Torque at high revs

[ed_crouch]

Sorry to repeat this, but I have more info now!

Did a rolling road run, and got the power plot. It confirmed what I already though, which is that the engine really doesnt generate much torque over 5500RPM.

Its great from about 2k round to 5000, but then tails off, and theres really no point in going above 5500, cos you'de be better off in the next gear up.

Is this normal, or maybe I have a knackered cam and followers??

NCK engined 390SE, 59k miles, 1988.

Ed.
P.S. 255lb/ft at 4200 RPM, and 227BHP at 5000RPM. Torque is back down to under 200lb/ft by 5500RPM.

[350zwelgje]

I think it is normal, and you still have a great engine (like in envy with my standard 350i). In general RV8s are not supposed to be revy, and the main restriction is top end breathing. You probably have prove of that top end breathing now. Even when the heads are ported to its maximum, they are still restrictive. The heads are the main design limitation in general to get more bhp from the RV8. Think topcats do a new head design. You can try it, but these are very expensive.

Rob

[pwd95]

Never taken my current one over 5k never tried TBH, but the 400SE I had used love to rev up to 6k.

[shadowfax]

238 bhp at 5400 and 254 lbs ft at 4300 I got on the NCK 400 SE

[ed_crouch]

Shadowfax,

Thanks for the comparison: this says to me that whilst peak torques are VERY similar(!), I think your extra horsepower higher up the rev range probably is a sign that your engine develops a bit more top end torque than mine (i.e. your torque curve probably doesnt fall off as quickly after peak torque). Mind you, that might be the extra 100cc...

Ed.

[gsx600]

On the 450 at the last 2 run with the same engine but diferent ecu's

Run 1 (4.0 ecu)
5000 rpm 232 hp max bhp
4800 rpm 260 ftlb max torque


Run 2 (4.5 ecu)
5600 RPM 266 hp max bhp
4800 rpm 260 ftlb max torque

So it would seem my max torque with current cam atc will probably not get above 260 ftlb, but with a decenter ecu might get my majic 300 bhp figure I dream off

[rev-erend]

ed_crouch said:

Sorry to repeat this, but I have more info now!

Did a rolling road run, and got the power plot. It confirmed what I already though, which is that the engine really doesnt generate much torque over 5500RPM.

Its great from about 2k round to 5000, but then tails off, and theres really no point in going above 5500, cos you'de be better off in the next gear up.

Is this normal, or maybe I have a knackered cam and followers??

NCK engined 390SE, 59k miles, 1988.

Ed.
P.S. 255lb/ft at 4200 RPM, and 227BHP at 5000RPM. Torque is back down to under 200lb/ft by 5500RPM.

Ed - it might have had a replacement cam.. those figures look like a stump puller..

Only way to tell is to measure the lift with a dial guage..

Just did mine and at the cam the lift is 0.505 inch

[Wedg1e]

I have yet to see it writ, precisely what cam the 390SE was supposed to have originally. All that's ever stated is 'high-lift' but nobody seems to be able to say what a modern equivalent (eg. 218 etc) might be.
My car now has an RPI RP1 in it which is supposedly a 'fast road hydraulic': it certainly seems to brighten up once you're past 80 or so MPH and/or 3500 rpm.
But it will happily rev to way past 6000 (although I don't make a habit of it)

[rev-erend]

This cam table shows all that's needed really ..

http://www.btinternet.com/~jon.wolfe/kentcamdata.h...

If you have a lot of lift (0.5 inch) and loads of duration .. 300 degrees then it's going to be pretty sports (if the rest of the system matches of course).

[ed_crouch]

Interesting...

Rev, I must admit to being chuffed with the torque figure. I'll have to get me a dial gauge and check it.

Presumably the lifters wont bleed down cos Im rotating the engine dead slow, skewing the result?

Ed.

[shpub]

Wedg1e said:

I have yet to see it writ, precisely what cam the 390SE was supposed to have originally. All that's ever stated is 'high-lift' but nobody seems to be able to say what a modern equivalent (eg. 218 etc) might be.

