Visit The Dirt Forum for More Information

Author Topic:   Is a 6 in rod a good choice of a 355
sledgehammer
Member
posted October 20, 2003 05:49 AM
Will a six inch rod give any advantage over the 5.7? I am thinking that it should increase the torque because of the longer length. I am not sure about the horse power which is why I am making this post. Of course if neither is true please correct me.

Thanks
Jim


outlawstock17
Member
posted October 20, 2003 06:47 AM
yes, a longer rod will give the engine "longer legs". it's easier on the cylinder walls, will stay together at high rpms longer and dwell at TDC longer to allow more time for the cylinder to fill.

"size doesn't matter" does NOT apply to "connecting" RODS....

rocket36
Member
posted October 20, 2003 09:46 AM
i bet you'll get lots of different opinions on this.
smokey yunick used to say "put the longest rod you can in there" and the 6" rod became industry standard.
john lenginfelter (think i spelt his name right) states in on of his books that the rod stroke ratio is very important but then goes on to say that he has never seen an increase in power on the dyno to prove the theory in back to back tests.
a long rod will make the piston dwell at tdc longer but when it is there it is not doing anything. the cylinder will fill when the piston goes down, then compress on the way back up before firing and going back down (basic 4 stroke cycle) so i think it is fair to say the advantage with a longer rod would be less side loading/friction.
maybe steve could elaborate further, he's probably done some testing.


racer17j
Member
posted October 20, 2003 01:15 PM
around here most of ther front runners are all running 6 in motors we have a 360 cid and 9-1 comperssion rule


outlawstock17
Member
posted October 20, 2003 01:29 PM
david vizard recently did a dyno test in speedway illustrated with the only variable being connecting rod length. the long rod engine made more horsepower and more torque throughout the entire rpm range tested. rocket, there's a lot more going on during the increased dwell time than you might think. a longer rod also increases the leverage the piston has on the crankshaft. durability also comes into play.

i'll take a long rod engine over a short one any day. rpm's.....yummmmm...

[This message has been edited by outlawstock17 (edited October 20, 2003).]

rocket36
Member
posted October 20, 2003 01:47 PM
thanks for the info,
i didn't say one was better than the other, i don't know, like most of us, i don't have access to a dyno and many motors to test, i was simply stating what i have read.
and i'm certainly not going to disagree with anything that david vizard has found and proven, he has most likely forgotten more than any of us will ever know.
the way i understand it is the rod/stroke ratio is what will have an effect.
for the record i would use a 6" rod in a 355 for no other reason than why try to re-invent the wheel.


outlawstock17
Member
posted October 20, 2003 01:59 PM
vizard's article says 1.9:1 is the magic number for a restricted engine......and 2.2:1 for an unrestricted engine. 2.2:1 is next to impossible to get......guess what a 302 chevy has?.....1.9:1.....now you know why they run so hard. i use a 6.200" rod in my 351w.....


sdhnc29
Member
posted October 20, 2003 05:07 PM
My testing has shown what has already been talked about . The longer rod will produce more power through the entire operating RPM range . Although peak torque is usually moved a little higher in the RPM range with the longer rod , it is all relative to the RPM range of a race engine . In other word's , your not coming off the corner at 1,500-3,000 RPM where the shorter rod can help .

There are many different positive affect's of longer rods and better rod/stroke ratio . All of which help to produce more HP and a broader torque curve .

Steve

P.S. Good info outlawstock17 and rocket36 !! Smokey Yunick and David Vizard are 100% correct .

------------------
Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


sledgehammer
Member
posted October 20, 2003 05:17 PM
Again this forum has proven to be a valuable resource. My next question would be is a 6 in rod the longest you can go on the 355 motor? Also has anybody had experience with the desk top dyno software and is it worth the 40 dollars?


outlawstock17
Member
posted October 20, 2003 06:10 PM
sledgehammer, i'm a ford guy but i'ma almost certain you can put a 6.125" rod in a 350. i have dyno2000 and there isn't a option for rod length.


sledgehammer
Member
posted October 20, 2003 06:13 PM
Outlaw,

Have you found the program to be useful?

sdhnc29
Member
posted October 20, 2003 08:10 PM
If you don't want a custom piston made and wish to use a shelf stock piston ,working around a 9" deck height , then 6.125" will be the longest rod . If you want to have pistons made , then yes you can go longer than 6.125" .

