RED-85-Z51

Ive got my finger hovering on the submit button on this SCAT forged rotating assembly at a parts site...it has everything I want...but the compression with 64cc heads is advertised by scat to be 11:1.

I dont want detonation worries, and I want to run no more than 93 octane.

Scat-1-40755

Forged crank, forged pistons, forged 6" rods, etc etc...383stroker.

Use will be street/cruiser, occasional strip use.

My original plans were 10.5:1...but I cant seem to find a kit that has the features I want that goes down that low, or doesnt go too low.

Im willing to use hyperutectic pistons in a kit...but would prefer forged.

dogfish246

I think you are good! Thats some crazy compression!

I think the honda s2000 has 11:1 compression and its used on the streets so... I would look at some other cars that have high compression and see what you can find...
Definitely never gonna be able to use regular or even mid grade, thas for sure!

Depending if you are using an LTx block or an L98 block you have superior cooling with the reverse flow cooling so that should help! (Oh wait, I see your name implies the L98)

GREGGPENN

The new Z06 motor runs at 11:1 compression. Have also seen a couple of forum members run over that. Tune is critical but it can be done.

Will it be a strip or street car? A/C running in summertime? 100+ degree temps?

Even more critical is to list the "features you want" if you want alternative suggestions/thoughts.

RED-85-Z51

Thats why I wanted to run 10.5:1 or thereabouts. I know compression=grunt if its running right.

What im looking for is a car I can drive 20 miles to and from work if I need to..A car I can take the strip a few times a year and flog for a few passes. A car I can take and blister the hides on if the need should arise.

Want it to be a 383, its already going 30 over, so why not?

I have heard so many stories on parts breaking and power limitations...I almost would only feel comfortable with a fully forged rotating assembly. My wallet would like a less expensive one...but whatever..I never listen to him anyways.

SCAT seems to have a very strong following from the SBC community, so I really want to run SCAT parts.

Their Series9000 cast crank is affordable, but cant find a reasonable number that someone can put on it as a power limit/rev limit.

forged I-beams are cheap insurance.

Forged pistons have to run a big clearance, and Ive heard they can use some oil...but resist damage more than hyeprs. Im really not sure on pistons..honestly.

RED-85-Z51

A/C in the summer @ 105+*...haha Florida baby.

65Z01

If the quench volume is reduced and the chambers dressed & smoothed you should be ok. Try to get more details on the heads & such.

cv67

The days of forged pistons running large clearances are past, most run failry tight these days. Dont worry about oil issues really.

11:1. If you have an efficient aluminum head, cam with some overlap youll be fine. Check with the mfr, some may claim a compression ratio assuming the piston is 0 decked, .025 in the hole, etc. Makes a difference. You can always remove a few cc from the head if you have to or play with head gasket thickness if need be.

RED-85-Z51

dont know how efficient, they are Brodix Ik180's.

cv67

What cam?Intake?

RED-85-Z51

Hoping to get an intake base from you, and run the SLP runners, and a ported stock plenum, stock or 52mm BBK throttle body.

Cam is the Lunati VooDoo 60101.

Exh. is TPiS Longtubes, TPiS front Y pipe, and out the stock rear Y (actually borla) and out Magnaflow mufflers.

cv67

Hmm, going to be close with that cam, have to figure the true comp ratio.
Have a base, just havent ported it yet. Whenever youre ready, same with the plenum

RED-85-Z51

Sent email to Scat on how thest estimate compression ratio @ 11:1


This is what I HATE...not knowing what kits to buy. Im willing to run cast crank and pistons, but not rods, but even then my options on compression are either high or low. Wish I could find a 70cc version of the Ik180 head but I cant find em anymore.

bjankuski

11 to 1 is not a problem but you must keep the engine cool if you want to use WOT and you must have a big enough cam to bleed off some compression. If you are just cruising around the engine can get hot (I consider 200 degrees hot), If you want to do WOT runs the engine must be near 160 to 170 degrees otherwise it will ping. You also need to keep your dynamic compression less then 8.5 to 1 run 93 octane pump gas.

My car is 11.4 to 1 on 93 octane pump gas but I keep it cool and have less then 8.5 to 1 dynamic compression. If I let it get hot (200 degrees) it will ping at WOT.

RED-85-Z51

Scat wants to know what my assembled deck height is..and I replied I am basing my purchase on compression. He replied he cant help me...

cv67

Tell them your block is stock deck height unless your machinist decked the block. 9.025 (?!) Let them do the figuring.

You cant figure out installed piston height until its mocked up. You can get measurements from their parts but still. .....

aboatguy

My 355 is a LT1 (but the differences between SBC GENI and GENII are not that big) my static compression is a little over 12.1:1 and its fine on pump gas...
I went with tight quench (pistons are .005 in the hole with .027 headgasket thickness) and a 230ish duration on a 110 LSA IOT help with DCR.

I drive the car daily, its good in traffic even on hot days with the AC kicking. IMO 11:1 will be fine on an aluminum headed SBC if you pay attention to quench, DCR and tuning. But if you are sticking with TPI lower compression with a smaller cam is probably the ticket..



Mike

RED-85-Z51

im keeping the TPI design, but a ported intake, big runners, and ported plenum, and 180cc intake runner heads...should breath good compared to stock...Id think.

