[SteveC]

Hello everyone,

I have been following the thread on the Dyno days with great interest but one thing that I don't understand is the relatively low Torque figure that tuned RB26's give. Don't get me wrong but compared to its BHP the figures are not so impressive.

can anyone explain why the RB (straight 6) should be sitting 100lb/ft below (roughly) when something like a porsche Flat 6 has got a higher torque figure than BHP ?

why do things like big block chevy lumps give such high torque, V6 ? there must be ways of manipulating these figures with cam/timing fettling.. as per Gary and others.

I don't disbelieve any of the Statements made regarding the power and Torque of anyones car but I believe that it is simply a case of researching which cams give the highest torque.

Until recently (1 year or so) the main focus has been on big BHP but now the stance has shifted, and rightly so, toward the quest for torque, could it be that we are not too far along the road for torque as everyone's attention has been diverted looking for ponies ?

I think that while most have gone for big power at high revs we should be producing max power at 5000 or whatever as per the dyno comparisons for torque and BHP meet.

This is going to be less stressful on the engine and make the cars quieter !!

if you change the cams so the BHP comes in at say 7000 rpm then does this magical 5000 odd number change or is this a fixed point in the curve. (I am talking about the point that BHP and Torque are the same)

thanks for any input...

Steve

 

[DCD]

Steve, you have to look at the RB26DETT for what it really is. Its relevatly small capacity of 2568cc is pretty tiny compared to a torquey 3.6 TT flat 6 of the 996 Turbo. We are talking one liter differnce here...plus Porsche usually tune their engines for low down grunt, hence the pretty unimpressive redlines.
I mean look at what power levels the 80s F1 1.5L engines used to achieve....and that was at very high rpm with absolutely no torque a low revs.

An alternative is to stroke the RB to 3L, 3.1 or 3,2. You will loose the ability to rev, but if well built, with good matching turbines you could achieve what very good torque levels.

 

[quattro]

have a read

this should cover most questions on the subject:

http://www.carkeys.co.uk/features/FE000373.htm

Rob

 

[JohnD]

What's the redline of an RB engine?
Isn't is around 7500-8000?

 

[hipogtr]

"Until recently (1 year or so) the main focus has been on big BHP but now the stance has shifted, and rightly so, toward the quest for torque"

I'm not sure when and where this happened?

Cya O!

 

[SteveC]

Dino,
There must be a way of getting a more proportioned Torque curve without boring out the lump though..?

HipoGtr,

The emphsis has always seemed to look for BHP at high revs, now though there is much more focus on the torque figures I don't know if this is a skyline thing or an attitude change in general, or even my own focus moving...

Rob,

thanks for the link, some good info.

The constant reference point for BHP calculation is 5250, so what exactly is that ?

The guy in the article states it is the constant but it doesn't say wether that is RPM, bags of fairy dust or lb/ft...

John the redline is about 8250 (rev limiter)

just more confused now..

 

[DCD]

SteveC....I was just giving the easiest opton...ie cc= more torque. I guess using small and lag free turbines coupled with specially designed cams could get you high torque, but you would be trading off the power. Ahh...compromises....

BTW 5252 is the theoretical rpm point where the torque curve intersects the power curve.

 

[quattro]

Answers

Steve

i won't bore you with the maths behind it, but if you work purely in standard units i.e power in watts, torque in Newton meters and rotation speeds in radians per second, then you would'nt need that number, all it does is convert to our beloved bhp, rpm and lbft.

rob

 

[SteveC]

Thanks chaps,

I think after the last few days I should dye my hair blonde and get an escort cabriolet !!

Compromise, not a good word.

/Steve

 

[JohnD]

Because the torque is the force and the hp the speed.

a 500 HP car with an 8000 rpm redline and the peak HP near 7000 will read lower torque compared to a 500 HP car with a 6000 rpm redline and a peak HP near 5500.

I don't know the reduction and gear ratio's but in general an 8000 rpm engine needs less force per revelation to gain the same speed.

Make your calculation.

[email protected]=~375 lb-ft
[email protected]=~477 lb-ft

This is also why a 540 HP truck @ 1750 RPM will reach over 1600 lb-ft of torque.

