924Board.org

[Karlio]

What upgrade valve springs are out there for a n/a race engine?

[MikeJinCO]

When researching valve spring setups for racing the consensus was to have a closed seat pressure of between 105 to 120 lbs(63-65 stock), Actual spring rate not as important, but should be probably in the 250 plus or minus per inch range This higher seat pressure is due to the well recognized valve bounce at higher rpms and the rate is similar to stock so the force to open and wear on the cam is about the same as stock. That is hard to pull off over here where most race grade spring are intended for push rod motors and roller cams so have much higher rates(350-500).

The NA head is different than the 931 head in that the 931 has rotators 0n all springs where the NA only on the exhaust so different setups required for the two valve pocket heights.

I eventually went with a setup for my 931 head from RD Spring in California a smaller outfit who makes the hipo setups for the Lindsey Racing 944's(8mm but shorter valves) and lots of motorcycle stuff. His setup consisted of spring seats, a soft(by US standards) 275lb Chevy LS motor spring and retainers modified to fit the stock 924 keepers which have I believe 6 degree rather than the more common 7 angle. I talked to him about the NA head difference and he said that he could work something out. The springs are single beehive style and the retainers are about 8gm vs the stock 28 so a significant weight reduction. The price was quite reasonable with all the machining involved and delivery on about 2-3 weeks which is unheard of these days(JE Pistons 10-12 weeks).

I talked to Dimitri Elgin at Elgin Cams last week who is working on the SCCA race cams(NA head) and he asked about springs so I told him this and he said he had worked with them before and would be in touch so there might be something going on there.

One factor making it more difficult is that almost all new style motors have small diameter 4 valve heads so all the parts are tiny compared to our stuff.

If I was over there I'd be looking at what is now used in old Alfa, Jag, Merc and BMW stuff for vintage racing, the BMW 1.6 and 2l motors probably not that different, 356 Porsche's had 9mm valves also. I would also try to find Jon Mitchell(Bournemoutth maybe?) if he is still around as he was the UK expert on out motors 20 years ago.
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Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

[924RACR]

Man, that reminds me I gotta ping Elgin and make sure they got my cam in the pile; shipped but haven't heard anything back... derp.

I still need to measure those springs I have... too many projects percolating right now, and I need to gin up some small 2.5mm shims for them to get the right compressed height...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Karlio]

Brilliant info that fellas, I know of Jon Mitchell and will get in touch and will be doing some research on other make springs.
Cheers karl

[Fifty50Plus]

I just put the Elgin cam in my IT-B NA engine. Hayes turned me on to 924 lifters from ACM in Sweden without the porsche/audi angled adjusters. The porsche/audi lifters didn't have enough range for the Elgin cam grind when they took off part of the back of the cam.
I also had to get Manley 8mm .080 in thick last caps that fit on the tit inside the ACM lifters. Then I had to get Alfa 9mm lash caps of various sizes that fit on the 924 valve stems. Quite a production to finally get the valve lash correct but I had no problems with this arrangement at the track.
My springs are still stock while the valve train is lighter. On the track, the engine had a slightly different feel with the Elgin cam but it still was running out of breath around 6200 RPM. CO was between 11.4 and 12.8 (4800-6200RPM) on the track with this cam while the IT-B cam was a consistent 12.5-12.8. Not sure why the difference when I made no other changes except the cam.
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1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA

[924RACR]

Measured three different 924 valve springs last night; still have to hash out the numbers and will post back with a summary.

The three springs tested were old stock springs (used, unknown miles on street), "fresh" stock springs with maybe 8 race seasons on them (so not really fresh, but much less use than the first), and an aftermarket set of springs for unspecified race use from a group buy (presumably here, I don't remember) many years ago.

Could definitely see the loss of rate with the more used stock springs, but was surprised that the "race" springs were much lower still.

Numbers to follow later...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Fasteddie313]

Was thinking, that the 941 engine, already having the crower rods, the main RPM limitation gone (stock rods), plus having light pistons, just needs springs and lifters upgraded (stiff and light/solid/shims), in order to not much worry about an RPM redline anymore..

