I took a clay imprint of the dome and cc'd it, I came up with 46cc's. My pistons are definitely .100 down in the bore, my block was a virgin 1966 425 that still had GM bearings. I did remove .015 from each side of the deck to clean it up. I figured compression height by measuring from the flat portion of the piston adjacent to the dome to the top of the wrist pin bore. Then I split the diameter of the pin and added the two. Here's the numbers I got. OEM piston- 1.465 Rebuilders Choice-1.465 Egge-1.410. Adding .500 to these numbers to figure pin bore centerline would put the Egge at 1.910 and OEM at 1.965. Siv-O-Lite lists their 401 pistons at 1.910, Ross at 1.930. Neither of those numbers jive with the measurements that I am getting from a stock piston. If a stock engine has .055 deck clearance and the Egge is .050 down further in the bore then I am right on with my figure of .100 down. Running back to back compression calculations that additional .050 deck clearance drops compression 1 full point from 9.56:1 to 8.43:1. My pistons came directly from Egge and the production date was 2-2013 On a side note the Rebuilders choice piston has the correct compression height but the dome is .070 shorter then stock. The one I measured was .290.
Your right on stock with .055 down. with the 4 of the 425 i took apart were .055-.060 in the hole. you deck the block .015 so a stock piston would be .040 in the hole. so the egg should be .090 in the hole. ---------- Post added at 08:34 PM ---------- Previous post was at 08:25 PM ---------- am getting 8.93 .100 in hole, 9.11,, .090 in hole,,, and if you deck it .020 more you will be 9.39 compression. ---------- Post added at 08:49 PM ---------- Previous post was at 08:34 PM ---------- thats with a 125 head cc. the fel pro black head gaskets which is all they make now are .033 compressed. you could even deck it .025
Sounds like your calculations are good,it sucks that Egge's listing doesn't inform people that they will end up with crappy compression with their pistons! I still think their listing is misleading if they list the compression distance as 2.25" at the top of the dome! There is no way to calculate compression before buying them. Did you talk to Egge for an explaination of why their 425 pistons are so crappy,and so dimensionally off from OE? I think you should still try for a refund,raise some hell over there,maybe they'll make them right in the future,or at least not mislead the next guy. That really sucks,I feel bad for you,I know how it is to be disappointed when getting parts that aren't going to work properly. I hope you didn't talk to Egge yet and are waiting for Tuesday to contact them to ask WTF! Anyway goodluck,and I hope everything turns out good for you. Derek
Ahhh, okay. He asked if I was a shop (no), so he probably quoted me the full retail price. Apparently, most suppliers have retail (consumer), and discounted jobber (shop), and WD (wholesale/warehouse distributor) pricing. It's absurd that Nailheaders cannot get an off-the-shelf performance piston! ...let alone a quality replacement!! :rant: Hey 487, good luck with your call to Egge. Hope they make it right.
That's one of the things I'm trying to get accomplished now. Will have to see how this set that was custom made works out. It's not going to happen overnight. Tom T.
Egge pistons are JUNK! Heres my reasoning: I decided to spend $325 on Egge pistons, rather that $650 on short skirt custom forged J&E's (big mistake). The new egge pistons are heavier than stock, regardless of over-bore. Had to grind lots off to get them all within 2 grams. Then, we noticed the top of the piston was recessed more than the stock, but we cc'd the dome and it was 2 cc's larger than stock. Why? why not just make it the same as stock? Then we put a piston and rod in the block, the piston was .040 in the hole at TDC. We cc'd everything with the new pistons and without surfacing the block or heads we came out with 9.1:1 compression. So we wiped .040 off the block. This brought the compression up to 9.78:1. Then it was to check piston to valve. the motor wouldnt even get the tdc without touching valves. Had to machine the domes to get a free flowing clearance. We still have to machine the heads and clean up the surface. I regret very deeply not getting those J&E's. DONT GET EGGE PISTONS! GET J&E OR SOMETHING ELSE CUSTOM FORGED. Again, egge pistons suck.
off-the-shelf performance piston..... Hey Tom, any developments on a final config for the Racetec pistons?
