph roll now, and it still pulls hard to 6K.
My setup has 180psi cranking compression, terrible quench (.081...yuck), yet runs just fine on 89 octane fuel (87 octane in a pinch) with 14* initial, 36* total. I don't know if it is the bad quench or what, but it loves a lot of initial timing. At 18*, top end power falls off HARD, but it will blaze the tires just by looking at the gas pedal. If I had time to mess with it more, I could limit the mechanical advance so I could run 16*-18* initial, and keep the total at 34*-36*. There is no noticeable difference with my combo between 34 or 36 degrees total, but anything more than 36* and it falls on its butt past about 3500 rpms.

Sorry for the ramble.

Thanks for the responses. I think that there are many factors that will determine what the initial timing should be for these vortec heads. Mine likes 18 degrees for some reason. One thing for sure, I really love the MSD breakerless distributor I installed last month. It really makes tuning the advance curve fast and easy.
Anyway, I'm headed to a local dyno here in Houston to tune this new combo next week. This will be my first trip to a dyno so I'm not sure what to expect. I'm looking forward to getting to the track to see how much time I've wacked off my 1/4 mile times, that's the true test. I'll update yall after the dyno run next Thursday.