I hear ya. I know I could simply eliminate vac adv and lose the pinging forever, but the benefits of running vacuum advance is something I wont give up on easily. Better mpg and cooler running temps is worth it to me.

Correct!

 

George, I'm pretty confident that I can tune this condition out. I just have not got around to it yet. It could also be related to the stumble that I often get at both idle and cruise speeds due to the 7530 Team G. I've played around with squirter sizes, but not acc pump cams. I can tell you AFR does lean out briefly, so I attribute this to a combination of a brief lean condition and vacuum advance.

I'm very happy with the cam so far. Your welcome to check it out if your ever down this way.

 

I've been happy with an 11.5:1 406 small block on 91. I tried to optimize the details. AFR heads, zero deck with reasonable quench, 243-251 @ .050 hyd roller, 110 LSA installed with two degrees advance, full time cold air, 160 thermostat. The first ignition curve I tried was very happy in the first four gears but it did not like being in fifth below 2400 rpm. I slowed the curve and on flat ground you can now get below 2000 rpm in fifth.

 

Well, it's official; I do NOT properly understand the factors that determine detonation... I thought I was starting to get it...

Unless the really low advance @ 2 degrees and the super low temps are staving off detonation...


To me this just sounds like a car that would drive down the streets like a diesel- powered by compression-based detonation with no spark required...


Adam

 

What? Ok, I think this is a huge potential learning moment for me.

How the heck does vacuum advance create cooler running temps and better MPG? That blows my mind...

I'm planning an EFI install this winter and from what I can tell that means I have to give up distributor vacuum advance and either move to a dual sync electronic distributor or an electronic distributor AND a crank sensor; does that mean when I make the swap I'll have higher engine temps and lower MPG?


I honestly don't understand why vacuum advance works or how it works or how these benefits are provided...


Adam

 

The two degrees of advance refers to the relationship of the cam to the crank. It is very common for a sbc cam to be installed with four degrees of advance for optimal "overall" power. By taking out two degrees of the advance (installed two degrees advanced) the intake valve closes later in the cycle. This reduces cylinder pressure at lower RPM. Less cam advance typically trades low RPM power and gains a bit at high RPM.

 

The advance in an EFI distributor is controlled by the computer. It is also monitoring vacuum and can adjust timing to what is set in tables for each driving condition. You have way more possibilities with EFI.

 

Thanks for that; I feel better now. I played with a dynamic compression calculator last week and saw what happens to dynamic compression when you retard the cam to crank timing like this (reduction of dynamic compression and thereby reduction of detonation risk). --YES! I still kinda get the basic fundamentals! Score!


Adam

 

I have the same intake and 650 DP. I cured my off idle hesitation using a 0.040" squirter on the primary side, pink cam #1 hole. I also found that increasing initial advance helped alot and I'm at 22*, 10* mech'l and 8* vacuum. Engine purrs like kitten at 1000 rpm idle with a retro HR 280/286 with 0.560" lift, 10.5 scr.

 

I'd be interested to know your timing curve. At some point I would like to address my locked out timing, but for now it just flat out works. No stumble, or bog what so ever. Easy starts hot or cold, and no ping at any road condition. The down side.....I lost a few mpgs and at the present time get maybe 12 mpg if the wind is in my favor.

In comparison my 355 got 17 mpg with the same gears, but running a 2000 stall. Now I run a 3000 stall with the 3.70 gears.

 

Has anyone in the 11-1+ club experimented with water/methanol injection ?

 

Yes, in the past on N2O drag cars and presently on a turbo car. Both of them use windshield washer pumps. Set to spray into the air plenum the same time as the N2O came on or the boost went over a set limit.

I don't think that it is practical for a street car.

Years ago some outfit was selling a water/meth container that bolted on top of the intake. It was simple, heat from the motor caused it to boil. The lid had a 3/8th rubber hose that you plugged into full manifold vacuum like your carb port. Under motor vacuum it would boil at lower temps. It was designed to add the most vapor under highest vacuum like cruising down the free way. My buddy swore by it in his hot rod Dodge.

 

Thanks.
I have a NOS Holley unit in the box, but no plans for it. I think better "fast burn" style combustion chambers have harshed the allure of these kits.
I could see them in certain truck applications being useful.

 

Forum: I posted on something similar a while back.
Say an engine was on the border line of detonation.
Wouldn't CAI, lower temps on fuel, oil and water make the difference?

Not sure how much difference this would make?

R

 

George,
If Tony has not change my cam from his engine then it is not a Solid Roller, It is hyd roller. It is not 250 duration, it is smaller, and it is in the 10 to 1 compression ratio sir.

 

I was thinking Diehard was also solid roller. Only relatively few of us on the forum actually have 420+ ci small blocks motors

 

I'll dig into the distributor to see where I ended up. I agree with Kubs about the advantage of having the timing controlled by a programmable computer. I have an MSD Digital distributor in the 11.5 car. IIRC it gives 20 different mechanical timing curves and ten vacuum curve by turning two dials. I knew setting up the ignition curve would be tedious with this car and today's gas. I have an MSD Boost retard box in a 6-71 car with 9.5:1 compression. I like that better because I can create any (even non-linear) curve I want. As I mentioned the curves that worked well in the first four gears were too much for overdrive. I bet if higher octane was available I could speed up the curve and pick up some mileage. I do pay close attention to feedback the car is giving and never overload it at low RPM. I'm pretty sure that somebody could hurt this engine if they did not know how to drive a high compression set up. This would be an appropriate case for drive by wire that would not allow overly aggressive throttle application in high load low RPM conditions.

I built a 10.7:1 377 for a friend with similar set up. It had something like a 3.4 ring an pinion with the same .64 OD (mine's a 4:11). We could get down to 1500 RPM in fifth with his. By 1800 you could ease in the throttle and start pulling quite well. His cam was similar but 112 LSA vs my 110 LSA, installed with four degrees advance vs my two degrees. His also had a Performer RPM Air Gap vs my Victor JR with a 1" spacer.

I think his typically gets 2-3 more MPG than mine. I get about 14 consistently. I'm in the Ozarks and the hills hurt the mileage and are a factor in the ignition curves. I've tuned cars that are pretty happy right up until we try to climb a hill in OD.

 

I think those factors can make a difference as well as spark plug heat range. On iron head engines I have found deburing sharp edges in the combustion chamber can make a difference too.

 

Regarding spark plug heat range; you're saying that switching to a cooler spark plug could drop temps a bit and reduce engine knock risk, or would a hotter spark reduce knock risk because you'd get a faster burn?


Adam

 

Related question: When you've got a high compression engine that's right on the border of knocking like this, does EFI help to reduce knock risk?

When you are at cruising speed and only push the pedal slightly you're thinning out the AFR and can get that knock- but an EFI is supposed to keep a constant configured AFR AND EFI injectors maintain the same level of fuel atomization at high and low air velocities, unlike a carb, right?


Adam