Turbo Cam info

[wazzu70]

There has been a lot of discussion recently about turbo cams and I thought it would be good to kind of compile the information in one spot. I am hoping this will be a good reference thread...so please don't gum it up with typical BF.c arguing.

I scanned a few pages from the book Forced Induction Performance Tuning A Practical Guide to Supercharging and Turbocharging by A. Graham Bell and posted it below. I think its a good starting place, but as usual all engines are not created equal and do not respond the same to the same modifications. The amount of back pressure you have in your system is key to choosing a cam which works well!











Hopefully we can draw in some of the more knowledgeable people to give their insights as the information posted above is a bit dated (although I think still relevant).


Here is a website with some decent info:
http://www.hamotorsports.com/cam-gear-tuning.html

• To increase overlap, you have to retard the exhaust, and/or advance the intake.
• To reduce overlap, you have to advance the exhaust, and/or retard the intake.

Simple cam tuning rules for boosted engines:

• Advance intake and exhaust => more low-RPM power, less high-RPM power
• Retard intake and exhaust => more high-RPM power, less low-RPM power
• Less overlap => lower EGTs, faster turbo spool, less fuel
• More overlap => higher EGTs, slower turbo spool, more fuel

Boosted engines don’t like overlap. The incoming cold air and fuel cools down the outgoing exhaust charge, condensing the exhaust gasses. This is VERY counter-productive in a turbo application since the engine needs no help from scavenging to fill the cylinder. I've heard this being called "turbo chill".

Cool, condensed gasses in the same space push less hard on the turbo, causing lag. HOT gasses are better at spooling the turbo, thus the advanced exhaust timing to open the valve sooner in the power stroke. This steals some of those hot, expanding exhaust gasses to help spin the turbo a little faster. When the piston is near the bottom of the bore, hardly any energy is going into rotating the crank anyway, so stealing expanding gasses won’t hurt anything. The retarded intake just helps cut down the overlap further.

Past threads with some good discussion:
Schirck cams versus stock S52 (Turbo application)

I'd like to know what "BMW" guys think that cams won't help their FI motors? Who are these folks you guys speak of? Everyone know's that cams help. The questions are how much at what boost levels Vs cost of the cams vs cost of other equipment. It's justification not validation.

George thanks for the info!!!!

Don, I think the problem is internet hear-say. I've read many times that Schricks are no good for turbo applications. I never really understood why, and honestly never dug into it deeper. Laziness on my part. I think it was something about the overlap not being ideal for a turbo motor or something.

With the small amount of thought I'd given it, couldn't some of that overlap be dialed out? I don't know. I'm pretty new to the inner workings of these motors and the VANOS system.

That all being said, I held off on a good deal a while back on Schrick cams because of that rumor. Simply because I plan to boost my car in the future after it's all been through with a fine tooth comb. Kicking myself in the ass now.

George, thanks for putting an end to the rumor, I for one greatly appreciate it! Off to the FS section to look for a set of cams. Bump my power a bit before I boost it, eh?

Yes it affects it differently, but you'll still find that most turbo cars with properly sized turbos to still provide power at redline will have a positive intake/exhaust manifold pressure ratio for most of their powerband.

The same physics that make overlap favorable for an NA car work on a turbo car due to the roughly similar intake/exhaust pressure ratio. This changes over the powerband, but in general the engine will respond about the same NA or "mild turbo" with a given cam grind.


Going off memory here, but I think my SR20DET has about 18 deg of overlap with 264/264 cams. It killed the bottom end (just like an NA car due to the overlap), but midrange and top end was greatly improved (just like the same NA engine).

Generally it’s a myth that cams that are good for an atmo engine will not be good for a turbo engine. Helping the motor breathe more efficiently is always a good thing. Additionally choosing cams that will have a broad power band or a narrow power band on an atmo motor will yield similar result on a turbo motor.

Overlap is fine on a turbo motor. The physics are still the same, and inertia effects (why overlap is good) are still there.

Truth.

Overlap IS determental. There ISN'T a myth.

Be careful Don. That statement is so broad that it's somewhat misleading. Overlap isn't 'bad' in a turbo engine. Just like any NA engine, there is a point beyond which greater overlap becomes more of a detriment than an asset, all else being equal. In typical street turbo engines, this threshold usually comes more quickly than the NA equivalent due to the use of 'convenience' (e.g. log) manifolds, small OEM turbos, and inefficient hardware that renders the engine incapable of generating good VE in rpm ranges where the overlap should be beneficial, and/or results in such a high PR across the turbine or standing waves in the exhaust manifold that neutralize the benefits of overlap.


There is an old rule that the better an engine runs NA, the more power it stands to make with a turbo. That's a broad statement that is correct. The reason why this simple fact gets lost is due to a common misconception that a turbo is 'blowing air into the engine', and that gets one into trouble.

