Camshaft Exhaust Lobe Question

[wantattype2]

After reading the post on 6262 turbo times and combinations, I would like to know what effect changing the exhaust lobe duration has on a turbo charged engine? Lets say for example we have a 6262 turbo with Champion ported irons & intake, stock exhaust headers and a 210 duration at .050 single pattern cam with 500 lift with 1.5 rockers. What effect would changing to a 210/206 or 210/214 dual pattern cam have if everything stayed the same? Just looking for the theory behind so many somewhat similar cam grinds.

Thanks for your replies!

 

[earlbrown]

Your question is much more complex than you're thinking it is. Quoting only the duration numbers at one lift doesn't tell you anything about the ramp speed or the shape of the lobe... The 'similar' cam grinds you read about aren't exactly all that similar. Different brands will quote different things or marketing reasons. Some will embellish the lobe size so people buying based on big numbers won't have dog...

but lets say all things are truly equal (they aren't)... increasing the duration of the ex lobe 8 degrees means you gained 4 degrees of overlap. If your engine can use more overlap, it'll help.... that same can change in an engine that has the right amount of overlap (or too much) will hurt....

Now lets say you spread out the LSA so the exhaust lobe got fatter but you moved them apart so the overlap stayed the same (we'll assUme the overlap was 'perfect') In this engine if the LSA was too tight, you'll gain power... if the engine doesn't like the last closing ex valve or the LSA was already too wide, you'll lose power


From what I've seen over the years, pick out the cam you think you need, then buy one 2 or 3 sizes smaller. With any luck, you went small enough.

 

[Nick Micale]

After reading the post on 6262 turbo times and combinations, I would like to know what effect changing the exhaust lobe duration has on a turbo charged engine? ........... What effect would changing to a 210/206 or 210/214 dual pattern cam have if everything stayed the same? Just looking for the theory behind so many somewhat similar cam grind..............

The internet provides us with a wealth of tech information as well as lots of advertising hype - good and not so good.

Questions like your's can be discussed with opinions, but since many other factors in a build can affect the final result, it will generate many opinions, but the "proof" can only be obtained when subjected to real world use.

One major omission here is that actual use and operating conditions are not given, are you looking for maximum performance for your build for street or track operation?

Cam manufacturers and vendors would like us to change cams every time we make a change to our build because that is their business. Do their latest and greatest cam profiles give us any more performance unless we are taking our build to the limit, probably not?

Maybe seeing many stock cams running into the 10's with good add-on parts has given me the opinion that just changing a cam that is working well in a given engine combination is not going to make much more power, if any.

When we get into expensive competition builds, we want the best match possible working under the rule limitations to obtain the most HP possible. To find the best choice then requires dyno and track testing, as well as knowledge of prior builds of ours, and others that have gone down the same road.

With all that said, if you feel a certain cam is what you want, go for it as I do not think you could make a bad choice!

 

[wantattype2]

Thanks for the replies. I guess I was looking for an over simplified answer. If a street car already had the recommended convertor, I would like to know if a smaller exhaust lobe would make a turbo like the 6262 spool faster due to increased exhaust gas velocity, or would changing the LSA be more effective ? Could you point me in the right direction on what to read to better understand the theory of camshaft design ?

 

[earlbrown]

A smaller lobe won't nessessaraly give you more velocity. A shorter duration lobe give you less time spent putting energy into the exhaust manifold. A bigger 'pop' on the turbo is one of the reasons I like higher compression on our turbo engines. (plus the higher static compression lets you get away with big cam lobes and maintain dynamic compression)

Could you point me in the right direction on what to read to better understand the theory of camshaft design ?

That's a can of worms right there!!! I know quite a bit about this stuff, and the only thing I really know about cams is that I don't know near enough!! And the more I learn, the more I realize I don't know.

 

[turbo96max]

Good question for a noobie like myself. Im looking for a cam and really want to learn about right and wrong as well. Car has a cam but I dont jnow for sure what it is so im replacing it. Was looking at como 212 212 but a friend recommended 212 206 ( webber) flat tapped. Goals are 10.80s w ported valved irons e85 120s sd front mount forged pistons ported stock headers soon ptc 9.5 nl is there really much of a difference? Looking at 25 30 psi .What has worked well for similar builds ? Eventually ill grab a 6262 similar turbo.now ill be running a pt70h w garrett .63 housing.

Posted from the TurboBuick.Com mobile app

 

[turbo96max]

Is there a place to get more info. I read the carcraft article which pretty much led me to believe the older turbos liked a smaller exhaust lobe such as say 212 206 but the newer more efficient turbos didnt gain from it and 212 212 would be ideal. *say all things being equal. Any input?

Posted from the TurboBuick.Com mobile app

 

[bison]

If the owner wants to spend the $$$ to run more aggressive ramps there are definitely things that can be done to optimize any given situation. I've posted about this many times before. You need to known the intake manifold pressure and the exhaust pressure. Duration numbers don't mean crap either. Who cares about duration at .050"? I sure don't. My engine isn't flowing anything useful at that lift. It's not possible to compare different lobe families without actually analyzing the lobes unless the masters for the lobe are the same.

 

[dandaman]

its really hard to say with out hard data. What works with one cars combo might not work with another. Header pipe sizes and exaust housing A/R play a roll too. Unfortunatly the only way to know is to test back to back the different grinds on one combo. We have 2 combos we race. One uses a gt3540r turbo with a 218/212 cam and has been 10.0@138. We wouldnt know if a 212/212 or a 218/218 would work better with out testing.​

 

[turbo nasty]

No matter the cam with stock ported irons/intake/headers and a 6262 w a .63 hot side your gonna have to lay (helluva lot more than 25 psi) the boost to it to run a good number. Good number IMO being high to mid 10's in a 3500 lb car and a 1.5 60'.
With that said all lobes aren't made the same..... so one company's 208 or whatever isn't gonna do the same as another simply based on lobe profile. So its a can o worms.

 

[Mike Licht]

To try ans answer your question somewhat simply, It is not about duration but about event timing, when the valves open and close, the exhaust can be moved to increase drive pressure on the turbo which will result in power gains and faster spool. If you change the duration you may also need to change the lobe separation or installed center line of both to get the events where you think they need to be. Different lobe lift rates and to some extent rocker arm ratios have influence here to. This is a very simple answer to a very complex question. If you desire more info call me, I will be happy to give you my thoughts for your application and if the gains would be worth the effort/expense, in many cases they are not
Mike

 

[turbo96max]

Thanks for the feedback fellas. Im thinking I may not need to worry about a cam for now. Converter and turbo need more immediate attention . Ill keep research ing for future swap.

Posted from the TurboBuick.Com mobile app