Alvin

iTrader: (2)

I've seen some valve spring issues cause some breaking up on the top end and hard power drops but those where with springs with some serious problems.

I have a car that is down on total about 25-30 rwhp and 2.5 mph (1/8th) from last year. I've checked just about everything I can imagine other than valve springs and a compression test. The car is down on power across the board but makes a very smooth graph.

The car has a .649 lift cam with .650 lift springs and they are of a brand we haven't used before so while they should be good we are hoping to find them a little off in seat and open pressures.

So has anyone had a car pick up across the board with a spring change?

1989GTA

Yep, I had the same problem. Car was down 25hp and was falling off instead of hanging on like in the previous dyno pulls. My Comp 26918 springs were down to under 100# on the seat. Put in some Manley beehives with 155# on the seat and the problem went away.

Alvin

iTrader: (2)

Well, checked the springs this morning and they where 460 open (at .650) and 160 on the seat. The only thing that concerned me is that they where real close to coil bind.

XtraCajunSS

iTrader: (2)

Being close to bind is not necessarily a bad thing... you can be too close but not likely with a spring rated to .650". Most spring manufacturers build in a good deal of leeway there to protect themselves. With those numbers I would say springs are not likely your problem but can't be 100% sure, sometimes harmonics come into play. What type of rocker arms are you using? What heads and what valves? Valvetrain weight will play a huge part with a cam that large.

Shane

Alvin

iTrader: (2)

Hey Shane! I appreciate you commenting on my thread. hope things are well down south.

The heads are TFS 215 CNC and I got them as an assembled set with their springs. I used Harlan Sharp Rocker arms and the valve train geometry looks good.

The car once made great power! Its just been steadily dropping since we built it!

One interesting note. I called TFS today and they told me flat out the spring is not good to .650 lift. I told him that his head documentation on his website said otherwise and he said he would change it today.

I'm not sure why they would say the springs are not good for this lift, Bind is at 1.08 installed height is 1.800 and the the spring I tested checked 460 lbs at 1.15

Heres a graph of whats going on. Take a look at the dates on the runs

XtraCajunSS

iTrader: (2)

Alvin,

I still don't know if the springs are the problem. Did you measure the springs directly to see the actual bind measurment? I would say further investigation would be necessary before calling the springs the culprit. If you would like, give me a call here at the shop and maybe we can brainstorm some possible issues.

Thanks,
Shane

njc.corp

alvin those numbers look good-

being close to coil bind is not the problem

what i dont like is seeing is 649 lift cam with 650 rating-

i like to have some extra pounds like 649 with a 660 lift-wether its makes a difference is not the problem just added measure-

i dont thing its valve springs-

how did it use to run before?

how and when did u notice this hp being down?

and was their any changes done in between?

spring numbers look good to me-

if the springs are out of the car get a second view by using someone else's spring tool-(if u really want to know )

u do a leak down? if so whats the numbers-

Thanks

Nick--

1.8t

In looking at your dyno, it doesn't look like valve float at all. Your down on power the whole way through the curve. I think something else is amiss in your setup. Re-visit your tune to make sure everything is still inline and then get some leak down numbers.

67Ranger

iTrader: (16)

I was going to say the same thing. I work as an engine builder and help out on the dyno quite a bit, and we had one that, on our 901 engine dyno lost something like 120hp (on a 350hp motor) in about 200 RPM. The engine wouldnt even make it to 6000. When we changed springs we gained about 300 more RPM and like 30 hp. Basically, our graph looked like it just dropped off the face of the earth. At the same time, get a spring checker (for on the motor), and see what they are at seat, and just make sure they arent way off, because I have also seen changing springs loose 30hp on a high end race engine just from harmonics, and have seen old springs make a little less power than new ones, but not much.

crashly

the push rods , that are a bit thin in cross section, will give simular results..
they can look like a 'pole valve'...

inspect the valve collets, if all SHINY, that could show not enough spring...


ash