And the reason is that the 390 more than any other wedge had more engine suppliers/specs etc than anyone else. Some engines were very breathed on while others weren't. Some of the NCK engines had a lot of trickery in them and as for the Andy Rouse engines which were John Eales engines etc etc they had a lot more triockery including slipper rings and so on. What Ed has is about right for a 390. Good for a 4 litre but not the ultimate figures that I have seen. To be honest almost every engine was a law to itself so making any sort of definitive statement would require one for every 390 that TVR made.

[Wedg1e]

shpub said:

Wedg1e said:

I have yet to see it writ, precisely what cam the 390SE was supposed to have originally. All that's ever stated is 'high-lift' but nobody seems to be able to say what a modern equivalent (eg. 218 etc) might be.

And the reason is that the 390 more than any other wedge had more engine suppliers/specs etc than anyone else. Some engines were very breathed on while others weren't. Some of the NCK engines had a lot of trickery in them and as for the Andy Rouse engines which were John Eales engines etc etc they had a lot more triockery including slipper rings and so on. What Ed has is about right for a 390. Good for a 4 litre but not the ultimate figures that I have seen. To be honest almost every engine was a law to itself so making any sort of definitive statement would require one for every 390 that TVR made.

Steve: slightly OT... do you have any info on the towbar your car has fitted? Did it fit between the rear wing and bumper or had you lost the wing by then?

[Brap_Brap]

350zwelgje said:

I think it is normal, and you still have a great engine (like in envy with my standard 350i). In general RV8s are not supposed to be revy, and the main restriction is top end breathing. You probably have prove of that top end breathing now. Even when the heads are ported to its maximum, they are still restrictive. The heads are the main design limitation in general to get more bhp from the RV8. Think topcats do a new head design. You can try it, but these are very expensive.

Rob

I'd have to disagree a little bit. I'm certainly NO expert on wedges, but I'll state that the exhaust headers suck a donkey's dork.

I don't know if mine are stock or 3rd party, however, they're tiny little tubes, that go 2 into 1, then 2 into one again. (not quite 4 into one)

NOW, compare TRUE breathing headers with none of the sharp angles or cylinder blending within 4 inches of the head. Compare this nice GRACEFULL meeting of exhaust MUCH farther back from the engine than what me wedge has... http://racingbeat.com/resultset.asp?PartNumber=161... (note: this is what both my rx-7's have) In the wedge's case, the headers have met up at an almost 45 deg angle.... p|ss poor design IMHO.... and they don't meet far enough back... they meet FAR to close.



If wedges had more gracefull meeting of flow farther back and less of an angle, breathing would be much improved,IMHO...

I realise due to the chassis, space is a great limitation on a wedge, but the headers I have suck compared to what I'm used to and would want to upgrade that long before heads were considered.

IOW, trying to pump in more air than you can expell is pointless.

Edited by Brap_Brap on Friday 1st June 03:41

[shpub]

Lost the wing etc a lot earlier. Tow bar comes out under the bumper. Really only suitable for towing light loads like my tyre trailer (250 kg).

[shpub]

"Man who compares rice burner with Blitish beef may end up with lice and two wedge." as they say down my local Chinky

The Wedge tubular headers are actually pretty good and in my discussions with John Eales on engine development, his conclusion was that it would be possible to spend a lot more money and only get 1 or 2 hp more. The Rover V8 does not like very flowing headers and a bit of back pressure works wonders.

I have used the same headers on the 520'S various incarnations including the supercharged and had great results - currently getting 500+ bhp out of the setup. The limitations are the heads and induction. Work here has far more benefit than the headers. Also the fuel system and ECU needs looking at. To think of it, the only thing I haven't worked on are the headers simply because they would be very hard to improve.

[rev-erend]

Brap_Brap said:

350zwelgje said:

I think it is normal, and you still have a great engine (like in envy with my standard 350i). In general RV8s are not supposed to be revy, and the main restriction is top end breathing. You probably have prove of that top end breathing now. Even when the heads are ported to its maximum, they are still restrictive. The heads are the main design limitation in general to get more bhp from the RV8. Think topcats do a new head design. You can try it, but these are very expensive.

Rob

I'd have to disagree a little bit. I'm certainly NO expert on wedges, but I'll state that the exhaust headers suck a donkey's dork.

