Degree-ing a roller cam & establishing pushrod length

[HighwayThunder]

Aftermarket Cam Ignition Timing

I installed a hydraulic roller cam in my 390.

Should the ignition timing be set to the factory specs for a stock cam?

If not, how does one determine where to set the timing?

Cheers,

[simplyconnected]

This post looks identical to one you posted on another thread some time ago. Your engine STILL isn't tuned?:

The manual for the 390 engine has tables for ignition timing, but that assumes that the engine has a factory cam. My cam is aftermarket (Comp Cams FE XR282HR-10).

Comp Cams tech support could not specify optimal ignition points.

Do the stock timing specs apply to the new cam profile?

The Ford manuals only apply to OEM parts. There is no way Ford could possibly anticipate someone would put a 282 degree duration cam in one of their engines.

Your particular cam has very little horsepower at idle speeds. That affects torque converter stall speed (stock converters will bog down the engine) and distributor centrifugal advance (as well as carb settings), etc.

It's very important, whoever works on your Ford engine, understands FE engines. Chevy builders have a difficult time to the point where some quit or overcharge to cover 'learning' costs. So, find an experienced FE engine build shop, one that have done many dozens of FEs. That's why your cam company couldn't help.

Since you have little power at low rpms, your distributor needs to advance much later than stock settings. There are many more considerations like; weight of your car, what fuel you are running, compression ratio, what rpm range you normally run at so you operate in the peak range of torque, etc. When you choose a cam, this should not be a 'blind' consideration but an experienced choice for the service of this engine. - Dave

There are three timing factors, Initial Timing, counterweight timing in your distributor and vacuum timing.
You have dramatically changed your camshaft torque curves. They happen at a much higher RPM, now. Is your transmission an automatic or manual shift? If an automatic, did you buy a stall converter?

Stall converters are a 'must have' if your camshaft has a long duration. All OEM converters lock up at relatively low rpm because even at idle speeds your stock engine still pulls hard. A stall converter lets the transmission slip until it gets to a high rpm to ensure you're in the power portion of the torque band. Stall converters come in different 'lock up' rpm ranges. The higher the converter is allowed to slip, the more costly they become. They also add heat from all that slip.

So stock converters on hot cams act just like you're letting the clutch out too soon. Even if you give a 'hot' engine more gas, the converter will bog the engine because the cam produces very little torque at low rpm. So, 'big cams' are designed to launch at high rpm and remain there through the gears.

Now, you're asking about ignition timing. Look at the torque curve for your cam and match your 'all in' timing to it. You can see why Comp Cams could not suggest your timing points because you have a custom build. An FE engine builder who is familiar with this cam will know where to time the engine. - Dave

BTW, we should move this thread and combine it with your cam timing thread.

[HighwayThunder]

Ignition Point Redux

I'd forgotten that I’d already asked the Ignition Point question on the forum.

The engine has been “tuned up” insofar as it’s been adjusted to run smoothly. But the car has never been driven.

I didn’t know that a long duration cam requires a torque converter that matches its power band.

The light at the end of the tunnel just got farther away.

Cheers,

[simplyconnected]

I'd forgotten that I’d already asked the Ignition Point question on the forum.
The engine has been “tuned up” insofar as it’s been adjusted to run smoothly. But the car has never been driven.
I didn’t know that a long duration cam requires a torque converter that matches its power band.

The light at the end of the tunnel just got farther away.

Cheers,

I took all your symbols out for the benefit of those who didn't understand your post. Your encription only confuses those who already have difficulty with English. Please don't do it again.

Engine building is not just a bunch of expensive parts to be thrown together. Your powertrain is a system that needs all the components to match a specific goal.
I don't know what you thought a hot street cam would do with OEM drivetrain parts but that is a question you should ask BEFORE buying parts. Start with a goal, then match the engine characteristics with the transmission, rear end gears and tires. If you don't, the weakest part WILL break (or the parts simply won't be compatible). - Dave

[scumdog]

My 55 F100 has early hi-comp 429 and it's fitted with 780cfm Holley. Edelbrock Torker intake, Isky 272 cam and headers. I run 2.75:1 rear-end gears. The torque converter is stock factory item.

