Question for the experts, about effects of running a hotter

[Guest bastaad525]

Okay, dig this. Was searching around the zcar.com archives, when I found a post from a guy giving his dyno #'s. This guy has a built, fuel injected L28 in a 280z, with intake, exhaust, ignition... all the usual stuff. The main point is his cam, which 475 lift 274 duration cam. I've seen cams with very similar specs to this being sold from a few places, and they are always advertised as having power from around 2-3k RPMS up until 6-6.5k rpms. Anyways this guy dynoed his car and got 155hp@5250 and 167ftlbs@4250rpms at the wheels. I thought that was kind of odd for a cam that MSA says "pulls hard up to 6000rpms". Anyways, it gets worse. I had also built up a fuel injected L28, doing almost the exact same mods to my engine, however since I had to worry about smog I stuck with the STOCK CAM. Otherwise our setups were near identical except my motor was pushing higher compression. Anyways I went and got dyno tuned and got 147hp@5350 and 161ftlbs@4300rpms... a bit less power but my peaks were at almost the exact same points, WITH THE STOCK CAM!! Since then I've also installed a hotter cam, 480lift/270 duration... and to be honest I haven't noticed a huge difference except for the much rougher idle, but that's besides the point. Why would his motor with cam that supposedly 'pulls hard to 6k' peak out actually slightly LOWER in the rev range than a near identical motor with stock cam??? Is this just a limitation of the stock EFI system? Another notable point, we both had installed adjustable fuel pressure regulators and bumped up fuel pressure, mine to 42psi, his to 45psi. Since then I'm transfered my engine into a 240z and bolted on rebuilt SU's with SM needles. I want to get it dynoed ASAP but I'm gonna be pissed if my power still peaks at mid 5k's. Another funny thing is, the guy that sold me my cam, as well as MSA who I call often when i have questions like this, both are of the oppinion that "hotter cams don't make MORE power, they just MOVE the range where the power comes in". What do you guys think about this?

[SleeperZ]

I can't speak to most of this, but a "hotter" cam will make more power because it makes more torque at higher rpm.

[David K]

i thought if you run a cam you should increase the fuel intake.

[johnc]

I hate to say it again, cuz its been said a million times: You have to look at the engine as a system.

 

The stock L6 cam in a stock, unmodified head is a very good match. Witness lots of ITS L24 engines that make 170hp at the rear wheels and close to (but not over) 200hp on very accurate engine dynos.

 

Swapping cams in an L6 without doing head work is basically a waste of money. Again, ITS L24 engines with stock (but well matched and assembled) internals, headers, SUs make at least 15 more horsepower then the two engines mentioned above.

 

Your cams are not the issue.

[Guest bastaad525]

So what your saying is, if you haven't done any porting, polishing, and enlarging of the valves, then you should stick with the stock cam? The only head work I've done is to switch over to stainless steel polished valves. I was under the impression that the cam would benefit my setup, as I have done: free flowing intake, exhaust, performance ignition, and the fact that I'm running a high compression .060 overbored motor (10.3:1 compression). I have tried to look at my engine as a system, as I've changed and/or upgraded almost every major part of the engine and rest of the drivetrain to boot. The cam was actually about the only thing I HADN"T done, well that and the uber-expensive head work. But with all that I have done, you think I'd have been better off with the stock cam?

[Kevin Shasteen]

BTW: I dont consider myself an expert, but; any answer as to why the two engines were similar can only be speculation since none of us know exactly what your friend did to his engine.

 

BTW #2: Your camshaft should've been the first item you thought of-relative to how well your engine flows air.

 

Basically what JohnC said; airflow is the key.

 

But, since we are speculating I will say this: there is more to a power band's rpm than simply the duration of a cam. Such as the Lobe Seperation Angle and the Intake Lobe Centerline...all these determine your Intake Valve Closing (Dynamic Comp.Ratios). This IVC not only determines idle characteristics but also at what point your peak power will surface-which is also relative to how well your other components were matched; or not matched.

 

The associated engine components will either compliment your engine and add power where you need it most in your power band; if you have chosen correctly. If you have not chosen correctly then you may possibly be suffocating your engine.

 

Xtra fuel is good-but air is the key to a performance engine and it is air that determines if when and or how much fuel/spark is needed. Your cylinder head is where the key to free power will be found-all other components should compliment your engine's ability to breathe. A better intake will help-but if your cyl.heads dont breathe well then you wont ever see true real increases in power.

 

A 270 duration cam is a good choice because it has decent street manners and moderate power increase-provided your cylinder heads can handle the xtra airflow.

 

My guess why your two engines have differing peak power rpms would either be the cam's LSA & LCA as well as one engine's ability to breathe better at those peak power rpms.

 

Anyone else?

 

Kevin,

(Yea,Still an Inliner)

[johnc]

> So what your saying is, if you haven't done

> any porting, polishing, and enlarging of the

> valves, then you should stick with the stock

> cam?

 

Basically, yes. In a stock L6 the cam and port flows are reasonably well matched. Remember, what we are trying to achieve is velocity, not ultimate port flow. If we can reduce mixture dillution through better scaveging and/or reduced reversion we increase power.

 

When you change the cam what you're trying to do is get more mixture through the engine. The cam (assuming its well designed) will do its job correctly but now the ports, valves, and combustion chamber act as a bottleneck. This keeps the cam from realizing its potential.

 

Now, I'm not saying swap back to the stock cam. What you have is a good cam. I would start thinking about simple porting work. If you haven't already, port match the intakes and the exhaust to the head.

 

Get a subscription to Circle Track Magazine and find the back issues that talk about beginner and budget head work. The basics apply equally to Chevy and L6 heads. Its not rocket science, just take your time and practice on a junkyard head.

[Guest bastaad525]

Heheh it wouldn't matter anyways, I'm stuck with this cam. I'm not gonna have the kinda money to switch back for probably some time. And that's a job that is still just a bit beyond my reach.

[Lockjaw]

One thing you did not consider is the larger cam may make more power on the backside of the power curve than a stock one, hence the claim it pulls hard to 6k or whatever.

 

I ran that cam in a 2.6 with a very early e88 head, header, sidedrafts, and I was spinning the engine to 7400 rpms.

 

There is more to it than just what the ports flow. Anytime you keep the valve(s) open longer, you are going to get more air/fuel into the engine. The larger the cam, the more compression you need to make up for the loss of cylinder pressure from the greater valve overlap.

 

Take a stock P79 ZX engine with 8.8 compression. Put a big cam in it with no other changes and the stock cam may in fact make more power due to the increased cylinder pressure from the shorter duration, and low overlap. In a 10 to 1 motor, the bigger cam will make more power.

[yo2001]

Originally posted by bastaad525:

dynoed his car and got 155hp@5250 and 167ftlbs@4250rpms at the wheels.

His car hasn't broken in yet couple 7k-7.5k with me, that thing will make more power in higher rpm. bigger isn't better I was told. The right cam is where you get most out of your engine.

[Guest bastaad525]

Good point Lockjaw. I've been talking to the guy, he doesn't live too far from me and hopefully soon we're gonna meet up and 'compare notes'. I'd like to see exactly what his dyno sheet looks like, how the curve compares to mine. Also he knows a good place to get it tested for cheap so I'm gonna get mine retested and see how this cam affected my car. Then of course I'll be back here loving it or ranting about it