young old car guy

Hoping someone out there can provide me with some good information for my situation. I have a '68 442 with a 455 from a '68 Tornado. The engine has been completely torn down, cleaned, tested, decked and honed and bored 60 over. The engine has all new parts, no expenses spared. Most parts came from Mondello. With my current setup I'm using ported aluminum heads, an offey intake, a HEI distributor, and a hydraulic roller cam with a 560/565 lift @ 239/249 & 110 lsa. Compression comes in right around 10.5:1. All this being said my first question is how do I determine what RPM my engine should idle at? Mind you this a fuel injected engine, so it will idle at the same RPM in gear and out. Right now I have the idle set at 750 RPM. If the need for vacuum dictates the RPM, then that shouldn't be an issue since I use a vacuum pump for my brakes. Question number two is in relation to question number one... what RPM should I set the initial timing at? This is an issue for me since the computer compensates for the RPM drop off the second I disconnect and plug the distributor vacuum. The spec card for the cam says that it likes about 16-18 initial timing. The engine sounds wicked with a lopey 750 idle, but is that ok?

PS, Since I don't know all the variables that go into determining what a car should idle at I thought that I might mention that I do run 93 octane with a true octane booster, a 160 thermostat, and some pretty cold ngk plugs.


PSS As an afterthought, when I adjust the distributor the computer compensates immediately for the change in RPM, so to advance the timing I rotate the distributor clockwise, correct?


Thanks in advance

cutlassefi

It's the IAC that's stabilizing the idle when you do anything at all to it.
Who's ECM is it? ProComp? It should idle fairly well at 800 or so, even in batch. Has to be in batch if you're running an HEI, unless you have a crank trigger as well. It obviously only does fuel?

You'll need to hook up to the ECM in some way, hand held, laptop etc. to set your parameters. Hows it run otherwise?

young old car guy

Thanks cutlassefi for the reply. The efi is by FAST. If I understand your question correctly, there is a signal generator connected to the tach side of the HEI. This is a tbi system not a port injection, sorry I neglected to mention that earlier. I understand that the idle air control motor is controlling the idle and is compensating once the vacuum advance is gone by disconnecting from the distributor. Allow me to clarify... on a carbureted system once you disconnect the vacuum line from the distributor and plug it, the idle drops down; this is the idle that you set initial timing by. My problem is that I don't really know what my base idle for my cam/engine setup should be, plus my idle doesn't drop like a carb once I pull the vacuum from the distributor. I'm afraid I'm setting the initial timing at the wrong RPM. If I set my initial idle at 750 RPM vs say 950 RPM is the initial timing setting going to vary much because of the mechanical advance of the distributor or this too low of an RPM for mechanical advance to kick in? Long of the short I don't have a reference to go by set my idle speed and hence the initial timing. Any ideas?

Thanks

young old car guy

Guess I neglected to mention in my last post that I'm concerned about this because I'm getting some detonation around 2500-2700 RPM, under light to moderate pedal, then its gone, hence the 160 thermostat, premium gas, octane booster, cold plugs, and a somewhat rich air fuel mixture.

Thanks

rustyroger

Maybe the timing curve needs to be reset to give less advance at midrange engine speeds to cure your pinging problem, or setting up a bit less initial timing might help.
What idle speed is recommended for your cam?, your particular setup will have its own best idle speed being a very non stock engine. Fast enough to idle without stumbling and keep decent oil pressure but not so fast sitting in traffic is annoying is what to aim for IMO.

Roger.

oldcutlass

My suggestion is to set your timing @ 34-36* BTDC all in by say 3000-3200 rpm, and let your initial fall where it may. Then set your vacuum advance to around 50*, it possibly can go higher or lower depending on detonation or surging. 750 rpm is not really that hi of an rpm for your setup. Just set it where the idle quality is best in gear.

turbobill

Generally speaking the best "initial advance" depends on valve event timing and compression ratio. Stock engines tend to like 5 to 10 degrees. With a cam like yours 15 degrees is probably a good starting point. The recommended 16 to 18 is good. Just make sure the engine will hot start at 18 degrees. If it won't, you'll have to custom tailor the distributor for less initial, and then have 15 or more degrees at idle speed

Total advance is dependent upon several factors as well. Generally, a total advance of 36 degrees is a good starting point, stock or modified. The "hotter" the cam, the sooner (or lower RPM) you want that total all in. 2000 RPM is a good starting point for you.

