I have posted about the way my 77 is not performing well after engine upgrades. I installed L98 heads with roller tip rockers, Comp Cam 270H, Edelbrock Performer RPM intake, Holley dual feed double pumper with mechanical secondaries, and 96 Corvette LT1 2 1/2" exhaust manifolds. TH350 with shift kit and 3.70 rear. After all this it was performing bad out of the hole. I had the timing set at 12 then 14 degrees and a total of 36 degrees at unknown rpms I could not see the tach to find out the rpms where. Well today I checked and the timing was set at 14 degrees with the vac advance disconnected and plugged. the 36 degrees total timing was at 4500 rpms. After doing some checking I took the distributor cap and rotor off and the mechanical advance was semi rusted and would not move freely and the vac advance does not work at all. I went to the auto parts to get another vac advance for it but they did not have one. The only one they could get was a borg warner type and it should be in tomorrow. I cleaned up the mechanical advance and got it working freely.Tomorrow I will install the vac advance and get the timing set and I really hope it will make a big difference in the way it performs. I'm going to follow Lars timing info and see how things go. This could be my performance problem RIGHT??? Could this have also caused some of my over heating problems?

 

I think you're on the right track, that could definetly cause overheating, your advance was comming in way too late. It would be better if you get it all in by 2500-2800.

 

I'm thinking it should be there after I install the new vac advance and since I've cleaned and freed up the mechanical advance. I hope it makes a BIG difference on the way it performs out of the hole.

 

You will be amazed! Will probaly need the advance spring kit and the Vac can is rated by how much vacumn you pull at idle. Get the right can to get you 16 degrees advance difference when you plug it in and use the set of springs to have your mechanical all in by 2500 Test run and go with the next heavier spring on one side and test again. Use 2500 as a base line. Some like a little more RPM before its all in. You are running extremely retarded now. Will cause overheating and a lack of power and throttle response not only at idle and low throttle but midrange also. The only time you were feeling the real power your engine has was 4500 and up. You found your problem!

 

So you think I should go a head and get the advance kit for the dist also they had a Mr Gasket one with new weights and 3 different sets of springs. Should i use the weights that come with the kit also? When I first checked the mechanical advance I could hardly move it by hand the weights would move a bit freer but still stiff. This will make my out of the hole better you think?

 

Use your oem weights, pitch the others. Use the Mr Gasket gold springs for HEI.

Chris

 

Right now you have no mechanical advance off idle, no vacumn advance off idle and 12 to 14 degrees initial. Lucky if it can get out of it's own way!
First, is your idle mix set for best vacumn? If so, proceed. Yes, get the Mr Gasket advance kit. Try the two gold springs first. Probably won't need the weights. No matter what, you want your Mech all in at 2500 as a baseline.
Best timing would be if you can get around 18 initial, 18 Mech, all in by 2500, total 36. And the vacumn can that will pull 16 degrees when you plug it in at idle with the idle vacumn your engine pulls.
Check and see what your total mechanical advance is once you get it loosened up and the springs in. I think 20 is standard. If so set initial back to 16 for a total of 36 with the vac can unplugged and hose blocked. If you have any pinging at all back the initial down 2 degrees and check. Run good 93 octane fuel. Get this all right and let us know how it goes!

Edit: Vetteadiction types faster than me.

 

For once I'm starting to feel like things are going my way now! I can't wait to get off work tomorrow and get this done. I was thinking I was going to have to put a different stall to get it out of the hole. I know I could put the gas to the floor and when it started to spin the tire and move the car I would let off the gas with it floored and it did not do nothing until over 3500+ rpms.

 

Different subject but, did the EDL Performer intake fit OK under the hood or did you have to install drop air filter?

 

My intake is a Performer RPM and yest it fit with a drop base.

 

The only place I can put the vac to the vac advance can is from the vac port on the side of the front bowel of the carb. The front base vac is going to the At modulator, the rear base port is going to the brake power booster, and the intake port is going to the PVC and headlights.

 

Check and see if there is vacumn there at idle, if there is your good. You could get a fitting with three ports for the intake or put a tee in your headlight hose if not. Or just try it ported and see how it works. This is going to be somewhat trial and error but your going in the right direction now.

 

Along with the good advice provided by 63mako. You'll see a major improvement and eliminate overheating problem. BTDT.

