Too much valvespring?

[CamKing]

Something is way wrong.
We do a lot of Turbo drag race BBC engines, and in a 555, a 269/269@.050", .440"/.440", on a 114 will peak above 7,000rpm.
With that cam, and 1.7 rockers, we run 275-300# seat pressure, and 700-750# at max lift

I mean i can make it peak wherever i want with boost curve shape. The later it spools and the later it hits peak boost thats where the peak power is on the dyno but like i said it seems to fall off faster than expected and seems that the fuel demand on the street pulls shows the engine not needing the fuel to maintain same afr. In my experience that means ve falling off equals power falling off.

So now im curious what to do. I hurt a lifter and need to replace them and the cam so wondering if i should change something or what could possibly be the issue of what its falling off

OK, I reread the first post, and I missed that the low peak rpm was with N/A. I think that's just because the exhaust duration is too short. With a 2.88 exhaust valve, a 555ci engines is going to need an exhaust lobe that's 10-16 degrees longer then the intake. Of course, that would be krap with the turbo.

[Orr89rocz]

Something is way wrong.
We do a lot of Turbo drag race BBC engines, and in a 555, a 269/269@.050", .440"/.440", on a 114 will peak above 7,000rpm.
With that cam, and 1.7 rockers, we run 275-300# seat pressure, and 700-750# at max lift

I mean i can make it peak wherever i want with boost curve shape. The later it spools and the later it hits peak boost thats where the peak power is on the dyno but like i said it seems to fall off faster than expected and seems that the fuel demand on the street pulls shows the engine not needing the fuel to maintain same afr. In my experience that means ve falling off equals power falling off.

So now im curious what to do. I hurt a lifter and need to replace them and the cam so wondering if i should change something or what could possibly be the issue of what its falling off

OK, I reread the first post, and I missed that the low peak rpm was with N/A. I think that's just because the exhaust duration is too short. With a 2.88 exhaust valve, a 555ci engines is going to need an exhaust lobe that's 10-16 degrees longer then the intake. Of course, that would be krap with the turbo.

With the turbos being mid mounted In the car rather than close to the exhaust ports, i believe i have lower exhaust energy due to less heat so the turbines are larger than needed so it should be breathing very well. I was considering adding 4-6 more degs of exhaust duration since it should be breathing more like a na deal with low backpressure. Not sure if that should help anything or not, or if the overlap should increase some to help spool abit more?

[CamKing]

I mean i can make it peak wherever i want with boost curve shape. The later it spools and the later it hits peak boost thats where the peak power is on the dyno but like i said it seems to fall off faster than expected and seems that the fuel demand on the street pulls shows the engine not needing the fuel to maintain same afr. In my experience that means ve falling off equals power falling off.

So now im curious what to do. I hurt a lifter and need to replace them and the cam so wondering if i should change something or what could possibly be the issue of what its falling off

OK, I reread the first post, and I missed that the low peak rpm was with N/A. I think that's just because the exhaust duration is too short. With a 2.88 exhaust valve, a 555ci engines is going to need an exhaust lobe that's 10-16 degrees longer then the intake. Of course, that would be krap with the turbo.

With the turbos being mid mounted In the car rather than close to the exhaust ports, i believe i have lower exhaust energy due to less heat so the turbines are larger than needed so it should be breathing very well. I was considering adding 4-6 more degs of exhaust duration since it should be breathing more like a na deal with low backpressure. Not sure if that should help anything or not, or if the overlap should increase some to help spool abit more?

Turbo, you should be running less exhaust(single pattern), on a 114-115 LSA

[Orr89rocz]

I’ve seen a few trends in the ls world that are starting to widen out the exhaust side but also seen a variety of cams work from na looking cams on tight centers to wide lsa cams. It definitely is interesting.

Now i just gotta decide if i should change springs out to something maybe smaller diameter and lighter with touch less spring pressure? Pac 1225 or similar? 1.55” spring vs my 1.645?

Since i never got an accurate dyno pull from 5000-7500 in a constant boost Level across the range i guess i cant exactly say its doing anything wrong or not?

