383 rod question

[gretchen/jason]

I was told by a local machine shop that the best set up for a 383 is to use the 400 sbc crank with 6.000 length rods with a piston made for a 383 with 6 inch rods .

 

I was shown on a bare engine how it worked as the wrist pin is actually behind the oil ring and as rods get shorter the wrist pin moves down the skirt . They claimed a common 383 uses a 5.7 rod with a typical piston but a 6 inch rod with a different piston will produce more power .

 

Now i have looked this up in the catalog and they do make a piston made for a 6 inch rod to turn a 350 into a 383 using a 6 inch rod .

 

Has anyone done or know anyone who has used this combo . Someone also told me i could use the short sbc 400 rods 5.477 length i believe they are with the stock 350 piston that had a 5.7 rod on it and still make a 383 .

 

I just want what gives me the most power and ill get the best pistons and such .

 

Jason

[grumpyvette]

Ive built BOTH 6" and 5.7" 383 engines many times, the differance in power might be 3-5 hp and a few hundred rpm differance in the torque peak at MAX

 

LOOK over this chart carefully

 

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

 

the 5.7" rods that DON,t have the pin intersect the oil ring are more stabile, the 6" rod combos are slightly lighter in weight and have a slightly better rod angle, not much gained either way

 

read

 

 

http://www.stahlheaders.com/Lit_Rod%20Length.htm

 

http://victorylibrary.com/mopar/rod-tech-c.htm

 

http://em-ntserver.unl.edu/Mechanics-Pages/Luke-schreier/unzip/Tension%20and%20Compression%20in%20Connecting%20Rods%20VI.htm

 

http://www.hotrod.com/techarticles/choosing_the_right_connecting_rods/

 

http://www.me.metu.edu.tr/me426/notes/Conrod/sld001.htm

[gretchen/jason]

Very good articles . I do like the pro and con section . After reading about shorter rods vs long rods it seems i need to go with the 5.7 rod as it seems the 5.7 rod is better at a lower rpm but seeing as i have forced induction that will help make up for any slight loss at higher rpms .

 

And reading that the longer rod might make detonaition a problem , and it produces higher cylinder pressures i dont think i want to go that route as the article i read clearly states that a 5.7 rod will be a bit cooler in the long run , and have lower cylinder pressure .

 

Thanks grumpyvette for the info it cleared up alot of things for me .

 

Jason

[gretchen/jason]

So for a update i ended up using the shorter sbc 400 rods with a stock 350 piston not much shorter then the 5.7 rod but since the 400 rods are forged h beam rods i figured hey why not use them .

 

So far everything lines up just fine .

 

Jason

[SilentNight1647]

400 rods are 5.65 rods IIRC the last 383 I built used those rods albeit stock GMs though motor makes good power and gobs of torque not a bad combination but then again most 383s are monsters just because of the inherit design.

[gretchen/jason]

Cool to know the combo works when ya went from a 350 to a 383 using that combo how much more noticable was the torque ? Im just curious as though ill be running a supercharger on my 383 . I took a stock 350 230 crank horses roughly and made 265 horses 285 ft lbs of torque to the tires with no mods but a supercharger .

 

Jason

[grumpyvette]

as a general rule a 383 sbc makes approximately 10% more torque than a similarly built 350, figure at about 40 ft lbs minimum gained on anything even close to a decent performance combo

[SilentNight1647]

Like grumpy said about 40ft/lbs sounds about right just because of the longer stroke but you can pick up more if you have it cammed right, right intake, right carb, are you seeing a pattern here? Motors respond best when you use parts that like each other. There is no reason to run a .656 lift cam in a street motor and your performance will suffer accordingly. Likewise you wouldn't run an RV cam in a race motor, pick out parts that are compatible and you will make more power than just throwing something together, but as far as your supercharger I've never had one anything I've built hell my 280ZXT is the only vehicle with forced induction I've ever owned but I would imagine it would compliment the low end grunt of a 383 nicely based on what I have seen of blown SBCs.

 

Edit: You did notch the bottom of the cylinders to allow the rods to clear right? The first 383 I ever built grenaded on the stand after I didn't cut a big enough notch on one cylinder tore the block up good, bent the crank, broke the rod, not a good deal.

[gretchen/jason]

Yep all the notches are being put in where needed . Oh and ive matched the flow of my heads to a cam i picked out that matches the rpm range i need plus its ground for a blower or NOS .

 

Ive had the heads cast iron worked over and bench flowed at my altitude it flowed a impressive 230-235 cfm give or take with a stock size exhaust valve arent they like 1.5 or 1.6 with a .490 lift the intake was similar but being it will have forced induction the intake runners were cleaned up just a bit .

 

Im full of questions probably some ive asked before but im learning from this web site thanks for all the info people i enjoy every bit of it .

 

Jason

[grumpyvette]

read these

 

 

http://www.centuryperformance.com/vacuum.asp

 

http://www.2quicknovas.com/happytiming.html

 

http://www.fourwheeler.com/howto/67578/

 

http://www.73-87.com/7387garage/driv...timing101s.htm

 

http://www.mortec.com/carbtip1.htm

 

http://www.hotrod.com/techarticles/choosing_the_right_connecting_rods/

 

http://www.airflowresearch.com/articles.php

 

 

 

http://www.bob2000.com/carb.htm

 

http://www.hotrodder.com/kwkride/timing.html

 

http://members.tripod.com/torquespecs/hi_po_chev.htm

 

http://www.hotrod.com/techarticles/building_a_cylinder_block/

 

http://www.wickedpontiacs.8m.com/tips.html

 

http://www.chevyhiperformance.com/techarticles/32458_build_your_first_engine/

 

http://www.sa-motorsports.com/blkdiy.aspx

 

http://www.sa-motorsports.com/diyport.aspx

 

http://www.chevyhiperformance.com/techarticles/95298_camshaft_lobe_phasing/

 

http://www.hotrodder.com/kwkride/degree.html

 

http://www.thedirtforum.com/degree.htm

 

http://www.symuli.com/vw/camp1.html

 

http://www.symuli.com/vw/camp2.html

[pparaska]

Probe makes a 383 and a 400 SRS forged piston for 6.00" rods that have the pin below the oil ring groove, not in it:

 

383:

Flat tops: part number 12337-xxx

Dished (8cc): part number 13719-xxx

http://www.probeindustries.com/Pistons/Pistons_SRS/Chevrolet/Chev_350.htm

 

400:

Flat tops: part number 12339-xxx

Dished (4.8cc): part number 12341-xxx

 

The thing I like about these is that they don't put the pin up into the oil scraper ring groove. They do this by using a 1/8" oil scraper ring and 1/16" top and second rings.

 

Whether these are too thin to be good on the street, I am not sure. But they spec 0.002 to 0.003" piston to bore clearance for NA applications and 0.003-0.004" for forced induction. Pretty tight, but the piston is very short and light. But the rock is not horrible either. I don't recall the numbers but they didn't seem to rock too much - hopefully the oil control and compression seal is reliable.