I have been searching thirdgen.org, turbomustangs, and camshaft manufacturers trying to get some info on turbo cams. Trying to pick something that is halfway decent.
The setup:
Shift gears at 6000 rpm
355ci SBC
882 heads 1.94 intake, 1.50 exhaust valves (full port, polished chambers
8.6:1 compression
---
LT1 intake
52mm throttle body
dual 2.5" compressor pipes
dual 3.5" air cleaner pipes to front-end fresh air
30"X13"X2.5" bar&plate intercooler (open grill-fresh air)
---
twin T3s, .63 A/R turbines, 60 trim compressors
1986 Chevy Camaro exhaust manifolds(ported) modified for T3 turbos
dual 3" downpipes to 2.5" exhaust

Current Camshaft - hydrualic flat tappet:
Overlap: (216+216)/2 - (110*2) = -4 degress
.454" intake, .454" exhaust
216 degrees @ .050 Intake
216 degrees @ .050 Exhaust
110 degrees LSA
105 degrees ICL (intake centerline)
115 degrees ECL (exhaust centerline)

Timing @ .004
Intake: 27 BTDC 65 ABDC
Exhaust: 67 BBDC 25 ATDC

Timing @ .050
Intake: 3 BTDC 33 ABDC
Exhaust: 43 BBDC -7 ATDC
---------------------------------
I was thinking of having a custom grind with these specs:
114 LSA
222 degrees @ .050 intake
218 degrees @ .050 exhaust
about .460" lift both intake and exhaust

What would I gain with this cam?

I have read all kinds of theory and real world stuff at turbomustangs.com written by INTMD8. Even though my current cam seems like a small LSA (110 degrees), I almost think it is best because of the small duration (216 degress I/E). What would I gain from the "new" cam?

Anyone have a better option? Comp cams recommended their 218 duration intake, 212 duration exhaust, 115 LSA. I don't really like that wide of an LSA. Calling Cammotion this week. I have seen LOTS of different profiles for almost the same engine that they recommend. Overall, I am kind of confused.

 

How do you like your powerband now?

Really, it’s not THAT different then the recommendations and what you want, the overlap (or lack of it) is reasonable, the duration is reasonable, the only weird thing is he tight LSA and 5 degrees advance.

If you have a reason to go in there I’d be tempted to try retarding that one maybe about 3-4 degrees (will extend your power band a little bit, the 5 degrees advance ground into it is a little weird) and make it a little more boost friendly and then decide if you need to change it after driving and tuning it some.

 

I like the powerband the way it is right now with the 216 duration cam.

The reason I was thinking of changing is because most of what I have read says "use a 113 CL or wider LSA". After looking at the actual open & close times of the turbo cams, I don't see how much I would really gain. Reading through Vizard's cam & valvetrain book doesn't help much. Vizard goes about it by having a tiny duration and long exhaust. Seems odd to me, but the general cam info is great.

I compared my current opening and closing times to some recommendations people have from Cammotion and I have found that my intake opening time is a little early and exhaust closing time is a little late (at low lift, approx. .005"). The big problem is that no one specs their cam at very low lift in a universal manner (constant lift number). That is why I am so confused. For instance, my cam has -4 degrees overlap at .050" and it has +52 degrees overlap at .004". The Comp Cams "turbo cam" has +34 degrees overlap at .006". I am guessing my current cam has about +58 degress at .006". Just a guess.

The 5 degrees of advance did look odd at first to me too. After looking at other cams out there, most have 3 to 5 degrees advance ground in. The Comp Cams turbo cam has 4 degrees of advance (115-111). The thing that is weird about my cam is he 110 LSA. But it all seems to work out with the 216 duration. Actually, the only reason I would like to go to a 114 LSA is for a slightly better idle. The power & powerband seem great with this cam. I am also curious about the reversion & "easier to detonate" of having more overlap and a more heated intake charge (I kind of don't believe that.....from Vizard). At the same time the info from INTDM8 shows that a small amount of overlap (like I have) is good.

I am open to suggestions & different theories.
83 Crossfire TA, do you have a personal suggestion for this setup?

