383 now or later

[Guest polarity]

I have all intentions of turning my 350 into a 383. Now my question is, should I take more time to do my project and go ahead and stoke this motor, or drop it in as a 350, and pull it out when I have more money to make a stroker?

 

From what I've been reading on past posts I would need a 5.7" crank (or 6" but from reading an older post that requires more work to have it clear the cam)

 

I did not understand this part (non-stock comp. ht. piston) I do not know what that is yet.

 

I would also need it balanced (already planning to have that done), good heads and cam. and it said it required having it bored +.030. (which the machine shop says I want to do with the motor anyway.

 

So once again my question was, should I go ahead and start locating these parts or wait and take the engine back out and do it later?

 

Approximatly how much do these parts run (really I guess just the crank as all the other things were already going to be done)

 

Billy

[Mike C]

Really this is a personal question, I guess. If it were me, I would continue working on the car, get all of the bugs sorted out, save some more money, and build another motor. This is me however and I wouldn't have to shell out any $ for a rebuilder. Especially if you are planning on different heads, cam, etc. Just put them all on the new assembly but enjoy the car in the mean time.

[grumpyvette]

Mike C

is correct, ideally you have two engines,(or at least short blocks) one in the car and one on the engine stand getting the full treatment, then come swap day its only a matter of one weekend to swap the engines, this also has the huge advantage of you always can swap back and forth and be driveing if the engine in the car has problems. this also has the big advantage that your driveing while the machine shop plays for weeks at a time with your engine that they promised would be ready six weekends ago!

[Guest polarity]

can some of the people who have a 383 in their car chime in with some of thier times and such.

 

I'm curious if it is needed in this car.. will increase performance that much that it is worth me paying between $600 - $1000 for all the parts needed?

 

Billy

[dmanzo57]

Here are some estimates assuming you are starting with a 350 that needs a rebuild...

 

~ $25 more for 383 pistons vs. 350

~ $325 for new 383 crank

~ $220 for new harmonic damper(SFI, external balance)

~ $60 for external balanced flexplate

~ $?? clearance block and rod bolts for stroker crank.

 

Don

[Owen]

How big is the balancer in this kit? 8" is way too big for the Z I think. I have a 6.5" one on my 383. Is the flexplate compatible with yuor starter, tranny, etc? I only know flywheels and had to make sure I had the right number of teeth, etc on the flywheel, etc (not hard to do).

 

And the cam, what power range? What about heads? The engine components should all work together for best power and efficiency.

 

If you're like me who took 3 years to get his car together and somewhat running, it would be better to have another engine to work on, especially if this is your only car. Figure out how you want to drive the car and see if that universal 383 kit will suit your needs.

 

"non-stock comp. ht. piston" this is a non-stock compression height piston? What compression would it give you? I heard somewhere a reason why the 5.7 rods are better but forgot why.

 

Owen

[grumpyvette]

the longer the rods the better the trust angle on the crank, the lower the ring drag and the longer the dwell time after TDC giving the cylinder pressure a better chance to release its energy to the piston, allowing a better high rpm power curve provideing the cylinder heads breath well.

look here

look here

http://www.iskycams.com/ART/techinfo/ncrank1.pdf

now look at the cylinders pressure curve,

http://www.auto-ware.com/combust_bytes/pv.htm

 

notice that almost all useable pressure is in the 25 degrees after TDC (right were the longer rods longer dwell time can use it)

 

what youll find if you carefully look into it is that the longer 6" rod has a SLIGHT ADVANTAGE over the 5.7" rod for several reasons , one is that the 6" rod has a longer DWELL time , what this means is that it takes slightly longer in rotational degrees for the 6" rods piston to move away from TDC thus allowing a slightly more effective use of the cylinders presure peak, that together with the better rod angle produceing less cylinder to piston drag allows the 6" rod spinning the same rpms as a 5.7" rod to produce slightly more power in the over 5000rpm to 8000rpm range IF the cam timeing and compression ratio are the same and about 1%-2% more if the cam timeing and exhaust scavageing are set up to take advantage of the longer dwell time. now if your not sure what Im talking about look at it this way, at 7000rpm the piston changes direction 233 times a second and has a power stroke 116 times a second now that means youve got a power stroke every 58.3th of a second so the longer rods slower acceleration away from the tdc possition allows the longer rods piston to more effiecently use of the cylinder pressure peak. to put it bluntly the 6" rod has a slight but provable advantage, or to paraphraze SMOKEY YUNICK " use the longest rod you can economically fit in the engine block for the best power curve"

heres a chart of a typical engine http://www.geocities.com/ljaya6390/analysis.htm