As for the vacuum advance, this is the icing on the cake. 10 to 12 degrees in the vacuum can is all that's usually needed. As you manifold vacuum will be lower (because of your cam) than something with a milder cam, you'll have lower vacuum at idle and very light load/low speed conditions. An adjustable aftermarket unit is what's needed. A stock vacuum can will be unsatisfactory with your cam.

Desired idle speed depends on how fast accesories must run and how tight your torque converter is (for creep and idle manifold vacuum). The "wicked idle" is normal for a cam such as yours. If 750 RPM seems ok, than that will work. Higher idle RPM's will give you more manifold vacuum to work with for vacuum accesories and the vacuum advance can. There is no "set" engine idle RPM.

Getting the timing curve and fuel mixtures right under all conditions will take experimentation to be optimal with your combination.

garys 68

Your detonation at 2500 means you have too much advance there and the ecu is not capable of compensating with A/F ratio. Without the ecu controlling spark, you're going to have to retard timing by changing the curve. Disconnect the vacuum advance and determine your timing at 500 rpm intervals. Pay close attention at the 2500rpm range. You can change total timing with a bushing swap and the rate of advance with different springs.
Youo might want to posty this over at LS1tech or pro-touring. They have efi sections and almost certainly someone with a similar setup.

young old car guy

thanks for all the repies. I'll double check, but I believe all my mechanical is in by 3200 RPM. I'll pull the vacuum off the distriutor, plug it and rev to 3200 RPM record the current timing and adjust accordingly, reconnect the vacuum line, check for 50* again at 3200 RPM, I'll also record where my timing is in 500 RPM increments before and after adjustment. This way if I adjust my timing backwards if you will, by checking timing at 3200 RPM I don't really have to worry about what the base idle needs to be to set the initial at. I'm praying I don't have to re-curve, I know how much of a pain that can be, hopefully playing with cruising air flow to my hearts content will help.

cutlassefi

Go ahead and set your cruise advance for 50 degrees with the vacuum advance like he said. Then ask him if he's going to chip in for new pistons.
Obviously don't do that, the other info was better, but you may need to slow your timing curve down and maybe even have less total timing, don't assume anything.
More info next time would have been nice as well. Contrary to popular belief that FAST tbi has its limitations, you're going to find out what they are pretty quickly.

oldcutlass

I bet 50 will be really close with his setup, I've seen it go as high as 55.

cutlassefi

I'll bet you lunch it's not.
My point is don't tell people to dial in that much advance just because it worked for you, unless you want to be responsible for the internals of their build.

garys 68

First get your mechanical advance set. Then you might want check what the vacuum advance characteristics are by hooking up a hand vacuum pump and recording the advance at varios vacuum levels.
After that you can decide if you have too much mechanical contributing to detonation, then change the curve to come in later with heavier springs. Or if that looks ok, you can change the vacuum advance with an adjustable to provide less advance.
One other thing, check the reccomended engine coolant temp with the efi system. At 160 it will most likely go into closed loop, but might not be optimal for your setup.

cutlassefi

This system is almost always in closed loop. It will revert to the previous fuel table/calibrations everytime you start it, then correct from there if needed. If it doesn't ping when cold then you can fatten the cruise air/fuel once it's warm. They come set at about 14.0:1 or so for cruise and idle and about 12.5:1 for wot. Set it to 13.5:1 or so at cruise and see how it runs but my guess is you have an overly aggressive timing curve or amount.

Let us know how you make out.

FIRST 442

I have a very similar set up but with a 362 olds.
I also have the FAST set up and had a lot of timing issues.
I had to put the lightest springs in my distributor, this helped but i still had problems.
I was never able to get the motor to run right with the vac. advance hooked up, it would sputter and run like crap with it hooked up.
FAST has some posts on their forum relating to this , check it out.

cutlassefi

All the more reason to buy a system that does spark next time. But people still tend to not look past the end of their nose.

Whatever.

garys 68

I think you have it backwards.
The light springs will give more advance earlier, likely to increase detonation.