confab

How much does this help torque production?

There's an old Super Chevy article I stumbled on called "Something Old, Something New" and basically it is a garden variety 355 that has been thoroughly blueprinted. Like, NASCAR blueprinted. The rest of it is mundane: Vortec Heads, 6" rods and a TPI. It is a streetable engine and a relatively cheap formula to do a knock off version of.. It makes 416 HP and 486 tq. Moreover, the torque production is incredibly flat. It is an excellent choice for an affordable street build.

Question: How much of this benefit is attributable to the 6" connecting rod?

ddahlgren

Read the article and from 12 years ago. I doubt the runners and base are still available if you know what a Sd base is. Cam is a tad short on specs and no doubt heart of the system and CR is not mentioned. Valve sizes and if any head mods would be handy as well. Basically the tell you enough to get excited but not to duplicate over a decade later with out a bunch of guess work. They are in the biz of selling engines and this is an ad for exactly that.

Longer rods will make an extended torque and hp range as it keeps the intake and exhaust from reaching critical pressure ratios as soon as the shorter rods.

confab

Thanks for the reply.

I actually ran across this sometime ago and found several parts of the article on the web. I couldn't find #3 (I think) and bought an old copy of the magazine just for it. It is scanned in image files here on the computer

Compression is 10.95 to 1.. Cam is a comp cams 08-304-8.

I was kind of interested in it because I already have the Vortec heads and SD intake. Was thinking of a stroker or maybe this?

Or, maybe a 6" stroker? I see the kits with the longer rods and wondered if they were worth the trouble and expense on a street engine.

confab

Has anyone actually built an engine with both? Back to back dyno results, possibly?

I saw another user building a long rod stroker.. Really nice work and parts, but the wrist pin protrudes into the oil ring groove.. Is something like this a longevity issue on the street, or no?

Anyone know?

Tom400CFI

IDK...TPI421, Rklessdriver and others could probably answer, but I'll point out this: The mag article is "candy" so be ware; their' gross numbers can be chopped by at least 50, possibly 100 "as installed", which is the numbers that we're familiar with these days.

Not that it wouldn't be a fantastic street engine; it WOULD! But you won't be seeing 420/480 when it's in your car. No way. I'd guess ~350/400 or so. Still, pretty wicked street engine.

confab

Yeah, I'm strictly street.. I don't like to spin over 5500, 6K.. And that super wide, flat, torque band looks like guaranteed fun from here.

confab

And a knock off looks fairly cheap and easy..

Not a major undertaking.

Tom400CFI

I agree. "Fun", is the right term!

drcook

Part 2

http://www.superchevy.com/how-to/eng...-machine-work/

Here is part 3.

https://imgur.com/a/FgCPh#0

Part 4

http://www.superchevy.com/how-to/061...i-small-block/

confab

Actually, I think I'm the one who uploaded that.

confab

Part 1

https://thirdgenfbody.wordpress.com/...-october-2005/

mtwoolford

Smokey Yunick considered a six inch rod (or longer) essential to Chevy small block build "factory 5.7 inch rods are too damn short".

MatthewMiller

In modern engines, everything I have heard from truly knowledgeable builders says that rod length is pretty negligible in terms of performance impact. There isn't any real magic to be found there. It helps reduce side loads on the pistons a bit, but not by as much as people think. And those loads increase with the square of the rpm, so if you aren't planning to rev the hell out of the engine it won't be an issue anyway (consider that a stock LT4 22 years ago was redlined from the factory at 6400rpm and designed to run for 100k miles or more). OTOH, the added mass of longer rods puts stresses on rod bearings and steals power due to the greater reciprocating mass. So there's a lot of give and take, and in the end not a lot of gain in performance or wear.

ddahlgren

Longer rods do work and have run them back to back with only a piston change to suit, same piston at different compression height. While in the early 90's geometry and air speed have not changed. Port limited or intake limited engines gain the most. They make the air speeds at 73 to 78 degrees after tdc lower where the piston is moving the fastest. This extends the torque curve in both degrees of rotation and RPM before reaching the critical pressure ratio.

What is a Sd intake??

confab

Thanks for the reply.

It is a special intake with flange angels and drilling that matches Vortec heads to the TPI runners..

"SD" stands for Scoggins-Dickey and Edelbrock makes one also..

cv67

Doubt youd notice a thing on a TPI car run whats affordable.

drcook

probably, I just get curious when I start reading things and then I am pretty good at finding stuff on the web, so I put it for the folks that aren't to read

rklessdriver

The oil ring support rail is not anything to worry about as far as durability. We have built hundereds of engines using them with no problems ever.

As far as rod length.... I use to be a big proponet of long rods. Mainly because I was a big fan of Smokey as was my father, but as the past 30yrs have gone by, I have had many oportunities to work for and with other engine builders. I also race in a regional touring heads up drag racing series against the highest caliber engine builders in this country.... this gives me the oportunity to consort with many of them about various things.

2 peoples contrary opinions on rod length really stand out to me. I am not going to name any names. They both post on internetz in certain places and you can find their stuff if you look..... However both of these guys are top tier engine builders.

First guy said that rod length matters so little, its almost not worth worrying over, espc when there are really important things an engine builder has to decide on first.... The rod connects the piston to the crankshaft and nothing more. He litterally worries about "important stuff" like induction first.... as far as short block goes he uses the biggest bore possible, sets a deck height as short as possible, and sets the stroke to get whatever cubic inch engine he is looking for and lets the rod length get decided by default.

The second guy likes using short rods and high piston speed. One of his winning EM engines had room to run a super long rod but he decided to run a shorter rod and ended up with a 1.4x stroke to rod ratio. The piston no kidding looked like a Diesel piston as a result..... No doubt this is a product of his experience with really BIG racing engines, lots of stroke and being backed in a corner where you have no choice but to run short rods.

Me personally.... I feel their are benifits in long rods and short rods. I build engines both ways depending on what the engine is designed for. I try to maximize whichever of those benifits apply as much as I can in the engines I build.... but I will not compromise anything really important to run a certain rod length.

No one theroy on stroke/rod ration is right or wrong because people are sucessful doing it many different ways. Best to educate yourself on the positives and negatives of each and do what you think is right. Just some things to think about.
Will

cardo0

I prefer to keep it simple. To short a rod and the side loading in the bore creates accelerated/excessive bore wear (as fou nd in the sbc 400). To long a rod and the piston ring pack becomes to tight. A min rod to stroke ratio of 1.52 is considered adequate.
Longer rods increase the piston dwell time at TDC - because of the rod angularity - which will help at high RPM. But that does take from the shorter rods piston slower travel through the angle where the cylinders builds max pressure enhanced at lower RPM.
While it maybe a concern for big budget race teams I've come to the conclusion that for us amatures we are better off with a rod length that allows a good piston ring package while long enough for rod/stroke ratio greater than 1.52. That leaves both 5.7" and 6.0" rods for 3.48" and 3.75" strokes. I know others will argue this but if you are going to a 4" stroke sbc your gonna have such a tight ring pack and terrible cylinder wear you may not have much of street motor or street engine life. John Lingenfelter (RIP) explains this.

Hope this helps.

JoBy

I decided to go with long 6.125 rods when building my 372 CUI. ( 4.125 bore and 3.48 stroke )
That is a 1.76 Rod length/Stroke Ratio.
My main reson was to reduce piston side loading and friction.
With the turbo cylinder pressure is higher for a longer part of the power stroke and with more rod angle.