I was using this calculator:

http://www.csgnetwork.com/compcalc.html

For our class we are allowed a .5 increase in compression before extra points are added (every 20 points bumps you up to a faster class). Since the '90 came from the factory with 10.25:1 I cannot go higher than 10.75:1. In the calculator I linked I input factory bore, .048 gasket, and standard deck height of 9.025 and a -5cc flat top piston, I get close to 10.25:1 So when I enter the specs for the 355 I want to build it turns out if I use a flat top -5cc, 58cc chambers, a gasket of .042, and a deck height of 9.015 it comes out to 10.7:1 with a .057 quench. If there is a better calculator out there I would like to know.

 

Are you sure you don't want to get some better heads right away also for the extra moey it might be worth up front?
Just my thought, I know money doesn't grow on trees but, you could put it together, and kind of be done with it, and then focus on tuning.

 

We are forced to use our factory 113 castings unless we want to run with the big boys where there are no points for mods, you just have a power to weight ratio.

 

I'd rather drive the car and have fun then wait on funds for heads. I've always planned to get a better flowing head but that's likely two years off.

I don't care what the mods will do to points and race class. It will fit in somewhere and be fun. I wouldn't be able to stand it if the car was done. It will always be gaining points from mods.

BTW Kubs if you need some tires I wound up with some 245/35/18 V710 tires. I got them from Ebay and they were incorrectly listed from a 285 series. They are almost as wide as my 285 street tires and would cost less points for TT. Did you look at mrc24x car setup? He's winning in TT with a hot cam a LTR intake.

Speaking of power to weigh ratio, I wonder if it would even make the TTA ratio with a 383.

 

[quote=Aardwolf;1572820836.]

BTW Kubs if you need some tires I wound up with some 245/35/18 V710 tires. I got them from Ebay and they were incorrectly listed from a 285 series. They are almost as wide as my 285 street tires and would cost less points for TT. Did you look at mrc24x car setup? He's winning in TT with a hot cam a LTR intake.[/ quote]

I can buy any tires, or anything race related, this year. I wont be running again until after my wedding in September. Everything we buy or make a down payment for I see disappear in the form of race tires and engine parts!

I forgot about Matt's setup. I have always heard the hotcam works better at high RPM which is why the short runner intake LTX car use them. I guess its worth a try if you got it. You can change a cam in a weekend if you need to.

Edit: The TTA ratio is 8.7:1 Remember the competition weight is with you in it and a 1/4 tank of gas, so if your comp weight is 3200 lbs you can be around 360 HP to the wheels, which would be good for our 113 heads and a good intake. My goal is between 360-380 RWHP for my pregnant 3400 lb car.

 

I like the Pat Kelley calculator better. It can be found on this page near the bottom. Download the version WITH VB runtime files unless you have VBasic on your PC.

With .030" over bore and a 5cc piston, I get 10.74:1 SCR and 8.1:1 DCR which is completely doable. Moreover, I used a .040 gasket with 4.060" bore and the hotcam. I used a 5.7" rod but don't remember for sure if that's factory length.

Change stats to a 383 and the numbers change to 11.5:1 SCR with 8.7 DCR. Obviously, this combo would be WAY more likely to detonate. FWIW, the DCR drops a hair with a 6" rod, but only about a 1/10th. You can see why an inverted dome (or dish) is better to build a "safe" 383.

So, asking for help on pistons before deciding on CID isn't the easiest request to fulfill.

 

Weight wise I'd be shocked if it isn't low 2800. There's not much left of it! The local post office keeps my daughters favorite candy on hand since we are there shipping parts out so often. I plan to make it lighter yet. You take points for being under weight in TT. Matt said he uses up extra points there. I will do that as well. You can have more HP then me then with the adjusted weight ratio.

I think I will stay with the 355 and put the money toward a track event.

 

In case you still buy new pistons (or decide on a 383 down the road), here's a good pic of the 113's that Ron (Cuisinartvette) just posted. [/

[The 113's (as you probably know) are the head with the black valves.]

Their combustion shape is pretty darn close to the inverted dome shapes I've seen -- probably as good as you can get. I don't see how you'd have any issue (with detonation) running any inverted dome (or D-Dome) piston with 113 heads. OTOH, you're probably looking at flat-tops with a 355.

 

Thanks for the info. I will have to play around with this.

 

The two calculators return different results for me.

I am looking at the 9928 forged KB piston, at $320 it fits the budget. It's only 6.4 cc with four valve reliefs. With the one calc it didn't look like a flat top would work at all. http://www.kb-silvolite.com/icon/fhr...tails&P_id=470

 

The Silvolite calculator was pretty far off when I tried it. To confirm which calculator was best, I called about my cam and got exact open/close events (not just .050 or .006" numbers). Then, I compared to the calculators out there. The Pat Kelley was dead nuts. The Silvolite said I'd blow the motor up!

With that KB9928 the PK calc provide numbers almost the same as the 5cc flat top posted earlier. As long as your rules allow 10.75SCR, the 8.1 DCR is well within the recommendations of ANY site you look at. And, PCM4Less (or any good tuner) will be able to make that work.

