[chiphead]

Originally Posted by ponchjoe

Yea, the 18cc 4.160 4032 pistons.

Did you measure final chamber size before you ordered pistons? I made that mistake on my original 400. Thought I had 72cc 670s, so I ordered 20 cc dish pistons for 9.2 compression with 3.75 stroke. Imagine my surprise years later when I actually cc'd the heads and got 77ccs! This was back in 2002-03 when I was led into the lower compression ratios and XE cams way of thinking.

For your 4.25 stroker motor, I ran the numbers. With 18CC dish, are you expecting 10.42 compression with 72cc (nominal) heads? That's too high for those 670s. That's perfect if you're going aluminum.

With high compression, you need at least a 228* intake lobe and 112-114LSA.

[ponchjoe]

Originally Posted by Jay S

Both the 702 and the 703 will quit making power at or before 5000 in the bigger engine. That Ultradyne 288/296 is rated at .0045” tappet, the Lunati is an advertised rating that is more of an acts like number rather than a specific tappet lift, it isn’t super easy to compare them using advertised numbers.

Lunati 703 is 273/[email protected]”

The Ultradyne I mentioned is 282/[email protected]”

The 702 is 267/[email protected]

The Voodoos have some extra assymetric's above .050” lift that older Ultradyne does not have.

With extra cubes and compression and that 288/296 Ultradyne’s LSA widened out to 112 LSA it idles pretty similarly to the 703 but out runs it everywhere, pull hard to 5500 and ifs quite a bit more pump gas friendly. Operates quiter also, since the profiles are not quite as aggressive. The LSA of the 703 is 110, it really needs to be wider to work well with the bigger cubes.

I would have preferred the 703 if you would have stuck with the small crank.

I anticipate compression about 9.6 or so if that matters. Although I keep getting over 10:1 when using calculators. DSS recommended 18cc dish to get to 9.6 so compression height must come into play that the calculators don’t know? I’m a little over my head on that stuff. Anyway, I will call Bullet and ask them for a recommendations.
Thanks again

[Jay S]

Originally Posted by ponchjoe

I anticipate compression about 9.6 or so if that matters. Although I keep getting over 10:1 when using calculators. DSS recommended 18cc dish to get to 9.6 so compression height must come into play that the calculators don’t know? I’m a little over my head on that stuff. Anyway, I will call Bullet and ask them for a recommendations.
Thanks again

I’d say that is going to pretty close to 10:1 with 670 heads. Like that other post says, that is likely more than 10:1 by the time you deck the block to get a better quench. I usually have the deck cut a minimum of .015” to get those pistons to about .010” to 015” below the deck. Your new set up often start out .025” to .030” below the deck.

Probably would have been better to get the optional 28 cc dish, then you could run those smaller cams.

[Skip Fix]

Tom Wilhite had a CNC cutter to open 670 heads to "open chambers".

[VCho455]

This calculator is better than most.

https://diamondracing.net/p-10-compr...alculator.html

[chiphead]

That's the one I use, it's very accurate and takes many of the minor contributors into account.

I'd like Ponchojoe to walk us through how he got 9.6 compression with 670 heads on a 455.

Like I said earlier, even with a 18cc dish that's going to be north of 10 compression. 10:1 compression, iron heads, the pistons more than .015" below deck and a small cam on a 110LSA is going to be a tall order on pump gas.

[ponchjoe]

Originally Posted by chiphead

That's the one I use, it's very accurate and takes many of the minor contributors into account.

I'd like Ponchojoe to walk us through how he got 9.6 compression with 670 heads on a 455.

Like I said earlier, even with a 18cc dish that's going to be north of 10 compression. 10:1 compression, iron heads, the pistons more than .015" below deck and a small cam on a 110LSA is going to be a tall order on pump gas.

That’s what DSS and Clegg came up with. I have since sent an email back to them asking how they arrived at it.

[Jay S]

DSS has a 28 cc dish option that is not listed on the website. It is a little more money, but not that much more. It would save yourself from a lot of future headaches and extra expense, and you can run the small cams.

