Just like to get a feel of opinions of people's experience with cam choices?

Now a lot of people swear by STD cams on a T34 engine, or a standard exhaust with a BD14 inlet. My old saffy was running twin 14's, and to he honest the car used to rev beautifully all the way to 7.8k, and over 5k seemed to have a second wind. It was a slightly low comp engine, 7.8:1, with a ported head and a T34/48. It made 369.8 bhp on the dyno, which I think was probably about 340-50 bhp in the real world. was running 24psi on greens, but used to wipe the floor with cars running much more boost on grey etc, so I think the RR was pretty close.

My point is, that as a 2wd car, it never lacked torque, and a couple of 4x4's I have been in with twin 14's feel just as nice.

My main question really is A) is the torque loss THAT bad on a 14 exhaust cam, that it makes the STD cam worthwhile? B) Are you better off running two of the same series cams, or is an aggressive inlet (bd16) good with either a STD exhaust cam or a 14?

 

Hotter cams on a T34 is a waste of time IMHO as the engine on standard cams is already capable of taking in more air than the turbo can flow, thats why they die off at high rpm, hotter cams will make very little difference when the compressor is maxed out.

 

Why do cars running a bigger exhaust cam feel happier to rev then? I know it probably does not match the dyno sheet, but the ass dyno says it feels better?! Bear in mind that my 2wd had a well ported head, so breathing would be better anyway?

With a T34 does the turbine not choke before the compressor runs out of steam?

 

When you fit both cams, the engine really would benefit from a bigger turbo at the same time, its not that you wont see *any* gains on a T34, like I said it just wont gain much.
With regards to if its the compressor or the turbine thats the real issue, its pretty much both really, they arent a bad match for each other on the T34 in the first place, although people do manage to get about 10% more power out of them when they fit the larger compressor wheel in what gets called a "T38" they end up losing response at the same time.
You're right that at the top end on the hotter cams it will pull better, but its only a case of that power drops off less, rather than power is gained, if that makes sense?
You end up hanging onto the gear for longer which makes it feel revvier, but in reality you've gained little in real world performance.
You mention that yours was still pulling hard at 7.8K, but I bet if you post the dyno graph you have not much over 200lbft of torque by then.

I see no point in trying to eek out a few extra bhp with different cams on a T34, when you could just change the turbo and unleash SO much more potential instead.

In general IME most tuners with the YB seem to find that a hotter inlet than exhaust gives a good balance, if you go too hot on the exhaust you end up with longer but weaker exhaust pulses at lower rpm, which tends to make the turbo then spool more lazily compared to the short sharp hit of the standard cam.

 

A BD14 exhaust cam is too long Will. Its a rubbish choice, unless you can get the engine to rev to 10krpm. It would possibly be kind of ok then I would guess, well, as long as the engine idle speed was set to 6K so you didnt notice what an arse it made of the rest of your engines operating range. LOL.

 

What do you find to be the problem Stu? Loss of low end response?

 

That response is based no experience with that spec engine obviously? as a inlet cam and a small amount of port work transforms a t34 engine

 

A bd14 is a good exhaust cam in certain specs, on a t34 I agree thoigh.

Are you talking about a t34 engine or in general stu, as if general we use massively bigger exhaust cams than a 14

 

Its the EXHAUST cam he is asking about jimbo, not the inlet.

My reply was badly worded TBH, apologies for any confusion.

 

Its only my opinion mate, but I think you had best define "Massively Bigger" then Jimbo so there is no confusion.

 

No worries, came across very much against any cams larger than standard

Course!

I'm not talking about average t34 or t4/gt30 spec engines, that's why I ask if you are talking about in general or for t34 spec as it wasn't clear!

 

Sorry for the delay, nipped over to vegas for a week for my 40th, back now and jet lagged, but what I meant was for you to clarify what you call "Massively Bigger" exhaust cams than a 14, not what are massively bigger turbos than T34's mate.

 

...a std exhaust cam is all thats needed in specs upto 600bhp! The secret specs cams are just std i bet! !

 

I cant say at which level mine changed but , I have to watch out what i say cos Sheady maybe watching.

 

Did you go to Sema when you were there, I just got back from there to .

Mark

 

Shit!!! Im in trouble now .

 

When you have a custom cam made is it all just guess work?

If you knew where you wanted the powerband to be would you have to order 3 differentially specd cams that "should" have the powerband where you want it, then pick the best out of the 3 ?

or is there some sort of formula?

 

No mate, I avoid anything to do with cars like the plague when I am away. I try not to even drive any If I can help it. LOL

 

Trial and error and educated guesswork.

Even the really sophisticated computer modelling software that manufacturers use and aftermarket tuners can only dream of having the data for, doesnt actually give you a definitive answer.

