Notices
Forced Induction Superchargers | Turbochargers | Intercoolers

wrong cam for turbo?what should I go with?

 
Old 07-19-2004, 08:58 PM
  #1  
Teching In
Thread Starter
 
Join Date: Jul 2004
Location: Bensenville,Il
Posts: 20
Likes: 0
Received 0 Likes on 0 Posts
Default wrong cam for turbo?what should I go with?

I had purchased a comp cam,dual springs and rockers. I picked the cam without turbo in mind but just purchases a Turbo Tech t-76 kit. The cam is supposed to go in this weekend but need advice on what to do. The turbo will not go on untill October maybe end of September. The cam is 232/240 595/608 112 LSA. I know this is not good cam for the log style manifold I should go with a reverse split and larger LSA. What would be a good cam, stock LS1 But still want it to sound pretty mean but with good performance in mind. What would happen using the cam I have now? ;

Thanks in advance
ryansblk98ss is offline  
Old 07-19-2004, 09:13 PM
  #2  
TECH Enthusiast
 
Wildman's Avatar
 
Join Date: Oct 2003
Location: Bakersfield, Ca.
Posts: 729
Likes: 0
Received 0 Likes on 0 Posts
Default

A good, inexpensive cam would be the 2002+ Z06/ls6 cam. Can get it right around $200 from SDPC.

By "MEAN", I am assuming you meant idle or lope. You do not want any type of lope with a turbo cam. And as you already stated, you want a reverse split and a large LSA to keep the exhaust back pressure from goin up into your intake.

Hope this helps,
Paul
Wildman is offline  
Old 07-20-2004, 12:29 AM
  #3  
LS1Tech Co-Founder
iTrader: (34)
 
Pro Stock John's Avatar
 
Join Date: Nov 2001
Location: Chicago, IL
Posts: 42,517
Likes: 0
Received 0 Likes on 0 Posts
Default

Noyzee had a tasty turbo cam for sale in other thread...

Your current cam will make more power than a stock cam for a turbo setup for sure.. Duration makes power. Might see stronger midrange at the expense of peak horsepower. With the overlap of that camshaft you might make the same power as if you had a mild cam in there...
Pro Stock John is offline  
Old 07-20-2004, 01:06 AM
  #4  
TECH Addict
iTrader: (5)
 
Join Date: Mar 2002
Location: VA
Posts: 2,321
Likes: 0
Received 0 Likes on 0 Posts
Default

230/222 or 234/226 with .570 .580 115-116 LSA would be a nice turbo cam. If u want the cam to be nasty then go with the larger duration and 114LSA.
LSs1Power is offline  
Old 07-20-2004, 09:27 PM
  #5  
TECH Resident
 
V8_DSM_V8again's Avatar
 
Join Date: Jun 2004
Posts: 840
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by LSs1Power
230/222 or 234/226 with .570 .580 115-116 LSA would be a nice turbo cam. If u want the cam to be nasty then go with the larger duration and 114LSA.
Those are ok cams... I have seen regular as opposed to reverse split patterns work phenomenally as well... I think they may even be better since the engine needs more help getting rid of exhaust than taking in air.
HKS 264/274 *advertised* splits kick *** in imports with restrictive factory manifolds and smallish turbine sides.

The idea here is to run less intake duration which allows you to open the intake valve alot later preventing overlap and therefore reversion. There are different kinds of reversion...

You can have intake charge get pumped back out after BDC because the intake valve was held open too long..

You can have it happen on the exhaust side in more than one way.. The valve opens too far before BDC, it vents then flows back in a bit because the piston has'nt moved that far up the exhaust stroke so cylinder pressure dips a split sec . It will get pushed out as it gets closer to TDC but flow still changes direction..

Now reversion can happen later too. The worst is having post TDC reversion on an engine with too much overlap.. The exhaust charge will make its way out the intake since the cylinder pressure drops below the exhaust manifold.

The goal is to have valve events just right...

