Technical > Matt Shaff's Engine Shop
Seat Pressure
masracingtd1167:
--- Quote from: coupemerc on January 25, 2014, 12:57:30 PM ---
--- Quote from: masracingtd1167 on January 25, 2014, 09:24:13 AM ---Jon mine are .937 diameter and a .750 wheel . I don't turn mine quite as high as you guy's do about 9400 max . I was thinking it might free up a little horsepower . I still plan on using 375 on the seat . My biggest concern is how much open pressure they had . I don't have a spring tester that go's that high.
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Bill... My spring tester goes to 1000 lbs max. I am going to disassemble each spring (mine are doubles) and then measure the force of the inner at max lift and then the outer at max lift. Then add them both together to get the total open force.
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Chuck that's a good idea I think I will try that . Not making a big change in springs going from the 1249 's to the 1248 PSI springs .
masracingtd1167:
--- Quote from: JrFuel Hayden on January 25, 2014, 11:19:41 PM ---We measure our closed spring pressure with the retainer, so we get the total spring pressure, just add the retainer thickness to your installed height. Also your spring supplier should be able to give you open pressure once you give them your valve opening.
Bill, I don't know your motor combo, but we replace our 1 1/2" dia PAC springs when they test on the car at 329 lbs. 330 is min with my 10,000 rpm motor at .938 lift, on the RR 23° SBC , new they install at 400. One of the best changes we have made was when I switched to the 1 1/2" PAC springs, they are more expensive, but I don't have to change them nearly as often as the triple springs. Unless we have some other problem, I only replace 3-4 springs all season.
Bud's non raised runner 23° only ran 260 lb springs. Our Hemi needs 420-440 lbs new, bigger valves, and high 9,000 rpm.
Back in the day when I had a dual engine BBC Top Gas car, and we wanted to be one of the 1'st Top Gas cars to go 200 mph, we did run 202 when we installed weaker valve springs, no other change.
So, if you are not sure what springs to run, check with your cam grinder, and be sure to tell them 9400 max.
Jon
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Jon I measure mine the same way.
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