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Posted by: serge914 Jul 13 2003, 04:02 PM

I went to my first auto-x today. It was quite twisty but there was one long sweeping stretch. On my fourth run a the end of it I took a look at my tach: 7500 Rpm
My engine is quite stock except for a pair of 44 Webers, a midrange scat cam and a Mallory Dist.
How many times can I over rev it like that before it decide to that enough is enough ?
What will give up first, the valve train ?

Posted by: URY914 Jul 13 2003, 04:09 PM

When I over rev I can hear the valves float. The springs aren't able to keep up with the speed of the rocker arms. The power drops pretty quick and I know it is time to shift. I would say the valve train would be the first to break something.
How many times can you do this before something breaks? Good question-no answer. Keep the valves in adjustment and try not to do it.

Paul

Posted by: Bleyseng Jul 13 2003, 04:37 PM

There is no power up there, shift!! Power band is much lower (3500-5000) rpms so stay there and shift for faster times. Get a rev limiter so you don't over rev.

Geoff

Posted by: Part Pricer Jul 13 2003, 04:41 PM

The power band dips shortly after 5,000 rpm. You may have been better off upshifting. However, sometimes that is not the best option.

I installed a 5,800 RPM rev-limiting rotor. Best $14 you will spend.

Posted by: redshift Jul 13 2003, 04:56 PM

7500? What gear?

You must have some stuff done to your topend.


M

Posted by: Bleyseng Jul 13 2003, 05:03 PM

He is probably driving around in second gear at the AX.

Posted by: seanery Jul 13 2003, 05:21 PM

he said he does have a cam, so maybe he does have a little power up there?

Posted by: street legal go-kart Jul 13 2003, 05:41 PM

revving a type 4 engine that high is likely to break a piston ring in a fairly short time
and next would be the piston
you could break something in the valve train first but i doubt it
what kind of fuel system are you using
l jet or d jet run out of fuel at or near the factory redline ,are you downshifting to attain those kind of revvs ?
at any rate

not a good thing without running a counterweighted crank


jt

Posted by: rhodyguy Jul 13 2003, 05:45 PM

will the rev limiting rotor fit/work an 009?

kevin

Posted by: Bleyseng Jul 13 2003, 06:40 PM

Kevin, you should switch out the 007 for a smock disgributor(djet or ljet) as they have a better advance curve =better power. You can order the rev limiter from PP that fits most distributors.

I don't think you will bend a crank, most stock 2.0l run out of revs due to the weak stock springs not fuel. My 2.1 djet dyno a/f runs show plenty of fuel until 6k where I shut it down.
Course the power curve drops off a cliff after 5500rpms.

Geoff

Posted by: serge914 Jul 13 2003, 07:14 PM

I have to apologize to all of you: it was 6500 Rpm, not 7500. My tach doesn't have any number over 7000.
I will try to find a rev limiting device for the Mallory distributor.
Honestly it was feeling like there was still some power over there, in second gear.

Thanks

Posted by: Bleyseng Jul 13 2003, 07:50 PM

Check this dyno chart out to see the torque and hp curves. Not much power after 5000 rpms
Geoff


Attached image(s)

Posted by: airsix Jul 13 2003, 10:38 PM

cam cam cam cam cam cam cam cam cam cam cam cam!!!!!!!!!!
He doesn't have a stock cam!!!!!! That looks like a dyno sheet for a typeIV with a stock cam.
He may have plenty of power at 6,000. Maybe even 6,500. A stock cammed engine is another story.
-Ben M.

Posted by: ChrisReale Jul 13 2003, 10:58 PM

Yea, but with a hot cam that can produce power up to 7000 rpm's comes the need to have rods that will handle the extra stress, and valve train that can also. If he doesnt have all the extra goodies that are needed for the power up high, an engine that blows is in short order

Posted by: Rob Ways Jul 13 2003, 11:57 PM

I have this problem too. You know when you rev it up because the car seems to float as mentioned. Also said, its not a good idea to high rev for long repeated sessions unless you're looking to replace the motor every 10K and you want your driveway to have lots of spots.

Try putting it in 3rd. You may not think you have time to go up and back, but good drivers can do it quickly even in a 914. When you go back to 2nd, you're probably on the brake straight anyway which is a good time to downshift.

Good luck!

Posted by: maf914 Jul 14 2003, 06:54 AM

I don't know if Mallory has rev-limiter rotors for its dizzy, but you can get rev-limiter features with their HI-VI electronic ignition control box. Or with similar MSD or Jacobs boxes. But that's another $150-200!

Mike

Posted by: serge914 Jul 14 2003, 07:29 AM

You are just right. I need more track time to be able to decide when it is better to shift up and down.

I checked with Aircooled.net and they have the Mallory Hyfire VI CDI with rev limiting for $160.
By the way those guys answers tech questions by email on a sunday night