Close the exhaust just before, at or very shortly after TDC ...

When cylinder pressure is about equal to exhaust manifold pressure that is the goal but dont do it too late or the cylinder pressure will drop bellow the E manifold since the piston is going down making room....

Open the intake valve a ways after the exhaust closing... The cylinder pressure should be below the intake pressure then..

The intake closing point is mostly an RPM deal on on turbo engine..

You don't need to keep it open as long for a mid rpm power band as an all out racing engine. In fact you will make more power in the mid RPM than the high rpm engine. At your target RPM too late an intake closing will result in that intake flow reversion I was talking about.. You had the valve open long enough for a good filling... now the piston pushes the charge out because you got greedy. Closing it too soon for your target RPM and you will close it before it can force the maximum possible amount of air into the cylinder. Since an intake stroke takes less time per cycle at a higher rpm you will have more open time and will loose out on some hp lower in the RPM range but have more peak... A lower rpm has more time for everyting to take place so it get as "full as it is going to get" long before a high RPM cam closes the big valve.

The exhaust opening is about RPM too... Open it sooner = better high RPM Opening it later = better low rpm power...

Too late of an exh opening (same closing point) and you have more left over exhaust in your cylinder and higher ex mani pressure.. A certain degree of this is engineered into factory turbo car cams to help spool They hold on to the exhaust longer to unleash more peak pressure on the turbine... On a ho hum street car that is fine...

Too early of an exhaust opening will take away some of the force that was pushing the piston down on the power stroke. A cam for an upper RPM will make more power there than down low due to this. But there are limits as in too early for even 8k rpm.. An opening event too early for 4k could be just right for 6,800...

One vote for a standard split cam here... It just has to be one with no overlap... in most cases the opposite of overlap... a spread.. Atleast 10* more exhaust duration than intake.. LSA will be dependant on duration probably in the 114-117 range for a performance cam... Alot of high perf cams for factory turbo cars have about the same EVC (exhaust valve closing) and IVO (intake valve open) points.. Those two are where you get the most trouble.. The other two IVC (int close) and EVO (ex open) are within reason all about matching a desired RPM for peak power.

DSM examples... theory applies.. numbers dont.

IVO: Intake valve open 7 deg BTDC
IVC: Intake valve closed 25 deg ABDC

EVO: Exhaust Valve open 42 deg BBDC
EVC: Exhaust Valve closed -10 deg ATDC

This is a CUSTOM comp for 4g63's

IO - 2 BTDC 203 duration 99.5 centerline
IC - 21 ABDC
EO - 45 BBDC 211 duratrion 119.5 centerline
EC - -14 ATDC

Now on a 2 valve engine you should close the exhaust valve later and open it sooner because it dont flow as good in fact you will want more duration than this example on both sides but a split about the same in the same direction... You still would want more exhaust duration than intake and 12 degrees or so of sepration between them so -2 ATDC to +5 ATDC.. ATDC means after top dead center so a - number is really before TDC. Then maybe -10 to -17 BTDC depending on the exhaust close on the intake... Before TDC which means a - is after TDC.. So the cylinder pressure of leftover exhaust can drop when the piston does and be below intake pressure.

NO engine gets rid of all exhaust.. You know you have the right specs on EA pro when you get good power, low ex man pressure and the least amount of residual exhaust %. There is also reversion and short circuit data. You can see the different kinds of reversion as they happen. I'd download the demo and play with cam specs. Screw up on purpose to see exagerated examples.. Then get serious.. When I have time I'll do a use EA to put up a comparison of a 234/226 vs some specs I cam up with for a regular split..

You can make big power with a small intake duration... Too big a intake duration means overlap and with a log manifold you WILL revert. So in reality those extra degrees of open before when you should have opened it just dont put any air in the cylinder... Any degrees after the optimum closing point is just wasted dynamic compression because it had filled enough and you should have shut the valve and started squeezing it already.

