[Wage92]

Originally Posted by cdminter59

Your stactic compression did not change but your DCR did. Sorry about the math mistake. Anyway .275 above the block is something to consider real hard. Personally I wouldn't build an engine with the piston that much above the block for the street. That is some close tolerances measure carefully. I might have considered it at .005 but not at .275. What happens if your block has been milled in the past? I think the best solution would be to use the 22.5 dished pistons with 5.7 rods. This assembly would give you 9.497 static compression and a DCR of 7.689. But you will still have to deal with the quench of .053". I can suggest something but you will have to contact Cometic Gasket INC. They will make you a custom head gasket with the compressed thickness and bore size you need. I would rather check on this and try to get closer to .040 for quench. But who knows you could use the .027 compressed thickness gasket and not have any problems. I remember back in the day just using the head gaskets from the gasket kit with a .039 compressed thickness with flat top pistons and 76cc heads with a DCR of .064" and never heard any pinging.

Hold on a sec. I thought the stack height stays the same no matter what rod you used?

[123pugsy]

Originally Posted by Wage92

Hold on a sec. I thought the stack height stays the same no matter what rod you used?

You need to know the compression height of the piston.

That's the height from the top of the piston to the center of the piston pin.
A piston for a 6" rod usually has a much smaller compression height.

[cdminter59]

Wage92, Is this the 406 Scat rotating assembly from Ebay (Skip White). Does it have the Probe 14cc pistons with a compression height of 1.140? If so then your parts stack height is 1.875+6.0+1.140=9.015. 9.025-9.015= .010 piston to deck height. Now to get the quench of .040 you need a Cometic MLS .030 compressed thickness head gasket. Or any other brand if you can find it. This will put you right at the edge with a static compression of 10.588 and a DCR of 8.512 so you really need a tight quench. Still should run on 91 octane so if you are using 93 octane you should be fine. This is why all information needs to be provided in the post or a part# to verify the info.

[cdminter59]

Originally Posted by Wage92

Hold on a sec. I thought the stack height stays the same no matter what rod you used?

No, it is (3.750 x .50) + rod length + piston compression height. The rod length and pistons will make a difference. This changes the crown of the piston to top of deck height.

[Wage92]

Originally Posted by cdminter59

Wage92, Is this the 406 Scat rotating assembly from Ebay (Skip White). Does it have the Probe 14cc pistons with a compression height of 1.140? If so then your parts stack height is 1.875+6.0+1.140=9.015. 9.025-9.015= .010 piston to deck height. Now to get the quench of .040 you need a Cometic MLS .030 compressed thickness head gasket. Or any other brand if you can find it. This will put you right at the edge with a static compression of 10.588 and a DCR of 8.512 so you really need a tight quench. Still should run on 91 octane so if you are using 93 octane you should be fine. This is why all information needs to be provided in the post or a part# to verify the info.

Yes that is the one, sorry should have mentioned it earlier.

[Wage92]

okay what if i put a .039" head gasket in, that would bring me down to 10.3 scr and 8.3 dcr, a little more manageable right? and have a quench of .049" which i dont think is too killer...

[cdminter59]

Originally Posted by Wage92

okay what if i put a .039" head gasket in, that would bring me down to 10.3 scr and 8.3 dcr, a little more manageable right? and have a quench of .049" which i dont think is too killer...

It should be fine. The suggested range from .035-.045 for quench.

[Wage92]

Originally Posted by cdminter59

It should be fine. The suggested range from .035-.045 for quench.

okay, thanks for the input guys, im not settled on this setup but im pretty sure it would work. Have an email into another company that deals in Scat assemblies and inquired about what setups they could give me that would have a little more dish in the piston. will update when i find out.

Edit: also would a dcr of 8.0 help at all, by using this cam: http://www.compcams.com/Company/CC/c...x?csid=88&sb=2

[cdminter59]

What I have read about DCR is you want to be in a range from 7.5 to 8.5. The engine makes the most power with a DCR of 8.2.

[lust4speed]

Originally Posted by cdminter59

It should be fine. The suggested range from .035-.045 for quench.

Memory isn't what it used to be, but I seem to remember that the safe range was up to .049". Way I remember it was the standard gasket thickness of .039" allowed up to .010" in the hole before the possibility of detonation really increased.

The other way around the problem is to open up the quench area large enough that it also won't cause detonation problems. I can't remember whether it was pretty low around .080" or higher in the range of .120"? The tighter quench is definitely the way to go, but sometimes you don't get to have what you want. Basically, the big number was why we got away with milling out the old TRW forged pistons (years ago before the beautiful D-shaped dished pistons became available) to lower compression without going into ping city.

