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[lozzzzzz]

Hi folks, thanks again for my warm welcome a few weeks back. 

I'm wondering what people think would be a safe rev limit to set my ECU to (aftermarket management in a Scimitar).  The engine is very ported in a number of areas, with full on three branch exhaust manifolds, and a very unrestrictive inlet track, the torque curve will have moved up the rev range.  So higher revs will yeild a good hike in power (fingers crossed).   But I really don't want to risk damaging it at all, it needs to be reliable and bullet proof. 

I've searched the forum and found that folk seem to think the MV6 limit is about 6750rpm with rumours of the police cars going to 6800-6900rpm (this was a police engine). 

I guess I'm wondering if anyone has heard of a standard bottom end coping with 7000rpm all day, or conversly has anyone heard any horror stories after a remap and slight raise in limiter. 

My current thinking is to go with a solf cut (retarded spark) at 6750 and a hard cut (no spark) at 6800.

Thanks for any comments you could leave.

[cem_devecioglu]

Hi folks, thanks again for my warm welcome a few weeks back. 

I'm wondering what people think would be a safe rev limit to set my ECU to (aftermarket management in a Scimitar).  The engine is very ported in a number of areas, with full on three branch exhaust manifolds, and a very unrestrictive inlet track, the torque curve will have moved up the rev range.  So higher revs will yeild a good hike in power (fingers crossed).   But I really don't want to risk damaging it at all, it needs to be reliable and bullet proof. 

I've searched the forum and found that folk seem to think the MV6 limit is about 6750rpm with rumours of the police cars going to 6800-6900rpm (this was a police engine). 

I guess I'm wondering if anyone has heard of a standard bottom end coping with 7000rpm all day, or conversly has anyone heard any horror stories after a remap and slight raise in limiter. 

My current thinking is to go with a solf cut (retarded spark) at 6750 and a hard cut (no spark) at 6800.

Thanks for any comments you could leave.

I dont think the standard bottom end will have problem with 7000 RPM.. its the coolant and oil cooling issues that will create problem before everything ..and besides whole day is really a tall order imo

[lozzzzzz]

Well this sounds promising, the cooling system is very much simpler in the Scimitar, with a nice alloy radiator and a massive 19 oil cooler with larger bore pipes to take care of the oil cooling. 

[cem_devecioglu]

Well this sounds promising, the cooling system is very much simpler in the Scimitar, with a nice alloy radiator and a massive 19 oil cooler with larger bore pipes to take care of the oil cooling.

this is good news..

imo its good idea to see oil (very important) and coolant temperature say at 6000 rpm after 30 secs.. (hot engine - outside temperature and speed important) then gradually increase the rpm(250 rpm)  and time (15 secs+ ) and watch the temperatures .. if oil or coolant quickly goes up stop the test..   

[cem_devecioglu]

and I must add I dont think  it will be necessary to stay at the rev limit for long times because even in races it will hardly happen..you must shift or you will loose time.. 

[cem_devecioglu]

during those kind of tune ups , you must be able to measure-listen engine knocks, but dont know how as I'm not a tuner..

[2woody]

Omegas are particulalry poor in terms of bottom-end reliability. Caused mainly by high coolant temperature selected by GM in the quest for lower emissions. You too will have the high coolant temperature ( and hence high oil temperature ) unless you've managed to change the thermostat for a lower setting. And that's true despite the external oil cooler I'm afraid.

Also, unless you've changed the cams, your torque peak will be no further up the rev range than a standard engine. The shape of the power curve ( at the top end ) is dictated by the cam timing, whilst the lower parts of the rev range can be boosted a bit by the dual-ram gubbins.

no-one has ever seen a different setting for Police spec cars, although we're aware of the rumours.

If you're able to go beyond the current engine speed range due to cams, etc. then I'd advise the following :-

a new set of big-end bearings.
a sump clean-out ( pay particular attention to the stuff you'll find inside the oil pick-up )
a lower coolant mass temperature
full-synthetic oil to prevent degraded performance with the high coolant temperature
an external oil cooler ( already done in your case )

and then I'd explore the territory up to 7000 rpm.

what does your inlet system consist of ?

and which fuel injection are you using ?

[2woody]

and I should have asked - is it 2.5, 2.6, 3.0 or 3.2 ?

[cem_devecioglu]

checking the net, ideal engine oil temperature range seems to be between 82 and 98 Celcius..

  when I hammer miggy for few minutes in summer against hills (and it doesnt mean full rev) it quickly passes 100 celcius even with a new thermostat.. so its easy to estimate oil temperature exceeds 100 celcius even in normal operation .. 