 

I am waiting on a recommendation from Cammotion. I just came across this cam.

Comp Cams XT262
218 degrees intake at .050", .462" lift
218 degrees exhaust at .050", .455" lift
114 degrees LSA

No other specs at CC's website. I am going to call tomorrow to get more info on it.

 

You’re worried too much about what everybody does and not enough about what the engine wants.

LSA is nothing, it’s just a number that we came up with for us to describe what the cam is doing without having to remember the actual locations of the valve timing events. The engine doesn’t care about LSA, it cares about when the events happen.

With a turbo cam the most important 2 events are the intake opening and the exhaust closing. Those 2 will have more of an effect on how the engine deals with boost and exhaust back pressure (the 2 major concerns in a turbo setup) then anything else.

That is exactly why I was suggesting that you tried the cam that you already had slightly retarded, since that would put those events in a reasonable location for a turbo setup. The only issue you’ll have is that retarding the cam will extend the powerband slightly and the exhaust lobe will really be bigger then you want, I’d focus as much time as possible on cleaning up your exhaust side if you run that cam.

Be aware that anything that retards the intake lobe (more LSA, retarding the cam…) will add top end. Increasing LSA does both that and decreases overlap which extend both the bottom and the top end, but flattens out the peak in the middle (the engine ends up happier over a longer range but doesn’t make as big a peak).

If I was picking a cam, knowing what I know about your combination and what you’re happy with now (and choosing from the available comp lobes, probably the easiest place to get a cheap, custom cam), I’d probably go with something like a 212/206 with maybe a 110 or 111 LSA ground with 2* advance. The only reason that I’d go with bigger lobes would be if you cannot get enough lift to take advantage of your porting on those heads with a H cam (I don’t remember what the lift numbers are for those lobes off the top of my head since usually I deal with the HR stuff…). Actually, the only other reason that I would go with bigger lobes is if you really felt that cam just didn’t have enough of a performance sound to it.

Going with bigger lobes will just extend the RPM range without increasing the breathing of the engine, so you won’t really make more power, just feel a little racier. Even then I probably wouldn’t go any bigger then 218/212 with a 112LSA (maybe 113). But if you really wanted to just extend the rpm range I’d probably take the first cam I suggested and retard it 2* from there.

The reason that you’re getting the big LSA recommendations are 2 fold, first, the obvious, “turbo cams have to have an LSA in the >114 range, everyone knows that” (right), and secondly, because you’re describing a combination with a fairly restrictive exhaust (“crappy manifolds” and small turbines). IMHO, I agree with that, but using something like the comp XE lobes you already have so little overlap that the whole deal will be happier with just a smaller exhaust lobe and you don’t really need less overlap, and the tighter LSA will keep your powerband in a more usable range and it will feel much better on the street, build boost faster, have more low end and a BIG FAT midrange to the curve.

Do you have actual flow numbers for those 882’s? Really good or bad numbers might change my recommendations some, but the fact is that the rest of your combination is tame enough that going much bigger then what I recommended will again, make the whole thing sound and feel racier, but you will not go faster, you’ll just run out of air.

 

I have been looking at a lot of cam spec card timing events, dyno combos with N/A setups, and reading Vizard's stuff about N/A with restrictive exhaust. I have read the more applicable section of Vizard's cam book over and over. He is kind of wishy-washy on some stuff. Also, he assumes all lobes are symmetric......which just isn't true.

You are right about me trying to figure out if "I need a 114 LSA because....". I have come to realize that I don't care about LSA or duration. I have been getting as much IVO, IVC, EXO,EVC stuff as I can. To me, that is what is really important. The tough part is that I have to guess at what lift (.004", .006", ???, .050") others are specing there cam at over at turbomustangs.com. I have to guess a lot. Someone will post a "this cam worked great" with all of the specs but not mention at what lift.

I think I finally decided to take your advice and ignore what everyone has done. Overall, I have a somewhat restrictive intake setup due to the heads (no actual CFM, probably 230CFM @ .500" from what I have read and seen). I have a very restictive exhaust before the turbo. Therefore, there is no reason to run a "big" cam (just like you said). I agree that going to something larger than about 220 degrees duration isn't worth it. It would just make a worse idle and not much more power.