[ponchjoe]

Originally Posted by Jay S

DSS has a 28 cc dish option that is not listed on the website. It is a little more money, but not that much more. It would save yourself from a lot of future headaches and extra expense, and you can run the small cams.

Thanks Jay. I’m waiting on a call back and playing with the calculator on DSS site with a 72 cc, .041 gasket the 28 would be at like 9.68 with the pistons .0015-2 in the hole.

[b-man]

9.68:1 with iron heads and a moderate duration street cam is pushing the limits on 91 octane.

Disclaimer: I’m not a super tuner and I like to leave myself some breathing room.

My very conservative 8.82:1 compression 421 (.041 over - 429.7 inches) with stock 9770716 heads, the 068 cam, super tall 2.56 highway gears / TH350 / 13” Continental will start to ping under load with anything more than 12 intial / 35 degrees total.

I have a 27.2cc dished piston in the 421, chambers were opened up slightly to 76.5 ccs by removing material on the spark plug side. Untouched the supposed 72 cc chambers started out between 73.6 and 74.2 ccs. Pistons are .007 to .008 above the deck with a .045 Butler gasket.

[Jay S]

9.68 would be higher than those smaller cams would want.

I ran the numbers with a 28cc and came up with 9.25, but I added in 1cc for cylinder scallops on to the 72 cc heads. Ball park guess yet.

[ponchjoe]

Originally Posted by Jay S

9.68 would be higher than those smaller cams would want.

I ran the numbers with a 28cc and came up with 9.25, but I added in 1cc for cylinder scallops on to the 72 cc heads. Ball park guess yet.

Well, after a conversation we will probably go to custom Autotechs as DSS told them the 28cc were not something that had a part number.
Here’s what we came up with from AUTOTECH

I’m 4.160 bore.

[chiphead]

I see a few flaws with this approach to selecting pistons.

Finished bore. Do you know exactly what your finished bore is? How are you setting bore clearance? Auto tech can set the skirt clearance if you know the finished bore down to .001

Deck height. Don't order pistons without knowing deck. Otherwise you'll have to deck the block a bunch afterwards. Auto tech lets you set the pin height if you know the number to use.

Chamber size. Do you even know the finished chamber size of your 670s? Never order pistons without knowing finished chamber. Any head work is going to change the chamber size.

Future growth. With a big piston dish, how are you going to raise compression if you swap to aluminum heads?

What ring pack? Metric or 1/16?

What ring pack placement? How deep are the cyl reliefs? Don't hang a ring on the scallops!

Not trying to be difficult, but you can paint yourself into a nasty corner with piston selection.

[b-man]

Wait until you know your finished bore size before ordering pistons.

Found out the hard way myself.

Bought 4.120 and ended up needing 4.135 due to unseen damage done previously by a ridge reamer.

[ponchjoe]

Man this is frustrating. I have put engines together without custom pistons and they ran good. This was the old speed pro forged. Now I’m just flat arse confused by all of this because I’m not a machinist but I guess some of you are? Seems like this stroker kit is becoming more of a pain and I should’ve just gone with making this a 408

[ponchjoe]

Originally Posted by Jay S

9.68 would be higher than those smaller cams would want.

I ran the numbers with a 28cc and came up with 9.25, but I added in 1cc for cylinder scallops on to the 72 cc heads. Ball park guess yet.

Jay, I’d love to talk to you sometime soon about this build if you are willing.

Joe

[Jay S]

Originally Posted by ponchjoe

Jay, I’d love to talk to you sometime soon about this build if you are willing.

Joe

That would be fine.
402.682.1663

[Jay S]

The 28 cc dish DSS was a custom piston because of the dish change. Those pistons are in an engine in my area. Autotec are nice pistons.

Icon makes a 4.25” stroker piston with a 30cc dish. I think it uses a 6.635” rod instead of a 6.8. Ic981 is the part#.

[67Fbird]

no 1 fix for power is HEADS. Not sure you can OVER HEAD an engine but even a STOCK engine will make more power with ONLY a head change. Adding cubes is NOT going to do much if you stick with stock heads. Bang for the buck is usually CAM, Heads, cubes.

[tom s]

Reread post #2!Tom