The best exhaust duration depends on the rpm range and the amount of boost you are running... More boost = more exhaust volume to get rid of so more duration.. More RPM means opening the exhaust valve sooner so more duration..
V8_DSM_V8again is offline  
Old 07-20-2004, 09:43 PM
  #6  
FormerVendor
 
qqwqeqwrqwqtq's Avatar
 
Join Date: Dec 2001
Location: WWW.SPEEDINC.COM
Posts: 2,444
Likes: 0
Received 1 Like on 1 Post
Default

More duration, more overlap will always be more power. Yes, even with a turbo.

For example, a 224/224 on a 112 will make more peak power than a 224/224 on a 116, at the expense of response and low end power. (boost threshold will be higher).

Overlap with a turbo cam is fine. Even if reversion does happen, you will still make more HP due to reduced pumping losses.
qqwqeqwrqwqtq is offline  
Old 07-20-2004, 10:49 PM
  #7  
TECH Resident
 
V8_DSM_V8again's Avatar
 
Join Date: Jun 2004
Posts: 840
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by INTMD8
More duration, more overlap will always be more power. Yes, even with a turbo..
Yes but to a degree depending on turbo backpressure so not always.. With a lower backpressure turbo system.. Like twins on a really good 4-1 header and the right A/R turbine with an efficient wheel you can use a big cam.. It will still crossover.. (more ex pressure than intake) but no where near as bad and no where near as early. However ALOT of overlap pre-pressure crossover will result in burning portions of the fresh fuel mixture in the exhaust manifold. Yes a small amount of overlap with a good turbo system is fine.

Now a tight turbine housing.. a not so high tech turbine wheel and a log manifold it will run like crap with those big cams.. Alot of overlap due to the high exhaust manifold pressure vs intake = alot of residual exhaust left in the intake charge. You trade one loss for another and lose more power.



Originally Posted by INTMD8
For example, a 224/224 on a 112 will make more peak power than a 224/224 on a 116, at the expense of response and low end power. (boost threshold will be higher).

Overlap with a turbo cam is fine. Even if reversion does happen, you will still make more HP due to reduced pumping losses.

Ask Chris at comp...I have had numerous talks with comps best turbo cam guys...

They have a 236/236 115 LSA custom grind with turbo specific profiles that rocks.. Provided you have good headers and alot of turbine flow.

With a turbo(s) you can get losses from too much duration too.. With overlap or lack there of being the same look at the intake valve closing points... Too late or too early means you missed HP. A cam will make its peak power where dynamic compression is the highest..

The whole point to a long intake duration on a non forced induction engine is that the engine is pulling all the air in and the airflow lags behind piston movement. With a supercharger or turbo the intake valve should close sooner since the air is'nt playing catch up with the piston much at all... Compress it don't blow it back out the intake port.

I just think never say never and never say always on some things. There are examples of what you are saying that definately prove it.. Just what most people are building does'nt look anything like those examples.

Honestly if money were no object just put a pressure sensor at the end of 1ft of metal tubing before the turbine.. Datalog your manifold pressure on the intake side too and send the data and complete engine specs to comp.. They will grind you a cam that will blow your mind.. The big deal is exhaust manifold pressure vs boost pressure across the RPM that will determine what cam specs are right.
V8_DSM_V8again is offline  
Old 07-21-2004, 12:16 AM
  #8  
FormerVendor
 
qqwqeqwrqwqtq's Avatar
 
Join Date: Dec 2001
Location: WWW.SPEEDINC.COM
Posts: 2,444
Likes: 0
Received 1 Like on 1 Post
Default

Well, I've tried 4 different cams in my turbo motor (std split, rev split, a few single patterns), various exhaust housings, measured backpressure, etc.

Even when my backpressure was nearly double boost pressure, the higher duration/overlap cam made more power.

