Robin L

You are correct in your impression.....IMHO. But there is a point, first you must be able to keep the valve and the valvetrain components followling the cam profile. There is a lot that goes into this though so different applications will respond to various factors. In general, we found on our hydralic roller cam engines that it took an incease in spring pressure to control the valvetrain. With that added pressure came flexing of the pushrod. I could actually generate loft from the pushrods release of the flex at the top of the lobe. On the opening ramp we would see an inverted curve and lose effective duration from the flex of the pushrod. We would then see where the pushrod would release and loft the valve past the lobe profile.

Cam lobe design is critical. We have seen cams with the same duration numbers @.050 act differently on the spin tron. One will totally lose control at the same spring than the other. THere are general guidlines that peope can use. But remember that just because one cam works well with a certain spring doesn't mean that a cam from another vendor will also. Stay with the recomendation of the cam vendor.

Robin

Robin L

Yep, if you want to play in the high RPM world then your going to have to pay. We were strapped with rules that limited our valves to steel. We also could not use Ti retainers or keepers. Then they limited our pushrod diameter. After that they limited our valve spring seat pressure to 160 pounds.

Look at a LS7 valvetrain. 3/8 pushrods, ti valves, beehive style springs, 8mm valve stems. And this is with an engine that is designed to only spin to 7000 rpm with a warranty! We hear about the lousy valves from people whose lash caps flip off the valve stems. In my opinion this is because they are floating the valve. Just because a rev limiter is set for lets say 7200 rpm does not mean that the engine won't see 8000 in a free spin without fuel or spark. If you miss a gear I know they are getting zinged past that. When the lash cams fall off it is because the valve train lost control.

Robin

99blancoSS

iTrader: (115)

damn *****! LOL




I think thats what we're looking at with my new combination.. 3/8's and a beehive PAC spring. I'm staying out of it and letting the pro handle it all this time. (Erik)

Robin L

Well on the dyno we thought so. But later we found that the valvetrain started to get "unhappy" about 7800 RPM. Remember this is with a stock roller cam that was only designed to go to 5500 RPM. The rules din't allow anything other than a stock cam.

It's very interesting to see what the amount of distress the valvetrain would handle. We like others in this tread spend a lot of time on the dyno testing parts. This is the engine dyno. We would mark the valve tips, make several pulls and look at the valve tips. We would change springs or shim the existing to higher seat pressure. Then we would start all over again. Now remember that our rules required "stock" hydralic lifters. They also required that they have pre loadn and that the lifter could not be "bottomed out" . The tech inpector had to be able to spin the pushrod when the lifter was on the base circle of the cam. For that reason we ran the lifter about .002 to .004 from the bottom. When we tried the normal pre load of about .060 the large spring pressure would start to collapse the lifter at 5700 rpm. We would see a dip in power on the dyno then it would increase when the boost was ramping in. Once we ran the lifter near the bottom the ram disapeared and the horsepower jumped.

A valvetrain can withstand some distress, but there is a limit. Finding where that limit is is like playing russian roulette. I have broken several valves in engines before I was on the Spin Tron. We solved the problems then when we had the opportunity we tested our failed combiation and the setup that worked. That way we knew what it would take to break a valve.
The last time we raced that class they had all the rules to keep us from spinning these things to the moon. A stock cam with a limited blower and limited pulley we wanted to find RPM. On the last combination the valvetrain would start to lose control at 6500 RPM. At 7200 it was not happy. But because our time was so short in the first 2 gears we would shift at 7400 RPM. Because third and fourth gears stretched out we would shift third at 6800. They also limited the gear ratio to a 3.73 so with a 26" tire we would go through the traps about 6200 to 6300 RPM .

Robin

Robin L

Good choice!. I am of the opinion that 99% of all valvetrain related failures are due to lack of piston to valve and loss of valvetrain control. If the valvetrain loses control it POUNDS the components until they fail.

Robin

GMH308

Thankyou Robin and others, very informative. One of the most interesting threads I have ever read. Cheers.

Hans Grüber

iTrader: (2)

Are the pusrods you used the 3M Metal Matrix rods?

http://solutions.3m.com/wps/portal/3.../MMC/Pushrods/

The specs are quite impressive on these.

40% less weight with identical dimensions and 55% less with a smaller diamater while retaining the same strength.

Louis

iTrader: (7)

Yes. We were limited to Steel valves, and again, spec cam profile, and then given a 7600 rpm limit, where the cam was designed for showroom stock racing and never saw more than 6400.

I have a few sets, but the results we saw were incredible.

Every combo is different. On the spintron, we used a shelf 921 and with the right installed height, it worked fantastic.

These motors were so tight, you missed a gear, you pulled an engine. It was that simple.

Fb0dy0nly

iTrader: (10)

Damn, that is intense. I would have to feel very confident as the driver behind that engine. Great thread, lots of educated posts. Havent had this good of reading in a bit.

Robin L

Yes they were. Several points I should make. Our combination used a very short 6.500" Pushrod. The Metal Matrix Pushrod that we tested was a 3/8 diameter. We tested the MM against a 3/8 with a .135 wall. Now remember that the larger diameter is where the huge improvement is strength comes in. The wall thickness helps a lot but not near as much as the diameter.
The 3/8 diameter .135 wall is heavier than the MM Pushrod. We saw a difference between the 2 pushrods. Remember that the MM requires steel ends, since ours was a short pushrod the area that was MM was small.

I should correct what I said earlier. Go with the largest diameter you can fit, then look at wall thickness. If you are limited by port location or size then a MM might work very well for you. But because of the cost I would look at Titanium Valves first.

We also tested some of the beehive style springs and retainers. I will get into that later

Robin

Hans Grüber

iTrader: (2)

Well don't leave us hanging....

gun5l1ng3r

Robin L,

I think you have my dream job!!!

Testing motors (advanced theories) in the racing division of one of the worlds largest auto makers... R&D budgets that includes mesuring machines more expensive than houses!!

Robin L

LOL really I don't have that job. Most of the testing that we have done is on our own dime with the support of sponsors. I am sponsored by GM Performance Parts. A lot of what we test is outside the GM environment.

I met Bob Fox from Trend Pushrods several years ago. When others didn't see any benifit of our idea to test stock style cams and valvetrain compnents Bob did. He allowed us to use his equipment to test on the kind of setups that are on the average performance cars. Most people with the Spin Tron are busy testing for Nascar or NHRA style combinations.
Over the years I have made a lot of contacts that have allowed us to play with equipment that I could never afford. Because of that we try to share that information whenever possible.

We have done a lot of testing for various sponsors. Those opportunities are what is priceless.

Robin

Robin L

I am digging through my notes. I will refresh my memory when I have the data.

Really if I remember they did better than I had thought they would. I only wished they had higher spring rates for our application. They were better than any of the singles (DUH). It took a lot of pressure to beat them with the added weight of the retainers.


Robin

gun5l1ng3r

I still think it is awesome that you share all of this mostly-unknown-to-the-average-gearhead information. It is technology and research like what is stated above that leads to production cars eventually sharing that same technology as the most advanced motor in racing...

Some of us can only DREAM of spending 1600 on JUST pushrods! Hopefully university will pay off in the end and allow me to start my own race team with my own Spintron and Carbon PR!