Someone recently told me that seat pressure is not the only important thing to look at with springs but also the spring rate... which as I understand is the amount of pressure it takes to compress the spring 1 inch.

Have 3 companies, each with the following rates


Intake Rate Exhaust Rate

Company A 239 lbs/in 302 lbs/in
Company B 216 lbs/in 254 lbs/in
Company C 157 lbs/in 254 lbs/in

Any of these 3 companies' springs have been used in various setups to spin to high rpms, on big boost (which is why it's in the FI section) and the springs have performed without issue in many a setup.

The question is whether or not they withstand valvefloat, it's been shown time and time again that they do. My question is more about what significance the rate has.

Why does the exhaust need more pressure to open than the intake? To close faster... but why?

What effect on performance does the valvespring rate? Positive correlation between engine speeds and valvespring rate necessity?

 

What are these springs for?? The rates sound a little low for a "B" engine.Also most dual spring b setups use the same springs for intake and exhaust.I know of no reason to use a higher rate spring for an exhaust.Typically the exhaust cam profile is less aggressive and the exhaust valve weights less than the intake.

 

It's for an Audi/VW engine with 3 intake valves and 2 exhaust valves per cylinder. The aftermarket springs are single on the intake and dual on the exhaust. Those are the specifications from the manufacturers.

Intake valve diameter is 26.95mm and exhausts are 29.85mm. That multiplies out to 3.14 x (13.475 x 13.475) x 3 = 1710.442 mm^2 for the intake and 3.14 x (14.925 x 14.925) x 2 = 1398.905 mm^2 for the exhaust. Peak exhaust flow area is roughly 82% of the intake. One of the 3 intake valves is at a different angle from the other 2 and this has an influence on the measurement of flow, I'm sure.

 

Part of the answer is the heavier exhaust valve.I assume its heavier because of the larger head diameter.The other is that single and dual springs have different characteristics.A dual spring can have higher seat pressure and less over the nose pressure than a single spring at the same amount of lift.I am not familiar with Audi 20v cam profiles but the exhaust may have more lift than the intake.Dual springs can have less coil bind at the same pressures as single springs.

 

I am not sure on what the factory valves are made out of so that I can compare the intakes to the exhaust. I know that the aftermarket valves are stainless steel on the intake side and Inconel 751 on the exhaust so the rough difference in weight due to different densities could be figured out.

I am using an aftermarket forged billet camshaft set with 10.45mm lift on the intake side and 11.65mm on the exhaust.

If a dual exhaust spring can have more seat pressure yet less over the nose pressure and less coil pressures in comparison to single springs... what advantage does company A have over B and C? The ratings for company A's springs are considerably higher and all 3 use a single intake spring and dual exhaust ones. What is to be gained from a higher spring rate?

 

Inconel is slightly heavier then common ss.Seat pressure keeps valves from floating and bouncing on the seat.To much over the nose pressure (max lift) wipes out lobes.Ideally you want to use as little spring pressure as you can to do the job.From my experience published spring rates and spec.s are rarely accurate.Pressures can verify from batch to batch.

 

So what you're saying is, the more seat pressure = the higher the spring rate = the higher the over the nose pressure?

To verify spring pressures, I am looking into purchasing one of these

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Axle &raquo;</TD></TR><TR><TD CLASS="quote">So what you're saying is, the more seat pressure = the higher the spring rate = the higher the over the nose pressure?

To verify spring pressures, I am looking into purchasing one of these

</TD></TR></TABLE>

Yes.
Just to use one spring set as an example if you had 80# on the seat on the intake at .412" lift it would be 178.5# (80+[239x.412]).On the exhaust with 80# it would be 218.5# (80+[302x.459]).
I have never used that one but it looks ok.Try to get a calibration spring in the range that your using.You want a tester in the 0-500# range.You probably never test a spring that is more than 300#.A 0-1000# will have half the resolution (lines) of a 0-500# one.

 

There a bunch of different testers, some are like this lever kind like in the picture. There are others that are just a little piston to put the spring into and then compress it with a vice and then there's this neat one that has software that comes with it that tells you rate of compression and all these neat things.

You mentioned the reading would be different but the spring ratings I have seen are different for the intake and exhaust. The intake would be at 54 and the exhaust at 80, for example. I am not sure if, for the exhaust, that is for each of the springs or for the dual-spring counting as one.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Axle &raquo;</TD></TR><TR><TD CLASS="quote">There a bunch of different testers, some are like this lever kind like in the picture. There are others that are just a little piston to put the spring into and then compress it with a vice and then there's this neat one that has software that comes with it that tells you rate of compression and all these neat things.

You mentioned the reading would be different but the spring ratings I have seen are different for the intake and exhaust. The intake would be at 54 and the exhaust at 80, for example. I am not sure if, for the exhaust, that is for each of the springs or for the dual-spring counting as one.</TD></TR></TABLE>

I have never see one of the ones that you put in the vise to be anyway near correct. http://www.goodson.com/store/t...eac80
These are the ones I run into the most.The spring rate they give for the exhaust would be for the combined inner and outer.

 

You can take two springs made out of the identical diameter wire, both at the same free standing height and OD but make one spring with 5 coils and the other spring with 7 coils. The spring with 5 coil turns is going to have a higher lbs/inch rate than the spring with 7 coils. However, the spring with 7 coils will live much longer because it does not have to work as hard, given that installed heights are equal.
The spring in question is for a 3 intake valve Audi that has a smaller light weight valve that does not require a heavy spring poundage to control its movement.
Bigger just does not always equal better. You need the right spring for the right job.