The truck will smoke the 305 X 15 tyres easily on take off.

But it is at its limit regarding the cam and convertor, it might be quicker in the quarter mile if I had a convertor with a higher stall- speed.
My 2 Kiwi cents worth!

[simplyconnected]

My 55 F100 has early hi-comp 429 and it's fitted with 780cfm Holley. Edelbrock Torker intake, Isky 272 cam and headers. I run 2.75:1 rear-end gears. The torque converter is stock factory item.

The truck will smoke the 305 X 15 tyres easily on take off.

But it is at its limit regarding the cam and convertor, it might be quicker in the quarter mile if I had a convertor with a higher stall- speed.
My 2 Kiwi cents worth!

Tom, I don't recommend anyone go much over 260 degree duration for a street engine. Again, for a street engine. Add another 20 degrees and you're fighting the throttle and brake at every light because it won't idle smoothly. The street fouls plugs and generally makes a mess out of a racing engine. For highway driving, ok. Just so the rpms are up there in the torque curve. - Dave

[scumdog]

Tom, I don't recommend anyone go much over 260 degree duration for a street engine. Again, for a street engine. Add another 20 degrees and you're fighting the throttle and brake at every light because it won't idle smoothly. The street fouls plugs and generally makes a mess out of a racing engine. For highway driving, ok. Just so the rpms are up there in the torque curve. - Dave

Yep Dave, from my experience I was pointing out you can run a decent cam but I was also pointing out it was the ragged limit as far as I was concerned.
The cam I have has caused no issues except for a staccato exhaust beat at idle and need for more choke on first start-up.

I forgot to add I also have roller-rockers and a Pertonix ignition fitted to a Mallory twin-point with no vacuum advance (it was all I could get in NZ at the time!)

But a 2,500rpm stall-speed torque convertor and/or 3.7 gears would probably provide a more exciting take-off!

[simplyconnected]

Right Tom, I agree. It's not the loping but undulations tend to make idle speeds impossible for anyone not very familiar with the car.

A 3.77 rear end would give you loads more torque at the rear wheels and a 2,500 rpm stall converter would be perfect.

Have you got an idea of what your 'all in' ignition advance is?
Initial timing + distributer centrifugal weight + vacuum advance = All In Timing. - Dave

[HighwayThunder]

Torque Converter research

Thanks to everyone for the helpful comments.

The factory manual specs the stock C6 converter to stall at 1800-2000 rpm. The new cam's power band starts at 2200 rpm.

Sought advice from the guy at the shop that rebuilt the car's C6. He recommended a converter with a stall of about 500 rpm over stock and to check with Summit as a source. Also, he advised that the converter could be installed by just pushing back the trans (without complete removal), making it possible to do in my driveway.

Summit offers a B&M Holeshot Converter, stall at 2400 rpm, direct fit to C6.

Comments, other recommendations?

Cheers,

[scumdog]

Thanks to everyone for the helpful comments.

The factory manual specs the stock C6 converter to stall at 1800-2000 rpm. The new cam's power band starts at 2200 rpm.

Sought advice from the guy at the shop that rebuilt the car's C6. He recommended a converter with a stall of about 500 rpm over stock and to check with Summit as a source. Also, he advised that the converter could be installed by just pushing back the trans (without complete removal), making it possible to do in my driveway.

Summit offers a B&M Holeshot Converter, stall at 2400 rpm, direct fit to C6.

Comments, other recommendations?

Cheers,

No more than 2,500rpm stall speed for a regular street car - otherwise thare's too much heat build up from the 'skip' plus gas mileage suffers unless you constantly drive with the revs higher than the stall-speed.
Again my Kiwi 2 cents worth!

