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Old 01-28-2004, 12:33 PM
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longest rods in std deck 454 bbc??

I have to upgrade to stronger rods before i swap in my roller cam. dyno 2000 predicts 713 Hp @ 6000rpm and 687 ft.lb @ 4000rpm. so i really dont trust my std BBC rods...

so the question is how long rods i can install?? i would like to atleast get +400 long rods, i dont mind installing plugs/ring supports as i have bad experience with locks comming out. but Oliver sells rods that are .500 longer how high can i set the pins up (i dont plan on running nitrous) but i still dont want the ring lands braking...

dyno 2000 predicts peak cylinder pressure of 274 psi at 5000 rpm.

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Old 01-29-2004, 07:35 AM
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You could probably run the +.500" rods in a short deck big block. Use a thin ring package (.043", .043", 1.5mm) and have your rods manufactured with small block pin diameter (.927") or smaller. The thing that limits your being able to place the ring package higher on the piston is the depth of the valve reliefs. To help in this area, use compression rings with reduced radial wall thickness. PC/Clevite has top rings with about .170" radial wall.
JE, CP, Ross and others can build these pistons for you.
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Old 01-29-2004, 09:15 AM
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With stock stroke of 4.00" you can run a 6.7" long rod at max. I would look at the lunati Pro Mods as a good choice for that kind of power. If I can be of any more help just PM me.


Chris
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Old 01-29-2004, 12:01 PM
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long rods

I would put a standard lenght rod in it.

The longer rods "do-not" make any more power.....

The shorter rods will keep the bob weight down and you can get a piston with a better ring package.

keith

For all of those that are going to reply about longer rods making more power /torque. Show me your dyno sheets.....

Also go read Reher-Morrison tech sheet #10 or Ron Iskenderian"s tech tips 2005
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Old 01-29-2004, 02:33 PM
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i have decided to run longer rods becaust i want to run the high compression (the best gas we can pump here is 98 octane) also i want to reduce piston speeds, piston acceleration and get the higher dwell at tdc. and lastly: the price of reg length rods and longer is the pretty much the same. which is also the case for the pistons...

and here is my oppinion on that topic for anyone interested:
the rod ratio in a gasoline engine determines the piston dwell at TDC. the longer the rod, the less downwards piston motion will be the result of the rod angle changing.

if the crank rotates 10 dergees, then a very short rod will be at a greater angle than fi the rod is very long. since the rod doesnt change length then some of the pistons downwards motion will be a result of this phenomenon, so the longer the rod, the longer the "dwell" and the longer the dwell the more complete combustion and higher cylinder pressure. The rod length is limited by other engineering conserns, like bloch deck height, piston height, and thus inherrent stability, and resultant wear. and so on.


In most large cubic inch engines it is hard to get a very high ratio. A Stock 350 Chevy has a 1.64:1 RL/S ratio, which is not very good. By increasing the rod length to 6" the ratio increases to 1.72:1, which is much better. You can squeeze a 6.1" rod in a 350 with little trouble, but longer than that requires plugging the piston pin bores after assembly to support the oil rings. It is not worth the extra expense for the little gains, so a 6" rod in a small-block Chevy has become common because everything fits right in. With endurance engines, longer rods are always better. Most endurance engines are using a RL/S ratio of at least 1.9:1 and some as high as 2.2:1. Before you go out and buy longer rods, let me just say that the gains are very small. This debate has been argued for years and will not end anytime soon. In my opinion, if are building an engine and need new rods and pistons, a longer rod will cost about the same. That makes the small benefits worth it. I would not waste my money buying longer rods if you have a good set of rods that you can use. Use that money to make more power elsewhere in the engine.

Rod Angularity

A longer rod reduces the maximum rod angle to the cylinder bore centerline. Less rod angle will reduce piston side loading; there will be less friction and less bore wear. Less rod angle also gives better average leverage on the crank for a longer period of time. A 5.7" rod with a 3.48" stroke (stock Chevy 350), will have a maximum of 17.774 rod angle. Switching to a 6" rod will reduce that to 16.858, assuming that the wrist pin has no offset. (on a ford small block, installing the pistons backwards will actually gain almost 20 Hp. since the piston acts like it was mounted on a longer rod, as the ofset is reversed, at the price of increased noise and wear)

Piston Pin Height

A higher pin height will reduce piston rock and aid ring seal. please no screaming and name calling about anything about a tighter ring pack, we are talking about pin height and pin height only. Moving the pin closer the the center of gravity of the pistons makes the piston more stable.

