hey guyz, I have a 383 in my 74 T/A, but i have used 400 rods and 350 pistons. I want to know if using 6" rods and special pistons really makes a difference in torque and HP

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Had a very clean bright Blue '91 Z28, but gone now
www.geocities.com/Z28bhr

 

How did you find 4.030 pistons set up for 5.56" 400 rods?

Anyway, I couldn't give a number on the HP or torque, but look at it this way, longer rods=more leverage for the crank, going to a longer rod I'd assume would have the same effect asd a mild rear gear change to a numericaly higher one..

In my opinion, for a street motor 6" rods are overkill, just too damn expensive, and you have cam to rod main clearance issues..

Go with a normal 5.7 rod, you'll have to get the motor re-balanced to do this.

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Shane McConnell
macgyver@thirdgen.org [*]Owner of a 1991 Camaro RS, 305 5-speed.[*]Owner of a 1979 Camaro Z28, 350/350.
(Reminder to self, change oil at 100,000 miles.)

 

You use standard 350 pistons with the short rods, nothing special about them. The 400 has the same deck height as all the other small blocks and used a shorter rod to make up for the difference.

Ck out www.theoldone.com for some info on rod length and how it affects the performance package as a whole. Go to the tech board and search the archives

Rob_O

[This message has been edited by RobO (edited August 01, 2000).]

 

Mac, you didn't really answer the question. I, too have a short-rod 383 shortblock in my garage, just waiting for the project money to roll in. I want to make a 6250 RPM, 425 - 475 HP engine out of it, and would like to find out if this reciprocating assembly is going to cut it. Cast crank, forged .030 over pistons, 5.565 inch rods, all balanced.

 

My race engine uses 400 rods. I've never tried one with 5.7 or 6" rods to compare the different rod length. I guess it all depends on the rest of the engine setup. Theoretically the shorter rod will increase the side load on the piston. It should also have an increased piston speed since the dwell is much shorter at TDC. The short rod is also cheaper to build since you don't have to worry about the rod bolts hitting the block or cam.

Before the consumer was flooded with aftermarket parts the way to build a 383 was using the 400 rod and crank with 350 pistons. The stroker pistons were not available or expensive.

I shift my engine at around 6400 and the replay tach says it peaks at 7000. It's still staying together and there's nothing exotic done to the bottom end.



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Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car and knocking on the SuperPro ET class
383 stroker (carbed) with double hump cast iron heads and pump gas
Best ET on a time slip: 11.857
Best corrected ET: 11.163
Best MPH on a time slip: 117.87
Best corrected MPH: 126.10
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!

Member of the Calgary Drag Racing Association

 

i'm currently building a 383 for my s10 daily driver. i'm going 6 inch rod myself. the 6 inch rod add to the efficientcy of the engine as well as give it a much flatter torque curve. when your building one that has to meet emissions the 6 inch rod really helps too. it allows for lighter pistons also which allows the longer stroke engines a little higher rpm capabilities. many other reasons, but that's a much longer reply.

 

Improving your rod/stroke ratio is a good idea. the longer the rod the better. idealy, you want a ratio around 1.8

The longer the rod gets, the better that ratio.

Good luck

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-86 IROC
Vortech stuffed EFI 406 in progress

 

Yep, the long rod is the ultimate set-up.

Dan - Your combination will be fine for a 6250 RPM motor, it's when you put on power adders that you need to think about stouter components on the bottom end.

425-475HP is easily attainable...with GOOD heads. Heads make horsepower, don't skimp on that department, induction as well.

You can easily get 475 HP out of a short rod 383 with good heads, a cam to match, and an adequate induction set up.

Steve

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Spohn Performance, Inc. - F-Body Suspension Specialists

 

I agree with pretty much everything he just said, but...

I had heard that due to the longer rods, you needed thinner pistons. I don't really recall what they were talking about specifically, but the article mentioned that the thinner piston was not optimal for a street engine (even though the rod/stroke ratio was better). I could be way off though, so take my fading memory with a grain of salt. Maybe someone will know better what I am talking about and can elaborate further. Heck, maybe with new alloys etc., it isn't even an issue anymore...


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1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock... all the suspension stuff... 9-bolt posi disk is in... K&N filter... 93 octane...

I got the GO... I need the SHOW... Interior is next!

 

It's not a thinner piston specifically. With the longer rod the pin has to be moved up to compensate, so it intersects tho oil control ring grove. As long as its put together properly it doesn't make much difference, and like they said earlier, the advantages outway the drawbacks by far.

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'87GTA w/ SLP Cold Air, MSD Coil, Airfoil, Gutted MAF, AFPR, TES Headers, HI-FLOW CAT, Flowmaster Catback, Energy Suspension Master Bushing Kit

 

I just posted this link at another post. Well here it is again.

BTW- I'm currently assembling a 406 with 6" rods and JE srp pistons. The oil ring requires an oil support rail. The pistons are smaller=less weight. One train of thought is with a smaller piston and "tight" ring package, the rings are closer affecting oil control. My opinion is, the higher the pin (as long as you don't get carried away) the less the piston will rock in the bore (better ring seat). But anyway, the link below is an excellent article about rod length.
http://www.ulster.net/~nubb/tech/rodslength.htm