I used the quoted word..."determental"...not my choice. I know full-well that overlap doesn't hurt on a FI application...and I've already stated the fact that 98%~ of the turbocharged guys in this forum are running a NA cam!!! The point is if you're buying a specialized cam, dont' buy a NA grind. Unless of course you get it for a song and a dance(bang vs buck as I stated earlier).

My only other point was I've never seen where anyone on this forum that has said that an NA grind wont' "work" on a FI motor. That's all. I agree with exactly what you say.

The old saying about the better a NA engine runs, etc etc....well the definition of "runs" in this application would be total HP output before turbo and after I'll assume? I mean that's kinda elementary. The engine that started with a larger HP output will still enjoy that status with the application of FI. BUT, BUT, BUT that doesn't mean it would enjoy the larger GAIN(%)of a lesser HP NA motor. Obviously, as you stated, hardware is a huge part of the equation when talking cams. Now if you want to say a NA engine AFTER it's turbocharged has a better HP potential with a NA cam grind that provides a large overlap vs one that does not, I'd have an issue with that. And so would every cam grinder in the industry.

| 3 Turbos | All Else Being Equal | Testing Thread | DYNO SHEET COMPARISON |

Will say numbers are correct [for Schrick cams] as referred to in earlier post.

Intake at 264 dur. (assuming this number was derived at .004 lift)with an install center (vanos off) of 116 will have the following timing:

Intake open 16 BTDC
Intake close 68 ABDC

Exhaust timing measured at 256dur. @.004 lift on a 108 install center as follows:

Exhaust open 56 BBDC
Exhaust closes 20 ATDC

Resulting overlap 36 degrees

In this case I would advance the exhaust cam.

Amount of exhaust cam advance will have to incorporate other aspects of the build (exhaust housing, type of manifold just to name a few).

Typically for a street turbo app the exhaust center will be in the 114-116 range.

So with the 256 exhaust cam on a 116 center the timing will look like this:

Exhaust open 64 BBDC
Exhaust Closes 12 ATDC

Resulting overlap 28 degrees.

What is the reasoning behind advancing the exhaust cam in this scenario?

In keeping the intake in its prescribed location and wanting to reduce overlap, advancing the exhaust (to a point) will result in higher exhaust temps/pressures while maintaining low rpm cylinder fill.

Retarding the intake to reduce overlap will mean later intake closing which in turn will start moving the power up or to right of the scale.

Most all automotive camshafts close the intake ABDC which is the beginning of the compression stroke. The later you close the intake valve the less charge the cylinder retains and can make or brake the torque curve.

On a boosted engine positive intake pressures will allow later intake closing but many factors must be taken into consideration when calculating boost pressures vs crankshaft position vs piston velocity and how they relate to intake closing.

Is there a textbook on this or are is it primarily the result of working with the cars/cams for long enough to have developed the knowledge?

In practice are you advancing the exhaust cam a degree or so then testing the power curve. Finding where things stop "improving" and then backing it off a notch?

Or is there some math that can be done to get close first?

Math will get you close, experience will get you closer.

There are so many variables but in the end it all comes down to balancing cylinder fill/retention across a desired rpm range. There are basics to follow which are addressed in much of the reading material out there however it is up to the end user/builder to refine, thats where the experience comes in.

Here's how I would cam it [Highboostingm3 setup... 3.05L 85mm x 89.6mm 8.5:1CR Medusafold].

Intake:
272 @.004
234 @.050
.435 lift
Vanos full travel
Install retard center no later than 114

Exhaust:
258 @.004
220 @.050
.430 lift
Install exhaust center @112

You will still have to make some changes to your manifold and it won't be optimum but the above or close to these numbers will achieve what your after.

You could go slightly smaller on the cams but across the board these numbers will make the broadest torque/HP.

I will tell you that your combination with some slight changes, the above camshafts and a decent non ported head, OBD 1 manifold and proper induction will hit more then 600 wheel torque by 4800rpm (aprox 22psi boost) and be capable of more than 700HP by 7400rpm.

I found this graphic pretty interesting too just to see how things change in relation to one another for different types of induction:

[cragg56]

Are you looking for manufacturers and cam specs or discussions on how camshafts work?

[wazzu70]

More looking for info on what works best and why for informed selection, but Its also helpful to know where to buy said cams. I have no association with any vendor or manufacturer.

Manufacturers (from billet or blanks):
Catcams
VAC Motorsports
Paul Burke (through Miller)
Bavarian Solutions
EVOSPORT


Manufacturers (reground or unsure):
ICS
Elgin
Colt Cams I think these are billet...someone please confirm.
Metric Mechanic
Web Camshafts


If anyone knows of other vendors/specs PM me and I will add them in this post to keep things clean.

[Worstenemy453]

Colt Cams, Hopefully to soon be supported by a certain tuner on here.

[chikinhed]

I like the idea of this thread. It may be a good idea to drag all the info that people have into this thread so that a simple search can find it here.

