Connecting rod questions

[Pablo]

How much do factory connecting rods + caps + bolts + std bearing weigh typically?

What is the typical weight of the small end of rod, and the big end + bolts + std bearing?

How well are they balanced to each other from the factory? I'm asking about the balance between total weight, and the balance between them for the small ends and the big ends.

How much weight can realistically be removed from the balance pads without weakening the rod if you were looking to lighten the rod?

If you can answer any of these questions I will be grateful.

Thanks.

 

[turbofabricator]

Sorry Pablo, but I don't haver the info you asked for, BUT......the only reason to lighten the factory rods is to allow higher RPM. With the cost of K1 rods, DITCH the factory stuff as they WILL bend if abused too much. They will live fine in a mid ten second car (and even faster) but, they bend pretty easy at that power level if they encounter detonation. K1 or better is what you will need to turn the engine much past 6000. Just my opinion.

 

[Pablo]

Sorry Pablo, but I don't haver the info you asked for, BUT......the only reason to lighten the factory rods is to allow higher RPM. With the cost of K1 rods, DITCH the factory stuff as they WILL bend if abused too much. They will live fine in a mid ten second car (and even faster) but, they bend pretty easy at that power level if they encounter detonation. K1 or better is what you will need to turn the engine much past 6000. Just my opinion.

Thanks for the reply turbofab,

Actually the reason I wanted to lighten the factory rods was to increase the balance %. Based upon some rough math estimates I have made, just using the stock pin in place of the TRW pin will bring my balance up close to 40% without having to add expensive mallory to the crank.

Based upon a lot of the research I have done I think a 50% or higher balance is preferable with these engines vs 36.6%. I guess an added side benefit to having lighter rods and pistons is more rpm capability and better acceleration. Mostly I want to minimize any lateral or torsional stresses the crank is seeing.

Another thing I was considering was simply skipping the balancing and saving money. If the factory rods and pistons are all pretty close tolerance then I don't completely see the benefit of balancing the assembly if I were to just put on lighter rods/pistons within the same tolerance as the factory stuff.

The only thing I'm wondering really is how out of balance the crank is from the factory. It would seem to me that if I got all the rods and piston combos really close then the only out of balance would be from the crank, flexplate, and balancer. The fact that they are lighter would only move my balance % higher which I want anyway.

Any thoughts on this? I also wanted to go with a BHJ damper and either verify that it has the same balance as the stock balancer or balance it to the stock balancer as an alternative (if it was significantly cheaper than balancing the whole assembly)
After dealing with the machine shop I've concluded that the less work I farm out to a machine shop the less chance I have for them screwing it up. I really hate having people do work for me, and furthermore the guys that are going to understand what I want to do are going to charge an arm and a leg vs the cheap guys that look at me like I am crazy.

 

[charlief1]

BALANCE THE WHOLE ASSEMBLY!! I'm cheap to but putting 1, 2, or 3K in an engine and having it vibrate apart is heart breaking. I did an NA buick in the 80's when most shops couldn't balance a buick 6 and I had hell. The mains and rods wore faster and I cracked a timing cover. I was road racing the car and I tore it down several times to fix what broke. I could get the engine out in 30 min by the time I gave up on the car.

 

[A2000RICH]

How much do factory connecting rods + caps + bolts + std bearing weigh typically?

What is the typical weight of the small end of rod, and the big end + bolts + std bearing?

How well are they balanced to each other from the factory? I'm asking about the balance between total weight, and the balance between them for the small ends and the big ends.

How much weight can realistically be removed from the balance pads without weakening the rod if you were looking to lighten the rod?

If you can answer any of these questions I will be grateful.

Thanks.

86/87 pistons are about 640 without pins------87 pistons tend to be a few grams heavier due to the different design-----both range about 792 with pins that are about 153----stock rings are about 40------rod brgs are 33 (std)------rod big end with brgs is about 1,260------sorry but i forgot to look up the total rod weight------if i remember tomorrow i'll look it up-------are they close????yes for mid 80 production tolerances--------would never pass in todays market-------and should never be considered for a performance engine without a good balance-------i grabbed three rods at random out of a box at the shop tonight and they measured 1,258-1,261 and 1,262------its really a small effort to get them to within 1 gram------flywheels are even farther off as are cranks and balancers-------a while back i did a really close balance and when i had it perfect before i removed it from the balancer all I did was swap balancers------i made no changes except go through a dozen units picked at random from a large selection------the variation was quite a bit...............RC

 

[turbofabricator]

Cheap and Buick are not two words to be used in the same week. If you want to use TRW pistons, use a high quality tool steel taper wall pin from Ferrea or JE, ect. That will gain you alot. (I run them in my engine). If you are just going to re-ring, do so as is. No sense balancing an engine that rarely sees the high side of 5,800 rpm. The BHJ balancer is a waste of money if you are running 11.0 or slower. Most aftermarket balancers are "tuned" to around 7,000 RPM. Some work good (ATI), some work VERY poor (Fluid Dampner) At certain RPM's a balancer can hurt the crank. Don't over think it. Lots of guys running 10's with stock internals. Set you desired ET/MPH goal and build it to suit. Search speedtalk.com for balancers and it will amaze you. Lots of good info there.

 

[Pablo]

Rich,

Thank you for the information. That is going to come in handy.


Turbofab,

Is there anything specifically wrong with using the stock pins with the TRW pistons? I've never heard of anyone breaking one.

