Tuning help on a 489CI FE

[Tony Fritz]

First time posting on this forum but not new to FE's. I have some questions for some experienced tuners with my 427 (489). My combo is: 489 CI stroker 427, Genesis block, Scat rotating assembly, JE domed pistons estimating 12:1 CR, Edelbrock MR heads gasket matched, Comp Cams HR cam 622 lift 252 & 262 Dur @ .050. BT MR 8V manifold with Carl's repro BJ & BK carbs, MSD 6AL ignition with MSD Pro Billet Dist. 3.89 rear gears and Tremec TKO 600 5 speed. 1st thing I noticed is what I consider low vacuum at idle....steady 6-7 on my vacuum gauge. Is this normal with an 8V and this cam? I also didn't have very good control of the idle. Carbs had 60 main jets and standard .020 secondary butterfly opening. I changed main jets to 64, put in 3.5 power valves instead of the 6.5 and closed the secondaries.This seemed to help a bunch. I can now set the idle at 950RPM and have some control. The second is the car had a very bad low RPM surge (1500-1800 RPM)when at cruise. I was able to get most of that out with advancing the timing and timing curve adjustments. I am running 18 initial and 39-40 total all in at 3200 RPM's. Does this sound like I am doing the right things? Car now drives pretty good but still not as stable at low RPM cruise as I would like. Is this because of the pretty aggressive cam or am I missing something? Thanks for any help and/or suggestions.

[blykins]

Pretty hot cam....it's not gonna want to be lugged around. 

The advertised duration for that hydraulic roller lobe is going to be very high.  You will have lots of overlap (with those lobes, over 100° of overlap).......no vacuum.

[jayb]

I agree with Brent that the low idle vacuum is due to the fairly radical cam; you are probably stuck with that.  My experience with timing on a cam like that is that as the RPM varies, if you have the timing coming in too soon it will then exaggerate the variations in idle speed.  I think your initial timing is about right but with those heads I don't think I'd run the total much past 36 degrees.  I'd probably put a different bushing in the MSD distributor to limit your centrifugal advance to 18 or so, and maybe go a bit heavier on the advance springs.  You probably don't need all your timing in by 3200 RPM because with those cubic inches you've got plenty of power at that speed.

Speaking of power, I assume you are happy with the full throttle stuff?  Sounds like a very nice combination...

[cjshaker]

I agree with Brent and Jay. That vacuum seems about right for the cam. I have about the same vacuum in my 427 with a 260/264 cam, stock stroke though. You can get away with a low cruise RPM like that in 1st or maybe 2nd gear, but under a load in 3rd (or 4th, you didn't mention auto or manual) the engine won't like it much and will likely surge a bit. Also, on the idle, with an MSD distributor, I've found that if the springs are light, or there's any slop in them with no advance, the weights can bounce or move around a bit and contribute to an erratic idle. Once a little RPM is engaged, and the springs steady under tension, that usually goes away. You can check this at idle by watching the timing mark on the balancer and see if it's moving at all.

Also, I'm a bit confused why you had to jet higher? Usually, if anything, these carbs usually need to be jetted down. And since the jets really have no bearing on idle quality, if it made a difference in idle, it's possible the primary butterflies may be opened too far, making the problem even more noticeable. When you shut off the secondaries, did you open the primaries more to gain back your idle RPM? If so, you may be exposing the transfer slot and that won't help any.

My engine is also very sensitive to idle adjustment, but with a lot of playing around, I've found the "sweet spot" where everything seems to work together to keep it at or around 850 RPM. The mixture screws are very sensitive combined with the idle speed adjuster; just a small adjustment makes a big difference. Kind of the nature of the beast when trying to get a fairly radical cam to play nice at low RPM.

[My427stang]

I think your curve is still a bit slow.  I would leave it at 18 initial but have it come in at 2700-2800, I also think your total is high if you have that much compression.  I'd be limiting it to 36-38

As far as the carbs, PVs don't affect idle, so although it could have been rich at idle due to a bad PV, the tight PV won't change idle.  They only open when the boosters have airflow.  However, assuming they fixed something, I am not sure if the carbs have a vacuum port like a regular 1850, but if they do (off the primary metering block) I'd check and see if that is alive at idle.  You likely have the primaries too far open and its idling on transition fuel, then when you need it at 1800 cruise, there isn't the transition fuel available the motor wants.

The recurve and carb adjustment should help drivability down low, and limiting the total should keep it from peppering the plugs. 

I will say, that cam is big, but so is your motor.  Do you know installed centerline and LSA as well as advertised duration?

[blykins]

From looking in lobe catalog, I think adv is like 318/329. 