I like the current powerband the way it is now. If I choose a new cam, I would like a idle that was slightly (or much more) smoother than what I have now and I would "settle" for slightly less mid-range torque. This leaves me right at about the cam 216/206, 112 LSA that you recommended. This is very close to the Comp Cams XT256H cam that I came across today that is 212/212, 112 LSA, 108 ICL, .447" lift. I still like the XT262H Comp Cam that is 218/218, 114 LSA, 110 ICL, .462" I lift, .455" E lift.
Either one of these cams will give me exactly what I am looking for in comparison to my current cam (I think). My current cam has +52 degrees of overlap at .004". The XT256H has +35 degrees of overlap at .006" and the XT262H has +37 degrees of overlap at .006".

I am still waiting on the Cammotion recommendation. 83 Crossfire T/A, I think your recommendation is better than the one Comp Cams gave me. Not surprising, you seem to know a lot about turbo, engines, and fab stuff. Also, neither Comp Cams or Cammotion asked about exhaust manifolds, exact downpipe size, muffler type, or even turbine type & A/R. They just wanted "free flowing exhaust???" and "how much boost???" How can they give a cam recommendation without the exhuast info. "Free Flowing" is a relative thing. Yeah, compared to a garden hose. The exhaust restriction is probably the most important parameter.

I am leaning toward getting the Comp Cam XT 262H. I have a month to decide before I actual buy the cam. The engine is coming out so it isn't a big deal to throw a cam in it. I still have a month to go on the current JYTT 305ci setup (EDIT: the cam is not going in this engine).

Thanks,
J

 

I have just finished reading that book. He really has no good info on turbo camshafts. I think that this is partly because the book is kind of old. I'm thinking that he started writing this in 1987 or so and published it in around 1990. I don't think that many people were putting turbos on there cars back then like now. There were only a few back then that came from the factory with turbos. Mostly Dodge and Plymouth.

 

It’s not so much that he’s wishy washy, its that he’s done so many of these tests that he takes it for granted that someone reading his stuff will recognize some things that he feels are obvious that change the results or the test and you didn’t even notice, you just think that he couldn’t make his mind up (I know, I’ve re-read parts of that book half a dozen times trying to reconcile stuff that he wrote and have usually found that there was a real reason for the changes from test to test).

I wish someone would do a real world test of something like his turbo cam recommendation but unless we all had infinite time and money it ends up a real crapshoot since he doesn’t give enough real details of the combination to reproduce it with any accuracy whatsoever.

comparing it to a lot of the posts at turbomustangs you have a much bigger issue of what different manufacturers mean by “advertised duration” (take a close look at any of them, you’ll find that not only does it change from manufacturer to manufacturer but from lobe design to lobe design, comp uses at least 3 different ways of calculating advertised depening on what lobe you’re looking at). The problem is “it worked great” is all relative. If you put 10psi on an engine that is totally mismatched for the blower you’re using, as long as you don’t have major detonation problems, comparing it to NA it will be totally awesome. And that is the means for comparison that these people all have. It doesn’t matter that if you really chose the right cam you might make 50hp more with out changing anything else, they don’t know that.

Secondly, some people may have totally different goals then you do. For example, Intimid8 (over there) selected the biggest cam that he could and still get a stock idle, he didn’t care that he made more power with a bigger cam (he did), if it didn’t have totally stock like drivability. I’m going with a totally different combination and I’m going with a totally different cam, comparing what I’m doing to what you’re doing is almost an apples to oranges comparison even though we’re both building turbocharged small blocks.

Lastly you said you were looking at vizard’s NA restrictive exhaust recommendations… I’d be aware of 2 things with that: 1- I’m actually a firm believer that exhaust flow on a flow bench does not tell you as much as you need to know about your exhaust to choose a cam, much less so then knowing intake flow, there are different dynamics in an exhaust port that require different consideration. 2- what you would do for a badly flowing exhaust port NA is almost the opposite of what you would do with a turbo.

That’s very possible, but more then I expect it to be.

