1

 

If you are concerned you can try to advnce the exhaust cam a lil (degree or 2) it should eliminate some of the overlap.

When your tuning cam gears though you should know ur clearances and then tune for power on a dyno.

 

Just to chime in w/ my own experience when I had crane stg IIs in my motor with 10,000 miles on it it was reading 260 across. Swapped in JUN III's and then the compression jumped to 270 across.

The cranes had larger primaries than the JUNs but the vtec lobes are much bigger.

 

So, what do think the VE is at cranking speed? VE at a running RPM is what tells you if you have lost or gained Dynamic compression.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Haleiwa-Brando &raquo;</TD></TR><TR><TD CLASS="quote">

Like I have said before, I'm new to this. I don't even know what VE means. I suppose I'll get it figured out someday </TD></TR></TABLE>

VE=volumetric efficiency

 

Also cam gear tuning only (To make HP numbers) can be achieved on a dyno and can not be achieved when road tuning.

But if your trying to dial out a problem, cam gears can only do soo much.

 

DONF so your saying that the static can actually be lower but when the motor is at say 1,500 rpms the dynamic can be the same or higher?

Forgive me for my stupidty hear but i would think that when calculating the dynamic compression several parameters would be involved in the formula and one of those would be static compression. So i am assuming that once your formula is calculated its always going to be a lower dynamic when you are starting out with a lower multiplier for a static.

Am i totally misguided here?

 

The thing is, you are only comparing primary lobe on your original cam to primary lobe on your new cam. However, you changed cams to make more power on the vtec lobe, not the primary lobe. You cannot measure that with a compression test unless you were to lock the cams manually into vtec and then do your comparison.
The purpose of a compression test is to see that all cylinders are equal to each other and to compare the same cam from one time to another point in the future. You really can't compare one cam to another. The true test is on the dyno or at the drag strip to see if your new cam was of any benefit.
BTW, cranking compression will change with a change of compression ratio in the engine, change of cam phasing in the engine, how well your rings and valves seal and by replacing cams with those of a different duration (thus changing overlap). Compression tests are good to judge the internal condition of each cylinder but not really for judging one cam to another.

 

 

Earl with the knowledge.

Thanks for the info.

 

 

If you have ALL the cam specs from the manufacturer, you can calculate overlap. I don't know that I have ever seen a full spec sheet from an import cam manufacturer. However if you degree in your cams, you could calculate the overlap number also. That is what is nice about DOHC motors, you can change overlap with your adjustable cam gears.

 

Here is some tech info on overlap
http://www.compcams.com/Commun...05736