Steve

------------------
Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


sledgehammer
Member
posted October 20, 2003 09:05 PM
With the 6.125 and a 9 inch deck height will I have to use flat tops or can I use a pop up? I am planning on using a set of double humps on this motor.

Thanks
Jim


sdhnc29
Member
posted October 20, 2003 11:18 PM
There is shelf stock domed pistons available for this combo . So you should be ok without flat top's .

Steve

------------------
Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


Raz_900
Member
posted October 22, 2003 09:36 AM
One of the big benefits of a longer rod is a lighter piston. I switched from stock 5.7" rods with ARP bolts to Eagle 6" SIR rods. The rods themselves are 8 grams lighter (and stronger to boot) and the KB LW piston for a 6" rod is about 50 grams lighter than the LW 5.7" piece (which is already significantly lighter than stock I think it was like 50-60 grams). So, by going to the 6" rods you cut about a pound of piston weight. Doesn't sound like much, but grab a 9" long chain with a pound weight on it and spin it at 6000 rpm (impossible, but you get the point). Less weight + less friction = faster revving more powerful motor.


Dixon
Member
posted October 22, 2003 11:55 AM
Not to cause a lot of controversy...

I have always been a believer in the longer rod theory, but after looking into an article in this year's PHR "Engine Masters" I'm starting to think there might be something to running really short rods.

A man by the name of John Satterfield, who owns Dutchess Automotive Machine Shop, www.dambest.com was a featured speaker at this summer's Advanced Engine Technology Conference. This is where the best come to learn and educate. Anyway, he has a 320 c.i. normally aspirated ford that makes over 900 H.P. with a single carb. (He also has his own line of carbs that power several Cup teams). His speech was about using shorter rods, and I can't remember the details but his website has links to a ton of articles written about him.

Just a thought...

outlawstock17
Member
posted October 22, 2003 04:26 PM
that guy is "tweaking" every circuit of the engine and probably turning it well over 10,000 rpms with ultra-lightweight and exotic alloy parts. i'll bet he isn't doing it with the stock length 5.09" rods and i'd gamble that it wouldn't last 500 miles, or in our case, a whole season.

a 358 inch winston cup engine with a roller cam, unlimited compression and a stout mix of nitro methane would probably make well over 1000 HP, but it wouldn't stay together very long...

Dixon
Member
posted October 23, 2003 01:39 AM
All I know is that he used some fuel other than nitro, a single carb, and shorter rods than stock. I'm sure he modified everything else you could on the heads and intake. What I'm saying is that this guy made some impressive power with short rods that shocked some people. If his logic holds it might shake up some of the ideas that people have about rod to stroke ratios.

Like I said, I'm not trying to start controversy, but his numbers do talk, and so do his patents.

Dixon
Member
posted October 23, 2003 01:45 AM
Well, maybe I am trying to start something...


outlawstock17
Member
posted October 23, 2003 06:49 AM
can you post a link to the specs on his engine? shorter than 5.09"?......i'm skeptical....no offense dixon, but i'll believe it when i see it.

with the kind of rpm's you'd have to turn a 320 inch engine to make 900HP, a real low rod/stroke ratio wouldn't provide enough dwell time to get the mixture in and out efficiently enough to make those kind of numbers. the more rpm's you turn, the less amount of dwell time you have. the only way to get more dwell time is with a longer rod.

i suppose a 5" rod would do the trick if the stroke was 2.5", maybe his engine has a huge bore and an extremely short stroke. JMO...

[This message has been edited by outlawstock17 (edited October 23, 2003).]

sdhnc29
Member
posted October 23, 2003 12:54 PM
The 900hp is not all that difficult to get actually , especially today . We were getting 795hp from a 291ci Chevy with old -8 Brodix heads back in 1979 . This particular engine was in a C econo dragster . The dyno pulls were started at 7,000rpm , and finished at 10,000rpm . With the heads available for both Fords and Chevy's today , 900hp is achievable even with short rods . Especially since your extremely limited on rod length in a Ford that small .

