Long rod 306??? 400 sbc crank and chevy rods.
 

Anyone ever hear of this short block. My friend has what he calls a long rod 306. He says it has a 400sbc crank and chevy rods.

What would be the advantages to having a shorter stroke and longer rods. Torque???

Get this he has ported victor jr heads a trick flow intake and a Vortech SQ trim supercharger on it.

The motor is sitting in a 1976 280 Z.

Sweet huh,

Doesn't DSS sell a long rod 306 setup now?

E

I dont know, but I plan on blowing up my shortblock sometime in the near future and I had never heard of a long rod 306 till he mentioned it.

I was wondering what the advantages of a long rod 306 would be.

WOW
 

I've heard of that combo before. Not sure if it produces more torque or top end. My guess is like any other stroked motor...top end. Does that 280Z run with the motor in the picts.? If it does I bet it's fast as hell...

Not yet but it will soon. Everything has to be custom made so its taking a while.

one of they guy's posted on the theory .(it was huge) it is suppose to add to torque and velocity of the air , partially because of the longer lever (fulcrum?) do to the longer rod. but like everything else it has to be part of the total package and not just changeing pistons and rods for a longer rod ,

stroke stays the same just that the piston ring is normally moved up to compensate for the longer rod so overall rod and piston height stay the same.

stroke can only be changed at the crank .

Well supposedly it has a 400 SBC crank.

No way in hell he has a 400 Chevy crank and rods in a 302. The 400 stroke is 3.75", no way thats going in that block without hitting cylinder wall. Not to mention is just won't even go in. And if it were in, it would displace 383 cubic inches with a 4.030" bore. I think he's mistaken. :rolleyes:

This is just my two cents but...I dont think longer rods would add much torque improvement anywhere in the rpm range or else they would be installed from the factory. If it is so cheap, and gives you more power with no adverse side effects then ford would have installed them to begin with, and advertised about it. I think that any improvements would be very very minor. Feel free to disagree.

It is by no means cheap. It definitely has chevy rods and I am pretty sure he said it had a 400sb crank.

He has over 6 thousand dollars in that motor easy.

I dont know I thought it was strange myself.

You're looking for Speed Secret #5 posted by jim_howard_pdx

http://forums.mustangworks.com/showt...threadid=31035

Usually when someone says they have "chevy rods" in their Ford small block, they are talking about the rod journal diameter. 2.100" diameter rod journals (standard SB chevy size) can be had pretty easily when purchasing an aftermarket crank and rods. The biggest advantage is less bearing surface. The less bearing surface there is, the less frictional loss there is. Another advantage is more bearing choices.

As for the long rod/more torque issue. I have always been told that a long rod motor will make more torque. I have never tested this theory and I dont have the knowledge to dispute it, so I have to agree with it.

As for the 400 Chevy crank in the 302 block, I am very skeptical of that. :confused:

Andy

jim_howard_pdx- Doesnt have a phuckin clue.

JMO,

Clue?
 

You believe he's got a 400 SBC crank in it? Do the math and see if you have a clue.

The longer rod will allow the piston to stay down in the bore for a longer period of time and will increase piston speed without increasing stroke. I can't think of a good analogy to really explain this though. The increased piston speed is what gives the extra torque.
The reason it's not done from the factory is because the clearances are much tighter and would be difficult to keep in check on a production line. The piston also spends more time at the top of the bore so piston/valve clearance could be a problem with a healthy cam.
I also gurantee that a Chebby 400 crank would be impossible to fit in a 302 block, heck I highly doubt that the two blocks even have the same length.

Welcome back Jim. Who are you trying to kid ? You can spot your posts after one sentence. :p
From every thing i've read heard and seen, there are some atvantages to running a longer rod because of the extra dwell time at TDC, but there is a point of diminishing returns, and to say the longer the rod the better the motor is nuts. If a rod the length of my arm worked miracles, don't you think that building full of engineers at Ford GM BMW ect ect would have covered the highway with them by now ?
PS: I talked to the Ford expert awhile back, at one of the major piston / rod companies. One i won't name that has been around since the beginning of time. His answer when i asked him if this long rod thing was what it was built up to be was ... he chuckled and said well, it sells magazines. Then he told me, I'll put a set together for you but you'll likely be disappointed.

If I believed he had a 400sbc crank in his 302 I would not have posted this I wanted some opinions.

It is unfortunate that all of us cant be know it all bull shlters like howard.:rolleyes:

Anyone that achieved a ram air effect on a dyno has more of a clue than I will ever have i guess.