I guess I'll stay with my testing and results, and you can stay with theory and hypothesis.
qqwqeqwrqwqtq is offline  
Old 07-21-2004, 01:05 AM
  #9  
TECH Resident
 
V8_DSM_V8again's Avatar
 
Join Date: Jun 2004
Posts: 840
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by INTMD8
Well, I've tried 4 different cams in my turbo motor (std split, rev split, a few single patterns), various exhaust housings, measured backpressure, etc.

Even when my backpressure was nearly double boost pressure, the higher duration/overlap cam made more power.
http://www.hotrod.com/techarticles/e...rb/index5.html

Don't beat up the valvetrain by going for extreme lift and duration numbers; it's just not needed! Turbo cams can be smaller than equivalent cams for normally aspirated engines operating in a similar rpm band.
Hmmmm

In fact, if a cam works through 5,500 rpm on a normally aspirated engine, it'll be OK to about 6,500 on a turbo engine in terms of its ability to feed enough air and fuel into the engine. Using just a 210-degree duration (at 0.050) flat-tappet hydraulic cam, mild heads, and 8.0:1 compression, a single TO4-series AiResearch turbo with a 66-70mm inlet inducer is capable of delivering 600 hp at 15 psi on a 350 Chevy and 850 hp at 25 psi with race gas. A big-block 502 fitted with the same series turbo--but now using a larger 76mm inlet and a 220-degree (at 0.050) cam--easily makes 700-800 hp on pump gas. Moving up the food chain, Ken Duttweiler's current 287ci small-block Chevy V-8 running in the NHRA BB/AT class makes 1,500 hp on 30-psi boost. The full-race mill has two 70mm-inducer Innovative turbos, a secret roller cam somewhere in the 250-275-degrees-at-0.050 range, and splayed-valve heads.
Hmm destroke and I'll bet that he has more exhaust duration than intake... The only reason why his duration is so high is the super high redline of that 287 needs it to make power that high.


One thing that does set most turbo cams apart is the lobe displacement angle (LDA)--115 degrees is not uncommon to reduce overlap. The turbo force-feeds air on the inlet side, so early intake opening isn't needed.
So a valve that opens as early as a naturally aspirated motor is a complete waste.. I think I said that.

But since exhaust backpressure can be a problem with a turbo, there may be more pressure on the exhaust side than on the inlet, and excessive overlap can create a reversion problem. Many engine builders run slightly more exhaust duration than intake duration to control the overlap point and help get rid of the exhaust gases.


Hmm... So if you have more exhaust duration than intake you will have less overlap AND less exhaust pressure so what overlap you may have is less of a problem.. Where have I heard that before.

Since he has log mani's no overlap is good overlap... I assume you have some 4 into one headers feeding your turbine housings... So some overlap yet still very much less than a non turbo car is a good thing.

Originally Posted by INTMD8
I guess I'll stay with my testing and results, and you can stay with theory and hypothesis.

I guess I'll stick with listening to and learing from the testing and results of people who design highperformance camshafts. As well as those who have built alot of turbocharged cars.
V8_DSM_V8again is offline  
Old 07-21-2004, 01:45 AM
  #10  
TECH Addict
iTrader: (5)
 
Join Date: Mar 2002
Location: VA
Posts: 2,321
Likes: 0
Received 0 Likes on 0 Posts
Default

It doesn’t make any sense for me why would someone use larger exhaust duration than intake on a Turbo car. I would understand if u told me a SC car, but not turbo. The turbo has two sides.... One generates air flow going to the intercooler and the other one gets exhaust flow from the motor to spin the turbine. So if u want a faster spool up u should increase the speed of the exhaust flow by pushing the same amount of exhaust through a smaller exit hence using a smaller exhaust than an intake (I asked a physics professor about that). It shouldn’t interfere with the top end because the turbine is spinning faster anyways with a smaller exh dur than int dur which leads to more air on the compressor side hence more air getting into the motor and faster spool up and response. Oh by the way, UK 4g63's are using 272/264 cams in their cars and also Boost Solution is doing the same thing now. I think most of the import people got used to hearing 264/272 or 272/272 and it became a trend to go with such duration. I personally think a 272/264 will give better power through out the whole range and still keep its top end capabilities. This is what makes sense to me and its my opinion
LSs1Power is offline  
Old 07-21-2004, 04:34 AM
  #11  
On The Tree
iTrader: (1)
 