The only caviat is you may need to adjust cooling so your temps stay below 190-200. And, you'll need to run good premium. 91 might not be good enough. That's where better heads and squish help out.

FWIW, a couple of builder's I talked to -- that don't regard DCR -- say they recommend staying below 10.25 SCR. That's because some motors ping when pushed past that limit.

There are a LOT of factors that help keep preignition at bay. Keeping lower water temps low is one of them. Alum heads is, of course a biggey. Combustion shape is another. Without something like the AFRs and an inverted dome (to create a centered charge), you can still center/consolidate the charge with good quench and removing ANY sharp edges from the CC. (Unless the KB9928's have radiused valve reliefs, have your builder add them (or DIY)). You will find any good builder say you're more likely to detonate at lower compression w/o correct quench than higher compression WITH a correct quench/squish shape. Don't go over .050 quench and try to stay closer to .040/.045. (I used .040 gasket and .005 deck when running the KB9928).

I can't personally guarantee you'll be fine, but I'm quite convinced it's doable by following the advice (as provided by others). Removing/rounding all sharp edges and getting quench correct will be the biggeys.

Edit: Most importanly, people/sites that put ANY stock into DCR say you can do this combo. FWIW, I used 6" rods for the KB9928 (as advertised) and 279/287 for the Hotcam adv duration with 112ICL/LSA. I also used a 4.030 bore, 3.48" stroke, .040 gasket and .010 deck. Finally, I used 58cc 5 (or 6.4cc) piston, and 4.060 gasket bore in the PK calculator. Also, everyone knows the hotcam has one of the mildest performance ramps. Logically, that helps bleed of compression (for people pushing compression limits).

 

I think most of the stations around me carry 91, only a few 93. Being a street car too I would like to be able to use 91 if I can. 10.25:1 will work for me but 10.75 is the max I am allowed.

They only way I can get close to a .040 quench with flat tops is if I want a 11.1:1 SCR, or 10.1:1 with -16cc dish and .031 quench. A -12cc piston would be perfect, but I dont think it exists outside of a custom CNC set.

 

http://www.probeindustries.com/Chevy...s_p/p2403f.htm

 

Those pistons will have terrible squish clearance, I would not use them on an engine at 10.7 CR. The dish should more closely match the head.

 

I didn't like their shape much either, but Kubs seemed to want 12cc pistons. (Specifically, I avoided using an FRS Probe for my build because they're dishes.)

I went back and looked at the SRS Series (2618 alloy) for these guys. They have a two inverted dome pistons with cc's where he wants them. http://www.probeindustries.com/Chevy...ns_p/12343.htm -- or -- http://www.probeindustries.com/Chevy...ns_p/12342.htm

From the standpoint of quench, the 9.8cc SRS Probes are certainly "safer" for both Kubs and Aardwolf. I as you, Brian agree that using an inverted dome vs dish makes way more sense. OTOH, getting the shapes exact (within an inverted dome) seems like overkill to me. (Brian, you mentioned that earlier in this thread.) If it was really THAT important, why aren't there more reverse/inverted dome choices? And, why haven't most other (larger relief) piston shapes been scraped? Why even make/market a dish in this day/age?

BTW: I'm a believer in DCR figures too. While I'd never go against the option of picking an inverted dome vs dish for ANY application, I'd be way less worried about a dish -- if the DCR is sufficiently low. I'd bet on quench DISTANCE and removal of sharp (hotspots) as being way more important to pre-ignition prevention.

 

I like those -9.8cc ones. They would give me a 10.5 SCR and 9.71:1 DCR. Those are made of better aluminum than the FRS pistons right? Is Probe a decent brand to put in an engine that see race time?

 

Alum is alum. The difference is the amount of silicon used in the alloy. Neither (4032 or 2618) alloy is better/worse for a mild 350 build. Piston-to-wall clearance will be the only difference -- with the 2618 (T6) alloy requiring slightly more clearance because of it's expansion.

There is nothing wrong with Probe pistons. A lot of people prefer them over KBs!

 

No way that DCR is right. Recheck your math/calculator.

 

Thats what I got using the calculator you gave me, and a Lloyd Elliot cam because he is porting my heads I am getting a cam from him.

226/230 111 LSA 106 ICL

Edit: Nevermind I was using duration at .050 not advertised. If you only know the @ .050 numbers can you find advertised?

Edit II: I found the lobes on the Bullet list. With a .026 gasket, .015 deck clearance, and 6" rod the -9.8cc gives me 10.5:1 SCR and 8.36:1 DCR. Is this more usable for the SRS piston?

 

You need the ADVERTISED duration of the cam for the 2nd tab of the calculator. Something around 278/282. Is that about what you used?

Edit: I posted while you were editing the post above. What's the lift numbers and rocker ratio on Lloyd's cam. He uses Bullet cams, so it would be fairly easy to figure out the lobes with more info. BulletCam has a website and all their lobes are posted there. Just click on Master List and Hydraulic roller tappets.

FWIW: I'm guessing you'll come out around 10.25:1 with 8.2 DCR. (I used .040 gasket with .005 deck)