 

btw for those of you that can,t convert MPa-to-PSI in your head

http://epics.aps.anl.gov/asd/me/UnitConv.html

 

btw if your still not able to get it 5.402 MPa=783 psi

 

now thats in about an 8:1 cpr engine you can reach 1200psi in a 11:1-13:1 racing engine or a engine with the correctly tuned cam and intake/exhaust pulse timeing to efficiently fill the cylinders, thats where most of the better torque comes from! also notice that the pressure is only high for about 30 degs of the total 720 deg cycle and its only able to do usefull mechanical work for about 20 degs of the total 720 degs

 

now if thats a typical smogger 350 chevy.

a 4" bore has about 12.588 sq inchs of surface area x 783 psi /720 degs in the cycle x 20 degs of usefull work= 273 ft lbs of torque applied to the crankshaft every 90 degs, but kick the pressure to 1200psi in a 11:1 engine, and that same 350 makes 12.588sq inches x 1200psi /720degs in the cycle x 20 degs of usefull work= 419.7 ft lbs of torque, now alot depends on the dcr and volumetric efficiency but you should be getting the idea here by now!as long as the cylinders can fill completely you get a good fuel/air burn so you get a good cylinder pressure curve against the piston each time the cylinder fires,THE ENGINES TORQUE CURVE INCREASES WITH THE NUMBER OF EFFECTIVE POWER STROKES PER SECOND, at very low speeds theres not enough air velocity to mix the fuel correctly or produce a effective ram tuneing effect but as the rpms increase the cylinders fill very efficiently untill the rpms reach a point where the cylinders just don,t have the time necessary to flow

enough air through the valves to fill the cylinders , remember a 5000rpm the intake valve out of 720 degs in each cycle opens for about 250degs of effective flow even with a hot roller cam, now thats only about 35% of the time and theres 41.6 intake strokes per second , thats only 1/60th of a second for air to flow into the cylinder, I found this graph that shows the relationship between V.E.(VOLUMETRIC EFFICIENCY) and AN ENGINEs torque CURVE http://www.n2performance.com/lectures/lect1/n2perf5.gif

 

WHAT THAT GRAPH SHOWS RATHER EFFECTIVELY is that its your engines ability to fill the cylinders that increases your power and the more efficiently you do that the higher the rpm level you can acomplish that at the more power your engine makes, remember the formula for hp is (torque x rpm/ 5252=hp)so moveing the torque curve higher in the rpm range increases hp

[Guest Anonymous]

Owen .. is your 6.5 harmonic balancer for a 400 crank that is externally balanced or a special 383 crank that is internally balanced. Where did you obtain the balancer and cost?? What size rods?

[Guest Anonymous]

Correct me if I am wrong. but I found that Northern Auto Parts (1-800-831-0884) has a stroker kit for $599.00 with new cast crank, pistons,rings. all bearings including cam,oil pump, Crane cam,roller timing set,freeze plugs and FelPro gasket kit.Apparently this internal balance 383 stroker kit will use the stock 350 5.7 rods,harmonic balancer,flexplate with a special balance plate on the new cast crank.Question: What is the advantage to internal balance with 350 parts as opposed to external balance with SBC 400 parts? I am looking for a very mild build with cubic inches not special performance parts

[grumpyvette]

Using 5.7" or 6" rods with the 3.75" stroke crank requires a piston that has shorter compression height than the 350 stock piston.

 

true but thats a big plus, it makes the piston lighter in weight,the 6" rods have the advantages listed aboveand yes before someone else mentions it the lower oil scraper ring does go through the piston pin holes upper edge but properly done its not a problem

[Guest Anonymous]

Non-stock compression height piston.... 350 and 400V8 SBC use a piston that measures 1.54"-1.56" from pin bore center to piston crown. 400V8's offset the increase in crank stroke by shortening the rods from 5.7" to 5.565". Using 5.7" or 6" rods with the 3.75" stroke crank requires a piston that has shorter compression height than the 350 stock piston.