 

[kingsley]

bhp = (lbft x rpm) / 5252

ie power = revs x torque

Increase either revs or torque and you increase power. If you don't increase revs but you increase torque, you increase power. Similarly, if you manage to increase revs and hold on to your torque, you also increase power.

Because the RB26DETT is a high revving engine (for a road car), the power figure will always look high for the amount of torque compared to other engines.

Redline is at 8000rpm, I think (I don't have one yet).

 

[kingsley]

Originally posted by DCD An alternative is to stroke the RB to 3L, 3.1 or 3,2. You will loose the ability to rev, but if well built, with good matching turbines you could achieve what very good torque levels.

Is the max bhp of an RB26DETT modified like this about the same as standard (ie does ability to rev drop roughly in proportion to capacity (and presumably torque) increase)?

 

[Rich J]

If the other knew u were on here Kingsley they would have a fit!

Nice to see you still talking the good stuff m8, are you planning on a new car?

 

[Mycroft]

Put simply, fully efficient torque developement from turbo'd cars is partially a product of heat, not the main 'plug' of torque (which is just filling the chambers) just the full exploitation, if the exhaust gases leave the head too quickly (which happens in a high flow exhaust) then engine is termed as running cold at lower RPM, (just as the terminology in spark Plugs) run it too cold and the torque generation efficiency is decreased. The fall off is not very great but it is does blunt the performance.

Most good designs of exhaust are tuned to mitigate this problem, it is at its worst around 2k to 3k by restriting the flow of the gases, this makes the head hotter and more efficient gaining a bit back at this rev band.

Kakimoto Exhausts have the best design for this, their 'twin-leaf' design works very well at keeping the head hot at low revs and yet does not choke the high rev 'clearing' so essential for not generating too much heat causing the BHP to drop at higher revs.

The exhaust I designed for my Soarer is based on the Kakimoto design principle.

That is it in precis'd form.

Extract from a response given by me on the Supra forum.

 

[kingsley]

Originally posted by Rich J Nice to see you still talking the good stuff m8, are you planning on a new car? [/B]

Hi Rich, it's been a long time! Yes, I am thinking about my next car. Much as I like my Calibra, I'd have to spend a lot of money on it to get it up to 400bhp and apart from its luggage space it still wouldn't be half the car that a Skyline or Supra TT is. I have to be realistic about things so I'm, er, shall we say, 'evaluating my choices'

PS. Never been in a Skyline yet (apart from one that was parked) - don't suppose you fancy doing something about that if I'm in your area at some point? Perhaps best to carry on this conversation by Email as it's drifting off topic. Drop me a line (Email address is in my profile).

 

[kingsley]

Kakimoto Exhausts have the best design for this, their 'twin-leaf' design works very well at keeping the head hot at low revs and yet does not choke the high rev 'clearing' so essential for not generating too much heat causing the BHP to drop at higher revs.

Where is the link for the discussion in the Supra forum? I don't know where the Supra forum is yet but I would like to read about this twin leaf exhaust design.

 

[kingsley]

Talking of increasing the torque, has anyone tried fitting a positive displacement supercharger to a Skyline ... in such a way that a bypass valve opens once the turbos have started to produce boost of their own? (as long as the blower is carefully chosen and set up, with the bypass valve open it should not create much power-sapping drag on the engine).

That is, assuming that you can fit it under the bonnet ...

The main problem with fixed displacement blowers in terms of ease of installation is that they are normally mounted AFTER the throttle body, though I have a few ideas for how one could possibly be installed further upstream.

 

[Mycroft]

I'm afraid that was as far as it went really, apart from the antagonism.

I'll append it none the less;

http://supra.highspeedhostinggroup.net/public_html/vbb/showthread.php?threadid=37

 

[Jebu]

hi guys

can somebody pls explain to me how exactly does fitting cams increase torque?
and what kind of cams are good for RB engines (as in manufacturers etc) .. thinking of putting one in!
would it be advisable?

thx!

 

[Rich J]

Yes Kingsley i agree, but if u did go skyline or supra u would not look back, calibra is a good car but the others are a different league. If i'm buy i'll call ya mate as we have a different skyline now from the black one u saw.

Cams change torque varying on there profile, basically controlls at what time and duration the valves open allowing the fuel and air to be burnt, and then on a twin cam engine when to dump the burnt gas etc.

Thats the basics, sure someone has more time to go in detail, but i'm off to work now