Is 0.050" PTV clearance safe enough for a race engine? It's Auto, so, no miss shifts.

 

What do you guess ???

Christian

 

yeah that fine i guess on a precisely built tight tolerance race engine, not good for a stock production hyper internal parts engine. Even a lot of race engine stick with the .080/.100 standard.

 

guess who!!! j/k.

Not sure. Refering to Vindicator Camshaft and 59cc TFS215. That must be tight.

 

I mean race use, no DD, but stock short block if that matters.

 

Sure go ahead and do it and risk your engine, its your choice. .050 is the size of a spark plug gap, would you want your valves that close to your pistons moving at 6000 rpm's. Ask yourself how risky you dont mind being. If you dont mind the high risk and are cool with not running the normal standard PTVC then go right ahead.

 

I got your point.

So, if 59cc gets 0.050" PTV. How much should be the Head cc for a safe 0.080" PTV. I got around 62cc for heads. Is that correct?

 

How would you feel about a 239/248 110+2 cam with .040 gaskets, 62cc heads and -6cc pistons?

 

You would need more CC than that, more like a 66-67 cc head if you get .050 with 59cc's. That would get you close, but keep in mind you also need .100 on the exhaust valve.

 

Sounds like it would be fine since you would have -6cc in the pistons, that is a lot of relief.

If i was ever to run a big *** cam like a magic stick or a texas giant or any other cam in that range i would definetely run at least a -4cc piston. Head choice does play a big role in it too.

 

I took a look at this video and I decided to play SAFE with my Valve train and PTV:

http://www.youtube.com/watch?v=i_NpzU4pGjc

This is for 7000 rpm but 6800 rpm will be the same...

What do you think?

Christian

 

Then Piston notching is the best way out or stock replacement forged pistons with valve relief.

Any part# for suggested replacement forged pistons with enough valve relief for 59cc TFS and vendicator.

 

Any forged piston with some valve relief in it would work ok, I like Diamond pistons personally but any forged piston it pretty much fine. Keep in mind though replacing pistons also involes freshining up the cylinders at the machine shop and all the work of dissassembly.

 

hmm... now im starting to wonder about all these guys running trex's w/ stock heads & bottom end. i never really hear anyone checking ptv clearance, or at least posting.

 

I think only a few people really check most just take the "it clears" line and assume that as long as it clears it is perfectly fine to run. It just increases risk.

 

One thing I do not really see mentioned much anymore, and perhaps lifter technology has improved to the point that it is less relevant; but when I was in this line of work 12 years ago, we had to give hydraulic lifter motors more p/v clearance than solid lifter counterparts due to the fact that the hydraulic lifters would pump up as the rpms increased. So basically if you determined you had .060 clearance with a mocked up solid lifter, then in theory you would have .060 clearance with the hydraulic lifter adjusted to the correct preload you used. However, in reality, you would have much more clearance down low as the lifter would bleed down and your preload would actually be increased and your duration affectively decreased, but as the rpms increased your oil pressure would increase applying more pressure inside the lifter plunger consequently pushing the lifter cup upwards, this combined with the fact that the lifter had less time to bleed back down would cause the lifter to actually decrease the amount of preload affectively increasing your duration which would decrease the amount of p/v. Of course the cam manufacturers then came out with anti-pump up lifters and the type R lifters that actually run near 0 preload to prevent this from happening, but i wonder if this still occurs with the stock type lifters most of us are running. If so, we should definately stick with the larger side of the p/v clearance recommendation. I know it was not that uncommon to run solid valvetrains with good springs as tight as .040 /.060 and sometimes even tighter in the old SBC. On a side note, Rhoads actually produced the variable duration lifter based on this principal, they just created a lifter to make the problem even worse.

 

Good point but at the point where PTVC is of concern(TDC exhaust stroke) the valves are almost closed and the lifters are probably barely being compressed compared to the amount they are compressed down when the valve is at higher liftes when the piston is way down in the cylinder bore.

 

Is most of you are talking about hydraulic rollers.....the textbook .080/.100 minimums were more aimed towards a solid valvetrain although a properly set-up solid valvetrain could be tweaked tighter.

A hydraulic roller valvetrain at the RPM levels most of us routunely spin them to (7K ish) is always on the verge of valvefloat and in fact all suffer from varying degree of valve control loss at those RPM's. What does that mean....it means the valves aren't precisely following the cam lobe any longer and what started as .076 P to V is now .020 or worse. Many of you are lightly tagging pistons and wont know about it till your engine comes apart and see the small eyebrows in the pistons the valves started forming from lightly tagging at high RPM's.

A high revving hyraulic roller set-up needs more P to V than a similar solid roller set-up. A solid roller has no lifters pumping up and bleeding down with oil creating potential stability issues and also has the benefit of more seat and open pressure to keep that cam lobe (and valve) glued to the lifter and following the exact events the valve and piston have in relation to one another (and making more power by being able to do so).

I also agree that running less piston to valve is a better gamble with an A4 car, but none the less the operative word is gamble. I'm a pretty good manual transmission driver as I have been banging gears as long as some of you reading this have been on the planet and all I can tell you with a manual trans car is stuff happens....I missed a shift trying to pull 3-4 in a nanosecond and hit 2nd instead of 4th....it happens to the best of us with a tight "H" pattern shifter. Needless to say I logged 8508 RPM's and I felt I clutched in and saved it pretty quickly (oooops!). This was with my solid roller 383 I normally shift around 7300....if I had a hydraulic roller and even the textbook minimum P to V clearance I would have bent a bunch of valves if I was lucky or simply grenaded the engine. Moral of the story is you have to be more conservative with an aggressive hyd. roller combination and pushing those tolerances closer and closer just begins to quickly narrow your window for a mishap. And dont think "it wont happen to me"....it will and it's just a matter of time.

IMO if you have much less than the .080/.100 rule, take the extra time to notch your pistons.....its really not that big a deal.

Tony M.

 

^^ Well said.

Agree 100% on notching pistons, it is well worth the time and effort.

 

Good info...and as witnessed by one of the videos I saw of your car, you can bang the gears like a ****.