272in/264ex vs 256in/264ex cam setup test results

Righto. With reference to this thread:

http://www.mkivsupra.net/vbb/showthread.php?t=45313&highlight=stagger

Due to being interested in the claims about this inverse stagger setup, I bit the bullet and bought in a 272 intake cam and a set of adjustable JUN cam gears.

In the 272/264 cam test, the intake cam was set to 3deg retarded, and the exhaust cam was set to 4deg advanced.

In the 256/264 cam test, the intake and exhaust cams were both set to stock timing.

The conclusions is - the 272in/264ex cam setup isn't anywhere near as good as my existing 256in/264ex one. Turbo spool was massively impacted, about 500rpm more lag in 3rd gear (look at the graph and wince at the 272 setup's performance) and the road speed graph shows just how badly the performance of the car was hit.

There isn't much test data, but what there is supports my conclusion very well. I did 2nd and 3rd gear properly, but after the results with 3rd I didn't bother with any serious datalogging of other gears. Not only is the data very conclusive, the car felt terrible to drive, especially as I came from the far superiour 256in/264ex setup. Felt like I'd blown something expensive, I was frankly shocked at just how bad it drove, and the graphs back this up - observe the 3rd gear lines in the road speed comparison. The difference is staggering, and much more pronounced than I expected.

I had to pull fuelling when off-boost just to make the car driveable. I was running richer across the rev range under all load conditions, which means the cylinder filling was impacted badly. If I am using the same duty cycle, I'm injecting the same amount of fuel. I'm seeing the same pressures and vacuums in the intake plenum, but less fuel is being burnt = less air is physically getting into the cylinder during each four stroke cycle. As the only thing that changed was the intake cam and the timings of both cams, it had to be this setup causing the poor filling.

I concluded from this that attempting to remap out of this richness would be a waste of my time - I may recover some power and even some turbo spool by getting out of the 9:1 afrs, but I would only ever be chasing after the performance of the 256/264 setup - and I'd never reach it due to the simple fact I needed less fuel for the same circumstances. This was further proven by when I swapped back to the 256 intake cam and reset the timings, lo and behold the car fuelled perfectly on an unchanged map once again (I had to add back in the fuelling I pulled when off boost!). Suddenly the car was a joy to drive again, responsive and fast with that glorious DBB spoolup

I don't know if this is what you wanted to hear, but there you go. I have no tuner interest, I don't sell cams (well, apart from the 272 intake one, sigh), and I'm as suprised as you are.

Additional notes - Road speed vs time, the 3rd gear line for the 256 setup has an anomalous blip at 3.9 seconds, possibly wheelspin or just the datalogging having a fit. 3rd gear comparison - the 256 setup actually starts at a lower boost as the throttle was put down later than the 272 setup - those data are from a 1st to 2nd gearchange, wheres the 256 data was from a coasting state. The fact it overtakes the 272 setup so fast is another nail in the coffin as far as I'm concerned.

Still, at least I got to swap my valve stem seals while it was all in bits Now disregard this utterly and go buy my spare 272 intake cam

-Ian

Cam comparison.zip

Did you try the 272/264 combo on stock cam timing?

The timing was what was suggested...to make sure the engine had the same overlap.

But no the stock timings wern't tried on the 272/264 cams...as timing alone couldn't make it much better.

It was massively worse.

i'll stick to my 256/264 setup then:) thanks for sharing your data with all.

Hmm, makes me think I should swap my 264 for a 256. Well done Ian for the time and effort.

EDIT - I meant to say,

Buy the 272 it's GREEEAT

I have the same 272in 264ex setup ready to go on the car with the JUN gears, I have to admit that this has put me off some what.

Ian once again great work with data to support your findings

Did you try the 272/264 combo on stock cam timing?

Nope, I couldn't prise it out of the engine fast enough That may have improved matters but at the expense of about 8 degrees more overlap, which means bye bye idle quality and low down shove.

I got what I wanted out of the test I'm convinced the 256/264 setup is spot on for what I want out of the car, and if I may be so bold most people would benefit from this, it's a very good setup. The engine breathes great up to the stock redline instead of choking up at 5500rpm+ like stock camm'ed cars, but the idle isn't badly affected and low down isn't noticeably worse. It gave excellent results over stock cams with hybrid twins as well as a single.

264/264 may be OK still, it may even be better than 256/264 - someone needs to do a test

-Ian

264/264 may be OK still, it may even be better than 256/264 - someone needs to do a test

 

-Ian

Well volunteered!

How would changes in the ex cam affect things?

Ian, would the 256/264 set up suit a BPU'd car? Or better for hybrid/single set ups?

Well volunteered!

Haha no thanks, I'm sick of tightening up bearing caps in sequence.

How would changes in the ex cam affect things?

I don't know, the reason I did a real-world test was because I don't really know enough about cams to theorise it. If I find a good resource on it I'll be reading up for sure.

-Ian

Ian, would the 256/264 set up suit a BPU'd car? Or better for hybrid/single set ups?

Yes but

As in, but by this point your stock injectors will be flat out and your stock fuelling charecteristics, while coping with BPU, won't 'know' about the better breathing up top. I've found this when mapping, once you get north of 5500rpm with bigger cams in, you need to push in more fuel than before that - the stock map starts tailing off as the engine breathing isn't, as far as it's concerned, there.

Does that make sense?

-Ian

If I find a good resource on it I'll be reading up for sure.

Let me know if you do

264/264 may be OK still, it may even be better than 256/264 - someone needs to do a test

 

-Ian

Give me a discount on your mapping costs, and you can run the test at the same time

Although I don't have adjustable cam gears.

I wonder if it would make a difference if you remapped the ignition timing.

First the pulleys, now the cam

Good write up Ian and interesting findings

The pulleys are still on Nic, lovely bit of kit, well engineered although they are set to stock settings and hidden under the plug cover which is a bit daft but I have an excuse

As for ignition timing, I've already got 15deg more advance under 4000rpm up to about 0.8bar

-Ian

Great Tech Ian, wish i'd seen this a while back, I might have not bought the 264/264 set up.

Great Tech Ian, wish i'd seen this a while back, I might have not bought the 264/264 set up.

A while back it was only posted yesterday!!

Bigger cams do help breathing at high RPM...we think that if you get a built head and raise the rev limit you'll see an appreciable difference uptop...but Ian's not going for a raised rev limit.

So just to clarify this was in a stock head?

Great write up and thanks for testing Ian.

Another BPU question. I was considering mild cams, ie 256/264. I understand what you say about the stock ECU not knowing that the extra breathing is up there. How could you overcome this in terms of management? E-ultimate/PFC?

And you should post your results on that SF thread, if you havent already.

So just to clarify this was in a stock head?

Yes Stock, only the cams have been changed from stock.

A while back it was only posted yesterday!!

Lol, I meant as in if i'd known that the 256/264 set up was so good, I might of bought those rather than the 264/264 set up, that I bought a while back. .

 

264/264 may be OK still, it may even be better than 256/264 - someone needs to do a test

 

-Ian

Ian when i get my car sorted and my T67DBB fitted (i have 264/264 already in), i will come and see you for mapping, you can also run some tests if you like to compare.

Ian when i get my car sorted and my T67DBB fitted (i have 264/264 already in), i will come and see you for mapping, you can also run some tests if you like to compare.

Hey! Get to the back of the queue! LOL