I'm pretty sure that if a "short" rod and a bad rod stroke ratio was the best performing combo , then all the Cup guy's would not be going to shorter and shorter strokes , with longer rods .

Steve

------------------
Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


norightturn
Member
posted October 23, 2003 07:44 PM
I couldn't find anything about this particular motor on his website, but I'm going to call him and see if he can explain his research. I'll let you all know when I find something.


sledgehammer
Member
posted October 27, 2003 12:06 PM
Is a 6 inch 350 and better or worse than a 5.7 inch 383?


wissota3x
Member
posted October 28, 2003 08:57 AM
I have ran just about every kind of combination imaginable.One of the best motors that I had was a 383 with 5.7 rods.It had Ohio pistons,stock rods,externally balanced.I ran humper heads 2.02, 1.6,bowl hogged.Bullet 290 300 cam.This combo was awsome but because of the external balance they would self distruct.With the same cam,heads and everything else in a 406 with 6 inch rods it was a turd.I also had a 362 spec motor with roller cam ,light recipricating,6 inch rods that ran real good also .I think its all in the combinations that match up good with each other.One of the best running motors on our track right now is a 3.335 stroke,4.155 bore,6.200 rods.


Dixon
Member
posted October 28, 2003 05:54 PM
Everyone,

I emailed John Satterfield and he said that "he was too busy to give a good explanation" of his findings, but that there have been numerous papers written about it in SAE articles. He didn't give me any links to them, but he did pose a question to me:

Why are all PRO Stock drag cars , that
are running 500 ci , running a 9" deck ? Why did chevy copy ford's 8.2 deck ? Why do the PRO stock truck in drag racing use a 8.5 deck ? Next time one of your friends or your self has the time , build a 302 ford using a 8.2 deck. Then take all the parts out and put them in a 400M block 9.5 deck and see how it runs.

I'm not so sure what to think of his response, but the taller decks do allow for longer rods...

Any thoughts?

outlawstock17
Member
posted October 28, 2003 08:26 PM
my thoughts? he's blowin' smoke up your **** .


rocket36
Member
posted October 29, 2003 04:56 AM
well, i guess you never know. he may just have a point.
most of the aftermarket blocks seem to have a taller deck height to allow for larger stroke crankshafts by lifting the cam higher up in the block (also have wider pan rails) not really for extra rod length.
i think a lot of top level engine builders/developers went up in rod length, then back down and possibly back to the longer rods but it probably depends entirely on the required power curve from the engine.
still for most of us building engines the best bet for a 355-412 would be a 6" for sure.all the parts are relatively easy to source and reasonably priced, but if you've got money to burn build a 18 or 15deg engine with 6.125 rods, but hey if we had that kind of money you wouldn't be building your own.


sdhnc29
Member
posted October 29, 2003 12:57 PM
First of all I've been taught to be a little suspicious of people who answer questions with a barrage of questions . Either they are trying to be too philosophical , or they are dodging the ultimate answer . I do believe that Satterfield has done R&D work in the area of long vs. short rods . I am also sure that in some test that has been preformed , he has had results supporting his claim . But , to generalize that shorter rods are better in every application is wrong in my opinion .

Secondly , I read this article from the Popular Hot Rodding PHR Engine Masters seminar . The following is what was written and is relevant to this topic . I simply copied and pasted it here .
------------------------------------------
(John's speech was enlightening, especially as he walked us through the research and design of his personal engine project. The 321-inch Ford small-block was radically altered to optimize airflow and fuel droplet dispersion, resulting in his target of 800hp in naturally aspirated form approaching 9,500 rpm.

John raised plenty of eyebrows when he recommended shorter connecting rods! His extensive research on rod length found more benefit in shorter rods in most situations. This is the polar opposite to the "longer rods are always better" theory most of us have grown up believing.

