347 Stroker RPM Question

[mirose]

Ok, I have several hundred miles on my car and I am now getting the guts to push the RPM's a bit here and there.

I have noticed somewhere between 5000 and 6000 I start to miss and sputter....which according to some recent posts may be a rev limiter thats in the EFI module that Mass-Flo uses. I just wonder how I can be sure its not a fuel delivery issue, or a clogged fuel filter or whatnot. Under 5,000 rpm I have no issues at all. Any thoughts would be appreciated.

This all being said...the car doesn't come with a "red line" on the tach...LOL So I wonder what people would say is the red line for a small-block ford stroked to 347? Or is it more complicated than that? (probably) I wish I could give you more info about my cam, lifters, valves etc...but I didn't build the engine and the guy that did is a local drag competition engine builder and he said "its my secret unless you want to take it apart and look for yourself...what I put in my engines is what sets me apart from the competition and I don't go telling everyone what my secrets are"

Fair enough, I guess....(so lets not let the thread become a commentary about my relationship with my engine builder )

thanks

Michael

[Gordon Levy]

Realistic rev limits on a hydraulic roller 347 is 6500 rpm's. Depending on cam it could be less.

[Tennessee Tim]

The "red line" will depend almost entirely on the things that your engine builder refuses to tell you. I won't comment on your relationship with your engine builder other than to say that things he's keeping secret can be fairly important to understanding the limitations of your engine. I can understand him not telling anyone what he puts in his own engines, but I have never heard of a builder who won't tell you what he puts in engines he sells.

The "red line" can be determined by a number of things, the most important of which is probably valve float. Obviously, you want the revs to be limited to a speed below that at which the valves begin to float. Where valve float begins depends on all of the things your builder won't tell you.

Valve float is just one consideration, though a very important one. Another consideration is what your torque and HP curves look like. There's no point in letting an engine rev to 7000 when horsepower peaks at 5500 and torque peaks at 4000.

If your rev limiter is adjustable, a decent, safe starting point is about 5500. If the engine still fels like it is pulling strong , keep kicking it up by 250 RPM or so until you can feel the power start to roll off (or you experience valve float).

Tim

[JKleiner]

Originally Posted by mirose

I have noticed somewhere between 5000 and 6000 I start to miss and sputter....which according to some recent posts may be a rev limiter thats in the EFI module that Mass-Flo uses.

Mass-Flo uses the Ford A9L ECU which has a factory setting of 6,250 RPM. That's not to say that it couldn't have been flashed it to a different point but I'd think that's where Chris would have left it unless you requested otherwise.

Jeff

[rick8928]

Ask your builder what his recommended redline is-doesn't require him to disclose his "secret sauce" contents.

[mirose]

Thanks guys...good info all around.

But lets just pretend for a moment it isn't the rev limiter..but in fact is another issue...any thoughts what would be causing this symptom? I think Jeff is right about the 6250 being the set point for my system...I am 99% certain I was getting my first hints of the problem closer to 5500 than 6250...Of course, my tach might not be calibrated perfectly, so its possible that It is still a rev-limiter issue...but lets suppose everything is correct...and I am getting the issue below the rev-limiter cut off....what should I be checking out?

Thanks

Michael

[Bob Cowan]

Originally Posted by mirose

...but lets suppose everything is correct...and I am getting the issue below the rev-limiter cut off....what should I be checking out?

Thanks

Michael

There are three major areas that could be causing your problem.

- First would be valve float. But, assuming that your engine builder really does know what he's doing, that's probably not the case. I would ask the builder what valve springs he used in those Edelbrock heads. If he used whatever springs came with the heads, they might be suspect. But if he replaced them with a quality part, then you can probably move on to something else.

- Second, Fuel delivery. Go to some web sites like Aeromotive, and calculate fuel requirements for your engine. Take a look at your fuel pump, lines, carb, etc. Are you delivering enough fuel to feed the engine at those RPM's?

