Let's talk about cams!

[ForcedFirebird]

Why does the timing cover have to be pulled?

To remove the cam?

[SappySE107]

Oh, thought we were talking about just the springs. Didn't even catch the cam mention.

[bob442]

Why does the timing cover have to be pulled?

I LOL'd

[geoffinbc]

If your going to turbo it later just keep the stock cam for now. A cam made to optimize a turbo will not be good for anything else.

[BillS]

If your going to turbo it later just keep the stock cam for now. A cam made to optimize a turbo will not be good for anything else.

X2

I've seen several guys go part way to a half assed conventional build, using parts like cam that weren't suited to turbo use, and then have to backpedal (expensive) or live with a less than suitable set up (annoying).

Get it running and turbo later. You can get great results just from a bolt on turbo, and if you decide later to get more power by rebuilding the engine using forged pistons etc., you can play with cams then.

[wade braaten]

I used compressed air on a BBC to replace valve stem seals, worked great, yes the piston will go to bottom dead center. I took an old spark plug and modified it to work with the air. it takes alot to unseat a valve when you are pressing 120 psi against it. If the valve leaks enough for the valve to drop, you need a valve job anyway so replace the springs then I did all 16 valves with no problems and would take less time than the rope trick ( like that too though ).

[beastberetta]

If your going to turbo it later just keep the stock cam for now. A cam made to optimize a turbo will not be good for anything else.

not necessarily true, jon 3400-95-modified has a trubo cam nd hes spraying a 100 shot nd runs 12.67 so it must be good for his car. i believe cam specs are .217/.240 duaration nd .517/.556 lift. couldbt wrong on the lift.

[geoffinbc]

Duration and lift don't tell you much. You need to know the overlap and advance in the cam to know enough about it to determine if it is a cam optimized for a turbo or n/a. And in no case will a cam designed for one application be "just as good" in the other application.

[ForcedFirebird]

I used compressed air on a BBC to replace valve stem seals, worked great, yes the piston will go to bottom dead center. I took an old spark plug and modified it to work with the air. it takes alot to unseat a valve when you are pressing 120 psi against it. If the valve leaks enough for the valve to drop, you need a valve job anyway so replace the springs then I did all 16 valves with no problems and would take less time than the rope trick ( like that too though ).

I like the rope trick just in case you have to leave the job unfinished for some odd reason. You aren't required to leave the compressor on. Having done springs/seals both ways, it doesn't take any longer either way. I just used a compression tester and screwed necessary fitting in to adapt to an air chuck.

[ForcedFirebird]

Duration and lift don't tell you much. You need to know the overlap and advance in the cam to know enough about it to determine if it is a cam optimized for a turbo or n/a. And in no case will a cam designed for one application be "just as good" in the other application.

That's not so true anymore to an extent. I have used cams with significant overlap on boosted applications with good results. People are shying away from the "zero overlap" theory these days. A lot of positive pressure engine info has been outdated - Corky Bell's book still has a lot of valid info, but some has been proven wrong over the past few years.

[Spitfire]

Question?

I have Desktop Dyno 2003 and Engine Analyzer Pro 3.3 and get wildly varying results program to program.

How much HP/TQ can I realistically expect from an LX9 with a 65mm TB, performance MAF, 27Lb injectors, ram air CAI, a high octane tune, (OBD II) and equal length headers?

[geoffinbc]

That's not so true anymore to an extent. I have used cams with significant overlap on boosted applications with good results. People are shying away from the "zero overlap" theory these days. A lot of positive pressure engine info has been outdated - Corky Bell's book still has a lot of valid info, but some has been proven wrong over the past few years.

Um I don't think I ever said you could not use a cam with overlap on a turbo app. Overlap used correctly is never a bad thing.

[ForcedFirebird]

Um I don't think I ever said you could not use a cam with overlap on a turbo app. Overlap used correctly is never a bad thing.

What other specs are generally associated with turbo vs. N/A? LSA was thought to be best if kept tighter, but that was to decrease overlap to "keep boost pressure in". Duration was kept low again to keep the overlap low (some even go to the extreme of negative). Lift has nothing to do with N/A vs turbo, neither does lobe center.

It was always thought that boost would be blown out the exhaust when in positive pressure, but it's not a reality in a turbo situation because the exhaust pressure is somewhere around double that of the intake manifold pressure - gasses tend to go where the pressure is lower - but the airspeed also plays part. So, generally a cam that does good N/A will also be a good cam for turbo. Supercharging is another story.

[Joseph Upson]

It's a balance on a turbo motor, the max ratio between boost pressure and exhaust pressure varies and may not necessarily be as high as 2:1 at your desired boost level, especially when you consider the effect that turbine housing, wheel and trim size has. The closer a turbo motor expels exhaust gasses similar to a naturally aspirated engine, the more overlap you can run. There is some truth to the overlap theory side effects but it can go both ways although you're likely to see trouble when back pressure is too high. Too much exhaust back pressure on a turbo motor with high overlap can affect cylinder fill on the intake cycle. The greatest concern with overlap on a turbo motor now is the fact that most of us are using MAP sensors that depend fully on vacuum pressure to help tune and idle and excessive overlap makes a mess of that.

Never had a problem running a stock cam with a turbo motor, or a turbo grind with an unboosted motor. I'd expect a good na cam to work just fine with conservative boost levels but I certainly wouldn't shy away from a tighter LSA than commonly suggested 114.

[NateD4]

I have a reground stock 3400 cam that is for sale cheap. If you search my name you can see specs on it. Let me know. I don't think its super wild, just a bit more lift then stock. If I hadn't decided to go to a 3900 in my Fiero I'd have it in the 3400 that was going in it.