LMAO!!!!

I use a 5.40" rod with a 3.00" stroke.... and no, I don't use a chevy crank. :rolleyes:

I honestly can't see where it makes a *huge* difference. It's a good theory, though.

Actually a long rod will help you more in the topend range. The longer dwell time at TDC promotes combustion when the piston speeds are much higher, so it's ideal for high revving engines. On the lowend it will actually hurt you because you're not taking advantage of the dwell time (engine is turning slow enough for efficient combustion), and the increased piston speed doesn't allow as much time for cylinder filling when the valves are open. IMO it's just hype, the gains or losses in either area will be minimal. Spend the money on something else.

I'm not sure there is a right or wrong on this subject. It depends on how long a rod you're talking about, and what the application is for the engine you're building. I'm gonna put a link here ... its a long article, but its very interesting, and there is a lot of logic in what he says IMO. Its related to some Honda modifications so you'll have to get past the honda part (about the middle of the article where it starts ... "Long rod .... You have no idea how many")
This was written by a guy some say is the Albert Enstein of engine design, and others swear is the biggest con man since P.T. Barnum.
http://www.theoldone.com/archive/crv...trokeratio.htm
Like i said its long and technical, but there is a lot one could learn here, and food for thought and probably debate too ;) :D

I brought this up to my Dad and he had a couple of interesting points.

#1 big car companies havent jumped on this band wagon because of all around engine performance.(the longrod mainly helps in max Acceleration less than 5% of normal driving)

#2 in WWII Royle's royce made some long rod airplaine engines 15000.+ rpms but had problems with deceleration and piston life due to small piston skirts.

#3 what rod ratio's are top fuel and funny car using. also indy if anyone knows.

#4 as far as the car companies why arent they using aluminum blocks and heads in all there cars and turbo's on every model.

#5 Tehnically thats what weve done by using a smaller 302 piston (height same bore)in our 351 (my street ??? car ) but that wasnt the reason why.(so we didnt really increase the rod just decreased the piston height)

#6 I would race Jim Howards race winning 428 or what ever any day of the week and we'll see who wins.(ps the drag car not my street car) boost versus long rod.

#7 race weight can help more overall that a longer rod.

its interesting but not worth the time its been given . now cams thats something i still need help with

Choose to believe or not, but my experience having been lucky enough to witness an actual dyno test of 3 motor all identical except for rod length, cough they were Chevy's but the theory is the same cough, all three motors dynoed within 10hp and ft/lbs of each other at the crank with no accessory. The only think that was noticed was while they produced the same power and relative power curves the curve it self would shift either up or down a little bit, a little bit being less then 500 rpm, but you could lay all three graphs on top of each other and they would basically all lay on top of each other if you shifted the rpm +/- the slight shift in rpm. Me personally after seeing that no longer subscribes to the theory of long rods being better... especially since the long rod shifted the rpm up without a any real power gain. Well personally I would rather make same power a little lower on the rev scale and keep my motor altogether a little longer since revs will kill your bottom end as fast as changing you oil will. Now I don't thing that the slight shift up in the revs would promote that much faster wear but if you are spending the money and are putting something to together that compared to stock will have accelerated wear anyway, why put it together with just one more thing that will cause faster wear (the slight shift in RPM's being higher).Now that all that has been said the three motors were not extreme examples of rod lengths but were common lengths used by allot of people when doing there Chevy's IE the long rod motor was a 6" rod vs. the stock 5.7 and If I remember correctly the shorter was a 5.4 just because if they were going to test the rod length theory they had to put something to together with short rods.


When he tells you it has a 400 SBC crank is he sure it is not a 400 ford crank? That was actually a popular swap before all the after market crank manufacturers started making new stroker cranks. The 400 ford crank has enough meat in it that it could be offset ground in a variety of different lengths and to the Chevy or Chrysler rod bearings and ford main bearing sizes. The 377 kit that is sold to this day by many vendors is based on a 400 crank with stock throws, Chrysler rods and Chevrolet pistons in the 9.5 deck block.

Damn!!!.......I bet your right 400 ford crank.

When I heard it had a 400 crank in I just assumed chevy since he said it had chevy rods:o

Im gonna go crawl under a rock:eek:

The thing about it is, it can't be a 400M crank in it either. They have a 4" stroke, it will not fit in a 302. And from my understanding, this is a 302 block.

The thing about it is, it can't be a 400M crank in it either. They have a 4" stroke, it will not fit in a 302. And from my understanding, this is a 302 block.