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Valve spring setting for turbo boosted engines ?

General engine tech -- Drag Racing to Circle Track

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dannobee
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Re: Valve spring setting for turbo boosted engines ?

Post by dannobee » Mon Nov 25, 2019 10:19 am

The one that comes to mind is the early porsche 930 turbos. Same valve sizes as the NA cars, same valve spring and retainer, same valve length. The intake and exhaust valve spring installed height was 1mm less on the turbos. Difference was made up with a couple more 0.020" shims under the valve springs.

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Re: Valve spring setting for turbo boosted engines ?

Post by ptuomov » Mon Nov 25, 2019 10:54 am

dannobee wrote:
Mon Nov 25, 2019 10:19 am
The one that comes to mind is the early porsche 930 turbos. Same valve sizes as the NA cars, same valve spring and retainer, same valve length. The intake and exhaust valve spring installed height was 1mm less on the turbos. Difference was made up with a couple more 0.020" shims under the valve springs.
The boxer six has perfectly spaced pulses and the valve seated load requirements don't go up because of blowdown interference. I think that they may have increased the seated load because they increased the valve seat width, to keep the pressure at the valve to seat interference where they want.

Very different for twin turbo cross-plane V8 with log manifolds, where either the 180 or 90 degree blowdown interference can really cause big differences between cylinders.

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Re: Valve spring setting for turbo boosted engines ?

Post by Turbobuick6 » Mon Nov 25, 2019 11:56 am

I cannot buy the "Boost holds valves open" or "you need to multiply boost by valve head area"

Unless someone can prove me wrong with legit data.

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Re: Valve spring setting for turbo boosted engines ?

Post by MadBill » Mon Nov 25, 2019 2:06 pm

I can sort of accept the possibility of needing to deal with boost at IVC on a supercharged engine, only because at RPM above that for which the cam is optimized, IVC will be 'too early' and the valve will prematurely slam the door on the slightly-higher-than-cylinder intake pressure, but at that point it's the lobe ,not the spring that is controlling valve motion, deccelerating it to hopefully touch down lightly on the seat.

For a turbo engine, as mentioned above, the intake side, apart from bigger numbers, is no different than in an NA engine since many turbo engines have higher exhaust than intake pressure -at best roughly equal- and that pressure acts to similarly increase the cylinder pressure.

If someone can explain exactly, event-by-event, how the SC case demands more spring, I would truly welcome the understanding. :-k
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: Valve spring setting for turbo boosted engines ?

Post by ptuomov » Mon Nov 25, 2019 2:35 pm

Turbobuick6 wrote:
Mon Nov 25, 2019 11:56 am
I cannot buy the "Boost holds valves open" or "you need to multiply boost by valve head area" Unless someone can prove me wrong with legit data.
I can't either, because that logic is silly, especially on the intake side.

What's not IMO silly is the exhaust valve at the closing point bouncing, if the 180-degree exhaust blowdown pulse from the other cylinder arrives in the victim cylinder at the same time as the valve spring is trying to close the victim cylinder exhaust valve(s). This is not an issue just with turbo cars, it's in my opinion an issue with any cross-plane V8 with log-style exhaust manifolds. The presence of high exhaust manifold pressure with turbo however magnifies the issue.

People running six cylinder engines and twin turbos don't see any of these exhaust blowdown problems.

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Re: Valve spring setting for turbo boosted engines ?

