Timing questions

[Scorpio]

I have Dave's (Dave Ray) Small Body HEI dizzy on my SBC. Mech spring set blue/ silver. Has Crane 9960-1 adjustable vac. Dave recommended initial at +12, vac on at 22-24 and full mech (vac off) at 36. Got the 12-23 at 700 RPM no problem. My question is with full mechanical (vac plugged). I hit +36 about 2500 RPM but it keeps climbing leveling off about +44 at 3000+ RPM. Just put in new engine and builder wants total timing in 32-36. Backing full mech down to 36 would drop initial to 4?! I'm brand new to timing so I may not grasp this fully. Any advice is welcome as I don't want to screw up this new performance SBC. BTW has MSD ignition so can't use modern dial type timing lights. I used old school timing light without advance dial. MSD tech says this only way to time their ignition systems. Reason - Multiple spark at low and extended spark at high RPM confuses the modern lights.

Other forums indicate Dave has instruction to alter mech advance however when I contacted him (long story short) and asked for more information to help me understand his recommendations he basically accused me of challenging his authority and cut me off. Seems according to him Crane instructions to do this are wrong so I am at a loss to know whether or if I should try to modify the max mechanical advance to achieve Dave's recommended 12-36 off vac initial & full advance.

 

[Fox80]

It sounds like Dave (never heard of him) has to much mech. advance built into the dist. You have to look to see if he uses bushings on the advance stops to set the total mech. advance, if not then someone else or him in my opinion needs to re-set the total advance. All dist.'s have a stop for retard and advance movement on the base plate, cheap ones (ie, GM performance, Petronix, E-Bay specials, etc) use a peg just stuck in place and are not really adjustable by the end user, better ones like MSD or Mallory have bushings that come with them that increase or decrease the size of the pin in turning increasing or decreasing the total advance. You are looking for 22-26 degrees total advance is usually what most dist. seem to work good on for all around motors, it sounds like you are getting closer to 32 so you need to lessen the total advance. Now because you are running vacuum its not that critical to get the inital spot on because the vacuum will pull it way up any way at idle or cruise speed. Some guys would set the total advance to 36 and hook the vacuum up and drive it see what it does. However if this were a non-vacuum dist it would idle like crap at 4 degrees, I would get the dist. correct myself because that much total mech. advance is going to be hard to tune around once you start dialing everything in.

 

[DoubleV]

That Dave is one angry man. He'll go off on anyone who limits their mechanical advance by welding the slots and tell everyone the only way to do it is by using the proper weights and center bar...... then not tell you which ones to use because he doesn't know. AFAIK he has never even stated exactly what the problem actually is when welding the slots. I just don't get that guy.

 

[Scorpio]

Thanks Fox80. My story is constantly evolving and I am getting closer. I found a old engine builder that still had a Sun what I call a dizzy spinner. In face, I'm getting 24 for total mechanical advance. He changed a spring because he felt the advance was starting too low and advancing too fast. At the moment, I have 12 initial and 36 total and have the vacuum advance plugged. He also recommended I change metering rods in the 600 Performer and though for what I have an air/ fuel ratio closer to 13 would be good. With the fuel changes, things seemed to be going much better.

I'd like to know if the following makes sense. I spent quite a bit of time talking with a custom car/ engine builder at a local car show this weekend. Since I know very little, anyone who seems to know more is an expert to me. That said, I am a scientist and things he told me made sense -
He strongly avocated getting the vac advance back in the game. And, although most seem to recommend using manifold vacuum, he said in my particular case to take it off the ported side. Unfortunately my new fuel pump may have just taken a dump (TBD this evening) so have not had a chance to experiment with this. He also told me the fellow who just built my 355 configured it worng for my street use. According to him, my 230/ 230 duration cam is 1) too much for my 9.4 compression and 2) great for things like circle track and off shore racing where you want to be happy at high RPM's. He suggested replaing the 280H with a 256H grind (212/219) that would put the power down in the RPM range where I would be happy with the performance. And, among other things, allow me to stop the car when at idle in gear where I currently have vacuum about 4. He went on to say that I would need probably 10-11 compression to be happy with that cam (bigger cams need more compression). My builder selected flat top pistons so I could use pump gas, hence the 9.4. This guy explained that the 9.4 was static compression and, due to the bleed off from this cam, a much higher static compression would be just fine with pump gas since in fact it is the dynamic compression that matters. So, make sense?