Naturally, this recommendation is based on research, and hopefully we'll be able to follow up this suggestion with an article detailing the work behind John's suggestion, since we don't have the space to elaborate here.)

-------------------------------------------
To answer some of the questions that john asked Dixon , I'll mention the following .

I am not aware of any 9" deck height pro stock engines , not that there isn't any . Pretty much every Ford and Chevy pro stock engine that I know of uses a 9.300" deck height . The shorter strokes are becoming more popular . By shorter I mean 3.700" . With a 3.700" stroke , and a 4.625" bore , you have a 497ci engine . Based on a 1.000" CD on the piston , you can use a 6.450" rod . A pretty short rod for this type of application . With this "short" rod , you end up with a rod / stroke ratio of 1.72 . Just so happens that this is the same rod / stroke ratio as a 3.480" stroke Chevy with a 6" rod . A 3.00" stroke with a 4.125" bore makes a 321ci engine . Using a 5.700" rod gives you a rod/stroke ratio of 1.9 . using a 5.400" rod gives you a ratio 1.8 . Now ......using a stock length 5.090" rod give you a rod / stroke ratio of 1.7 .....WOW ! Guess what , they are not hurting on rod stroke ratio no matter what ....lol

Chevy copied Fords 8.2 deck height block for the published reasons of weight reduction to meet federal fuel mileage regulations . My personal feeling on this is that whatever GM , Ford ,and Chrysler have ever made , race car engine builders and manufacturers have ALWAYS made better . The big 3 manufacturers are building there engines for the street , not to be run in circle track or drag race applications . The operating RPM range in a circle track or drag race engine is totally at the other end of spectrum from a street engine . These days they are simply looking to have the lightest engine , small cubic inches , and enough torque to get the car moving . All out performance has not been a priority .

As for his last statement/question to Dixon , it makes no sense .

I have not been impressed with anything that Satterfield has said yet about shorter rods . HE need's to define what he is considering "short" rods in any application so we can see what the h@ll he is talking about . A 321ci 800hp engine is not that impressive by 1980 standards , its already been done .

just my opinion

Steve

------------------
Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


outlawstock17
Member
posted October 29, 2003 02:01 PM
dang steve, that was a "novel", lol.....i had one written too but decided to change it to "blowin' smoke", lol.

satterfield sounds like he wants to re-invent the wheel or something.....maybe he wants to make it square!

if you want to get off the front of the push truck quicker, use a short rod. if you want your engines to stay together and win races, use the longest rod you can afford or fit in it.



sledgehammer
Member
posted October 29, 2003 04:57 PM
What would give me the best performance:

A .275 dome piston with 64cc chamber head or

A flat top with heads angle milled to 49cc

Both applications would be with the 6 inch rod.

squid
Member
posted October 29, 2003 08:42 PM
sorry to just jump in but i have a a set a H-beam 6.125 rods they are new and never used. i was told and never put it to paper but you can buy 6" 383 pistons and this will work in a 355 with these rods. was gonna try it but rules dont allow H-beams now. give me a holler if your interested.


outlawstock17
Member
posted October 30, 2003 06:59 AM
i'd go with the flat top angle milled heads deal. when you angle mill, not only are you decreasing the chamber size, you are decreasing the valve angle. i believe this is where a lot of extra power is found through efficiency. only allow a reputable machinist to angle mill your heads. i've seen a lot of good castings wind up in the scrap pile. once you take it off, you can't put it back on.....and the intake mounting surface angle changes when you angle mill, so that may need to be addressed...

[This message has been edited by outlawstock17 (edited October 30, 2003).]

Dixon
Member
posted November 04, 2003 12:16 AM
Everyone,

I appreciate the responses to this matter, especially yours, Steve. Sorry for misquoting the HP figure, I thought it was 900.

I wasn't too happy with the response I got from Mr. Satterfield, but what can you do? I emailed him again trying to get him to expand on the subject just a little bit, but he hasn't answered so I guess we'll just have to wait until someone can really explain the research he was talking about in that magazine.

Anyways, thanks again. I love this forum, you always learn something about cars or life in general.

Back to the Archives