20v 4age Rev limit

[mulkers]

My bro has recently gotten an 86 with a 4age silvertop 20v, with what i assume is a pretty conservative rev limiter at 7000rpm. It is stockish, save for larger injectors, an EMS ecu, MSD outboard coils, ram tubes, and an exhaust.

I am after the factory rev limit, and recommendations for a higher rev limit, as it seems very restricted, and still pulls very hard.

Cams and head work will be done shortly, and the limit will be changed then, so i was enquiring as to what was a safe, and higher rev limit.

Cheers

[Roundy]

i might be wrong but i think the rev limit is somewhere in the vicinity of 7800 - 8000

[TooF]

the n/a 16v will happily spin to 8k im pretty sure the 20 is around the same,

[The Last Streetfighter]

My 20V ST rev limits at just over 8k bog stock.

Not sure what it revved to before the speed sensor fix as I did that at the same time I got the Tacho cluster.

[adamaw11]

I think mine used to limit at 8200, but my tacho might have been slightly off all along. my 16v also seemed to show just over 8k iirc

I reckon 8500ish would be an acceptable limit with cams and headwork.

[Sam_Q]

from what I hear its 7500 without a speed sensor input and 8000 with

[psychofox]

With a stock engine I woudn't bother taking it much over 7500rpm. It's certainly not making any more power....max power on a stock ST is around 6800-7000rpm Set the rev limiter to 8000 and don't worry about rod bolts letting go.

[-GT-]

Mine climbs all the way to the 7800 limiter, definately past 6800-7000. Fletcher, surely yours did to?

Blacktops are 8200rpm.

But why does it have bigger injectors in it if it's stock? Anyway, 8000rpm would be suitable, for after cams and headwork i remember someone with racing experience saying in a thread on here that late model 4age stock bottom ends should be fine for 8500rpm with just a good balance and cleanup. I think it was that they started stretching stock rods at about 8800-8900?

Don't take that as anymore than a recollection of someone else's opinion though, i can't find it now, but i'll keep looking.

[The Witzl]

A correctly wired silvertop 20V 4A-GE has a factory rev limit of 8200rpm.


Without the SPD signal to the ECU (speed sensor), the rev limit is reduced to 7800rpm as the ECU thinks you are "free-revving" the engine.


I know this as i tested it personally on Finney's 20V once i finished the conversion.

[JP]

I've had the same experience as Witzl on both the AE101 and AE111 20V swaps I've done.

You get a premature revcut with the speed sense wire disconnected, with it connected it revcuts around 8200

[-GT-]

Actually i think you've told me that before Karl, sorry guys
Can you remember which wire that is? ie colour, where it comes from? Anything to help me find it easier when i go to connect it?

[The Witzl]

Purple wire with a white trace. (V-W)

All of the EFI AE92 cars already had this wire going to their factory ECU (you'll find it in the area behind and below the ashtray).... so it's just a matter of attaching this wire to the 20V ECU, and Bob's your mother's brother.


Look.. i even have a picture!! This is the original 16V 12-pin ECU connector, which i am re-pinning to suit the 20V ECU pinouts for same connector. The SPD signal will be on this connector, as clearly seen.

[-GT-]

So it's coming down from the dash/speedo cluster? Sweet, thanks Karl.

[The Witzl]

yup
Coming down from the dash

[Blind Kid Seeks]

just digging up an old thread for fun.....

Witzl... can you confirm, my AE93sx did have the purp/white wire at the ECU, that now i have plugged my Purp/white SPD sense wire into the 20v ECU in the SPD pinout, that all is well and should now be recieving a signal to raise the RPM cut...

perhaps my Tacho is out.. still seems like theres a 7800 rpm cut.....

will have a closer look at the wiring again.

[JP]

the auto ecu's have a slightly lower revlimit than the manual ECU's. The 16V violet/white wire is he 4 pulse per revolution speed signal which works fine when pinned to the 20V ECU's speed signal pin.

[-GT-]

That being said, i've noticed on occassions (and i think much more frequently after first connecting it, less so now???) that mine still rev cut occasionally at just under or around 8k, seemed a couple of hundred rpm short. Mainly 1st and 2nd gear, but i'd get caught out by it hitting the limiter a bit earlier than expected or it seemed to cut at different points from one shift to the next. Does seem to have stopped doing that and maybe i rely more on my ear these days too.

I did think this could be lag in the tacho indicating a bit less than actual revs as i've definitely seen my tacho indicating way less than my ears and limiter are telling it's doing - say after a big couple of blips on a downshift when the tacho's swept right up twice then in gear and full throttle from 7k or so - tacho has still been at 7,7-ish when it's definitely 8+ and confirmed with the limiter.

That's very occasionally but an example of what i'm talking about but exaggerated - finally getting around to my point, maybe it is actually at 8,2 but your tacho was lagging a little and only looked like just on 8? Check your engine codes, if there's any issue with the speed signal you'll get the code for it. If not, you're at an 8,2 limit. Does it hit 8,2 some of the time?

[BLK_20v]

Pretty sure that "any" code on the ecu will drop your rev limit. Also what ecu do you have?

Rumours are that the b/top 6spd has a slightly lower rev limit in first

Manual Silvertop - 8200 Limiter (Confirmed personally)
Manual Blacktop - 8400 Limiter (Confirmed personally)
Auto Silvertop - ???
Auto Blacktop - ???

If you are worried about tacho lag, hold it on the limiter, it won't hurt it if the engine is warm.

[dnegative]

My brothers would spin to 8200, had a microleb so somebody picked that number. Never had any issues

[BLK_20v]

I've ran one at 9000 without issues for months.