Don’t know how high it would really flow but has an “aggressively” ported head supposedly..

Think it would be a good compliment to finish off that engine build..

Probably possible to do without pulling the head.. Not too super expensive, good peace of mind upgrade for known to fail parts (cracked stock lifters)..

I’m not usually one to preach high RPM on these engines, because I think the cost/benefit is quite high, but the expensive part is already done on it (rods)..
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80 Turbo - Slightly Modified

[924RACR]

OK, here's what I've found... first the raw data, please check my work as I've not done this before, could easily have screwed this up.

Units are US/Imperial: inches lift and pounds of force.

New-ish stock spring (8-10 seasons of racing):
Lift Force
00.102 100
0.200 136
0.297 165

Tired old stock spring, likely from factory:
Lift Force
0.100 81
0.195 108
0.280 131

This aftermarket set of springs:
Lift Force
0.097 76
0.200 101
0.290 125

To my calculations, this gives rates as follows:
Stock new-ish: 333 lbs/in
Stock old: 278 lbs/in
Aftermarket: 254 lbs/in

It has been suggested that the aftermarket springs would be designed for a race cam with higher lift, and so could have a lower rate to work better with a higher lift and avoid valve toss I think is the technical term.

So this all makes me think maybe these aftermarket springs may not be a good match with our Elgin cam, since it's limited on lift...

I also need to add: the aftermarket springs were 0.100" shorter than stock, so I added exactly that much shim to the installation to keep the free height the same... not sure if that was exactly the right thing to do or not, but I am for sure quite new to this. Details on the shims used below...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[924RACR]

As noted, I had to add some shims to get the same free height with the aftermarket springs I tested; difference was about 0.100".

To accomplish this, I was able to find a very nice set of shims that fit perfectly, ID was 0.570", OD 1.25" in 0.050" thickness so I was able to double them up... in case someone else is searching for these...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[924RACR]

Another post to tie in Mike J's posts...
https://www.924board.org/viewtopic.php?t=45261

Note that he's referencing a closed pressure target of around 110-120 lbs for a race motor vs. stock around 65; indeed, my tests with the springs all seemed to show a closed pressure of around 60lbs. So more shims wanted...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Cedric]

[Mike9311]

These are Gegge's below.

Remember gegge was using the 6mm stem valves which are lighter. Same route I am going valve wise but my springs are not as aggressive as what he used below.

Part# PAC-1233
Name PAC-1233 Ford 4.6L 4V 0.500 Lift Ovate Wire Beehive
SKU PAC-1233
Alt Part# PAC-1233-16
Description Ford 4.6L 4V .500 lift Ovate Beehive Valve Spring
OD Large End 1.025
ID Large End 0.662
ID Small End 0.567
Install Height 1.670
Load at Installed Height 105
Spring Open Height 1.120
Spring Open Load 270
Recommended Valve Lift 0.550
Spring Rate (lbs/in) 300.000
Mass (grams) 42.50
Coil Bind (max) 1.060
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

[924RACR]

Interesting; I measured a rate of 333 lbs/in on my fresher set of stock springs... lower seat pressure, but could address that with shims...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[924RACR]

So I heard back from Dema (Dmitri) Elgin late yesterday; he confirmed what we might think, that for his cam we'd want to stick with the stock springs (though get new) and probably shim them up to 90-110 lbs at the seat. Which, by my calculations, means 0.050-0.100" worth of shim with the rates I've measured.

Emphasis on new, as even the fresher springs I tested have seen many races. Might be great for street use still, but not ideal for racing.

Unexpectedly, in digging to try to find a source for new stock springs, I seem to have found them at the most unlikely place: the dealer! Sure to be not cheap; I'm awaiting a reply from the dealer I emailed (who had them shown on their website) to verify fitment and availability.
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Fifty50Plus]

Vaughan, we went thru this about 5 years ago. No stock springs to be found so we had a bunch of sets wound in Australia as a group buy after looking for other suppliers. Dan coordinated it. There wa a problem in that they were weaker than stock but we all put them in our engines anyway. No stock springs available anywhere. If the dealer truly has original springs, we should buy them all.
_________________
1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA