Experimental CAM Timing

[PetrolHeadPete]

Thought I'd share the results from a recent dyno run (dyno dynamics "heartbreaker")
This is after my recent head rebuild that I PH'd recently. This is a std 4L 2002, with CATs and normal exhausts, non-mapped MBE.

At the time of the head refitting, some dialogue with B-Tech pointed to a possibility to adjust CAM timings a little from the standard to try and make more mid-range torque at the expense of top-end power. I prefer engines this way. They were basing this on some simulation results optimized for mid-range and based on on their standard CAMs. They now supply all the bits I used on my rebuild (I have nothing to do with B-Tech btw)

So I set the timings up as per their advice. The engine has now done over 2.2K miles and is running nicely. Popped the CAM cover the other day to take a peek and everything looks as fresh as daisies. The oil is nice and clean too.

The plots below show two runs with everything "normal". Peak power was around 322-ish and peak torque around 319. But its where this happens that interesting...4700. And its still making around 250lbsft at 2000. Happy with that. Chose to limit revs to 6500-sh which was a good choice as the power graph is just flat out there.

The other 3 runs are with the air-box off...just for fun. OMG! Tuned length IS criticial. Those guys running their S6's with air filters pushed into the throttle bodies...get an air box back on!



Note the mention of gear:3 at the bottom of the plot refers to the cal point on the dyno I think (done right at the start of the session)...the power runs were done in 4th.

[nrick]

I think it is only me not running an airbox, not because I don't want to it is just that is how the car came. I am going to play with trumpet lengths of about 60-70mm and designing a custom carbon box with stacks.

Looks like 322 is the figure to beat!

[spitfire4v8]

I did a lot of testing on SP6 airboxes about 3 years ago, the std box is very good. You have to be careful what you do with the lengths as it's very easy to lose power in important areas for gains of only a handful of hp elsewhere. I'm just about to start making non std airboxes after some more development on our race t350. Just cant decide whether to make them in stainless like the alfa V6 inlet pipes or in carbon.
322hp is very poor Our std tiny 3.6 makes 366hp / 300lb.ft

[gordonsalive]

Spitfire,
Will you making them for re-sale? I would be very interested if you do, let me know costs and when you are planning to have some done by.

Thanks

John

[PetrolHeadPete]

Goal was more low and midrange torque.

Have a look at this plot also done on a Dyno Dynamics:

http://www.pistonheads.co.uk/gassing/topic.asp?h=0...

Compares very favourably and more torque almost everywhere (by a good margin)...but for sure less power up the top end (where I seldom drive).

What type of RR were you using ?

[dpd3047]

Nice one Pete very impresive torque figures seems to have done the job still making 300 ft lbs at 5500 rpm like you say max power is not what you need on a road engine.

Edited by dpd3047 on Wednesday 15th June 10:44

[Russian Rocket]

what cam timings are you using?

I have just rebuilt my top end (you were right about the valves) and have 113.5 and 107.5

[PetrolHeadPete]

Here's an interesting comparison against the TDI power/torque plot from the 4.3/4.5 rebuild thread.

So this is my standard S6 with revised CAM timing against the TVR Power standard 4.0S rebuild.
As long as you dont want to rev the knackers off it, it outperforms nearly up to 6000rpm.

[Robertjp]

Pete, if u understand correctly they are some impressive results!

Am i right in thinking this (in my lamens terms) give you much more low down grunt and 'real world' drivability?

If you rarely red line your car / keep the revs v high, this is going to lead to a much easier car to drive quickly?

What is the downside?? A little less pull higher in the rev range (6k rpm plus?) Little less top speed? (...like THATS a problem )

And...a stupid question i guess for most - but how is the timing dictated / changed? I always understood it was fixed by the camshaft...but you used standard parts so maybe im completely wrong?! Probably a dumb question that one but im a bit confused!

edited to say - google is my friend and i should have known the answer to my question regarding timing. So...the raltive timing between valves does not change here (as fixed by the camshaft), only the relative timing between crank, exhaust cam and inlet cam?

Edited by Robertjp on Monday 4th July 15:11

[Speed eight]

PetrolHeadPete.
This is what I like.
Well thought out, well presented and a GREAT result.
You must be so pleased.
This will be one fast ride. Forget the very top end it's too close to call.
Real world is where we live.

Regards.
Speed eight.

[PetrolHeadPete]

Robertjp said:

edited to say - google is my friend and i should have known the answer to my question regarding timing. So...the raltive timing between valves does not change here (as fixed by the camshaft), only the relative timing between crank, exhaust cam and inlet cam?

Edited by Robertjp on Monday 4th July 15:11

Correct
It feels fast i must say
I sometimes head up to 6 to 7k where still feels ...well...fast

Dpd3047...nice one! Anyone who doubts your knowledge can take a moment to reflect . It does exactly as you predicted

And thanks Mr Eight i like cold hard facts and graphs rather than "guess work" and assumptions

[Robertjp]

So...are you going to keep the timings a secret??