383838's Avatar
 
Join Date: Jun 2004
Posts: 121
Likes: 0
Received 0 Likes on 0 Posts
Default

"More duration, more overlap will always be more power. Yes, even with a turbo."
That's assuming the turbo is large enough to waste the air being unused with falling way out of it's efficiency ratio. Your car has responded well because of the size of your turbo's, plenty of air for 1100+hp, but all turbo cars are not that lucky.

There's WAY too much involved for the "what's a good turbo cam" question. It's like asking "what's a good car". It all depends...
Without getting into a cam theory debate, which I'm all for I just hate to type, ANY cam will make power with a turbo, just like any cam will make power NA, supercharged, etc. It's all about efficiency with turbo's though, you want a cam that keeps your turbo in it's sweet spot for maximum power. Larger overlap cams will require more RPM from the turbo to create the same manifold boost as a no overlap cam which is no big deal if the higher RPM of the turbo keeps it in it's peak efficiency island. However, for all intensive purposes the cam you have now will work, but with stock heads a small reverse split, like 2-4 degrees would most likely make more power. If you're running a mid 230 duration cam, say a 236/234 on a 115, there is still going to be no mistaking that car's got a cam in it. It'll still lope pretty hard, no worries.
383838 is offline  
Old 07-21-2004, 08:19 AM
  #12  
TECH Resident
 
V8_DSM_V8again's Avatar
 
Join Date: Jun 2004
Posts: 840
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by LSs1Power
It doesn’t make any sense for me why would someone use larger exhaust duration than intake on a Turbo car.
Exhaust Backpressure is the reason... On one side you have air getting forced in... so you forced more in than normal. On the other side you now have all this extra combustion byproduct but now you have a turbine restricting flow.

Originally Posted by LSs1Power
So if u want a faster spool up u should increase the speed of the exhaust flow by pushing the same amount of exhaust through a smaller exit hence using a smaller exhaust than an intake (I asked a physics professor about that).
That is done on some factory turbo cars along with tiny turbos to keep Mr or Ms I cant change my own oil from complaining about lag...

Originally Posted by LSs1Power
It shouldn’t interfere with the top end because the turbine is spinning faster anyways with a smaller exh dur than int dur which leads to more air on the compressor side hence more air getting into the motor and faster spool up and response.
It interferes with the top end.... You will make more low rpm power and spool sooner but kill the top end. It decreases peak exhaust back pressure at upper rpm making.. You waste less power on the top end pushing exhaust out and have less exhaust left in the engine.



Originally Posted by LSs1Power
UK 4g63's are using 272/264 cams in their cars and also Boost Solution is doing the same thing now. I think most of the import people got used to hearing 264/272 or 272/272 and it became a trend to go with such duration. I personally think a 272/264 will give better power through out the whole range and still keep its top end capabilities. This is what makes sense to me and its my opinion

The 272 is really only a 213 duration at .050 cam.. You really are'nt going to see an extremely drastic difference with any combination of the HKS cams.. There is no overlap on any of them.. Its a 16v turbo engine alot of duration is'nt needed which is why the biggest cam I have ever seen is a 220 at .050..
V8_DSM_V8again is offline  
Old 07-21-2004, 02:35 PM
  #13  
TECH Addict
iTrader: (5)
 
Join Date: Mar 2002
Location: VA
Posts: 2,321
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by V8_DSM_V8again
Exhaust Backpressure is the reason... On one side you have air getting forced in... so you forced more in than normal. On the other side you now have all this extra combustion byproduct but now you
have a turbine restricting flow.
You can decrease the back pressure by having a good exhaust or larger AR on the exhaust side and still keep your faster spool and better response. So you are saying force less air inside the motor and force slower air outside the motor into the turbine? It should take more time to move the impeller on the exhaust side to generate air on the compressor side and u wont have as good response and spool up.