- Finally, ignition. If you're not making enough spark soon enough, at high rpm's it will break up. If your volumetric efficiency is really high, you don't need as much spark advance. Try advancing the spark timing 3-4*, and see what happens. If it gets worse, try retarding it 3-4*. If it gets better, you can recurve the distributor. Make sure your plugs, wires, and coil is up to the task.

[bbk347]

Red line is not how many RPMs you can actually get from an engine before it explodes (although many people do drive that way... well technically it is I guess!) but like Gordon said it depends on the cam (and heads, intake system/exhaust, ignition, and fuel system) and up to what RPMs the cam is still producing power. When the power drops off, there's no need to spin it any higher. Have a dyno done and the read out will show you where the power nose dives. That's your red line. I bet it's lower then you might think.

[bbk347]

PS: My first build was a 347 and MY redline (not the car's) was under 6500RPMs (about the time I could see my life pass before my eyes!). I had 3:73s in it and things happened very very fast. Like on star trek when they went into wop speed and everything got blury! Half the time I was shifting it just because it was spinning up so fast (and my depends was filling up so quickly) that it was scary! Quite a potent little engine! Enjoy!

[Wayne Presley]

I would pull the plugs, see what they were gapped at. Gap them down to .032" and retest.

[mirose]

Thanks again for the info, guys. I am going to follow up on a lot of this. And, in fact at some point I am going to find an engine guru near me who can spend a few hours going over things and checking out my engine and making sure I'm getting the most out of it, and that its set up properly.

As for follow up, I slowly took it up to 6000, maybe 6250 rpm today and in fact thats really where it started to act up, which is really pretty much what Jeff said was the rev-limit for my unit.

I checked out my dyno sheet, and My max torque was at 4300 RPM (417 ft/lbs) and it went down from there. They maxed the RPM's at 5800.

-M

[frankeeski]

Originally Posted by mirose

my unit.

I checked out my dyno sheet, and My max torque was at 4300 RPM (417 ft/lbs) and it went down from there. They maxed the RPM's at 5800.

-M

Mike, This says a lot. I suspect you were in the first two gears when you nailed the rev limiter. The trick, on the track mind you, is to keep the engine in the max power band while up shifting thru the gears. As you notice, the car start falling flat past 6000 RPM. Shift at 5800 and keep the revs between the 4300 and 5800 mark, when drag racing at the track, and that will turn you the best times. Traction it going to be a big limiting factor as well.

[Danner]

Originally Posted by rick8928

Ask your builder what his recommended redline is-doesn't require him to disclose his "secret sauce" contents.

for me, this type of thing is the strangest idea ever. I want to know exactly what is in my engine, and whatever his 'secret sauce' is, it's probably bull. An engine builder that I would trust would stake his/her reputation on consistent build quality, a deeper knowledge of parts to suggest, and tuning skill. No secrets, just experience and proven ability.

As far as 347 RPM, it all depends on the internals. you can get 9000RPM with solid lifters and a cam to match, but every engine has a bottleneck, and yours probably hits one before 9000. make sure the bottleneck is something that doesn't kill the whole engine if you hit it.

[Dan Babb]

Does the Dyno sheet tell you what your Air:Fuel ratio is at the higher RPMs? Wonder if they stopped the pull at 5800 because your A/F was getting to high or the peak numbers were just dropping and not worth going higher on the RPMs.

If the A/F is ok, then I always thought that there really isn't a reason to go over the RPMs where you're HP numbers are dropping off.

[TAnderson]

ignition. If you're not making enough spark soon enough, at high rpm's it will break up. If your volumetric efficiency is really high, you don't need as much spark advance. Try advancing the spark timing 3-4*, and see what happens. If it gets worse, try retarding it 3-4*. If it gets better, you can recurve the distributor. Make sure your plugs, wires, and coil is up to the task.

What he said... Your problem seem consistent with not enough initial timing.