[Tony Fritz]

According to the Cam Card adv dur is 314 & 329 so Brent you are right on. The Lobe Separation is 112.0 and the installed center line is at 108.0. As far as the carbs I tried a little richer jet thinking the surge may be from a lean condition. It had no effect on the surge. Easy to switch back. I wasn't sure if the PV affected idle so with that low vacuum I changed the PV's to 3.5. Knowing now that the PV doesn't effect idle should I go back to the stock 6.5 PV?
I agree with the timing suggestions and am quite sure the stock light silver springs were causing the surge by allowing the timing to vary at low RPM. I went to a heavy silver spring and a blue light spring (chart "B" on the MSD sheet) to keep the timing curve steady but after looking at the MSD sheet again it shows all in at @ 3500-3700 RPM with the blue bushing. I can experiment with some other combo's if you think the timing should be all in sooner. I will change bushings to limit total timing to 36-38. As far as WOT power.....well I haven't quite got there yet as it only has about 200 miles on it. But I can tell you "leaning" on it pretty hard through the gears it pulls like a freight train.
Thanks to all that have responded. I really appreciate some knowledgeable in-site if for nothing else to confirm my thinking.

[cjshaker]

I'd keep the power valve that you have in it now. It should be right for the vacuum. As for jetting, you'll just have to figure out what the engine wants by either using an Air/Fuel ratio gauge, reading plugs and/or having someone follow you to watch the exhaust. With that much displacement, it may like the heavier jetting. I can't say for sure.

Jay can comment better about the timing curve because I have no experience with aluminum heads and modern chambers.

[blykins]

Agree with Ross on where I would put the total timing and where it comes in at.  Edelbrock chambers aren't the most modern, but the extra squeeze should make it more efficient.

I would also use an AR3910 plug with that compression.

[nhsohc]

Just to add my useless thoughts:
Had exactly the same issue w/ the white car after installing the cammer.  First, had to change the power valve in the stock BV Holley from the 6.5 (stock) to a 3.5, again due to low idle vacuum.  You could see the gas dribble out the boosters at idle as the 6.5 was part open.  Second, the surging at 50-55mph road speed w/ a 3.5 rear w/ 28" tires was very annoying.  Tried messing with the timing and got nowhere.  Finally added 3.7 rear gears and it was at least drivable.  Drove to Ohio with 3.7's.  Final solution; used 4.56 gears.  Just don't drive much over 55 on highway.  Stock Ford cams & stock pistons; just the overlap and duration is such that drivability is tough.  Would be great on a superspeedway! (As designed).

Car still stuck in garage!
Thanks

[Tony Fritz]

Brent,

It has NGK V-Power 8's in it now. How do those compare to the AR3910's?
BTW, are you going to Beaver Springs next month for the FE Race & Reunion?

[blykins]

Not an NGK fan, so not sure.

No, I won't be there.

[My427stang]

I'll just chime in on the PV statement. 

You are almost certainly not surging from a lean condition, at least not related to PVs or main jets. At your rpm in 4th, even if you are on the boosters, the vacuum is likely high enough to keep a 6.5 closed.  If you are in 5th, then you likely have a bit more load on the engine and you could have some PV fuel, but going as low as you are, it's likely not opening, and of course a PV opening too early would make it rich, not lean

I do not believe in the 1/2 idle value for PV selection at all, it's.  It was an easy way for Holley to recommend PV sizing, but as you get lower in vacuum, or much higher, it makes less sense. If it were me, I would want the extra fuel under load to make sure it doesn't go lean under load.  6.5 may be early but really you need to look at vacuum at cruise, and at light roll on. Idle is almost irrelevant. You may even find that the 3.5 is opening and closing during the surge, or it may not ever open until you really hammer it.  I have even seen rich surging.

My hunch, stab a 5.5 in them and forget it, and focus on throttle blade setup and make sure the IABs are clean then work on  idle and transition circuits second.

[CaptCobrajet]

I didn't see it mentioned above, but you might also want to run through the valves and verify that the preload is okay.  If it happens to have a few valves cracked open, it will do all of that funky stuff you describe, have low vacuum, etc., and it will clean up at rpm and you won't really notice it.  Try adjusting to zero depression of the lifter, and then turn the adjuster to achieve .050-ish preload.  If you have short travel lifters, they should be set to about .005 off the bottom cold, which can be tricky if they are pumped up now.  You can do it with the same idea as the regular stuff, only adjust for .025 depression after the "slack" is out.

[Tony Fritz]

Blair,

I have been through the valves a couple times just to be sure. It has Crane #355532 HR lifters with T&D street rocker set up. I don't think these are "short travel" lifters?? I started with 1/2 turn preload but would hear slightly noisy lifters when warmed up. I attributed that to the aluminum heads increasing lash when hot. Measured the adjuster travel and set at 0.60 preload cold which is just over one full turn. Seems to be OK.....runs a little rough when cold but smooths out after 45-60 seconds of running.