Originally Posted by V8_DSM_V8again
It interferes with the top end.... You will make more low rpm power and spool sooner but kill the top end. It decreases peak exhaust back pressure at upper rpm making.. You waste less power on the top end pushing exhaust out and have less exhaust left in the engine.
As i said before you can always have a larger AR on the exhaust side to solve this problem and also if u noticed i said larger intake duration than exhaust, But higher lift on the exhaust side than the intake to allow All/Most the exhaust to get out of the engine.




Originally Posted by V8_DSM_V8again
The 272 is really only a 213 duration at .050 cam.. You really are'nt going to see an extremely drastic difference with any combination of the HKS cams.. There is no overlap on any of them.. Its a 16v turbo engine alot of duration is'nt needed which is why the biggest cam I have ever seen is a 220 at .050..
213 in a 2.0L is like 230 in a 346CID 5.7L V8. I still concider it big for a 2.0L. Thats why u see 572CID engines running 248/257 at .050 and still idle fine with no problems. I just cant wait to see the results from Boost Solution about the cams he is going to test. I'm sure there are people here on the board that tried split patterns VS reverse split patterns on their turbo cars. They can join the debate.
LSs1Power is offline  
Old 07-21-2004, 02:59 PM
  #14  
TECH Resident
 
V8_DSM_V8again's Avatar
 
Join Date: Jun 2004
Posts: 840
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by LSs1Power
You can decrease the back pressure by having a good exhaust or larger AR on the exhaust side and still keep your faster spool and better response.

Yes you can run a better exhaust manifold and turbo then a different cam... ... but my point was that the ratio of the exhaust manifold pressure to the intake manifold pressure determines what cam specs are right... So some guy goes hey I have x turbo and a log manifold and need a cam... Not I want to change my turbo, manifold and get a cam.


Originally Posted by LSs1Power
So you are saying force less air inside the motor and force slower air outside the motor into the turbine? It should take more time to move the impeller on the exhaust side to generate air on the compressor side and u wont have as good response and spool up. .
OMFG

I'm saying a cam with the correct valve timing events for a turbo will force more air into the engine with a much smaller duration than a huge intake duration cam. Any duration before the intake stroke does nothing on a turbo engine as compared to a NA motor. The amount of duration after the intake stroke reaches BDC is alot less to.. Truth be told too much intake duration than what you need for your RPM goal and you just fresh charge back out the intake as the piston rises...


Originally Posted by LSs1Power
213 in a 2.0L is like 230 in a 346CID 5.7L V8. I still concider it big for a 2.0L. Thats why u see 572CID engines running 248/257 at .050 and still idle fine with no problems. I just cant wait to see the results from Boost Solution about the cams he is going to test. I'm sure there are people here on the board that tried split patterns VS reverse split patterns on their turbo cars. They can join the debate.
213 with 16valve heads is alot..
V8_DSM_V8again is offline  
Old 07-21-2004, 03:20 PM
  #15  
TECH Addict
iTrader: (5)
 
Join Date: Mar 2002
Location: VA
Posts: 2,321
Likes: 0
Received 0 Likes on 0 Posts
Default

This is worthless and pointless.... U are not going to convince me and I'm not going to convince u.... So let the guy who started the thread pick a cam based on what he saw here or he can call a cam company to help him with it. I'm sticking with the reverse split cam for a turbo charger engine.
LSs1Power is offline  
Old 07-21-2004, 03:32 PM
  #16  
TECH Resident
 
V8_DSM_V8again's Avatar
 
Join Date: Jun 2004
Posts: 840
Likes: 0
Received 0 Likes on 0 Posts
Default

I don't give an aviating coitus if I convince you... Everything I learned is from camshaft designers with decades of experience.
V8_DSM_V8again is offline  
Old 07-21-2004, 03:46 PM
  #17  
TECH Addict
iTrader: (5)
 