Hey Cuisanart....how much hoggin out can you do on a stock base?

also, I told him it was a stock block, and he said he couldnt help me...

cv67

Plenty...it wont be a top end roaster but TPIs arent anyway. It will burn some rubber though.

Post up some part#s on pistons, rods, etc maybe we can do some figuring from whoever this salesperson is youre dealing with.

RED-85-Z51

Rotating Assembly.
http://www.summitracing.com/parts/SCA-1-90455/


includes crank 9-350-3750-6000 series 9000 cast steel

and rods 2-ICR6000 forged I-beams

and pistons are +5.00 forged flat tops.

Heads- Brodix Ik-180 assembled heads.http://www.summitracing.com/parts/BRO-1021004/

Cam- Lunati VooDoo 60101

VAlve lift -.454int .468ex
Lobe lift- .303int 312 exh
Adv Duration 256 int 262 exh
Dur @ 0.050" 213int 219 ex
Centerline 108 int 116 exh

And Ill be running 1.6RR's instead of 1.5's

GREGGPENN

The first thing I note is how small your cam is. It's rare to see someone choose a cam even smaller than my small 383 cam. Though my duration is not that different (215/215), my lift is quite a bit higher -- to get much needed air in that stroker. But, you're not here to ask for a cam recommendation I take it.

With the DCR calc most commonly recommended, I ran some figures for you. As a result, I say pull your finger off that Scat button for a minute.

To get the advertised 11:1 compression for that r.assm., it took a .040" thick gasket, 4.060 hole, and .005" desk (which isn't too far off from what I'd expect). Specific SCR would be 10.98:1 with that config. The bad part (IMO) is the 9.35 DCR (dynamic compression ratio), that you'd get using that Voodoo cam.

Personally, I don't think the RA you picked is a bad choice, I just think you could use a bigger cam for a 383. OTOH, I don't know your emissions consideration, plus even with 20-degrees more adv duration, you drop only to 8.75 DCR. That's still awfully high.

This post has historically been one of the most referenced posts on 383 strockers, compression, and considerations. I recommend you read it. Specifically, take note of the DCR vs temperature chart 2/3rds down the page. I think it goes a long way toward answering your question. (BTW, David Vizzard wrote or references this chart -- I forget which.)

By looking at that chart and (liberally) considering another 1/2pt leeway for alum heads, I decided 8.25DCR was about the most I should go. Even then, I realize I NEED to keep water temps under 200! Note, this recommendation is consistent with other sites recommendations. (It's tough to understand some of the info and links, but after reading them a couple of times, it finally soaks in what they're saying.)

Since you (like me) are building a 383 torque monster -- and want a smaller cam, I think you'll be much better off with lower compression. Besides what I've said above and the info I point you to, I will add that practical builders say even 10.5:1 compression can get you into detonation issues. Head, quench, timing, water temps, tune, etc... are all critical to pushing the edge on compression. By contrast, the difference in 11:1 and 10:1 compression is only about 10hp. For someone building a torque monster, that 10hp is NOT worth the possibility of a head/cam swap -- just to correct a mistake!

Consider an (inverted dome) piston in the 12cc-18cc range. 12cc's gets a meager 10.05:1 SCR but the DCR is still 8.6DCR. That's still high by most standards, but a good tuner and low water temps can make it work. Probe 12345 would the the piston I'd recommend for that option.

If you've got the dough, 16cc SRPs are way cool! You'd have a super-low rotating weight and all the advancements in piston technology (for street cars). SCR would be 9.66:1 with a DCR of 8.25:1. That's the DCR I chose for my build -- which is still fairly high. If you think the compression sounds too low, just remember, you're building a 383, not a 350. That, plus a TPI and a small cam will provide all the grunt you need/want!

If the SRPs are too expensive and you want to go even cheaper/safer than the Probes, you have one more option IMO. That's an 18cc KB 9926 piston which gives you 9.5SCR with 8.1DCR. That's still plenty high and eliminates any problems of detonation. Lower octane and/or higher engine temps come back into the picture with this config.

With the 1st option (Probe) uses 6" rods, the SRPs can be either, and the KB's are 5.7". Many people would recommend the shorter rod for a lower-revving TPI motor. OTOH, there are those who'd pick the lightest SRP option with the 6" rods -- to get a lightweight, snappy-revving motor. You pick what's right for you.

The KB's are still great too -- especially when you compare the price and weight to a standard, factory-quality piston. IOW, they're still a good option.

With forged rods and a Scat9000 crank, you'll be perfectly fine, w/o any worry of crank issues. FWIW, I had the same issue trying to press for an exact answer on the Scat9000's ability to handle torque and/or HP. Best I could determine is at least 600hp and 500TQ. But, that's not the WHOLE story. To break that crank, you'd need to totally hook up on a hard launch with more power than listed above -- using good drag radials. IOW, unless you're building a race car, you won't break that crank. You wouldn't even get close to breaking the softer cast Eagle -- if that's what you wanted to do. You simply don't need forged. (BTW, the other way to break a crank is with excessive rpms -- which, again, is something you'll never do with that TPI! LOL)

I think that should address all the questions you've asked in this and recent threads.

gp