How To Get A Smoother Torque Curve? 16v

[monty69 6]

Basically my carbed s16 205 struggles for grip in when accelerating out of bends, the engine is worn but on the rollers only made 143atw at 6700 and 140lbft at 5200. It will be rebuilding one in the summer with a lsd, maybe with moderate cams, but would like the torque to be smoother and not as peaky. The torque rises sharply from 1500rpm but at 3000 there is a flat spot in the torque curve- maybe even goes down slightly, before rising sharply at 4000. It peaks at 5200. Do all mi16s have a flat spot? It doesnt help in 1st gear as once 4k is reached its bye bye traction.. To drive it feels really lively in mid range, but torque drops off after 6k. So basically what mods smooth out the torque and stop it tailing off so fast? Some people winge about the gti6 engine, but im thinking the smoother delivery in a 205 would make for a quicker car on track.

Torque lbft

2000 87

3000 116

4000 114

5000 137

5200 140 peak

6000 137

7000 120

Edited March 2, 2009 by monty69

[welshpug 1,661]

got LSD?

[dcc 855]

Mi's have the double throttle body effect, surely that would cause a bit more of a "surge" of power than the more standard single throttle inlet of the gti6 or even the 8v's. not sure how much of a difference this would have with wide open throttle, but surely it has a big effect upon the lower revs, seeing as one of them doesnt open at the same rate as the other.

[Anthony 1,003]

Is the ACAV working properly? Not sure how it looks on the dyno, but certainly to drive a S16 with working ACAV feels like it has a reasonably linear power delivery, whereas one with broken ACAV has a very noticeable surge when it comes on-cam around 4000-4500rpm or so.

 

Mi's have the double throttle body effect, surely that would cause a bit more of a "surge" of power than the more standard single throttle inlet of the gti6 or even the 8v's. not sure how much of a difference this would have with wide open throttle, but surely it has a big effect upon the lower revs, seeing as one of them doesnt open at the same rate as the other.

S16's have a single butterfly throttle, and to be honest, the twin butterfly setup on the Mi's just means that you have a more progressive throttle.

[pug_ham 244 3 Cars]

Is the ACAV working properly?

 

Basically my carbed s16 205 struggles for grip in when accelerating out of bends

 

Graham.

[Anthony 1,003]

Opps, my bad - missed the carb bit

[Cameron 16]

Have you got a rolling road print-out? Its difficult to see a flat spot there to be honest. Most production engines make their peak torque below peak power rpm. Can't you just adapt your right foot?

[Batfink 201]

its not the engine thats the issue. Look at keeping the wheels in better contact with the road, at minimum have a strutbrace, look at fitting an LSD to move power to the right wheels and maybe look at the camber you are running on the front...

[danpug 1]

What tyres do you use? My old very healthy mi16 on tb's had very good traction most of the time, just decent tyres did the trick.

[brumster 135 1 Cars]

In chatting to Richard Longman he was telling me how the mi16's have an inherent flat spot that it fidgety to tune right but, while mapping my car on bodies, it wasn't an issue for him because of the nature of a 3D mappable system. What I take from that is that maybe it's more noticeable on a carb setup, particularly if you're running off a straight old dizzy?

 

But an LSD and/or better tyres/geometry is probably cheaper and easier than moving to bodies, and more effective for the money I suspect

[Cameron 16]

Just a thought, how much throttle pedal travel do you have? If you've fitted carbs you may need to alter the linkage to get a bit more travel.

[bales 1]

What suspension and tyre do you have?

 

These made a massive difference to my car, in all honesty when I had standard suspension and 185 P6000's in the wet it would spin up in 5th in anything other than dead straight line.

 

As soon as I got my GAZ coilovers and there was no squat at all and with T1-R's I get so much better traction its unbelievable!!

[dazEmad 0]

I get much less wheelspin now when on track with tb's and curborough definatly showed this. Even though now it has more power and much more torque the power delviery is very evenly spread instead of the sudden kick after 4000 rpm. In fact now i can get wheelspin at 2500-3500 rpm which it never did before. Its now less stress on the tyres and i cant really justify getting an lsd for it, although im sure it would still be better with an lsd.

[pee vee 1]

are you running lots of camber on the front wheels at all mate?

[monty69 6]

It has goodyear eagle f1s 30psi, standard shocks, skip brown -25mm springs (not much stiffer than standard). Havnt checked camber but the tyre wear is perfect. Before i had the power steering fitted the steering was very heavy both ways due to the heavy engine, i know there is nothing wrong with the suspension. I know it only has 140lbft but it feels like way more, to drive it feels very punchy, almost like a small turbo, and then starts to tail off at 6k. I will be going down the mapd ignition route when the engine is rebuilt, id just like the top end power to not fall away as fast, and for a smoother power delivery like the gti6. Will the right cams acheive this, or will a properly ported head be needed to hold onto the torque for longer?

[rapidcossie 0]

I have a throttle bodied S16 which makes 150 ATW.

 

I get excellent grip from bends even in the wet running 888's.

 

I do have a LSD tho.

[richsmells 2]

It has goodyear eagle f1s 30psi, standard shocks, skip brown -25mm springs

 

Are they "roadspeed" dual rate springs? I have exactly the same setup and it's bad to be quite honest. Anthony fitted them with new genuine shocks and hard top mount rubbers.

 

It spins up when pulling away without even trying and mine's just a 1600, it's crashy and skips over bumps. I'd look at some better shocks.

Edited March 3, 2009 by richsmells

[James_R 3]

I'd put a 22mm ARB in the tail and see what it likes and as said maybe make the throttle more progressive.

[monty69 6]

Yes they are roadspeed but not dual rate, as when the weight is on them the bottom coils compress solid. I find them very mild, the smoothest lowered ride i ever driven, no skipping over bumps - maybe its because of the extra weight of the s16 engine- quite a bit heavier than alloy 8v. I think i will look at throttle linkage as its a short throw one.

[Cameron 16]

I think i will look at throttle linkage as its a short throw one.

 

Ah, that could well be your problem.

Edited March 4, 2009 by Cameron