Join Date: Mar 2002
Location: VA
Posts: 2,321
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by V8_DSM_V8again
Everything I learned is from camshaft designers with decades of experience.
Good for you


Check this thread out and show it to your camshaft designers who had decades of experince because i think they need to learn something new
http://forums.evolutionm.net/showthread.php?t=88765
LSs1Power is offline  
Old 07-21-2004, 04:47 PM
  #18  
FormerVendor
 
qqwqeqwrqwqtq's Avatar
 
Join Date: Dec 2001
Location: WWW.SPEEDINC.COM
Posts: 2,444
Likes: 0
Received 1 Like on 1 Post
Default

[QUOTE=V8_DSM_V8again]http://www.hotrod.com/techarticles/e...rb/index5.html
QUOTE]

Damn, to think I wasted all that time under my hood and on the dyno, when I could have learned everything there is to know just by picking up HOT ROD magazine!

LOL!
qqwqeqwrqwqtq is offline  
Old 07-21-2004, 11:25 PM
  #19  
TECH Enthusiast
 
Unusual T/A's Avatar
 
Join Date: Mar 2002
Location: ft worth tx
Posts: 602
Likes: 0
Received 0 Likes on 0 Posts
Default

[QUOTE=INTMD8]
Originally Posted by V8_DSM_V8again
http://www.hotrod.com/techarticles/e...rb/index5.html
QUOTE]

Damn, to think I wasted all that time under my hood and on the dyno, when I could have learned everything there is to know just by picking up HOT ROD magazine!

LOL!
LMAO! I agree with ls1power until proven otherwise.
Unusual T/A is offline  
Old 07-22-2004, 10:56 PM
  #20  
TECH Resident
 
V8_DSM_V8again's Avatar
 
Join Date: Jun 2004
Posts: 840
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by LSs1Power
Good for you


Check this thread out and show it to your camshaft designers who had decades of experince because i think they need to learn something new
http://forums.evolutionm.net/showthread.php?t=88765


You know what here is a quote from that site.

Well, idle with the AEM and the 272/264 is LIKE stock.
Like I said they are SMALL cams.. Good heads plus forced induction = small camshaft. In reality the duration specs are closer to a stock LS1 cam and not even comparible to an LS1 performance cam.. Translate HKS specs into US cam specs from metric and they look like baby cams compaired to one for a 2valve per V8. It is a 16valve turbo motor... I think the exhaust side of that head outflows a stock LS1 intake side. Thats apples to oranges..

A HKS 272 = 213* at .050. Its a 213/203 at .050 combination THERE IS NO OVERLAP INFACT THERE IS A SEPERATION of 2-3 degrees when there is a 272/272 combo so it is wider with 272/264 by about 5 degrees.. So at .050 the exhaust valve closes about 8 degrees before the intake.

a 264/272 comes out to around 108* lobe seperation advanced 8 degrees...
Intake centerline 100* exhaust is 116*...

A 272/264 comes out to around 108* lobe seperation advanced 9 degrees...
Intake centerline 99* exhaust 117*


I am willing to bet that if you used adjustable cam gears to dial in a 264/272's Exhaust closing and Intake open points at .050 to match the 272/264's it will walk all over it. I'll put even more $ on the table if I can run my comp exhaust cam with a with a touch more duration (7 degrees) and lift in the exhaust side instead. Then run HKS 272 intake. I actually run a std pattern 220/220 at .050 (HKS 272 is 213) right now since I don't have excessive backpressure and there is'nt an overlap problem anyway.



An LS1 with a huge turbine housing like a thumper, headers and a well designed exhaust system may well work good with a bigger single pattern and even a reverse pattern cam. However my money, pinkslip, first born etc is on a single pattern with just enough duration for the intended powerband.