Also suggest you take the time to read through the sticky at the top of the section on timing. Its long, but well worth the read.

 

Well I picked up my vac advance can and the Mr Gasket advance kit today and installed them (gold springs). Took the 77 out to warm it up and started the timing job. Unhooked the vac advance and plugged it. Set timing at 18 degrees and then set the timing light to 36 degrees and increased the rpms all 36 degrees were in around 2800 rpms but when I took it up to around 3000 rpm the timing was at 38 degrees. So I backed off to 16 degrees and total was them 36 degrees around 2800 rpms. Hooked up the vac advance can to the manifold vac along with the lights and checked the timing again it was still 16 degrees. Took it out for a try and WOW what a difference Like a different car!!!! When I floored it at any rpms I never heard any pinging or spark knock. Can I go to 18 degrees which will give me a total of 38 degrees since I did not have any spark knock? Or NO? Can I change the springs to get it to come it quicker? Maybe try the silver springs? Or are the gold bringing it in the quickest? The springs I took off looked just like the black ones in the kit they were even black. Are the stock springs like the black ones in the MG kit or do you think someone has changed them already? Let me hear back from you all on this and THANKS FOR HELPING ME OUT

 

Dumb question I know, but does this timing adjustment with the mr. gasket gold springs and total timing in by 2,500 also apply to a stock 350, or only to a somewhat worked motor?? I might could squeeze some hidden pep out of my stock 350 with this until I get my new crate?
KC

 

It should help with yours I'm sure. You need to see where your timing is now. As you can see by my post I had problems with the stock dist that could happen to yours also.

 

Well first I want to give a SPECIAL THANKS out to Kevin (63mako) for all the help and taking time to talk to me about timing my 77. Also THANKS to everyone else out there that posted info. I feel I have it nailed down now here is what I found and did to fix it. I changed around all my vac lines to the right locations checked for vac leaks which I found 1 the vac advance line was leaking. Cleaned up and got all the mechanical advance in the dist working found that I had to use only 1 of the silver springs to get my mechanical advance to come in at 2500 rpms When I used 2 of the gold springs in did not fully advance until around 3200 rpms. I also had to replace the vac advance can the stock one was bad so I bought a ACCEL adjustable one. So here iswaht I did hooked up a vac guage to intake port adjusted the Holley to get the highest vac so carb is now dialed in. And this is my final timing 16 degrees initial timing 36 degrees at 2500 rpm and with the vac can 52 degree at 2800 rpms. It was at 60 degrees with the ACEl can hooked up but I adjusted the can to get it back down to 52. It sound much better and the throttle response is GREAT. I did not take it out for a ride it is raining like cats and dogs here. But I'm sure it is going to run like a scalded dog when I do take her out. I may still have to do some fine tuning to the timing if I'm getting any pinging or spark knock. Oh and another plus to it all my headlight now pop up faster than they ever have. Again THANKS to all who posted and Kevin for all the time and extra advice!!

 

Good job! You could stretch out the gold springs a little if you want 2 springs. When the weather clears up, take it for a ride and see what you got. You can always fine tune it a little. If you have any ping back your initial down a little. The L98 heads have fast burn chambers and the 36 all in @ 2500 rule may not apply. Think 32 or 34 is recommended for fast burn heads. You got the basics now. You can run it, make one adjustment and run it again. Never change 2 things at once. You can always go back to where you started. With close to 300 RWHP and 3.70 gears with the 270 cam that thing should launch well. Nice talking vettes with you on the phone, Glad to help out.

 

Yes! Proper timing curve will make a huge difference in any motor and factory specs are not for performance. More for emissions. See the timing sticky at the top of the tech and performace home page.

 

Well I got a chance today to take my 77 out for a ride and it ran SUPER!!!! Foot brake to around 1500 rpms and it was out of the hole like crazy! It turns on right away now I ended up with the timing initial at 15 degrees 35 degrees at 2500 rpms and total of 50 degrees in at 2800 rpms Now it feel strong at any rpms from 1500 to 6000 rpms. It will smoke the tires out of the hole burning them until 2nd gear and leaves around a car length in 2nd and a good squake in 3rd. And it was through all the gears in no time. I'm VERY happy. No spark knock or pinging.