Post by cjperformance » Mon Nov 25, 2019 6:26 pm

This reminded me of a thread from 10 odd years ago,

viewtopic.php?f=1&t=17780

There were a few good comments ,
This was my comment from back then,,

""QUOTE Re: the great blown valve spring theory debate!ReportQuote

Post Fri Feb 12, 2010 3:02 pm

Many years ago I had a good running bog stock 200ci falcon 6cyl, I decided to put a turbo set up on it, get it going then when proven and driving , I built another engine (250ci) to put the going turbo setup onto. Definetly NOT high lift, high pressure springs etc in this deal, BUT this is what happened, 
The good running engine when fitted with a basic draw thru carbed turbo setup, using only 6psi boost for the initial setup ran great up till 3800rpm where it would pick up random detonation, black exhaust smoke, no more increase in power, AND when brought back to idle it ran like a dog, as if it had got to valve float and pumped up some lifters. I did some chasing/looking, this was my first boosted engine so I was raw on the subject. I ended up being told by the guys at Vine Turbo's to take the preload off of the hydro lifters on the intake only and check back with the result. I did so and the same thing happened, i got some valve train noise at the same time- but it would come back to a clean idle. I checked back to them with the result and was told that half way thru the exhaust stroke that the intake valve can get popped off its seat if the springs cant cope and that this was caused by the pressure pulses/spikes in inlet pressure as other inlet valves close and even though with a turbo the cylinder holds more exhaust stroke pressure than when n/a, the pressure difference across the inlet valve can become greater and a spring that just coped in n/a form would not cope when boosted. Their advice to me at the time was to shim or replace the inlet springs. I used .060" spring shims and when set up with the regular lifter prelaod the engine ran fine with 6psi boost up to 4500rpm which was as far as I was game to take a stock 200ci with boost.
I was told by others at the time that it was my stock cam, my ignition, jetting etc etc, When I ran this by the guys at Vine Turbos they told me that on a stocker, just up the spring pressure, you'll be fine, and it was.
I was later shown a solid cam from a boosted chrysler 6cyl that had a lot of damage to the opening ramp on all of the intake lobes that they claim was a result of springs that did not cope with the intake pressure spikes- causing the lash to be taken up in random spots across the opening side of the lobe, the owner had also had problems with bent intake pushrods.
, and the exhaust manifold and turbo exhaust housing from the same engine that was heat damaged, not-they claim- due to overlap causing fuel blow thru but from the intake valves allowing some a/f into the exhaust stroke which would then burn in the ex manifold causing the damage.
Seemed logical, and seemed to work.

I dont do much with s/c engines but if this theory was applied to an s/c engine, the cyl pressure at the time the trouble occurs in a turbo engine would be lower in the s/c engine which 'should' (theres that word! lol) make the problem worse!

Going on this I agree with some more intake spring for a boosted app, but also the specific combo of boost, cam, spring, valve etc is going to have bearing on the outcome.

Didnt solve much with that, but gives something else to chew over!

Craig. END QUOTE""

Now ten years on to be honest im none the wiser, but im still finding a need for more spring on boosted stuff, i dont really care why anymore but it needs it.
Also, Ford Australias development if the "Barra" 4.0L i6 single turbo engine has followed the valve spring force increase. The 1st series of these engines did not upgrade the springs in the turbo model which is fine till you get up around 13+lb then suddenly they have problems. They run hydro lash adjusters which suffer pump up due to loss of valve control and hold valves open, quit making power and run ragged back at idle till the adjusters bleed out again. These engines can make fantastic power in as stock form, with factory turbo, manifold(in & ex) cams etc, but the springs let them down. In the uprated(higher boost from factory)models Ford Australia simply fitted springs with more seat pressure and problem solved. As in the aftermarket, the only mod internally needed to make big reliable hp is a valve spring swap. Of course you do reach a power level where further engine mods are required for strength. Point is , these like any other boosted engine require more spring force to do the same rpm as boost is added.
Craig.

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Re: Valve spring setting for turbo boosted engines ?

Post by ptuomov » Sun Dec 01, 2019 2:34 pm

Craig — was that with six cylinders blowing into a single log manifold and single scroll turbo?

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Re: Valve spring setting for turbo boosted engines ?

Post by cjperformance » Sun Dec 01, 2019 5:39 pm

ptuomov wrote:
Sun Dec 01, 2019 2:34 pm
Craig — was that with six cylinders blowing into a single log manifold and single scroll turbo?
Yes , log manifolds on both. Single scroll turbos aswell.
Craig.

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Re: Valve spring setting for turbo boosted engines ?

Post by ptuomov » Sun Dec 01, 2019 5:44 pm

cjperformance wrote:
Sun Dec 01, 2019 5:39 pm
ptuomov wrote:
Sun Dec 01, 2019 2:34 pm
Craig — was that with six cylinders blowing into a single log manifold and single scroll turbo?
Yes , log manifolds on both. Single scroll turbos aswell.
It’s a total anarchy in that exhaust manifold, compared to the beautiful order of twin turbo straight six! I can see more seated valve load being needed.

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Re: Valve spring setting for turbo boosted engines ?