A restrictive turbine housing and wheel combination wont do so well with that. IT IS'NT ONE SIZE FITS ALL WITH TURBO CAMS... It's all about what the turbo system is.

From a Comp Employee

http://www.dsmtuners.com/forums/show...ight=comp+cams

If all else is equal, a cam with a tighter lobe separation, more overlap, will have more peak torque. OF COURSE THIS ONLY APPLIES if the EXHAUST BACK PRESSURE relative to the intake pressure is NOT TO HIGH. This occurs because of the late exhaust opening point. However, the torque is "peaky" because at higher rpms the cylinder needs an earlier opening to allow time for the exhaust gases to be effectively removed from the cylinder. The peak horsepower WILL BE LESS because HP is time, rpm, based. So as the torque falls quicker with a tight lobe separation the peak hp will also DROP. The reason for this has to do with the time available to expel the exhaust gases. It is much easier for a cylinder to remove the exhaust gases at 4k than it is at 5k. Try to think of it as the injector available time to inject. As the rpms increase there is simply less time to do the task. If you want to obtain the highest torque numbers but at a higher rpm, you need to increase the duration as well as close the exhaust later.

As far as volumetric efficiency is concerned, let’s assume that the intake closing is at the same point with two setups. Setup A we have an exhaust opening of 42 degrees before bottom dead center (BBDC). In Setup B we change the lobe separation 5 degrees. The exhaust opening is now at 37 degrees BBDC. We just allowed the exhaust gases to "push" on the piston for another 5 degrees. This will increase the VE. However the torque will fall off quicker as the rpms increase so the peak hp will be less. This is because of the lack of available time to expel the exhaust gases. Now this assumes that the intake closing is not changed. If it is, a whole new range of possibilities can occur.
Hmm tighter lobe sep = hp at lower rpm Wider lobe sep = HP at higher RPM...


http://www.gmhightechperformance.com...ICK/index.html

Comp billet roller 230°/230° duration, .608-inch lift
Race weight: 3,430 pounds
Best ET/mph: 8.57 at 159.87
With just 230* duration single pattern...

Tell him he should have run a 234/226 and watch him laugh and blow your doors off...

. YOU DONT mother trucking need a big cam anyone suggesting t-rex like duration is something illegal..

What I mean by a good cam for a restrictive manifold is like 220/230 ish... or so depending on the size and RPM range of the motor maybe slightly smaller or slightly bigger...

With a really good (only log you left in the toilet) turbo system run a single pattern.


http://www.hotrod.com/techarticles/e...rb/index3.html

A turbo engine doesn't require a big cam to make power. The Bennett-designed, Comp Cams-ground hydraulic roller gets the job done and requires little maintenance. It pulls nearly 15 inches of vacuum at idle--good enough to run power brakes. Stock-style lifters, dog-bones, and spiders work fine, too. A big solid roller would raise power but decrease reliability on the street. With 0.550-inch lift and 236 degrees of duration at 0.050, the seemingly single-pattern profile actually has different intake/exhaust opening rates carefully tailored to a turbo motor's characteristics..
In other words it still has 236/236 at .050 but the lobe design is a turbo specific profile.. Less overlap than a normal 236/236 due to different ramp rates. Why 236 instead of 230 like the buick? Buicks dont rev as high as a smallblock v8 with a 3.25 stroke..

If you want to tell these guys they are wrong feel free...

www.compcams.com

mailto:[email protected]


Originally Posted by INTMD8
Damn, to think I wasted all that time under my hood and on the dyno, when I could have learned everything there is to know just by picking up HOT ROD magazine!
Yes and well all know the real reason that they have what for any of us is an absolute dream job is that they are mechanically retarded...

OMFG... This magazine was around before pong and cable TV... It is'n an HP tv infomercial..

Last edited by V8_DSM_V8again; 07-23-2004 at 12:07 AM.
V8_DSM_V8again is offline  

Thread Tools
Search this Thread
Quick Reply: wrong cam for turbo?what should I go with?


About Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: