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Why do pistone eyebrows vary so much?

824 views 10 replies 7 participants last post by  tjm73 
#1 ·
Do you need deep piston eyebrows with TW heads?

I was looking at different pistons for a TW head and I noticed that the Mahle pistons have 6.2 cc eyebrows and the trick flow Made by Wiseco have 2.5 cc eybrows. I remember years ago Ross had a 302 piston for TW heads and it only had 2.0 cc eyebrows and I remember calling them and I think they said that the TW heads with the tilted valves don't need a pocket as deep as 20 degree heads. I wonder if the Wiseco pistons with the smaller 2.5cc eyebrows would clear a .600 lift cam and 11R190 heads? Have any of you ran the Trick Flow pistons from Wiseco with high lift cams?
 
#3 ·
The problem is, idiots are very creative. ;)
one of the first things i designed was a clutch washer and my boss asked me why it has this complex inner shape to it. i told he i was trying to make it idiot proof to kep the washer into place and get rid of an issue we had seen on another drill clutch in testing. her responce was... they will just make a better idiot and just make it round.
 
#6 ·
If you're at that point, you should have a custom piston anyway. Most catalog pistons are for the average build, not a one off or racing application. Just the ring package used tells you that.

You do a ton of these builds and see more than I do but there's no need for a 1/4 inch of valve clearance with some of these mild engines.
 
#7 ·
Might as well just set your self up with a dart block. I had a 69’ 351 Windsor I was going to build and I bought the block for $200....no ####ing was was I going to spend $1000 to race prep the block and then stuff it full of expensive internals for the block to maybe last. Woody built me my dart block 363 and it’s amazing. No regrets lol


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#8 ·
I had a Dart 363 from woody before, but this time I just can't see having a block capable of 1500 HP when I'll be lucky to make 500, plus the Dart will add like 50 lbs to the car
 
#9 ·
If you want your valve reliefs to be absolutely accurate you'll need to send in a sample with the center of the valve marked. You'll also need the valve diameters and the lift at 5 and 10 before and after split overlap. You'll also need to measure the actual valve angle and twist, and the total free drop (from the leading edge of the valve)

Good luck, kiddies!

In the mean time, most piston manufacturers just guess. Mine were probably more accurate than most, only because we also built about 250 motors a year, so we got to actually measure them. Giving a piston manufacturer total lift gets you an educated guess. Even with mine, I've seen .580 hit and .720 clear...with the same relief.

The 11R (or, as I like to call it, the B303 of the cylinder head world) has about .430 of free drop and hardly needs a relief at all.
 
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