i have begun my 383 build and there is another thread in here somewhere about that but i have a new question.. its a 383 scat crank. speed pro flat top pistons with single reliefs. scat I-beam rods. on top is going GM fast burn heads . the cam is a 292 degree hydraulic crane cam. i have done my calculations and i am up around 11.1 compression. i will be running our premium unleaded fuel which is 98 octane but pay no attention to that as our grade to fuel here is different to yours in the states. ( i believe our 98 is like your 93 but dont take my word on it) . i am scared i may get some detonation at this compression but im unsure. timing was just going to be a standard36 . i could go to dished pistons to lower the compression but i dont really want too and GM fastburns should also be mated with flat tops . anyone with experience in this area?

 

Me thinks 11:1 too much for typical carbed street motor on US 93.

GMPP ZZ383 has OE fastburns and OE dish pistons.

I think I already suggested dish piston in other thread? I still do precisely because of comp/gas. Suggest you first choose a static compression ratio you'll be comfortable with for a long time. Ask that Q here & you'll get many diff answers. Suggest you also steer clear of those Dynamic compression DCR discussions/calculators ... for most folks, me thinks DCR is more a minefield than majic.

Suggest you then choose the exact head gaskets that're Both compatible with your heads & readily available to you. Then choose a piston w/ "reverse dome" aka "inverse dome" similar & quite like a dish ... then have the block decked/machined to yield about 0.040" quench.

Most 383 pistons yield about 0.025" deck clearance down in hole in a stock uncut deck. So, look at GM gaskets 10105117 or 14096405 ...they're about 0.028" thick w/ about 5.8cc volume. Cut-mill deck to LEAVE about 0.010"-0.012" of deck standing proud above 383 pistons. With that 383 appoach & your fastburns, a piston w/ about a -20cc volume (dish) will yield about 9.5:1 scr ... -15cc dish about 10:1. I'm not gonna rewrite a book about it ... it'll work. G'Luck!

 

98Ron (Australian) is about 94Mon/Ron (USA)

Yep you'd be at about 11 to 1. But dont let that scare you. Im assuming those heads are designed to work well with only 32-34 degrees of advance if they do thats good.
Assuming you:
1. Keep your quench at .040 or less
2. Use a cool air induction
3. Dont let the motor run hot
4. Dont let motor run lean
5. Use a conservative ignition curve
6. Use a free flowing exhaust.

Id say you'll be fine with all that compression and 98 fuel.

I built a budget 383 for a friend. It ended up with 10.5 to one but had old style iron heads and no cool air. It detonated at first but we fattened up the fuel mix (use a wide band O2 gauge) and slowed down the ignition curve and it runs brilliantly on 95RON. It cranks over 220psi. You have aluminum heads, a more modern chamber and insulated manifold so you are in a better position for running more compression.

 

thanks simmo and jackson . both very good info . i agree that 11.1 is borderline and may be too much but i like its power. i will have to go back and read that other post again jackson to refresh.i want to skimp on machine work as its $$$ here so im prob going to leave the block as it is and plus i dont want to go messing with the V when changing deck heights. i hear it causes dramas with vortec manifolds when the heads move further in.

simmo i plan to run a 160 stat and the rad is big 4 core. hope it stays cool. cold air induction ill look into but no easy set up there.all the rest is all good.

i have the same heads on the vet but its just a 350 so i dont think it is a problem. my mate has the same heads on his car as well and he runs 40 advance( big overlap cam but- i think its offroad cam no2) . im thinking i cant hear the detonation/pinging but at high rpm who the hell can ? it may be happeneing.a 383 could only be worse with the bigger stroke etc?

 

I have a 383 with AFR heads. Compression is just under 11:1 and I run 93 pump gas with 36 degrees of timing. No problems and lots of power. With aluminum heads you can run a little more compression than a steal head.

 

My first 64 cc heads, flat tops....... with a 232/238 solid roller cam was very detonation prone. It just required a bigger cam.

Before I would use dished pistons I would use a bigger head CC

I'd try it and if it has problems just go for the bigger cam.

 

What rear end ratio and trans? Your shooting for an on the edge motor. Everything has to be well matched and carefully planned to get the results you expect. Cam duration is about where you want it to run the compression with flat tops but gearing will be the key to using that much motor in a street application. Might also have vacuum issues. See the LSA thread on this page.

 

milling 0.010"-0.015" from deck has very little effect on "V" ... however, stock vortec intake gasket dimensions are about 1/8" thick ... that's very thick ... FYI there are lotsa aftermarket vortec intake gaskets available in both 1/8" and thinner 1/16". You can easily zero deck ... then run the half-thickness gasket & retain fit & good port alignment within V. Regardless which chamber or piston volume you settle on ... you should attempt an ideal quench height. G'Luck!

 

thanks to everyone else who has joined in. im taking on board everything you have all been saying.

L79racer good to hear you are having no trouble as your package roughly the same as mine.