And turbo

those would be perfect numbers all things considered, I just didn’t know of any lobes with those numbers off the top of my head (like I said, I recommended something based on known XE lobes)

Yes, they will move you in the direction you’re wanting based on your current cam, but I really think that you want a smaller exhaust lobe and later intake opening like I was recommending to compensate for your tight exhaust side. I think that the sorter exhaust lobe and later event timings (not as much advance) will get the pressure in the chamber down more before the intake valve opens, which I believe will be a loss of efficiency issue with your manifolds and turbo selection.

Huh, well I didn’t have you in front of me to ask, but I could make some reasonable assumptions, for example, since I know that you’re planning on cutting/welding stock manifolds, use T3’s and I know what the leftover packaging is like, I know that you’re not going to have a “free flowing” exhaust, and that backpressure management will be a major issue with your combination.

Tell us what cammotion says… I was surprised with what they recommended in my case and in most cases…

 

Cammotion recommends:
specs at .050"
IVO -3 IVC 37
EVO 46 EVC -14

overlap at .050" = -17 degrees
214 intake duration at .050", .440" lift
212 exhaust duration at .050", .417" lift
115 LSA
110 ICL
price: $150
------------------------------------
Comp Cams XT262H (so called 10-20 PSI)
specs at .050"
IVO -1 IVC 37
EVO 47 EVC -9

overlap at .050" = -10 degrees
218 intake duration at .050", .462" lift
218 exhaust duration at .050", .455" lift
114 LSA
110 ICL
------------------------------------
Comp Cams XT256H (so called 8-15 PSI)
specs at .050"
IVO -2 IVC 34
EVO 40 EVC -8

overlap at .050" = -10 degrees
212 intake duration at .050", .447" lift
212 exhaust duration at .050", .447" lift
112 LSA
108 ICL
------------------------------------
Crane Cams 100052 (N/A)
specs at .050"
IVO 3 IVC 33
EVO 43 EVC -7

overlap at .050" = -4 degrees
216 intake duration at .050", .454" lift
216 exhaust duration at .050", .454" lift
110 LSA
105 ICL
-------------------------------------
83 Crossfire T/A Cam
APPROX. specs at .050"
IVO -2 IVC 38
EVO 37 EVC -11

overlap at .050" = -13 degrees
216 intake duration at .050", .454" lift
206 exhaust duration at .050", .432" lift
112 LSA
110 ICL
----------------------------------------

Tough decision. Mark, thanks for all of the help on this. I will continue to think it over for a while. Some are so close it is like splitting hairs.
The XT262H seems to be the "wildest" cam. The XT256H and 83 Crossfire TA cam are close and in the middle and the Cammotion seems to be the most tame in terms of peak and would give the widest powerband.
Overall, I still can't make up my mind as of right now.

EDIT: fixed XT256H IVC degrees

 

Naw, go back to what I originally wrote. Based on comp XE lobes I suggested either 212/206/110 or 218/212/112. The first one I would definitely have ground with 2* advance so it would turn out to be:

-2 34
35 -9

it would have -11* overlap.

WRT to the lift I would use an intake lobe for both the exhaust and the intake and I would use the bigger of the 2 available XE lobes so your lift would be .447-I and .432-E (with 1.5 rockers, I would use 1.6 rockers with all of these cams unless your heads won’t tolerate the lift numbers that you end up with).

With the second one I’d probably grind it with a more normal, 4* advance to maintain the power band that you want, but real world, I think that it will play better with the turbo setup also at 2* advance:

-1 39
40 -8

and that would have -9* overlap

lift would end up .462-I and .444-E (with a proper exhaust lobe, .447 if you decided to use an intake lobe), again, same comments about the rockers, as a matter of fact, same comments across the board about the rockers.

The second cam will definitely make more power, but I think it will also move your power band upward significantly.

My $.02: I don’t like seeing the overlap numbers quite that low…, my recommendations with much tighter LSA’s then the rest still have A LOT of negative overlap, and something like cammotion’s -17 degrees is approaching the numbers that vizard suggested (if I remember right he was suggesting something in the -23* range).

