General Question to engine builders: Degreeing cams

[Walperstyle]

Ideally, what kind of overlap would you want to have on your cams? and roughly where do you have the intake open and exhaust close.

I do understand the math behind this, but the open and close points of these are more important then the actual centerline/centerlobe max height.

I have crower V3 Turbo cams, JWT cam gears, GT35R .84 turbo

Performance level 5 - Stage 3 - Forced Induction Race - Drag Race and radical Street/Strip. Requires #84184 spring kit and compatible ECU upgrade for optimum results. Lope at idle.
INT/EXH - Dur @ .050” Lift: 222°/222° RR: 1/1 Gross Lift: .401”/.401” LSA: 114° RPM: 1500 to 7000 Redline: 7500

shim on both sides is 0.006 I believe. Wanted it tight to avoid 'chatter'.

Engine is on a stand, and right now I believe I have the intake start to open 13' before TDC, and EX close at 5' before tdc. I think overlap is fine, but maybe I should retard the intake 5 degrees or so?

[waxball88]

Someone help this guy out so i can learn a thing or two.
:D

[Walperstyle]

Other buds on KA-T.org are saying drop them in, then degree on the dyno, but these are pretty wild cams.

[rcdad123]

don`t know much about degreeing cams, but i would definitely do a clearance check between intake and exhaust valves and valves to piston. i had bad experience on spitting valves out the exhaust. that would take a turbo out at the same time. ouch!

[Walperstyle]

^Timing/Degreeing would fix that. I don't know of any cam maker that would build a cam that would be too dangerous. Stock cams can be bad if they open and close at the wrong time.

[Walperstyle]

Update:

INTAKE OPENS 9' BTDC
INTAKE CENTERLINE 103' ATDC
INTAKE CLOSE 34' ABBC

EXHAUST OPENS 30' BBDC
EXHAUST CENTERLINE 87' ABDC
EXHAUST CLOSE 5' ATDC

Other people say i should have:

The average ka, 350-450hp, 7k limit, install at 124 intake cl, 118.5 or so exhaust cl.
that would make the intake not open until after TDC. Just curious, this theory applies to SR engines as well as KA.

Still looking for some more advice.

[Kingtal0n]

There is alot more to the opening and closing points of the valvetrain than just common knowledge of parts and physics. When the engine is running, there are specific variables that can not be accounted for, such as helmholtz, which will affect cylinder fill events in lieu of cam timing- or despite it. You may have a situation in which an acoustic pressure wave desires entry to the cylinder but is blocked by a valve opening too late- with your attempt to retard the intake timing in effort to gain some cylinder filling after the piston passes BDC.

You cannot possibly account for all the variables, and that is why tuning the camshaft on a dyno where you can see the results as actual numbers is "recommended". The only problem with that, is the other variables you cannot account for, such as heat soak, time between dyno runs, fuel temperature, oil viscosity, etc... Such variables will affect results as much as your cam timing may, and your "real world results" may in fact not be what they seem.

To avoid the wear and tear associated with repeated back to back dyno runs, I would simply set the camshafts to the manufacturer's recommendation and leave it there unless you notice an area that could use significant improvement-
such as a torque graph that seems to peak and fall rapidly despite constant boost, or a torque graph that slowly climbs through the entire run, where it should instead be more of a straight line at constant boost considering the capability of the compressor. Such instances tell you that volumetric efficiency is changing as the rpms change- this is where valve opening and closing points may be tweaked to provide more area under the curve.

[Walperstyle]

lol, thanks for telling me everything and nothing at the same time, haha. I already get all that stuff. Real world Dyno is different then theory, always. And for sure, the KA head and Inter-cooler will have pressure drops. In my math for the turbo I already guessed minum 1psi pressure drop, probably upwards of 2.5psi. (but its still guessing)

Note: There is information on KA-T.org that says crower's original cam card was wrong. Previous owners had to do a lot of adjusting... and these guys cannot be found today. Otherwise I'd be asking them directly.

What I'm asking is what kind of overlap would i be looking for with a stage 3 turbo cam? I believe overlap is more important then center lobe, pending where it lands ofcorse.

As for the compressor, I already figured out I can easily make 500hp, but boost would kick in after 4000 rpm. Looking to set these cams at a good midrange power, and let the ECU and turbo help with the top end. Mid to top is important for me.

HP goal is 500hp, 94 octane. The BSFC suggests going E85, but we simply don't have that many stations up here in Canada with corn. So I will probably have a 94 and E85 tune.

[Walperstyle]

If anyone knows where Brad D from winnipeg, or SMracing are. I'd like to have some first hand experience. Karey D's 700hp has BC not Crower cams, but are probably the same thing, and he says to just 'drop them in at factory timing'. Being I'm not 100% sure of the difference between BC and Crower, I'm not going to do that.

[Kingtal0n]

As for the compressor, I already figured out I can easily make 500hp, but boost would kick in after 4000 rpm. Looking to set these cams at a good midrange power, and let the ECU and turbo help with the top end. Mid to top is important for me.

HP goal is 500hp, 94 octane. The BSFC suggests going E85, but we simply don't have that many stations up here in Canada with corn. So I will probably have a 94 and E85 tune.

1. The goal for most street cars should be 4,000 RPM of usable powerband. So if you are shifting by 7,500RPM you want peak boost (and hopefully peak torque) around or before 3,500. The more power you want to make, the higher you need to shift this curve to take advantage of the displacement, when you intend to run pump gas. Otherwise, it simply takes more boost, and that means higher octane fuel.

So your option for pump gas comes back to the spool characteristic of the turbocharger given the displacement of the engine. You must select a compressor that can meet your power goal (55lb/min +/-5lb/min) and do the math to figure out where 18~psi is going to land you 500 horsepower, at what RPM, or better to say this: when will just over twice the volumetric efficiency of the engine give 500 horsepower?

If we are talking 122 cubic inches then (122x7000/3456=247CFM *.069= 170horsepower @ 7000rpm given 0psi of boost (using atmospheric pressure) assuming 100% VE. Double the effective pressure and you have 340 horsepower, and in fact, most SR20 engines running 15psi on a compressor that can support (40lb/min) tend to produce about this number on pump gas- again assuming 100% VE (that means aftermarket cams), notice OEM camshafts on SR20 engines tend to produce much less power? Because VE is dropping by that 7,000rpm, simply.
You want headroom in the compressor for overlap losses and drivetrain losses. Giving some up to overlap can be a good way to clear out the cylinders between events, although it is wasteful. On the path to power, sacrifices must be made.

That is where you are going with this "cam degree" talk. You are trying to maximize only the VE of the engine- regardless of the boost pressure used, or compressor flow sacrificed. Although in fact, as boost is factored into the equation, the effects of pressure and the relative sizes of the exhaust manifold plumbing and anything after that- including the way the wastegate vents the exhaust gas- all comes into play... but it does not directly alter the breathing characteristics of the engine, so cam timing that yields 100% VE with atmospheric pressure is going to give the engine that same opportunity when boost pressure is applied, plus or minus the effects of the turbocharger being in the way, and the routing of the exhaust gas by the wastegate, and the additional pressure/heat contained within the plumbing of the exhaust system.

Traditionally, in the search for the best possible VE across the board, you could run the engine at atmospheric pressure or low boost, and dial the cams in for best torque area under the curve.
edit: You may need to adjust the exhaust cam afterwards, reducing overlap, when using a small turbine. (while I was sleeping I thought of this possibility to include)
Forget magic numbers, there arn't any, unless you find the exact same combination of parts somewhere else with paper results, and even then its still not a sure thing.