 

Just as i thought. The formula for the perfect camshaft is

Piper (kent or newman) + ŁŁŁŁŁŁŁ = the perfect cam

 

Well not really, as they have little experience of specific engines in reality, so its a case of tuners being able to give them enough information to work with, and even then its only ever going to be in the right ballpark rather than anywhere near as finely optimised as manufacturer cams are.

For turbo use, cams are less of an issue (dont get me wrong I am NOT saying they dont matter) as they arent the only very drastic factor shaping the engines performance like they are with N/A (again dont think that means portwork or compression ratios etc arent important, they are, but they wont make the dramatic effect a cam change will)

And of course manufacturers have to be obsessive about economy and emissions, aftermarket tuners need to consider these, but not to the same extent.

 

I fully understand that headwork, turbo, compression ratio and rod ratio have a huge effect on what cam will be suitable.

I just meant that if you can give a cam company the engine spec and are prepared to spend the time and money trying different cam specs eventually you will find a cam does what you want.

Good thread.

 

Correct

Lots of dyno time is the real key.

 

Nice one! Happy 40th btw!

How was Vegas? hoping to get there next year for around my 21st in September!

Anyway, back to topic, where were crossing keys is where you said you wouldnt go any bigger than a 14 exhaust cam, I don't understand, is that for a t34 spec or in general?

A 16+ CAN be a a good exhaust cam for example, that has, off the top of my head 1.5/6mm extra lift, similar on the duration maybe a couple of degrees extra.

In my (limited) experience, cam timing plays a big role and can make, or break a cam. I believe people slating bd14s don't release its full potential and can make it seem at fault making a laggy engine.

All IMO

 

Jimbo u do have limited experience, your daddy is speaking for u, we all know this LOL!

 

No mate, just modest and take everyones opinion on board

 

I'm sure jimbo has more direct back to back yb experience already than most of us will ever have!

 

I'd argue that point a bit mate. Simulation software now IS incredibly powerful, some of the stuff i've been using recently is industry standard both at OEM and F1/WRC level. The simulations are incredibly accurate subject to the quality of the data entered into them.

For example, even going back to 2002 when Cosworth were developing the Focus ST170 with Ford, their engine simulation was validated on an engine dyno to within 2% accuracy. Moving forward nearly 10 years, things are even more accurate now.

My dissertation this year is to do with variable valve timing and i'm hoping that my own simulation will validate within a 5% accuracy margin. With the software simulation I can see the affects of changing my cams to assymetrical, increasing/decreasing duration, increasing/decreasing lift, alterations to the timing where peak lift occurs etc. Not only that but I can see full analysis of the valvetrain in terms of cam follower inertia, stress, oil film thickness, wear load, camshaft bending dynamics - even down to the cam belt tension!

Last time I checked, it was pretty hard to check all those variables by trial and error testing?

Admittedly the software license for this is $30,000 a year, (fortunately i've got access to it as part of my degree) but you can literally target any changes/areas of interest with the click of a mouse and evolve a camshaft through to the final stages before getting a prototype made.

 

Morning Jim, Vegas is awesome as long as you spend no more that a week there I reckon. I think teh 4 days I went for is ideal as while its big, its not THAT big. I would plan a couple of resorts a day, start at one end and work down. Seeing rivers inside hotels and shopping centers that make the trafford centre look both small, and low budget is absoluitely incredible. The gambling is good too if thats your thing. oh, and you MUST jump off the stratosphere, its 900ft to the floor... what a buzz!



Ah, got ya. My answer is in direct relation to this topic as the OP is asking about a T34 engine. Lift isnt the problem in the exhaust cycle, its duration, and specifically overlap. I asked you to clarify "bigger" as most readers will assume that the YB BD range of cams all get wider and taller as the numbers rise and thats not true, the 10/14/15/16/16+ etc are just part numbers really.

 

I think you misread what I said then.

What I said was:
you're talking about differences of a couple of percent on an N/A engine, I'd say that already wasnt definitive, and the moment you introduce different turbos into the mix on a FI engine it gets even less accurate.

And for the aftermarket guys the problem isnt the software, although at the 30K you mention I cant see too many rushing to buy it, the problem is like I said, the lack of data.


Whack a YB engine with a set of BD16 cams and a GT35R into your software and see what it says for me please?

 

Interersting thread. I was told not to bother changing exhaust cam until power levels exceed 550bhp.

And Chip - delete some pm's. I know you are popular but not 500 pm's popular

 

Rich, done mate.

 

Awesome! Yeah,I planned 3days and nights then Hawaii for few nights, it does sound absolutely awesome,

I'm with ya, that's what confused me, but yes, that was just an example we go up a lot on duration Too hense saying it seems a little strange comment like