.Gkull where your heads alloy and did your cam have much overlap?

63mako im going to have 355 gears possibly 3.08 since it will be 383 i hope ill have the torque for it. i am leaning towards only a 2500 stall so i can cruise on the highway without flaring all the time. i wont be hitting the strip otherwise i would probably go a 3000 to suit this cam.

jacko the gaskets ill be using are felpro 1010. they are the only ones i would use on alloy heads as i have never had trouble with them before marking the heads when they come off. they state on the packaging there .039 thick . is that about 1/20? do you think its a good idea to run pistons with the double valve reliefs ...i know it isnt much but that extra cc may help a little bit.

 

I'm running to the best of my calculations right at 10.7 to 1. I have a long duration solid cam with aluminum heads so it is OK. I have run cheap gas, by mistake and it will detonate on 89 octane.

 

is that a 383 Gordon... actually i just looked at your profile, no need to answer that now.

 

Of course Dart 215's with factory porting to 221 cc. The difference between 110 and 112 when you get into over .600 lift and over 232 degrees at .050 is very minor

 

You want opinions here is mine. You are planning to much motor for 3.08 gears and an automatic. I don't think you will be happy with the combination and with a stock deck and .039 gaskets you will have around .065 quench. I see detonation and streetability issues with 11 to 1, stock deck, big quench and your gearing. I would drop compression to under 10.5 max less would be better. I would also go with a smaller cam and a 112 lsa. Onother option is at least 3.73 gears and a bigger convertor, a richmond 5 speed or a lower rear gear and HD OD trans. Driveline durability is another issue that you will find out about at your planned build level.


Gkull has 4.11 gears and a TKO 600RR 5 speed

My build is a 500+ HP 383 plus a 150 nitrous shot, D&D Chevy/ Viper T56 six speed with a 2.66 first and .80 .62 fifth and sixth and Tom's 4.11, axles and halfshafts.

As you can see the above builds have all matched their gearing to the build level of the engines.

 

i hear what your saying mako. i cant afford to go changing out transmissions for other auto,s or manuals etc since the Th350 in the car drives fine at the moment . all i have to do is shift kit it and im away. i guess i would consider a T700R for the 4 speed option.

i am compromising but what do you think about 2500 stall with 336 gears . 355 gears if i must and that should keep me out of trouble with flaring and not be reving its **** off on the hiway.

 

I've gotten away with it before, with an iron head 427. Just keep octane boost and a distubutor wrench in the car at all times! Hot days and shaddy gas stations could cause problems Ask me how I know

 

If you stick with the TH350 and a 2500 torque convertor with 3.55 gears cut compression to 10.5 or less with a zero deck block and drop to a XR288HR or similar spec cam on a 112 LSA. Your still compromising but it will get you close to 500 HP and TQ. It will be a better combination, better matched, more streetable and run your vacuum accessories. At this build level as close to .040 quench you can get is the best and everything you can do during the build to minimize detonation I would do. Listen to Jackson, he is giving you good advice too. Fastburn heads make best power @ 32 to 34 degrees advance so that will help some.

 

ok some will shake their head at me and some will maybe give me the

-i have redone the maths. with the fastburns, minimum decked block,flat tops im at 10.6 .......the dished pistons would give me 9.8

-i will keep the 2500 stall but go with 355 gears.

-i have to stick with this cam 63mako. its what i have and dont want to settle on another $$

i believe our 98 fuel here which is our premium may be better quality then yours. (dont quote me on that) but yes ill run octane boost if i have too and keep that ring spanner handy

ill be back in 2 weeks to tell you if im a fool and should have done what mako and jacko said ( i did listen very hard) or if i get away with it and am happy.

hugie dare i ask?

 

I think your going to have a blast!!! There is nothing like the sound of a high compression vette w/ a nice cam. You may want to invest in two piece timing cover and an adjustable timing chain for @ $250 +- $50 It will give you alot of engine tweaking ability
IMExperience w/ pinging/detonation it rarely happened but on a long ride to the shore I was stuck in traffic and I filled up at a Shell station. Lets just say their super wasn't very super . I had to use oct. boost and still had to back of 2 degrees. I soon as I got home filled up w/ 94 Sunuco, bumped the timing and it ran perfectly

 

thanks hugie. i already have a rollmaster and 1 piece cover but thats ok. im just waiting on my block to be assembled, it is a standard bore block getting bored 30 over.this motor is for my 71camaro but the vet is already very similar except for a roller cam and its 350. i put in crane cam 119611 into that. i was very tempted to get a roller block and run the same cam in the camaro as i know they are awesome but here rollers are just way to overpriced for what they are .

 

10.6 and 11 are not too far apart but with the cam you have you will probably be ok on detonation @ 10.6. where 11 to 1 might have been a problem. You can dial the timing back with the fastburn heads too. That helps. What is streetable to some is a PITA to others. You will have probably have fun. It will sound like a beast!