I would love to get a spin in your car to feel the difference!! It seems like a very low cost change that can significantly improve real world performance.

Is it really as it seems - that TVR chased headline horsepower and sacrificed performance almost EVERYWHERE else in the operating range??! I dont understand why...surely 0-60, 0-100 times unaffected, only top speed? I guess this must be really important to some people?!

Are you running standard 3.46 diff and box?

[Robertjp]

spitfire4v8 said:

322hp is very poor Our std tiny 3.6 makes 366hp / 300lb.ft

322 doesnt seem poor when you look at the entire operating range, and the relative figures to a 4.0 S engine?!
Any chance you can overlay your figures to Petes graph? Any advice as you what you think is different??

[PetrolHeadPete]

Robertjp said:

So...are you going to keep the timings a secret??

Is it really as it seems - that TVR chased headline horsepower and sacrificed performance almost EVERYWHERE else in the operating range??! I dont understand why...surely 0-60, 0-100 times unaffected, only top speed? I guess this must be really important to some people?!

Are you running standard 3.46 diff and box?

Timings: B-Tec can advise, or email DPD

Horsepower. You know BHP stands for Brochure Horse Power, right

Diff etc: All standard

[spitfire4v8]

Robertjp said:

322 doesnt seem poor when you look at the entire operating range, and the relative figures to a 4.0 S engine?!
Any chance you can overlay your figures to Petes graph? Any advice as you what you think is different??

I'll try and get a graph up for the 3.6 if I can. One thing i note on the graphs above though is that the induction and exhaust driven peaks in the curve aren't at the same points in the rev range on the graph comparison .. changing the cam timing won't affect the resonances in the inlet and exhaust tubes, so that's somewhat strange .. it's as if the tvrpower graph is skewed to the right on the rpm axis so making it appear worse than it really is?
Edited to add .. worked out why .. your graph isn't done with an engine driven rpm reading .. the torque axis should say ifFtLb if it was, so your graph rpm is skewed down the rpm axis so inflating it's torque numbers. The big peak "hump" is at 4700 or so on yours and 5100 on the other graph, so doing 47/51 x 320 = 293 lb.ft for your engine in reality. About right for a 4 litre engine, but you're still down on the top end ..





edited to include 3.6 graph with engine driven rpm .. only makes 280lb.ft not the 300 i thought, but still compares favourably to the corrected other engine numbers, and 40hp more at the top.

Edited by spitfire4v8 on Tuesday 5th July 19:13

[dvs_dave]

That graph on the other thread ran to about 7300 rpm. How does it compare when you factor in the same rev range, and spitfire4v8's correction?

That would be a more accurate comparison of the two would it not?

Also are your numbers at the wheels/fly/hubs as that also has relevance when comparing absolute numbers as in this case? The TDI plot was measured at the hubs....so apply whatever correction factor you see fit without starting an argument.

[PetrolHeadPete]

All figures are flywheel

Not quite sure i follow spitfires point
Seems you're saying the rolling road is
misreading rpm because it measured it at the wheels
with a 1.00:1 transmission ratio to the fly?

[dvs_dave]

Ok, try altering the numbers from the TDI plot to represent flywheel power and re-plot it.

I'd say a 5% transmission loss is reasonable to assume without argument.....Spitfire??

FYI, the TDI plot was done at <5 degC ambient, having just had it's 12k service so it was in tip-top tune.

[spitfire4v8]

The point is that the engine torque figure will be wrong because the dyno thinks the engine is spinning at a different speed to the actual speed of the engine (tyre slip and errors in the rpm/mph factor). Although the dyno measures the torque reaction on the load cell and the roller speed it doesn't measure engine torque directly, it works it out .. and the engine torque guess is skewed when you don't have a good representation of the engine rpm. doing rpm off the rollers ratio (as appears to be the case on your graph) isn't good enough for good repeatable testing, though is often used for things like dyno shootout days where it's easy and quick to run different cars without having to get reliable HT rpm pickups. IYSWIM. As Dave says above : compare dyno graphs at your peril unless the dynos are well known and run to the same standard. It's a minefield.

[stainless_steve]

spitfire4v8 said:

I did a lot of testing on SP6 airboxes about 3 years ago, the std box is very good. You have to be careful what you do with the lengths as it's very easy to lose power in important areas for gains of only a handful of hp elsewhere. I'm just about to start making non std airboxes after some more development on our race t350. Just cant decide whether to make them in stainless like the alfa V6 inlet pipes or in carbon.
322hp is very poor Our std tiny 3.6 makes 366hp / 300lb.ft

Stainless steel would be cheaper