The other thing about cammotion’s recommendation is the relatively low lift numbers for the duration… if your heads really do flow around 230, I’m sure that they don’t do it at .400, so you’ll never get to the point that you’ll use that flow. If you don’t get the lift much in excess of .450”, I suspect that you’ll be limited to a _useful_ rpm range below about 5200rpm (it will probably rev higher but power will fall fast), and basically all this extra valve timing becomes irrelevant, it’s just wasted motion and killing the bottom end for no gain up top.

So looking at all this… I don’t like the single pattern cams at all, the single pattern will just be kicking you in the nuts without a better exhaust side on the car. I think that cammotion’s recommendation is too tame, I think that their recommendations are usually too tame unless you have a killer head porter that can make heads sing at low lifts. I think based on what you’ve said, my first recommendation is probably the best fit, but _if it was my car_ I’d run the second recommendation with the exhaust lobe on the exhaust (I’d run the intake lobe on the exhaust if I was sure of the quality of the exhaust valves used in the heads).

Real world… I doubt that you’ll try more then one or 2, and your impressions of how well they work will be more influenced by the turbo setup then by the cam choice.

 

Yeah, I screwed up on the duration that you gave. That cam sounds good.

The numbers for the 2* advance look better than the 4* degree of advance for this setup. The mid-range comes in strong with the current Crane (N/A) cam at the same time as full boost. It has kind of a peaky 2-stroke feel to it. It gives the false impression that it is a "fast car" because of the hit. It would be a lot more streetable with the 218/212, 112LSA, 110 ICL. It is mainly a street daily driver during the summer. I think I will have Comp Cams grind this one.

I see this one making peak at about 5000 rpm or a little higher. Not bad.

I didn't like it either. I guess they did take into account the crappy manifolds & small turbines. At high rpm, there is less time for reversion so I don't see the need to go that negative on the overlap. I would rather try an "in between" cam with -7* to -12* overlap before I went to something like -17* overlap.

After looking at flow data for some GM 461 2.02/1.60 I realized that I don't have 230CFM on the GM 882. I guess I was thinking of the 461s 235 CFM rating. I think the GM 882s are probably at about 215 CFM at .450" lift using/guessing from the 461 flow data. The int/exh. is probably around 75% to maybe 80%. I did spend a lot of time trying to get the exhaust ports "right".

I agree that a single pattern would not be optimal. I know my heads don't flow well so a wide LSA, low lift cam is not a great choice here. So the Cammotion cam is out of the picture. I am going to have Comp Cams grind the 218/212, 112 LSA. It seems like a good choice for what I am after. It should clean up the idle a bit, smooth out the powerband a bit and widen it. It would also be the best in terms of exhaust upgrades when compared to the 212/206 cam. I might make some weld-el headers next winter in the time is available.
I am going to use an exhaust lobe for the exhaust. I don't thinking gaining the extra lift and harsher ramp rate of an intake lobe would be worth it.

I put about 300 miles on the turbo setup last fall before the snow started to fall. I was knee deep in tuning the 730/$58 code. It is my first turbo rig so of course it felt fast. I left the N/A cam in it because it didn't seem that bad of a choice. It was a brand new cam I had and didn't want to buy another one. I wanted to see how it went with that one. Being my first boost rig, I figured I had to learn by doing some real world testing. Now that I know a bit more and the engine is coming out I figured why not try to make it a little better since the funds for a new cam are available. I guess I am trying to "get it better" this time.
I am going to stick with my 1.5 rockers at first and give it a try. Using 1.6 will give a .492" lift and that is getting up there for stock heads. The 1.6 I/E will also give a little more duration. I may go to 1.6 later, but I will stick with the 1.5" and see how it goes at the track.

The new specs (Comp Cams custom, 83 Crossfie TA speced):
specs at .050"
IVO -1 IVC 39
EVO 40 EVC -8

overlap at .050" = -9 degrees
218 intake duration at .050", .462" lift
212 exhaust duration at .050", .444" lift
112 LSA
110 ICL
114 ECL

Comp Cams Xtreme lobes (hydraulic flat tappet)
Intake: 5442
Exhaust: 5207