Deck Height, head CC, CR Dilema

[temurphy3]

I'm a NooB, and I'm trying to understand the CR, deck height and Head CC information. In the spring I am planning on building a street 2332 (84x94) with a forged counterweighted crank, 94's, FK-8, 44 IDF's, Steve Tims stage 2's @ 57cc's. Everything has already been chosen.

Now using the engine calulators it says I need a deck height of .103 to achieve 8.75 CR (FK-8 on pump gas). From what I've read the Only / Best deck height is .045-.060 (clearance for possible self destruction) and best quence? Detonation and pinging occurs after .060?? I dont get it!!

so My question is,
What is the difference if I (A) set my deck height to .045 like it should be then have the heads cc'd larger and dish the pistons to get 8.75 or (B) Set my deck height to .103 like the calculator says? It appears the cumbustion volume is the "Change" and what is needed for low CR 8.75 Right?? They both seem like its doing the same thing but one underneath the deck and the other above the deck. Is there anone that can please explain the difference and "whys" between these two different scenarios?

[RockCrusher]

Your doing the math right so pat yourself on the back.

You are correct in all your assumption or conclusions. Why do you want 8.75? At .050 you'll get 9.85. The FK-8 can handle that.
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[sgmalt46]

you can step cut the heads to add cc's or semi hemi cut. or use .060 copper head gaskets?why so low compression? you can run .060 deck for 9.6 or .080 for 9 to one . the tighter the deck the better.but you can run that big deck if you want that low compression. it's just not the best. but easy and cheap.

[temurphy3]

I want/have to run on pump gas. Gas is also about to get worse here in NY. In the spring it will be 15% ethonal. but in order to lower the CR to 8.75 something has to change.
My main question is why is is not OK to have a deck height greater than .06 but it is OK to increase the Head CC and or dish the pistons? These both seem to be doing exactly the same thing of increasing the chamber volume.
So why cant I add .103 shims? If I do I will have a "pinger" anything greater than (>.060)? This would be the easiest /cheapest route.
What exactly is better about the increased CC's and dished pistons? Pinpointing the burn location??

[Bad bug]

Wow a 2332cc street t1, i would live to build one of these. But at 15% ethanol i guess you would need more compression to truly burn that air fuel charge. Ethanol burns slow and the added compression would help.

[sgmalt46]

i agree with that. but if your set on 8.75 set your deck at .043 and use .060 copper head gaskets from cb. that will give you .103 deck? that's the cheapest way to go. but the fk8 works best with at least 9 to 1.remember the cam really is the deciding factor in compression pressure. the more radical the more it bleeds off compression . that's why i can kick start my harley easy with a huge cam!

[rosevillain]

Wouldn't step cuts, head gaskets, head spacers, and deck height all be the same thing? I'm just trying to figure this all out.

[temurphy3]

Sounds good and easy but what is this warning of going above .060 for the deck height when adding shims would do bascially the same thing? Is it expected that when you buy new heads they are CC'd within reason to what you want?
I imagine 66 cc's is too large but if I had a deck of .050, 84x94, and 66 CC heads I would have my desired CR of 8.75.
Would the semi hemi heads not work properly? Whats bad about them?

[temurphy3]

Sorry I didn't mean shims above I meant .60 in copper gaskets

[grimace007]

please please please dont semi hemi steve timms beautiful work... if i were you id consult steve timms directly when your getting ready to buy HIS heads he will points you in the right direction and what has worked for him on what is sure to be hundreds of motors with very similar setups to your own.
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[sgmalt46]

yes it's all the same. it's just best if the piston is as high as possible.you want combustion happening in the head not in the cylinder. it's just best.you can just shim it at .103 it's not a big deal.it will be fine.i would run the copper head gaskets if it where me .so i can run a tight deck .045-.060

[Glenn]

I have a 2180 with a FK8 and Steve Tims Stage 2s and I run 9.5:1cr.

I also live in NY and have no had any problems running 93 octane.
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[sgmalt46]

i agree with glenn run .060 deck for 9.6 and run it! and stop thinking about it. ive run 9.25-9.50 with 110 cams with no problem . and fk8 can handle 10-1

[RockCrusher]

Just .103 shims....in any combination....is NOT the way to go and neither is a Hemi cut. Do as recommended and talk to Steve Tims. Better to buy a larger cc chamber from Tim and keep that Quench area TIGHT. Too much deck will lead to an engine that is so touchy about the fuel grade and timing that you'll pull your hair out.
_________________
[email protected] Please use email for all general inquiries.

I will be happy to speak to anyone who has a serious inquiry (meaning real potential business for RC enterprises) or a parts order. Due to machining noise causing missed calls all calls will be returned promptly.

[vwracerdave]

Way too much Internet BS myths about running tight deck. I've built several engines with.080"-.090"" deck and none have any pinging issues. I'm running .080" deck in my 2165 and it runs strong down the drag strip and on the street.
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2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[raygreenwood]

Uh...none of the deck measurments listed here are actually "tight".
Other than just getting compression up or down... an .060" deck is fairly hot running and inefficient. It keeps most of the flame front down in the barrel instead of up in the head.
I would should for about .045" to .050" max. Talk to your head guy about what you need to do with your heads to get the compression you want with a deck in that range. Ray

[vwracerdave]

Ummmm.... The flame front starts at the spark plug and finishes at the piston which is already traveling down the cylinder when it gets there.
_________________
2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[slalombuggy]

[DarthWeber]

Just a couple of points to add to what slalombuggy said, Gene Berg has used his 191S stock VW I beam rods to 9500 RPM in a race motor with no problems, they recommend a max of 7500 in street use. These rods have stronger SPS bolts though.

The stock VW crank is in fact forged, not cast.
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[slalombuggy]

You're right, I should have said non-counterweighted or stock crank instead of cast crank. My mistake. Good point about Berg rods.

brad