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-   -   Does a stock 930 have a rev limiter? (http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/373552-does-stock-930-have-rev-limiter.html)

Mark930 10-22-2007 07:48 PM

Does a stock 930 have a rev limiter?
 
I've got an 86 930 completely stock, I've been autocrossing it and have had it up to 7000 rpm's about twice a run and have still not hit the rev limiter if there is in fact one. I usually run in first gear for the whole run and run between 3000 and 7000 rpm's, will these high rpm ranges damage the motor?

F350Lawman 10-22-2007 09:47 PM

I have a rev limting rotor in the distributor, I believe they all do. It will cut out around 6800-7000 (according to the tach). I try to avoid hitting it though. It will happen very rarely, maybe a 2nd gear wheel spin or hard uphill 2nd gear pass (once).

If you are running 7K often, you are heading for some BIG repair bills. JMHO

sand_man 10-23-2007 03:08 AM

I have my crank-fired ECU (Electromotive XDi) rev limiter set to 6,500 RPMs.

Honestly, I'm not sure if the stock dizzy and/or CDI box have a rev limiter. I know that the MSD 6AL CDI box (a common replacement when the Bosch unit goes down) has a rev-limiting feature. Back when my '87 was bone stock, I was accelerating hard from second to third, and before I could make the shift, the crappy OEM rubber centered clutch disc disintegrated, and the tach needle went all the way as the engine lost it's connection to the tranny and just free-revved!

If you intend on seeing regular high RPM exchanges (especially if extended), at a minimum you'll need ARP rod bolts. The stock rod bolts have been commonly called "cheese". On a more track oriented engine (not sure if that applies to Auto X), race valve springs and retainers are a common change.

Obviously, the rod bolts can be changed without having to split the crankcase, but while you've got the engine out and in pieces, terrible urges take over, and you become a human avalanche tumbling down a slippery slope.

sand_man 10-23-2007 03:14 AM

For the occasional and typical short burst, or the owner manual advised spirited run, you should be fine. What I described above, in my other post, is more of a regular and extended scenario...

equality72521 10-23-2007 03:20 AM

Quote:

Originally Posted by F350Lawman (Post 3547004)
I have a rev limting rotor in the distributor, I believe they all do.JMHO

Don't bet on it though, the rev limiting rotor can easily be replaced with a non rev limiting one.

NathanUK 10-23-2007 12:16 PM

When changing to an MSD the stock rev limiting rotor has to be replaced with a non limiting one as it can overheat & burn out.

The problem with high rpm is the stock rod bolts as Sandman suggested.

Rev limiting.
http://67.129.153.73/CGv2Production/...gs%5C04030.jpg

spuggy 10-23-2007 04:39 PM

Quote:

Originally Posted by sand_man (Post 3547120)
If you intend on seeing regular high RPM exchanges (especially if extended), at a minimum you'll need ARP rod bolts. The stock rod bolts have been commonly called "cheese".

...

Obviously, the rod bolts can be changed without having to split the crankcase, but while you've got the engine out and in pieces, terrible urges take over, and you become a human avalanche tumbling down a slippery slope.

Heh.

+1 on the ARP versus factory rod bolts. sand_man's spot on there.

However, discussion on the engine rebuilding forum indicates that a stretch gauge is vastly preferred over torque or angle measurement methods, for accuracy. And you would have to split the case for that...

Also probably worth noting that the Turbo Carrera owner's handbook has a specific warning:

Quote:

Maximum speed of 6,000 rpm should not be exceeded for normal driving

Increasing engine RPM to 6,700 rpm is only permissable for short periods if needed for quick acceleration
78 and up, the CDI does the rev limiting is my understanding. But the "6800" mechanical limiting rotors can cut off quite high.

I know it's Auto-X and you're trying to save a shift, but 7,000? Power's falling off a cliff on the stock motor by then, surely?

David 10-23-2007 04:47 PM

It's been a few years, but I vaguely remember hitting my rev limiter during an autox at about 7200 rpm.

wcc 10-24-2007 05:00 PM

I would say yes that a stock 930 has a rev limiter. It's controlled by the CDI and not by the rotor.

JFairman 10-24-2007 06:24 PM

The CDI cuts out at 7200rpm and when it comes back on large flames come out the exhaust...

...pretty dramatic orange flash of light in the rear view mirror at night.

NathanUK 10-25-2007 01:55 PM

Woudl it matter how many wires the CDI has or did they all cut?

JFairman 10-25-2007 03:20 PM

Mine has a permatune that was in it when I got the car so I don't know...

I did hit a rev limiter accidentally while accelerating in first once at night as I described and my overboost switch is not hooked up so it wasn't that.
I'm not sure if it was 7000 or 7200rpms where the ignition cut out... it happens too fast.
I've read it is 7200rpm.