Rings

As the compression height is reduced, the space for the ring pack also get reduced. This can be a problem on some engines. It is good for power to have the top ring as close to the top as possible, but this is limited to the strength of the top ring land. As it becomes thin, it becomes weak. High output engines (especially nitrous engines) need a thicker ring land to keep the cylinder pressure from pinching the top ring. In my opinion, if you have to compromise ring location, it would be better to run a slightly shorter rod.

Skirts

Shorter skirts are usually combined with a shorter piston for a longer rod, but they are not really related. There is no reason to reduce the size of the skirts just because the pin location changed. A shorter skirts are used to reduce friction and lighten the piston. The cost is a little less stability, but it is arguable that a lighter piston with a higher pin height does not need the extra stability. For a street car, I would increase the rod length if it meant a reduction is skirt size. Most of the things listed here are for competition motors to gain a few hp, not worth a lot of effort for most street engines.

Piston-to-Valve Clearance

A longer rod decelerates toward TDC and accelerates away from TDC slower than a shorter rod, so piston-to-valve clearances are tighter with a longer rod. This may require deeper valve relief's in the piston (but probably not). A short rod is just the opposite, there is more clearance because the piston decelerates toward and accelerated away for TDC faster.

Piston Velocity

A longer rod reduces peak piston speeds slightly and delays peak piston velocity until the piston is further down the bore, which gives the intake valve more time to open more. Peak piston velocity is usually somewhere around 75 ATDC and since most cams cannot fully open the cam until at least 106 ATDC, it leaves the valve as a major obstacle when airflow demand is at its greatest. By delaying peak piston velocity, even if it's only 1 or 2 crankshaft degrees, it can allow the valve to open another 0.010-0.015", before peak airflow demand is reached. Not a huge help, but a step in the right direction. With a 350 Chevy, switching to 6" rods from 5.7" ones will delay peak piston velocity from 74.5 to 75.5.

Piston Acceleration / Deceleration

Reducing piston acceleration / deceleration from and toward TCD will reduce tensile loading of the rod, the number 1 cause of rod failure. A Chevy 350 with 5.7" rods will have a peak piston acceleration rate of 101699.636 ft/sec/sec at 7000 rpm. Swapping in 6" rods will reduce that to 100510.406 ft/sec/sec at that same rpm. That is a reduction of 1189.23 ft/sec/sec.

Intake Runner Volume

Since it is easier for an engine to breath with a longer rod, less runner volume is needed. This allows more room for an intake system (this is a very small gain, but is real).

Exhaust Gas Scavenging

A longer rod is moving slower at TDC, which reduces the speed of the exhaust gasses during the overlap period. This reduces the scavenging effect at low rpm and reduces low rpm power slightly (makes the engine run more cammie). A short rod on the other hand moves faster past TDC and increases the scavenging effect and help low rpm power.

Ignition Timing Requirements

Due to the fact that the longer rod moves past TDC slower, it gives the charge a longer time to burn. So you need less timing for peak power. Using less timing also reduces the chance of detonation; so higher compression ratios can be used. Switching from 5.7" to 6" rods on a 350 Chevy can allow as much as 1 full point increase in compression. In other words, if you could only run 9.5:1 with 5.7" rods, you could run 9.6:1 with 6" rods.


Longer Rod Pros

Less rod angularity
Higher wrist pin location
Helps resist detonation
A lighter reciprocating assembly
Reduced piston rock
Better leverage on the crank for a longer time
Less ignition timing is required
Allow slightly more compression to be used before detonation is a problem
Less average and peak piston velocity
Peak piston velocity is later in the down stroke
Less intake runner volume is needed

Longer Rod Cons


Closer Piston-to-valve clearances
Makes the engine run a little more cammie at low rpm
Reduces scavenging at low rpm

Shorter Rod Pros


Increased scavenging effect at low rpm
Helps flow at low valve lifts (a benefit if the heads are ported with this in mind)
Slower piston speeds near BDC
Allows the intake valve to be open longer with less reversion
More piston-to-valve clearance
Can allow for a shorter deck height

Shorter Rod Cons


More rod angularity
Lower piston pin height (if the deck is not shorter)
Taller and heavier pistons are required (again, if the deck height is not reduced)
More ignition timing is required for peak power

some of this must be attributed to grape ape racing...