I'm shooting for low tens. I was already most likely running sub 7.2s in the 1/8th with a completely stock long block. I never managed to run the number quicker than my sig though. After getting it to that level I decided to race the car in extreme heat (95 deg) and blew an HG, coasted to a 7.3 first pass. Used that as an excuse to pull it and refresh. I'm not worried about making the power, I'm worried about holding it together. H/c should make that within reach i think
This is why I have really been looking at what seems to break on these engines and addressing those issues specifically. The damper topic you mention is really fascinating (ill have to look at the speedtalk posts) and that
is one thing I think may be contributing to crank flex. I tried to get torsional vibration test data from BHJ for the buick V6 but I got ignored. That would be neat to see, a stock 350 has significant twisting action without a damper. Wonder what a hot lc2 looks like.
I would prefer to keep eng rpm under 5500 as well to help keep flexing of stuff under control.

So to sum up my total digression into another topic, I think (key word, think... if I'm being retarded please feel free to say so) that with a 4 prong attack - 5500 rpm limit, girdle, 50% balance, damper- I will significantly reduce crank flex and main cap movement. I guess a 5th prong would be to go internal balance but thats a big money jump.

Anyway I really value the input, any further input would be welcome!

 

[ijames]

Pablo, if you are most worried about crank flex I know it may not be in the budget but going to a forged crank will cut the flex in half compared to the cast iron crank - 4340 steel is twice as stiff as cast iron so it flexes half as much for the same applied force. That has got to be easier on the main caps and webbing. If you could find a Cat or Eagle, then just get internal balance BHJ and flexplate (same price as external balance and you were going to buy them anyway, right ?). Or, I think Nick Micale still has some of the Eagle cranks already machined for external balance.

 

[turbofabricator]

I agree with Carl, above. Main caps failure is probably caused more by crank flex, than weak caps. Talk with Dan Strezo (DLS) about this, too. He can set you up with a stroker kit, and then you would gain a BUNCH on torque, especially at your target 5500 rpm.

P.S. You ARE being retarded. You're trying to race a Buick V6. Everyone knows you can't go fast with a V6.

 

[49-blues]

Pablo- have you received the girdle yet?

 

[charlief1]

Since you have it out of the car, I'd go ahead and redrill the main feed oil holes for better oil to the bottom and radius all of the corners throughout the oil passeges. Cheap but helps. A good deburring of the valley would be a good idea too. If you can afford it I'd go ahead and put billet caps in at the same time. Not cheap but helps keep mains from breaking/walking.

 

[Pablo]

Thanks for the tip charlie, Ill have to look into that.

Thanks for the suggestions on parts guys but I am trying to keep this a budget build up. :wink:

 

[A2000RICH]

86/87 pistons are about 640 without pins------87 pistons tend to be a few grams heavier due to the different design-----both range about 792 with pins that are about 153----stock rings are about 40------rod brgs are 33 (std)------rod big end with brgs is about 1,260------sorry but i forgot to look up the total rod weight------if i remember tomorrow i'll look it up-------are they close????yes for mid 80 production tolerances--------would never pass in todays market-------and should never be considered for a performance engine without a good balance-------i grabbed three rods at random out of a box at the shop tonight and they measured 1,258-1,261 and 1,262------its really a small effort to get them to within 1 gram------flywheels are even farther off as are cranks and balancers-------a while back i did a really close balance and when i had it perfect before i removed it from the balancer all I did was swap balancers------i made no changes except go through a dozen units picked at random from a large selection------the variation was quite a bit...............RC

pablo-----sorry but i must have been using a NASA calculator when i posted the above numbers-------the TOTAL weight of the rods minus bearing shells is about (three at random) 700-695-692--------big end measured 490-496-488-------2481F pistons measured 567 no pin-----721 with pin------the trw pins are within a couple grams of the stock pins so why not use them???the TRW pins tend to be a couple tenths larger than the stock ones -----the stock ones tend to fit a little loose in the TRW pistons...........RC

 

[Pablo]

pablo-----sorry but i must have been using a NASA calculator when i posted the above numbers-------the TOTAL weight of the rods minus bearing shells is about (three at random) 700-695-692--------big end measured 490-496-488-------2481F pistons measured 567 no pin-----721 with pin------the trw pins are within a couple grams of the stock pins so why not use them???the TRW pins tend to be a couple tenths larger than the stock ones -----the stock ones tend to fit a little loose in the TRW pistons...........RC

The pins that came with my trw pistons are way heavier than the stock pins. I think they are about 65 grams more. Maybe I got an older set of trws, I read they started coming with lighter pins.

 

[A2000RICH]

The pins that came with my trw pistons are way heavier than the stock pins. I think they are about 65 grams more. Maybe I got an older set of trws, I read they started coming with lighter pins.

there was a time when they came with heavy pins that put the piston/pin combo near the factory piston/pin weight------but i haven't seen any of them for several years-----maybe stock from a supplier with slow moving inventory........RC

 

[Pablo]

Probably. I got them off ebay for a very very good price.

 

[A2000RICH]

Probably. I got them off ebay for a very very good price.

i checked out my stock of those pistons-----i still have a few of the "old" ones with the heavy pins-----in my inventory the heavy ones are in printed black and blue boxes with a picture of a car on the top-------the lighter ones are in plain white boxes with a pasted on sticker for labeling-------they have inner holes of .375 vs .590 in the lighter (later) ones------they weigh 215 g -------this puts the piston/pin weight really close (about 10g) to that of a stock piston ------what this means is that you could really use them without rebalancing the crank, balancer, flywheel-------thats what was probably originally intended------ most guys want to take advantage of the lighter weight of the newer design but it does have to be rebalanced.............RC

 

[Pablo]

Yep those are the ones i have, the pins are exactly 215 grams.

I'd still like to use the lighter stock pins, still can't seem to find a reason not to since all it would do is increase the balance factor %

 

[charlief1]

I'll give you onw to think about pablo. A 6.65" carrillo rod with a ross piston and the pch at 1.247 in a 4.1 bored to 4". How's that for a kinky combo.