[simplyconnected]

Now wait a minute...
If you buy a cam with a "Basic Operating RPM Range of 2,200-5,800" (these numbers are right off the page), why on earth would you run OUTSIDE these numbers??? Isn't that why you bought this cam in the first place?

So now here we are changing stock parts to accommodate the new service. Yes, 'service'. This engine is intended for a specific service and it ain't 'getting groceries'. It is a street racing cam that needs at least 9.1 compression ratio, headers and a stall converter to match the cam.

This cam will NEVER render good gas mileage by any stretch. It creates NO power below 2,200 rpm then it unleashes all your engine has above that. A 2,500 rpm stall converter is a MINIMUM for this cam. I would look for something a little higher. Yes, 'slip' creates heat but you obviously need the converter to slip.

What rear end gear are you running? - Dave

[scumdog]

Right Tom, I agree. It's not the loping but undulations tend to make idle speeds impossible for anyone not very familiar with the car.

A 3.77 rear end would give you loads more torque at the rear wheels and a 2,500 rpm stall converter would be perfect.

Have you got an idea of what your 'all in' ignition advance is?
Initial timing + distributer centrifugal weight + vacuum advance = All In Timing. - Dave

Dave, as mentioned my Mallory is an old race-type one without any vacuum advance, I have a Pertronix unit inside it and run an equally old Voltmaster coil. From memory I have 12 on the crank and 24 on the dizzy. (The motor doesn't like low grade gas!)
The reason for the 12 degrees initial is to TRY to compensate for the lack of vacuum advance when cruising. When racing I used to knock it back to 9 degrees or so to spare the motor getting hammered to death.

Fave,

[HighwayThunder]

How it works?

OK, so I'm trying to visualize how this works...

Stock cam stall speed is 1800-2000. Fast idle is 1500, warm idle is 500. Even at fast idle the car should remain motionless. Give it a little gas, rpms increase past 1800, the converter "catches", and the car starts to move.

With the aftermarket cam and a 2400 converter, the rpms have to increase past 2400 for the converter to "catch".

Is it correct that at 2400 the acceleration curve of the tire rotation will be steeper than it would be at 1800, resulting in tires "breaking traction"?

BTW, rear end is stock 3.00:1.

[simplyconnected]

Close, but not exactly. Even at idle speeds your car still pulls forward, doesn't it??? You let your foot off the brake at a light and the car rolls forward. The converter is slipping as it should because a torque converter takes the place of a clutch. When the light turns green you raise rpms and slowly let out the clutch. The whole time your foot depresses the pedal the clutch is slipping. Let your foot off and the clutch stalls, or locks up. If your engine speed is too low, the car will buck. The same happens with an automatic.

...All OEM converters lock up at relatively low rpms. At idle speeds your stock engine still pulls hard but the converter lets the transmission slip until it gets to a high rpm to ensure you're in the power portion of the torque band. Stall converters come in different 'lock up' rpm ranges. The higher the converter is allowed to slip, the more costly they become. They also add heat from all that slip...

...Even at fast idle the car should remain motionless. Give it a little gas, rpms increase past 1800, the converter "catches", and the car starts to move...

There is a drastic difference between 'slipping' and 'locking up'. At fast idle (1,500 rpm), your car is pulling HARD. If the converter was locked up your engine would labor and buck.

Torque converters still pull at low rpms, otherwise your car wouldn't move, but they slip, like 'feathering' the clutch for a smooth start. Once they get to 'stall speed' they lock up.

...With the aftermarket cam and a 2400 converter, the rpms have to increase past 2400 for the converter to "catch"...

No, the converter still pulls while it is slipping. At 2400, the new converter locks up.

Do you know why we use rear end gears like 3.90:1 on a street or strip machine? 3.0:1 is more for highway driving or the Bonneville Salt Flats, where we have all day to reach top end speed.

.. Is it correct that at 2400 the acceleration curve of the tire rotation will be steeper than it would be at 1800, resulting in tires "breaking traction"?..

I have no clue as to what 'the acceleration curve of the tire rotation' means.