Rod quesion

[Guest Anonymous]

Hello question for you all, rods... ive seen everything from the stock 5.7 up to 6.250 i understand that increasig the rod length will help smooth out an engine by giving it a better rod to stroke ratio question is what exactly does this longer rod do? will using a longer rod decrease torque on the same engine that uses the stock 5.7"?? will the longer rod allow higher RPMs??no holds bar on tech info please...

Thanks DAN

[labrat]

From what I understand, the higher rod/stroke ratio increases piston dwell at TDC after ignition, increasing cylinder pressure, and increasing horsepower while reducing detonation. I'm kinda fuzzy too about specific effects on horsepower/torque, but long rod + short stroke = good thing.

[Guest Anonymous]

Check this link out, there was a good discussion on rod/stroke ratios that might prove useful

 

http://www.hybridz.org/ubb/ultimatebb.php?ubb=get_topic&f=1&t=001167

 

 

This is also very interesting reading

http://www.airflowresearch.com/Articles/A3-P1.htm

[Guest scca]

short rods generally have the HP lower in the rpm range

 

longer rods raise the HP rpm.

 

obviously you need different cam profiles and such for this but more HP and at a higher RPM.

[Guest Anonymous]

You wouldn't think so looking at the torque curve of that motor in the Hot Rod article...

[Peternell]

Hey, Grumpyvette, I've read nearly all of your posts and thought about replying earlier but haven't.

Just wanted to say THANKS for Sharing your knowledge with us (well at least me) on this board.

 

Your info is: Relevant; Correct; Helpful; on and on....

 

Not to say others haven't also provided very good and creditable info (I also thank those people too) but I value your input.

 

THANK YOU

(now back to our regularly scheduled Rod length discussion)

[Guest Anonymous]

well thanks their guys, im just sorry i missed that discussion last month! anyway that AFR write up was pretty damn impressive! i was thinking of doing the same thing but using a 3" crank with some 6.250 rods, making 320 , i think that would be a wicked screamer of a motor! money!! anyway interesting to know! also, i remember reading at one point or another about the nissan VQ series motor in the maxima and hopefully new Z, being incredibly smooth due to its insanely high rod to stroke ratio. cool stuff!>>>. DAn

[grumpyvette]

Peternell thanks for the ego boost

 

Hydra

 

Im running 10.65/1 actual (pistons were said to be 10.5/1) and that works just fine because any detonation in an EFI ,ECU controlled engine is monitored and the ignition timeing is retarded with bad quality fuel, now remember the DYNAMIC COMPRESSION ratio is NOT THE SAME as the STATIC COMPRESSION RATIO. as your cam overlap timeing increases through either tighter LSA EXAMPLE (104-110 degs)rather than the more common in a factory cam(111-116 degs) or increased durations ,lately factory cams tend to run 190-215 degs@.050 so durrations of more than 220@ .050 tend to bleed off some compression at lower rpms. so setting up an engine with a larger duration and tighter LSA will allow you to run a higher STATIC COMPRESSION ratio than a WIDER LSA or a lower durration. also thrown into this mix is the fact that ALUMINUM heads dissapate heat faster than IRON heads allowing about 0.6 additional compression (aluminum over IRON) so to answer your question if your running a cam in the .210-.220 and 112 LSA with aluminum heads 11/1 will be about max, if you go tighter than 112 LSA and and more than 225 in durration you can go slightly higher, but keep in mind that LSA,s of less than 112 or durrations of over 220 drive the STOCK ECU for the engines EFI control nuts with bad sensor readings (out of the parameters they are designed to handle) you must either reprogram the ECU or change to non-stock sensors

and yes the longer rods and aluminum heads make the engine much more octane tolerant BTW look at this;

http://www.airflowresearch.com/Articles/A3-P1.htm

 

[fl327]

hey grumpy, you dont need any 62 vette parts do you, we just restored three and have boatloads of

extra.

[grumpyvette]

look here it MAY give you some IDEA were they can be sold

http://forums.chevytalk.com/forums/Forum64/HTML/005334.html

[fl327]

ask the man who calls himself longrod 327 about that one, guess what hes building....

[Guest Anonymous]

My rods are longer than yours!

 

j/k guys... carry on

[grumpyvette]

I have a 6" rod 388cid engine in one of my vettes now and yes the longer rods help move the torque curve up the rpm range slightly and yes they help prevent detonation , the differance is not great but noticeable, and if your starting with no rods my advice would be put the longest rods in your engine that will fit!! not only does it raise the rpm range slightly it also widens the torque curve slightly , now like I said not by a great deal over 5.7" rods but enough to be worth chooseing the longer rods a better choice if things like less bore wear,inproved rpm,less detonation, and wider torque curve matter to you, on the dyno the differance is mostly over 5000rpm and something like 3% in hp max from what I see but it is there!

[Guest Anonymous]

So Grumpy, assuming everything is optimized (polished chambers, no sharp edges, tight quench) what would you recon to be the highest compression ratio I can run without detonation on 91 octane gas? I will be using aluminum heads, a cam with between 220-225 degrees at 0.050 and 6.125" rods in my 327.

[Guest Anonymous]

hey grumpy, I was am putting a 388 together but thought that I could not use a 6" rod. could you help me out to figure out how to make a 388 with a 6" rod. I want to run around 10:1 with a roller cam that weighs wiht .502" lift and 260 @50. Heads are Dart aluminu with a 72cc chamber.

 

thanks in avance for any advice.

 

Jake

[John Scott]

If I'm not mistaken, the pistons for the 6" are a litle lighter, too.

JS