[PRH]

We have had dynoed some blown stuff where we wanted to be pretty sure the valve train was happy in the upper rpm, so we ran them with a carb and intake na first, that way we could have a better read on what the valve train was doing before putting the blower on.

[Old School]

The comp hi tech lobes, both .420 and .440 are very mild by a lot of today's more modern lobes. I have run them in bbc with 240 seat and 600 open with the same weight valves you have without any sign of float shifting at 6800. I really don't think you need that much spring unless the boost from the turbo's require that much more spring. Normally aspirated I really cannot see needing that kind of pressure, needless to say how much it will shorten lifter life.

[Orr89rocz]

We have had dynoed some blown stuff where we wanted to be pretty sure the valve train was happy in the upper rpm, so we ran them with a carb and intake na first, that way we could have a better read on what the valve train was doing before putting the blower on.

And what did you find? Did the blower setups need anything different on springs? Or did rpm range change?

[3V Performance]

Can too much valvespring seat and open pressure cause valvetrain instability? I assume yes from increased deflection but do you think this is too much for this application? I like to think i have more pressure than needed but certainly not enough to cause issues

555” BBC. 2.300” stainless intake valve probably 140-146 grams
1.88” inconel exhaust (turbo car) probably 130-133 grams?

Springs are manley nextek 221425 set up at 2.00” so that should be around 340 seat pressure and close to 790-800 open at my lift. Intake is around .076” to bind. Exhaust .123” which maybe a concern?

Cam is 267/272 deg with .440 lobes, comp hi tech family for street stability. Heads are a ported dart 345 cc casting, flow over 425 cfm. 7/16” .160 wall pushrods

Car was nosing over around 6000 when dyno’d all motor. Peaked 5900-6000 then started falling off quicker than expected. I thought maybe because it had a slightly small throttlebody for the setup and running dual 3” exhaust temporarily at the time, figured that killed power and rpm potential. Seems to do the same in boost tho based on the fuel curve. Efi car so my fuel table generally follows the power curve shape and it seems to be falling off after 6000.

I thought it would pull higher to 6400-6500 peak. Talked to one guy who is good with valvetrain says he thinks my exhaust side is unhappy. Possibly unstable, floating or bouncing? Im not sure but could explain the power falling off. Seems to think there could be too much spring on it.

I just not totally convinced. Thoughts?

Yes it can and I see it all the time on the spintron.

[3V Performance]

Blower is completely different then turbo when it comes to cam.

What kind of back pressure are you seeing?

[Orr89rocz]

Blower is completely different then turbo when it comes to cam.

What kind of back pressure are you seeing?

I have only run it to 15 psi boost. Backpressure is likely less than 1:1 with this deal, i have a good bit of turbine capacity so i suspect it is less than boost at these lower boost levels. Wastegates have 4 psi springs in them and make 4 by themselves and its about 1 psi of boost per 1 psi co2 commanded on the gate.

[Orr89rocz]

Measuring deflection. I dont have my spring compressor handy so no checker spring yet to compare

But advertised rocker ratio lift at valve should be .751 at the exhaust side with no lash. I set it at .017” lash and turned it over. Saw .720” lift. Should be .734” by the specs. 0.014” deflection by specs but wont know for certain til i do it with the checker spring

[ptuomov]

What does the exhaust manifold / header look like?

[Orr89rocz]

What does the exhaust manifold / header look like?

27-30” long primary long tubes. 4 into 1 collector

[ptuomov]

What does the exhaust manifold / header look like?

27-30” long primary long tubes. 4 into 1 collector

Then it’s probably not exhaust blowdown interference, you’ve got a lot of separation.

[Orr89rocz]

Measuring deflection. I dont have my spring compressor handy so no checker spring yet to compare

But advertised rocker ratio lift at valve should be .751 at the exhaust side with no lash. I set it at .017” lash and turned it over. Saw .720” lift. Should be .734” by the specs. 0.014” deflection by specs but wont know for certain til i do it with the checker spring

Ok checking springs with same lash .017” gives .744 lift. With regular spring and same lash .720”.
So .024”. Is that acceptable?

What are signs of unhappy valvespring action on retainers and locks and top of spring? Appears to Me that they been moving around as the undersides are marked