[cem_devecioglu]

checking the net, ideal engine oil temperature range seems to be between 82 and 98 Celcius..

  when I hammer miggy for few minutes in summer against hills (and it doesnt mean full rev) it quickly passes 100 celcius even with a new thermostat.. so its easy to estimate oil temperature exceeds 100 celcius even in normal operation .. 

so fully synthetic will be definitely necessary if you are going to rev it for prolonged periods

[cem_devecioglu]

checking the net, ideal engine oil temperature range seems to be between 82 and 98 Celcius..

  when I hammer miggy for few minutes in summer against hills (and it doesnt mean full rev) it quickly passes 100 celcius even with a new thermostat.. so its easy to estimate oil temperature exceeds 100 celcius even in normal operation .. 

so fully synthetic will be definitely necessary if you are going to rev it for prolonged periods

if I remember correctly , Omegatoy solved the turbo miggies  problem with changing to the fully synthetic but cant remember SAE number..

[Kevin Wood]

My current thinking is to go with a solf cut (retarded spark) at 6750 and a hard cut (no spark) at 6800.

That's about what the standard ECU does, IIRC, so that would be a safe starting point IMHO.

As said, though, standard cams will peak at about 6K RPM so little benefit in going any higher. If in doubt a dyno pull will reveal where it's peaking.

Of course, with a less restrictive intake setup it might now respond well to cams that allow higher revs but there isn't exactly a wealth of experience here on what you can get away with so start small and work your way up.

3.2 has a forged crank so might be a stronger bottom end but, if, as 2woody intimates, the problems are with lubricating the bottom end it doesn't really matter how strong you make it. 

[lozzzzzz]

2woody,

The modifications include

The inlet, will have two cone filters hidden under the front nose cone (don't like the boy racer look) for a cold air feed from infront of hte radiator.  Followed by two large bore ducts striaght to the ported (but not enlarged) throttle bodies.  The the plenum and ali runners have been matched, the plastic base plate has been ported a lot to take it out to the same cross sectional area as the the rest of the inlet runner system (there was a large venturi here, great for tumble at low RPM, but aweful for high end flow).  The the ports in the head have been lightly ported, the conbustion chamber left alone.  the exhaust ports have been a little more agressively taken out and the lump for introducing air has been completely removed, then the ports taken out to match the new hader plates.  The exhaust headers are full 27" by 1.5" primaries, followed by two 2.5" SS exhausts that remain separate right through (no CATS obviously). 

I see what you're saying about the cam timing, but I'm still expecting the peak to shimmy up the revs a little due to less retriction at high flow rates (read high rpm). 

I wasn't aware it had a bad rep for bottom end relaibility.  I need it to be tough in keeping with the rest of the car, I need to be able to bounce of  the limiter and not worry.  When I asked the questions I was expecting an answer like "the big end bolts stretch at 7k" or something similar.  But its cooling thats the issue. 

I've bl**dy forgotted which thermostat I chose when I got a new one, but I would imagine I went for the hottor one 

The oil should definatly be cooler though as the new oilstat will force oil to the cooler at a (lower) temp (not yet) chosen by me

The ECU is a Canems jobby, with a MAP sensor added.  Oh yer and its a 3.0 MV6, Its late one I think 2000 ish, the grill is part of the bonnet, rather than the bumper. 

Cem,

I think I will change to fully synthetic after its fully mapped and all the teething problems are sorted. 

I fancy going the last little bit and getting cams and enlarging the throttle body, but it costs so much, the cams are over £300 and the throttle body is a lot too, and its a bit beyond my lathing skills for now

But I'm keeping my fingers crossed for a good power figure, 250 would be ace

The Canems ECU folk did a project capri MV6 (3.0) and got 238hp with the only modifications being a different inlet system upstream of the throttles and different exhausts downstream of the (rather shocking) log manifolds (oh and one of there ECUs). 

Thanks for your help with this one folks, I think with all that in mind I'm best sticking to the standard limiter. 

[2woody]

Followed by two large bore ducts striaght to the ported (but not enlarged) throttle bodies. 

You appear not to be using the lower inlet change-over valves (the bagpipes) - this will cost you a lot in low-down torque.

Are you using the upper change-over valve in the plenum top ? - if not, then you'll cost yourself a lot of mid-range torque.

I see what you're saying about the cam timing, but I'm still expecting the peak to shimmy up the revs a little due to less retriction at high flow rates (read high rpm). 

you might be right - it'll be interesting to see - maybe a hundred revs or so ?

I've bl**dy forgotted which thermostat I chose when I got a new one, but I would imagine I went for the hottor one 

There is only one - that's part of the problem. GM chose a relatively high "normal" coolant temperature.

But I'm keeping my fingers crossed for a good power figure, 250 would be ace

Can't wait to see the dyno plot - it's been a while since anyone did any decent tuning work on one. Are you going to take a standard 3.0 as a comparison ? ( dynos can differ 15 hp from one to the next )

[tmx]

Not much they will go bang! V6s aint about high RPM's thats what VTEC/VANOS is for