Noticed these on the site when i was browsing around. Anyone have any idea what the difference between the "Vtec" and "Vtec Turbo" springs are?

"Vtec Turbo"
http://www.skunk2.com/Merchant2/merc...roduct_Count=1

"Vtec"
http://www.skunk2.com/Merchant2/merc...roduct_Count=0

Thanks, Joe

 

My guess is vtec turbo's have a higher seat pressure.

Little quiz:

Given two of the same engines running the same cams, same rpms the only difference is one is running 20psi of boost. Why does the turbo engine need more seat pressure?

 

ok lets say im going buill the motor now and boosting it later ...could i run the turbo springs w/o adding the turbo...what would happen??

 

Its not a issue of not working without being in a boosted application, But in a forced induction setup when selecting cams and springs you want to select the cam with the highest lift but with the least amount of duration, look at it like this, you want all the boost you can get into the cylinders(highest lift) but at the same time you need to open and close those valves ASAP as to not leak boost back out the valves(less duration) which is how long the valve is open, The stronger spring seat will allow you to keep those valves opening and closing under the most extreme pressure, were a weaker NA spring would give under those extreme loads(pressure) limiting you on power output and spool-up time, and in some cases spring failuer Is this what you were looking for KJ?? I may be off, its been a wild week Happy easter!

 

Pretty much. Explaination so everybody understands:

You need the seat pressure to be higher because with 20psi of boost on the backside of the intake valve you have now a force trying to constantly open the valves. More boost = more seat pressure. This becomes an issue at high boost levels 40psi and greater.
Simplified way of looking at it. Imagine the valve as a flat disk with an area 1^2in. (not real size, this size makes the math easy). With 25 psi of boost acting on it you now have 25 lbs of force trying to open the valve. Now if the valve spring offers 50 lbs of seat pressure N/A it now only has 25lbs of seat pressure under boost. If boost is raised to 40 psi on the same setup you will likely float the valve due to boost pressure and rpm causing an extreme power loss and possibly bent valves depending on cam and valve head size.

Now in actuality a valve really doesn't act like a flat disk due to the shape of the stem and slope to the head but hopefully the flat disk analogy made the concept easier to understand.

Now the higher the seat pressure the wear the valvetrain is going to have. This most effects cams and rocker arm pads. So you have to do a trade off.

A setup I'd consider for a motor that starts out na for a while and moves to boost is the omnipower which offers a low seat pressure of 55lbs and handles a lift of 14mm. This will work out great n/a and once you go turbo most cams only run lift in the range of 11.5mm to 12mm so you have 2mm worth of shim you can add to raise seat pressure. I'm going to try this on a motor soon inder the same n/a going turbo in the future motors. You do need a spring tester and a tool to measure install height to do this correctly though.

As far as cams for turbo I'm leaning more towards moderate lift moderate duration on high rpm motors right now. Seen better results than high lift and low duration.

 

Im just gonna get some Buddy Club Stage 4's and run 50psi and call it a day..... I think my motor will probably do the same...

 

dont you need longer longer duration to make power up in the rpm's. thats what jeff evans said even on turbo cars

 

Yes To a point,(BTW evans is the shizzel ) to much duration on a boosted car will hinder performance, duration is good as long as there is little to NO overlap, and with most cams that carry a long duration you get overlap, Overlap can be dialed out with adjustable camgears but on a set of NA cams if you were to dial out all the over lap you would be left with a cam that would be as good if not worse than any OEM cam on the market, High lift "lower" duration is a optimal cam choice of forced induction setups, take a look at some NA cams and there specs and then look at some Turbo cams and specs, the lift will be there, but duration will be less.

 

I'm leaning towards mixing cams in high power motors right now. Like a moderate N/A intake cam and a stock itr exhaust cam. Jun2 intake cam is nice as well as skunk 2 stage 1. The mix of a moderate intake cam and a "small" exhaust cam works pretty well on motors spinning 9k plus, enough overlap for good high rpm scavanging but not too much to effect spool. This also only works well on motors with a manifold with a good merge collector and decently long runners. For people who might want to do some experimenting I'd suggest to stay away from cams with large primary lobes like skunk 2 pro1's and most toda cams.

 

Nice explanation but all i was wondering was the difference in the spring not the duration issue, already had that down long ago. though for those who didn't know.