Post by cjperformance » Sun Dec 01, 2019 6:14 pm

ptuomov wrote:
Sun Dec 01, 2019 5:44 pm
cjperformance wrote:
Sun Dec 01, 2019 5:39 pm
ptuomov wrote:
Sun Dec 01, 2019 2:34 pm
Craig — was that with six cylinders blowing into a single log manifold and single scroll turbo?
Yes , log manifolds on both. Single scroll turbos aswell.
It’s a total anarchy in that exhaust manifold, compared to the beautiful order of twin turbo straight six! I can see more seated valve load being needed.
Yes, twin turbo i6 is the ideal setup for sure. That said, with a few bandaids in place these single turbo setups certainly work. Do a bit of googling or youtubing on "ford barra turbo" , pretty inpressive for what they are.
Craig.

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Re: Valve spring setting for turbo boosted engines ?

Post by Tom Walker » Sun Dec 01, 2019 6:57 pm

Craig, I believe your experience cited 10 years ago was very revealing why the possibility exists that boost may require more spring. The pressure waves created in your engine were probably anarchy as mentioned.
Thanks, that was a fantastic write up.

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Re: Valve spring setting for turbo boosted engines ?

Post by Turbobuick6 » Tue Dec 03, 2019 8:52 am

When we boost NA engines and see a need for more valve spring, I am not convinced it is the boost. I am still under the impression, there was always an issue in the valve train just a boosted application makes it much more noticeable.

Again, give factual data showing the need for the higher spring pressures and I may change my mind.

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Re: Valve spring setting for turbo boosted engines ?

Post by Orr89rocz » Tue Dec 03, 2019 9:46 am

Turbobuick6 wrote:
Tue Dec 03, 2019 8:52 am
When we boost NA engines and see a need for more valve spring, I am not convinced it is the boost. I am still under the impression, there was always an issue in the valve train just a boosted application makes it much more noticeable.

Again, give factual data showing the need for the higher spring pressures and I may change my mind.
If the boost amplifies it or make it more noticeable, then it would seem boost has influence on how the spring sees the valve mass, maybe requiring more spring pressures or rates or both? Or is it increased pushrod deflection from increased cyl pressure? Or does accelerating rate of the motor matter in valvetrain control, as more power would accelerate faster than na motor.

I dont have data either way but here’s something I found interesting. When i had improper valvetrain geometry on my sbc turbo car, i wrecked my valve guides in less than 500 miles i think it was. Started having issues I thought were float. I did not believe ignition. 12 psi i could hit what seemed to be a limiter at like 6500 rpm. At 15 psi i hit it at 6200...it was pretty consistent. When I investigated and found the guides screwed up, i had heads fixed, valvesprings tested ok so put them back in at the same specs but switched to much more stable shaft rocker system and set geometry to the mid lift method. Rock stable to 30 psi and 7200 where i crossed the traps lol. Twin turbo car with headers

my stock 91 305 sbc tpi motor with stock oem hyd roller at 207/213 deg .415/.430 lift ran good to 7 psi across its 4500-4800 rpm shift points. But never responded to more boost. Ran same times up to 20 psi at same air fuel. It required more fuel in the map to get there and keep same afr but did not show at track. I was gonna question valvesprings being old and worn, or maybe stock torque converter? I’ll never know lol

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Re: Valve spring setting for turbo boosted engines ?

Post by ptuomov » Tue Dec 03, 2019 1:19 pm

Turbobuick6 wrote:
Tue Dec 03, 2019 8:52 am
When we boost NA engines and see a need for more valve spring, I am not convinced it is the boost. I am still under the impression, there was always an issue in the valve train just a boosted application makes it much more noticeable.

Again, give factual data showing the need for the higher spring pressures and I may change my mind.
I don't think it's the boost either, I think it's the pressure waves in the exhaust manifold. Twin turbo V6 or even a single turbo V6 with long secondaries and isolation between sides doesn't have anything that bad going on in the exhaust manifold. In a single turbo inline-6 with a log manifold or twin-turbo cross-plane V8 with log exhaust manifolds, the exhaust pulses live in total anarchy trying to hurt various cylinders at different rpms. More exhaust manifold energy, greater the seated load needed by my logic.

More discussion here: viewtopic.php?f=1&t=58958&start=30#p833591

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