I am in the market for some turbo cams right now . I will be installing my head soon and want to install them at the same time.

I would think that Colt Cams would be buddies with Miller since they are practically neighbors.

Sent from my GTX3582R

[BadBoostedBmwM3]

I've never heard of catcams.

[cragg56]

I've never heard of catcams.

Neither have I.

Should add Metric Mechanics to your list.

http://www.metricmechanic.com/produc...ft-head-parts/

[Brody @ Miller]

I like the idea of this thread. It may be a good idea to drag all the info that people have into this thread so that a simple search can find it here.

I am in the market for some turbo cams right now . I will be installing my head soon and want to install them at the same time.

I would think that Colt Cams would be buddies with Miller since they are practically neighbors.

Sent from my GTX3582R

I have a feeling ICS uses colt since they are the only ones here doing regrinds and it was eluded they come from "Vancouver"

We don't use colt because they only do regrinds and do not have any masters for BMW anyway. There is a difference between a regrinder and someone who makes/programs masters for production use.

sent from my iCrack, forgive the auto correct

[chikinhed]

Years ago I had talked to Colt Cams about grinding some cams for me and the guy spoke very highly of himself. I didn't end up using them.

Sent from my GTX3582R

[Brody @ Miller]

Years ago I had talked to Colt Cams about grinding some cams for me and the guy spoke very highly of himself. I didn't end up using them.

Sent from my GTX3582R

I never got that from him, nice guy, ran into him in Vegas out of nowhere and he was a blast there!!! But, as you learn who what and where, we decided to stop getting regrinds done.

sent from my iCrack, forgive the auto correct

[chikinhed]

And do you have any turbo cams in stock yet?

Sent from my GTX3582R

[Brody @ Miller]

Nope

sent from my iCrack, forgive the auto correct

[biglou911]

im using paul burke cams .

[ruiemichelo]

More looking for info on what works best and why for informed selection

[Kame36sedan]

Does brody or anyone want to provide info on regrind cams? Seems you should stay away from them or no?

[wazzu70]

Regrinds are not necessarily bad, they are just more limited in what can be done with them. The outside of the cam lobe is hardened to resist wear, and if this is ground through to create the new lobe profile the cam must be re-hardened. Sometimes there are issues with the re-hardening and cam lobes can go "flat" or lose their profile due to being too soft. Also to create the new profile material is welded onto the cam lobe and then ground to the proper shape before hardening. There can be issues with this process too.

Billet cams just have less chance of issues and more options with regards to grinding them. They are the ideal but regrinds can be cheaper so thats why people choose regrinds over billet most of the time.

Just because you have a regrind cam does not mean you will have issues. I have a set of regrind cams in my car, and I am the third owner of them so they have seen plenty of use. I didn't have the budget for billets so I took the poor mans route

[chikinhed]

Regrinding cams has been going on forever and with everything there are successes and failures to be seen. I have used many regrinds over the years without issues and have been using a set of 'supercharger cams' that are a set of S52 cams reground by Elgin Cams. The regrinds look as new with no issues at all. If a cam is going to give you an issue it will usually happen fairly soon after the regrind or billet cam has been installed. The failures are from spalling where the hardened surface breaks away from the softer metal underneath.

Sent from my GTX3582R

[Kame36sedan]

What are the usual price ranges for regrind cams? It was mentioned that it was fairly cheap.

[chikinhed]

To regrind a cam can cost $250 to $300 per cam.

Sent from my GTX3582R

[Kame36sedan]

Should we post up good durations and setups for turbo cams for our cars?

[wazzu70]

Thats the point of the thread. The point is theory, not just who sells them. Google answers who sells them, theory answers which ones make sense and will be beneficial.

[paul burke]

I would love to play here but these threads get trashed to early in the game for me.

I understand but am not into the politics of " YOUR NOT A PAYING VENDOR SO YOU CAN'T ", which prompts me to say the following.

If I start a real engine builder type website for BMWs along the lines of Yellow Bullet or Speed Talk would any of you be interested?

This would be a site dedicated to crafting BMW performance engines, no advertising, no Bull crap, NO TROLLING!


Paul

[biglou911]

I would love to play here but these threads get trashed to early in the game for me.

I understand but am not into the politics of " YOUR NOT A PAYING VENDOR SO YOU CAN'T ", which prompts me to say the following.

If I start a real engine builder type website for BMWs along the lines of Yellow Bullet or Speed Talk would any of you be interested?

This would be a site dedicated to crafting BMW performance engines, no advertising, no Bull crap, NO TROLLING!


Paul

YES YES YES !!!!!!!!!!!!!!!!!!!! DO IT !!!!!


Sent from my iPhone using Tapatalk

[Robocop]

If I start a real engine builder type website for BMWs along the lines of Yellow Bullet or Speed Talk would any of you be interested?



Paul

Big time.

[sfdrifts]

+1