20v Hi comp piston, suggestions

[Rayray86]

I'm about a week away from ordering the internals for my Silvertop. I decided on going with BC 272 cams, and the BC 0.40 over piston kit. The kit comes with the option of Domed or flat pistons. I was wondering how much room I have to play with from the valves. should I get flat tops and have the head milled down..Should I leave the head and get domed pistons... or do I have room to mill the head annnd get domed pistons? any input would be appreciated, even input on a cheaper rebuild kit/cams then Brian Crowers. thanks guys.

[ga_goosh]

if it is for a silvertop then it is a non interferance motor so it will be imposible to smack the piston with the valves. blacktop on the other hand is an interferance motor.

you should be able to mill the head and get the domed pistons. if you want more compression you can always get a thinner headgasket. also if you want to mill the head you can get a thicker gasker to compensate for the milling.

what is the estimated cr of the domed and the flat topped pistons? do you have any boost plans in the future? what are the specs of the cams? do you have an estimated dynamic compression in mind? the cams alone could bump your compression. its kind of hard to estimate with out more info

[Rayray86]

I was talking to the "live help" when they mentioned being able to swap for Domed pistons I didnt ask them the Cr. but the flats are 9.0:1. The cams are BC Stage 2 (Int272/Exh272). No plans on Boosting in future.

[ga_goosh]

since there is no boost plans i would go with the domed pistons. the 9.0:1 would be a great turbo or super charged piston. you do need to make sure your cr is correct which means knowing the specs of the cams and calculating dynamic cr other wise your cr could be too low or too high for pump gas.

[dr.occa]

If no plans for boost then I'm for the higher comp pistons as well. I'd also upgrade valve springs and run a reinforced belt like the HKS timing belt. In fact I'd also use the 16v water pump and go from the hydraulic tensioner to the 16v pulley tensioner.

[Rayray86]

would 12.0:1 pistons be over kill for a daily driver?

[mandm177]

what was his name...Justin? in Victoria, TX? didnt he have some crazy built AE111 with high comp domed pistons? i forget his username, but i'd ask him for any advice. havent seen him here in a while though...

[dr.occa]

12:1 is way too high. You'd have to run race fuel to make proper use of that compression in that motor. It's not practical except for a race/track purposed motor.

[Rayray86]

Ah ok, I just figured since a stock Silvertop comes 10.5:1 I would be able to get away with 12:1. So I'd be better off aiming for the 11:1, 11.5:1 range? Its going to be my daily driver but I still want it to be able to hold its own.

[dr.occa]

High octane is a must.

[Rayray86]

I was lookin at some numbers and I was also thinking of just scrapping the BC pistons idea since the stock ST is 10.5:1 wouldnt I be able to hit 11:1 just by milling head down and getting a 0.5mm gasket alone? Or has anyone ever put oem BT pistons in a ST since theyre higher Cr?

[burdickjp]

blacktop pistons in a silvertop are a great choice for NA applicarions.

Your desired CR will depend greatly on your tuning capabilities and cam selection. I would say 12:1 is not hard for modern EMSs to make work with mild camshafts.

Where are you finding BC cams for 20v engines?

[Sam-Q]

blacktop pistons in a silvertop are a great choice for NA applicarions.

Your desired CR will depend greatly on your tuning capabilities and cam selection. I would say 12:1 is not hard for modern EMSs to make work with mild camshafts.

Where are you finding BC cams for 20v engines?

Blacktop pistons work out to being roughly 11.5:1.

I am surprised that no one has talked about the dynamic compression ratio yet. The greater the durations of the cams the higher the static compression ratio needs to be to compensate.

For me I find it frustrating that I can't pistons that are lighter than standard, I don't understand it. Tempted to use the original but I am worried about how they would handle being reved to 9500 with a higher compression ratio.

[dr.occa]

I'd be the most worried about hot spots. I'd polish or ceramic coat the BT piston crowns and then go with forged rods & balance them (within .6 grams - most aftermarket forged pieces are usually within that tolerance). Weight all the pistons to within .5 grams. If even one is out then see about finding another BT piston until you get them within that .5 gram.