[BuzzLOL]

.. LOL! Nobody was considering building an engine with the piston 0.275" above deck... that was just somebody's math error...

.. With a longer rod, you use a piston with a shorter compression height... or, if budget allows, a custom piston with the perfect compression height if nothing proper close enough is available off the shelf...

[Wage92]

what is a better piston brand Mahle or SRP? Or are they fairly close. This would be for forged dished pistons with 6" rods

[BuzzLOL]

.. OK, at the performance level you're talking: "400HP" from a SBC 400 for a fun road truck, everybody is OVERTHINKING this!

.. The stock SBC 400 with stock heads and crank/rods with merely flat top or domed pistons and a $50 Summit #1105 224/234 cam/lifters/Z28 valve springs added (and 4bbl. carb./intake if not so equipped already) will make 400 HP or close to it...!! And do it by 5500 - 5750 RPMs... shift at 6,000 RPMs or so... with torque peak around 4000 RPMs... pulling really hard from 2000 - 2500 RPMs or so...

.. or another combo:

.. Stock block, crank, rods, your first pistons choice but for stock 5.565" rods, your first cam choice (biggish for a fun road truck, but usable), and your first heads choice -> 375 - 500 HP depending on the exact heads used (165cc - 220cc range intake ports)... still by 6000 RPMs...

.. The 2nd cam you picked was just too big for your goals... wouldn't pull hard till 4000+ RPMs... wants to make 500+ HP... not fun truck compatible... requires other engine parts made of expensive unobtanium...

.. 6" rods make more power above 6250+ RPMs... basically, out of your needed operating range...

.. I'd suggest doing something like one of the two budget combos above... just add an ounce or two of kerosene or other octane booster to a tank of gas if you just can't tune any/all spark knock out with ignition timing/advance curve and premium gas... or can only get 91 octane premium in your area... no 93 or 94...

.. KB, TRW, or Summit hypereutectic pistons would be plenty for this build... and KB especially usually come with good compression height... and all have good price... adjust them to the gram weight of your stock pistons/pins and avoid paying for an engine re-balance job at this performance level...

.. Here's an article about adding a cam of duration similar to your first choice 230/236 duration (only expensive roller lifter type) to a mostly stock block/rods/pistons/heads SBC 383" engine and what it did:

http://www.hotrod.com/techarticles/e...p/viewall.html

.. Edelbrock E-Street heads would be a good pair of American-made somewhat budget Aluminum heads... although on the smallish side for a SBC 400"...

[BuzzLOL]

.. A 650 CFM - 750 CFM carb. or even stock Q-Jet 4 bbl. carb. is plenty...

.. Stock oil pan and oil pump is fine at this performance level... maybe add a high pressure bypass spring to stock oil pump or use a high pressure oil pump... I would avoid the power-consuming high volume pumps as unneeded ... add a windage tray if it doesn't already have some kind of one inside the oil pan...

.. What's your tranny? If it's an automatic shifting at only 3800-4000 RPMs at WOT, then it'll need governor springs to bring that up to 6000 or so for the engine to make its new power... or manually shift it when wanting that power... If a manual tranny, of course it can still simply be shifted as desired...

.. Whether you need/desire a different stall RPM torque converter will depend a lot on your current rear end ratio... and driving habits... and final cam choice... and final compression ratio...

[Wage92]

bringing this thread back because i have another question. I have settled on the skip white rotating assembly, i wanted internal balance but for the build this is going to be its not worth it to shell out the extra money. So this is the kit SBC Chevy Scat 406 Forged Rotating Assembly ft 30 4 155 Bore | eBay

As i was thinking about i think i will use a .039" head gasket and the piston will be about .010" in the hole, and typing that all in to a static compression calc, i got about 10.37:1 which as far as i know should run on 93 octane....

Lastly, for my dynamic balance i am trying to find a cam that will be mild and not cause any issues..
This is the one i have selected thus far: 12-246-3 - XTREME Energy

That cam gives me 8.34:1 dynamic compression...

I have aluminum heads, ive heard that plays into the picture...

Any suggestions? I dont wanna have any detonation problems, am i too close to the line? And will i be able to advance it or will i have to play with the timing to get rid of spark ping?


Edit: also if someone doesnt mind could they run my numbers through a compression calc and verify im doing it right? 4.155" bore, 3.75" stroke, 64cc heads, 14cc dished pistons, .010" deck clearance, .039" gasket (unsure of bore yet so estimate), 6" rods