Finally, DoubleV must have had some contact with Mr. Ray! I did not but the dizzy from him but did make contact to get info that might help me direct local mechanics on what needed to be done. To make a long story short, when I told a guy who's business is dyno tuninig cars that he had to use a non-dial back timing light (per Dave), this guy challenge me on that and since he did not know me or Dave from Joe Schmoo, I had no credibility. I followed up with Dave to get an explaination for why he had given me that directive and basically he called that guy and idiot and if all I was going to do was ask anyone and everyone just to try to prove him wrong, he would have nothing more to do with me! I responded that I was sorry he thought I was challenging his pronouncement, just needed a way to explain the rationale to the locals. He responded I was on my own and had been consigned to junk mail so not to bother emailing again.

 

[Fox80]

First off I have to say the guy you found with a Sun Spintron is a godsent, however I have never agreed with using stiffer springs/lighter weights to limit the total advance. The correct way is to not allow the plate to move that far by welding the slot or altering the bushing, the reason is lets say you limit the advance by 10 degrees, well springs fail/weaken then what you have is a potential for trouble down the road when you gain the advance back you thought you limited. I have been around this stuff a long time and I have done crap like that before and it almost always bites you in the *ss, send it out and have it welded or install a bushing on the stop pin. DUI ( Davis Unified Dist.) builds amazing HEI's for almost ever app. and can build it to have whatever you want for mech./vacuum advance into it, I have used their stuff on 700+hp circle track motors without an issue, however I like the MSD better if you like to have tuning capability, because they use bushings on the stop pins you can adjust it down the road, with a DUI you get what they build, short of modifying it yourself. This Dave sounds like a dipshit so move on if you choose to buy something else.

Now to the motor questions, the guy you spoke to sounds about right for his advise, I disagree with ported vacuum but alot of my friends disagree with me on it. I have a couple very close friends that build hundreds of motors a year each, one says ported the other says manifold. I say if you want your dist. to react exactly to what your motor is doing you have to use manifold vacuum, but carbs come with ported in them for a reason, it takes some of the radical actions of the dist. out of the equation, and it does make less work out of getting a car to idle smooth on idle. I copied and pasted a very long article that I swear by on here a while back, search for it and read it and you decide what route you want to go.

As for the cam, comp. ratio, I agree with him that duration number is very large for a small street motor assuming you are talking about duration at .050 lift. The reason builders do this is because guys want a motor that "lopes" or some sh*t because it sounds cool, to get that you have to give up low end power for the most part. By having that cam in your motor he is right on that you are causing parisitic compression loss by evacuating the cylinder before complete combustion has happened. Think of it like this a 12.0-1 comp. race motor with a large duration, big overlap, and large valve lift in it may only see 185psi cranking compression, change the cam to something meant for street you may see 230psi because the motor is working more efficient at even cranking speed, 400+ inch race motors don't care what happens below 3,000 rpm's they need the motor to run well at 8,000 rpm so as things spin that fast you have no choice but to keep the valve open longer with more overlap. In my little 260 Olds I used a cam with 206, and 212 duration, with .481 lift, with 110 seperation this helps a little motor build all the compression possible, now that motor is probably done making power at 4,500rpm but its a street motor, hope this helps

 

[84cutspreme]

With engine/cam combo I had a similar issue with vacuum. I originally built my 355 9.8:1 cr with comp cams 12-432-8 cam which had a duration of 230/236 duration and had barely any vacuum and not enough for brakes. I swapped it out for 12-422-8 which has duration of 218/224 and now I have about 14" at idle. I am happy with the performance as well, 1600-5400rpm range and I put 1.6:1 rockers on to give it a little more lift

 

[Scorpio]

Fox80 - I have noticed the controversy rage on other forms on how best to alter mechanical advance and I am still gathering and digesting the various arguments and may someday formulate my own opinion. For now, I was pleased that you generally agreed with the advice I received regarding a better cam choice for my street use - seems I'm following in the footsteps of 84cutspreme in this. Lopy engines always turn my head and, never having one, made me think I would like it. However, I think I am beyond lope in into the so called rough idle mode. My next step is to meet with the engine builder next week when I am back in town to discuss my performance issuses and see if he will agree to remedy this or if we will have to let our dogs fight it out. I hope we can come to a setlement as my recent and only legal battle was very enlightening and at the same time very frustrating/ disappointing. Regards