I should add, mines and '87 930 and it does not have a rev limiting rotor.

It does have B&B headers and single out muffler, K27 7200, 1 bar spring in origonal wastegate, Garretson halfbay intercooler and Powerhaus group B cams that are probably timed later than I like for a street car and DP935 air dam with large B&B front center oil cooler.
Powerband is 4500rpm to 7200rpm with no let up.

All that was in it when I got it.

I have a new K27 HFS sitting here waiting to go in along with Andial SC330 cams, new rockers, and a Tial copy wastegate.

spuggy 10-25-2007 03:45 PM

Quote:

Originally Posted by NathanUK (Post 3552423)
Woudl it matter how many wires the CDI has or did they all cut?

My 6 pin Bosch came with the '77 S tub. It doesn't cut at all, becaise they expected a rev-limiting rotor in the distributor. Apparently.

My '78 distributor didn't have a rev-limiting rotor - because the '78 CDI boxes do the rev limiter thing. Apparently.

See any potential danger here with a 915 box in stop-go traffic that suddenly clears after two miles of crawling? That rebuild 1,000 miles later cost me as much as it did to buy the car.

I have a rev-limiting rotor now, you can take that to the bank. It cuts off kinda high for my taste - but I'm running ARP rod bolts these days...

NathanUK 10-26-2007 09:12 AM

Ddi you break the tranny and the engine all in one go ?

spuggy 10-26-2007 06:25 PM

Quote:

Originally Posted by NathanUK (Post 3553860)
Ddi you break the tranny and the engine all in one go ?

Didn't break the tranny as such, but when it was opened to be refreshed and have an LSD and some WEVO bits fitted, it was found to have pre-existing issues from a long hard life and prior rebuilds (it was likely the original box) and was pretty much a lost cause - especially considering a mag-cased 915 wasn't an ideal choice anyway.

So Mike (MBEngineering) built up an alu-cased 915 he tweaked to suit the application.

NathanUK 10-28-2007 09:51 AM

Im guessing you could see the two shafts were trying to get away from each other?

spuggy 10-30-2007 04:12 AM

Quote:

Originally Posted by NathanUK (Post 3556740)
Im guessing you could see the two shafts were trying to get away from each other?

The bearings had been spinning in the intermediate and diff cases, yes. And the holes were elongated apart, yup. But I'm told that, on a mag case 915, the diff cover is also a cause for concern.

So I got a WEVO bearing retainer and a WEVO billet diff cover from our host (who can special-order anything from any of their regular suppliers even if not in the PP catalog, you just need to provide the part #), and Mike Bainbridge opened that puppy up.

There were also no dog teeth(? think that's what they're called) left on 1st, which explained why speed-matching and double-declutching didn't help one jot trying to shift into 1st when moving, and no bits of metal in the case - it probably had happened a long time ago.

Box had been gone through once or twice before, most likely, Mike found some non-factory parts in there... The odo shows 237,000 the car was odo-exempt in WA state and it wasn't working when the PO got the car...

The 5th gearset was an interesting mid-blue colour. Figured that oil slosh under boost on the track probably accounted for that - or maybe it got run out of oil a decade or two ago, who knows?

Given that it was a mag case and that so much of it was distressed, sourced a '86 alu-cased 915 with an oil cooler in need of a fettling and fitted an internal spray bar kit, WEVO bearing retainer, 65/40 LSD and tweaked the ratios (taller 2nd and 5th).

Couldnt' use the WEVO diff cover, because the factory oil pump fits under there, but the late, factory alu cover is much stronger than the early mag case part anyway. It would have been nice to use the WEVO part with the 930 bearing though...

NathanUK 10-30-2007 01:23 PM

Sounds good now. Not sure why you wanted a higher 2nd though. 1st to 2nd spacing seems fine in my 3.2 carrera, not sure I would want them further apart.

From what I can see in my '83 915 the side cover seems fine & the opposing shafts would seem to be the problem. My stock retaining plate came loose...
What would be good in that box is if a pump was strong enough to pull any loose dog teeth into a filter and keep them there until the box is rebuilt. I wonder if the swarf from the dog teeth damaged a bearing or two of mine.
Since my rebuild so far so good using the Wevo retainer & K-nuts.

A930Rocket 10-30-2007 02:33 PM

My 87 didn't appear to have a rev limiter any where (dizzy or CDI), but maybe I never took it to 7200? Now that I have my MSD6AL, I have my shift light set at 6000 and the rev limiter set to 6400.

timc 03-25-2008 10:41 AM

Quote:

Originally Posted by wcc (Post 3550676)
I would say yes that a stock 930 has a rev limiter. It's controlled by the CDI and not by the rotor.

According to the wiring diagrams for the 86, there is a speed sensor under the drivers seat, that shuts off the pumps just over 7k.


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