expected idle?

[Virg464]

Just curious as to what idle I can expect to achieve with the following set up. Right now I have it at 950-1000 rpm at operating temp, doesn't seem to want to go any lower, but I haven't really got into tuning yet. I just installed a MSD 6AL to work with the MSD distributor and my super digital timing light (HF special) doesn't like it. The initial timing is at 16 BTDC

400 block (4.375 bore)
RPM alum heads (large chamber 82 or 83 cc?)
JE pistons #131183, dome height .350", approx 10.5:1 CR
Comp Cams 23-713-9, hyd roller, Dur In/Ex 292/300 (242/248 @ .050), Lift In/Ex .549/.544, Lob Sep 110, Int Cent Line 106
Holley 750 (4150), DP4B Intake

Never had a set up quite like this.

 

[68 Sport Satellite]

It's auto trans or manual? Sometime a 727 Auto wants a slightly higher idle if the torque converter is not loose enough with high enough stall.

 

[T Brashears]

What’s the vacuum at idle? And yes that cam will probably not be happy with a stock converter. Chrysler idled some engines at 900,it works well for me.

 

[Geoff 2]

I would put the idle somewhere between s**house & awful......
Below is a warning from Erson cams about excessive duration with the BB Chrys. The 350-400 Chrys engines have the highest rod/stroke ratio of all the big blocks......meaning they do not tolerate a lot of duration at lower rpms.

 

[Geoff 2]

That cam will need at least 30* at idle [ yes, 30*!!! ] & probably closer to 45* for best idle.

 

[Virg464]

It's auto trans or manual? Sometime a 727 Auto wants a slightly higher idle if the torque converter is not loose enough with high enough stall.

727 with an FTI converter (3600 advertised stall)

 

[Virg464]

What’s the vacuum at idle? And yes that cam will probably not be happy with a stock converter. Chrysler idled some engines at 900,it works well for me.

I will throw a gauge on it and find out

 

[Virg464]

I would put the idle somewhere between s**house & awful......
Below is a warning from Erson cams about excessive duration with the BB Chrys. The 350-400 Chrys engines have the highest rod/stroke ratio of all the big blocks......meaning they do not tolerate a lot of duration at lower rpms.

View attachment 1740354

This is what I'm working with, but for my edification what would be the upper limit of duration for a mopar big block?

 

[AR67GTX]

This is what I'm working with, but for my edification what would be the upper limit of duration for a mopar big block?

242/248 is not there, but it’s within sight of max for a street runner.

 

[33 IMP]

I would be happy with a 1000rpm idle, in gear, and live with whatever results in neutral/park. 1200-1300 wouldn't bother me at all. I'd expect it.

 

[68 Sport Satellite]

That cam will need at least 30* at idle [ yes, 30*!!! ] & probably closer to 45* for best idle.

View attachment 1740355

that total timing at idle is the combination of initial timing combined with added vacuum advance timing. If vacuum advance is disconnected, initial will never be set that high.

 

[Virg464]

I should have added this is not intended to be a street driven car, 1/4 mile at a time. Sorry for that omission.

that total timing at idle is the combination of initial timing combined with added vacuum advance timing. If vacuum advance is disconnected, initial will never be set that high.

I'm running a MSD pro-billet distributor, so there's no vacuum advance (adjustable mechanical), I have it set up for the second quickest advance, and the limit bushing is set for 18 degrees more than initial. I'm still in the dark as to how fast this set up will want the advance to come in and how far past the initial advance I can go. As of right now theres a slight hesitation when I crack the throttle, but I think that may be due to the cam that's on the carb accel pump? Other than that the motor winds up VERY fast.

 

[33 IMP]

I have a race direct connection tach drive distributor in mine, with the factory curve in it.
The curve is there, strictly for ease of starting (imo). Full advance is in at a fast idle. I set the total and forget it.

 

[Joske2]

I have a 505 with 10/1 compression and a Hughes 246/250 @050 109 LSA and have 48 degrees timing at idle, vacuum included.
it will idle at 900 in gear, but i prefer to have it at 1000, and 1150 in neutral, so i have have a bit more fan speed for cooling at idle, and a bit more oil pressure.

 

[Geoff 2]

^^^^^^ Joske2 gets it.....

 

[forphorty]

Just curious as to what idle I can expect to achieve with the following set up. Right now I have it at 950-1000 rpm at operating temp, doesn't seem to want to go any lower, but I haven't really got into tuning yet. I just installed a MSD 6AL to work with the MSD distributor and my super digital timing light (HF special) doesn't like it. The initial timing is at 16 BTDC

400 block (4.375 bore)
RPM alum heads (large chamber 82 or 83 cc?)
JE pistons #131183, dome height .350", approx 10.5:1 CR
Comp Cams 23-713-9, hyd roller, Dur In/Ex 292/300 (242/248 @ .050), Lift In/Ex .549/.544, Lob Sep 110, Int Cent Line 106
Holley 750 (4150), DP4B Intake

Never had a set up quite like this.

Is this a stock stroke 400 or is it a stroker?

 

[Virg464]

Is this a stock stroke 400 or is it a stroker?

stock stroke

 

[Virg464]

I have a 505 with 10/1 compression and a Hughes 246/250 @050 109 LSA and have 48 degrees timing at idle, vacuum included.
it will idle at 900 in gear, but i prefer to have it at 1000, and 1150 in neutral, so i have have a bit more fan speed for cooling at idle, and a bit more oil pressure.

How far does the timing advance off idle? All in at around 2500 rpm? This is way past anything I've dealt with before. I've nudged the timing twice so it's at about 20 - 25 degrees adv right now and it seems to be happier than before. I have to get a light that will work with the MSD ignition to really nail down the timing. I appreciate the info.

 

[Geoff 2]

Virg,
I suspect your engine will be happiest with about 40ish degrees at idle. [ Advance the timing to 40* at idle & you will see what I mean ]. A 440 I built with slightly smaller cam [ idle timing is all about the cam.....] idles at 42-44*. This is probably too much for WOT, where 32-38* is reqd. The fix is quite easy. You use a dist with an adjustable vac adv. Get rid of the useless MSD dist & get a cheap Mopar dist from Summit that has an adj vac adv. The vac adv is connected to manifold vacuum [ MVA ]; that means, it is active at idle. The VA is load dependent, & drops to zero @ WOT. So if the VA unit adds 22*, you would set the initial [ static ] to 20-22*.
The Mopar dist can be used to trigger the 6AL.
Until you get the idle timing correct, you will never get optimum idle quality, vacuum & tip in performance.
I could give heaps of MVA success stories, here is one...

 

[Joske2]

How far does the timing advance off idle? All in at around 2500 rpm? This is way past anything I've dealt with before. I've nudged the timing twice so it's at about 20 - 25 degrees adv right now and it seems to be happier than before. I have to get a light that will work with the MSD ignition to really nail down the timing. I appreciate the info.

Centrifugal is fixed at 35, and it pulls 12-13 with vacuum, so low throttle position always 48degrees.
Before i had a Progression ignition system, so much easier to experiment with different settings.
On low RPM, so up to 2500RPM, it liked 48 degrees best, highway speed, 3200 to 3500RPM 55 degrees was best.
Thats why i have now 48 always, since the Progression Ignition broke down twice, so went back to a Firecore.