I don't know if mine are stock or 3rd party, however, they're tiny little tubes, that go 2 into 1, then 2 into one again. (not quite 4 into one)

NOW, compare TRUE breathing headers with none of the sharp angles or cylinder blending within 4 inches of the head. Compare this nice GRACEFULL meeting of exhaust MUCH farther back from the engine than what me wedge has... http://racingbeat.com/resultset.asp?PartNumber=161... (note: this is what both my rx-7's have) In the wedge's case, the headers have met up at an almost 45 deg angle.... p|ss poor design IMHO.... and they don't meet far enough back... they meet FAR to close.



If wedges had more gracefull meeting of flow farther back and less of an angle, breathing would be much improved,IMHO...

I realise due to the chassis, space is a great limitation on a wedge, but the headers I have suck compared to what I'm used to and would want to upgrade that long before heads were considered.

IOW, trying to pump in more air than you can expell is pointless.

Edited by Brap_Brap on Friday 1st June 03:41

The header tubes are 1.5 inches which is the best size for all but the biggest engines (5 litres plus..) and bigger and you will loose bhp and torque.

Space for them is limited.

And totally agree with SHPUB - it's the head and inlet that are the problem and not the exhaust..

Don't waste your money !

[Wedg1e]

shpub said:

Lost the wing etc a lot earlier. Tow bar comes out under the bumper. Really only suitable for towing light loads like my tyre trailer (250 kg).

Aye, I was thinking of a 25Kg kayak and about 65Kg of skeleton trailer to carry it

Roofrack on a convertible...

[adam quantrill]

ed_crouch said:

P.S. 255lb/ft at 4200 RPM, and 227BHP at 5000RPM. Torque is back down to under 200lb/ft by 5500RPM.

Don't forget that when you shift up a gear, the torque at the back wheels drops by the same as the ratio between the gears for the same input torque. So - for example - changing from 4th to 5th is a 0.8 ratio - 200lbf in 4th is 'worth' 240lbf in 5th.

The 'best' place to change gear then becomes an exercise in matching the torque curves before and after.

Having said that, there's a lot to be said for sticking in the same gear and not losing power delivery during the gear change. I've had many a smile from holding the wedge in third from, say, 2000 rpm with some jap crap (sorry brap brap ;^) alongside, maybe gaining a little bit, just to see them flying backwards when they hit 7k two seconds later and have to change up!

[Brap_Brap]

adam quantrill said:

Having said that, there's a lot to be said for sticking in the same gear and not losing power delivery during the gear change. I've had many a smile from holding the wedge in third from, say, 2000 rpm with some jap crap (sorry brap brap ;^) alongside, maybe gaining a little bit, just to see them flying backwards when they hit 7k two seconds later and have to change up!

Mmmmmmm

"Having said that, there's a lot to be said for sticking in the same gear and not losing power delivery during the gear change."

By the time I've wound out 2nd, (70mph or 110 km/h) you'd already be in third...by the time I'd wound out third (150 km/h @ 8k) you'd already be in 4th. It would not be me losing in the shifting! By the time I wound out 4th (240km/h @8k... as SHOWN in a screenshot) you'd already be in 5th and I'd still have one gear to go... (if you drove my 390) Now in all fairness, I'm not generalising "jap crap" like you are, I'm refering specifically to my modded rx-7.

I think the wedge might beat it for the first 60 feet due to my light flywheel and hence poor launch...after that it would be game over.

I'd suggest that you drive down to your local Mazda dealership, and for a lark, take an rx-8 for a test drive.

I'm not trying to highjack this topic, but the topic does says "high rev torque" and that's where Dr. Wankel's invention really does shine through.

Edited by Brap_Brap on Saturday 2nd June 03:55

[Brap_Brap]

rev-erend said:

And totally agree with SHPUB - it's the head and inlet that are the problem and not the exhaust..

Gee, Imagine having no heads.... or valves...or a cam.... or pushrods... or lifters... or springs or a timing chain or 3lbs or sprockets, or crank counterweights or any of that other useless mass required to drive your engine and that power used going to the rear wheels instead. LOL. Not to mention, with only 4 moving parts, what's t break? Crank counterweights splashing thru oil is like trying to run knee deep in water.... efficiency?

When the RV8 dies, it's 3-rotor 20b for me.
Also the engine/tranny/rear swap would shave at least 150 lbs off the car.

Edited by Brap_Brap on Saturday 2nd June 04:23