... and now i figured it was time to practice what i preach...
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Old 01-29-2004, 02:48 PM
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The rod stroke ratio, due to dwell time, also determines cam timing events.. . .critical in making power.

Chris

PS, deuce you remind me of someone I use to correspond with years ago, his name was Jesper and he was a tech on a camaro board.
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Old 01-30-2004, 06:02 AM
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rod ratios

I hesitate to write this because i am new to the site and i know that know one knows me. I enjoy good discussions on this typ of stuff.

Deuce what are your dyno results from the trial and error of testing this theory???? How much hp increase did you see between a 6.135" rod and a 6.535" rod.

I saw a chart on the difference between a 5.7 rod and a 6.0 rod sbc. The most difference anywhere in the piston from tdc was like.018 I can't believe that you can make big hp numbers with this change.

cstraub???

Give me your figures in cam timing events that are different between a 5.7 rod to a 6.0 rod,, And the hp/torque gain....
Did you find that the motor like a intake event that was advanced or retarded with the increased dwell time???? What did you do to compensate for the change that this will make to the exhaust events????

keith
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Old 01-30-2004, 07:40 AM
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Keith,
I cam engines on an individual engine combination. So each is different depending on the combination, power band needed, and components being used. I do "TRUE" custom cams. During the process of coming up with a profile rod length will effect opening and closing of of both intake and exhaust. With this said it there is a direct correlation to cylinder head flow, "how good is the head". The events are also affected by this so both have to taken into account. I have found a good set of heads with a long rod will take an intake opening later to make more power.

Chris
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Old 01-30-2004, 08:04 AM
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It has been my experience that a long rod engine does make a slight bit more horespower, but only in a maximum power drag race application. The longer dwell time at (and near) TDC is a positive influence on ignition advance, cylinder scavenging and cylinder filling.
As Chris has pointed out, a long rod is not beneficial unless the cam is designed to take advantage of the longer dwell at, and near TDC. And there is not a specific formula to determine the cam needed in a log rod engine. Best procedure is to graph the piston travel per crankshaft degree and design a cam with timing events that will work with maxiumum piston velocities. Long rod engine performance is also effected by intake runner shape and length as well as header design (especially the length of primary tubes and collector).
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Old 01-30-2004, 08:56 AM
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valve events

cstraub,

Let say that you have motor "x' It has a rod length of 5.7" the cam events were custom ground for this motor. Pick a horse power level of your choice........

Then you change the rod length to a 6.0" rod and everything else is exactly the same,compression,head flow, intake,exhaust ect,ect. (lets forget about the additional weight caused by the longer rod and say the bob weight stayed the same) Also that you can get the ring package the same.You get another cam custom ground For the change in dwell that the 6" rod created.

what will the hp/ torque increase be?????
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Old 01-30-2004, 09:03 AM
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None, if the camshaft is specific to the combo. I think I see in my statement where you are coming from...I then should have said a short rod engine with good heads tends to take more advance in intake opening.

Chris
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Old 01-30-2004, 10:06 AM
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i am running an enderle 8-stack injection system. 2-7/16 inch butterflies, The manifold is converted to EFI. The stacks are angled and have full bell (not siamesed crap...) the runnerlength from valve to stack mouth is 13,7 inches (which puts the 2 nd. order resonance frequency right around 5000 rpm)


My headers are 1-7/8. between 32 and 36 inch primaries (i know they are on the small side, and ideally i should run 34 inch long 2 inch promarise with a merge collector... but i havent gathered the currage to weld them up yet.... next winter perhaps.

the headers are going to exit paralelly at 30 inches so i can shorten and lengthen the primary lenght just by changing slip on tubes between collectoe and header. the intake bells can be changed from 10 to 15 inches (i have a set of 9,8 inch 13,7 inch and 15,1 inch stacks- but the short and long ones are paralell/ siamesed)

Im running 11.5:1 compression and would like the long rods to stay out ff detonation with aluminum head and 98 octane

BTW Chris how does this cam sound...?

the cam is Intake: .782 lift IVO 31 deg. BTDC, IVC 67 deg. ABDC, Exhaust: lift .720 EVO 67 deg. BBDC, EVC 31 deg. ATDC
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