With the design I sent them they will end up being a forged piston made of 4032 material. This way they should be fairly quiet at cold start & quiet warmed up. They will be a universal design. Diameter will range from 4.19-4.35". Each set will be custom made. The valve reliefs will have enough clearance for 1.94" valves & the pistons will fit either R or L. Compression heights & ring packages can mostly be accommodated. 1/16 & 3/16 or 5/64 & 3/16. They will be about (no set $$$ yet) around $750.00 which includes rings, pins & pin fitting. In the 5/64/3/16 ring package will only be available to what may be out there. 1/16/3/16 rings there are gaps in available sizes. On 401 the gap is between 4.22 & 4.25. The 425 is between 4.32 & 4.35. The dome will be higher to accommodate custom refinishing of the dome to get the exact compression ratio your looking for. Most 401 deck heights are 10.018-10.020 & 425's are 10.12-10.014 stock uncut decks. This is all I have at the moment. The more orders the $$$ could possibly go down. Again, by how much I don't know. This has taken well over a year to get this far. Tom T.
Don't quote me, but I think Greg's 401 has stock sized valves (although definitely ported) and a Comp Cams Thumpr. Last time I talked to him he was trying to finish up the build so he could get it on the dyno.
Thanks Tom! - 4032 material...Sounds good, that's what I have in my Jeep 4.6 stroker (KB fhr Icons). Will require 0.0035 to 0.0045" piston-wall clearance, which should keep them quiet. - I understand 1/16" rings are the hot tip.... 15+hp advantage without sacrificing ring seal or ring life.:TU: - A 4.22" bore is just over stock +0.030" (4.2175"). Hastings also has a 1/16" ring in 4.233" (+0.0455") and 4.25" (+0.0625"). - Compression height and quench distance... There's not a a lot of flat piston/head quench area.... does the quench on a Nailhead also take into consideration the dome(side)-to-head clearance? Wish I could draw a picture, but I think you know what I mean. -Weight... I'm not overly concerned, but would like lighter-than-stock. I'd be in for 2, maybe 3 sets, if we can get a group buy going. Who else needs some GOOD pistons????
Since 4032 material has a higher silicone content than 2618 they require less clearance at .002". 4032 does not have as high of an expansion rate as 2618. I usually go with .0025" clearance. The dome is "Rounded" in the corners where the "Nail" normally will make contact with the head when they are cut. You want to keep the quench area, the flat part around the sides of the piston, no more than .050" & no less than .020". Even stock they are not at .050". The original shim steel head gasket compressed thickness of .015"-.016" with a piston in the hole .040" (Rarely) is at .055-.056". With the piston in the hole .055" it's now .070"-.071". Now add a composite gasket which can be anywhere from .036"-.042" compressed, depending on manufacturer, you now have a quench area of between .076"-.097". And after many rebuild these engines they wonder why they don't seem to run as good as they did originally, even when they were tired. You've all heard me say it in the past, "When you think you've covered all the details go back, I bet you missed a few". Not only checking valve-piston clearances but also dome clearances to the heads & sides. It ALL makes the difference between an engine that runs OK or an engine that seems to run better than it should. When using a composite gasket you can remove up to .040" from the deck without manifold alignment problems. I could spend the next couple of days typing & NEVER give ALL the info nec. And for all those thinking that $750.00 is too much $$$ for a FORGED piston, think about what the others will cost as this does NOT include rings, pins or pin fitting. Tom T.
Looks like a good deal Tom. By comparison, our off the shelf CP pistons for the 4.6L Cobra (3.57" bore) were $800 with just pins and locks 4 years ago. They were over a thousand with the total seal rings (not gapless). Cheryl
Tom - You know I'll need a set... I plan to bring my 66 MT engine down after the holidays for teardown and assessment.
I need a set of quality pistons for my 425 rebuild also. Thanks for all the background work Tom and supplying the information.
The 4032 Autotec's are great pistons for the $. I've put over 1200 hp to them in turbo ls engines and used them in many applications from NA 850 HP pump gas BBC's to 500 HP tri power 389 pontiacs. Also had good luck with the similar Mahle pistons as well but they are not as quiet as the auto's.
i agree. first use them in my 340 buick build, told Tom T. to give them guys a call knew he was looking for custom pistons. they have a cheap price and are well made. the only thing was mine were the same weight as the stock cast piston but the pin was a lot lighter for the weight savings. one piston was also about a 1/2 thousands or so bigger.
