Connecting rod length options

[ShaunDonWe2]

I'm going with a custom piston if need be, what are my rod length options that are available out there? I see different lengths rods and want to know what to stay away from longer versus shorter for stock stroke crank thanks


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[dank GN]

Well if you are going with a custom piston you can have a rod length up and to 6.500 . I'm sure you could go alil bigger but the most common rod lengths are . 5.940,6.350,6.500

 

[earlbrown]

What crank are you going to run? Both stroke and journal size. That's what will limit your rod choices.

 

[ShaunDonWe2]

Ive got an cat 3.400 stock stroke and I'm pretty sure its the narrow journal crank, would like to stroke but if its no gain I'll pass.


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[earlbrown]

So you will need rods made for a Buck application since you're running a journals that are Buick sized.


With a stock stroke you can go up to 6.500 with no problem (if anyone actually makes a Buick rod that long).

Also, pay attention to the diameter on the little end. Standard Buick is 940 while SBC is 927.

 

[ShaunDonWe2]

So you will need rods made for a Buck application since you're running a journals that are Buick sized.


With a stock stroke you can go up to 6.500 with no problem (if anyone actually makes a Buick rod that long).

Also, pay attention to the diameter on the little end. Standard Buick is 940 while SBC is 927.

Ok thanks for the info, I'll be looking for rods then I will order custom Pistons


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[dank GN]

Talk to earl about a custom slug he knows what's up . Just got my beautiful slugs from him

 

[ShaunDonWe2]

Talk to earl about a custom slug he knows what's up . Just got my beautiful slugs from him

What brand are those nice[emoji106]


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[dank GN]

Race tec made them to earls custom specs

 

[750H.P.V6]

I'd keep it simple and use a stock length rod. That way you don't have to order custom pistons.

Neal

 

[ShaunDonWe2]

I'd keep it simple and use a stock length rod. That way you don't have to order custom pistons.

Neal

I wanted to try for an higher compression 9:5:1 or maybe higher. I have a gn1 aluminum heads and my deck height is 9.240 I think, also plan on using 0.60 cometics. I don't know where compression would be just trying something new.


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[dank GN]

lol compression isn't just some shoot from the hip thing . You have to know your deck hight . And you adjust the variables to get the compression you want . So I would have your machinest measure the DH and the cylinder head CCs . From those numbers you adjust your head gasket thickness to achieve your compression goal. If you can't get there with the head gasket u can then look at different piston dish volumes and port out your heads to get more CCs . But it definitely isn't something to just guess .

 

[TURBOELKY]

I wanted to try for an higher compression 9:5:1 or maybe higher. I have a gn1 aluminum heads and my deck height is 9.240 I think, also plan on using 0.60 cometics. I don't know where compression would be just trying something new.


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If you have a 109 block, your deck height from factory is a little over 9.5". If you're at 9.240, there was a lot of material removed. I don't think a 6.5" rod would be an option. Just stick to stock stroke stock rod and an off the shelf piston and rings. Put the money you save on machine work towards cylinder heads and a roller cam.

And as mentioned above, let your machinist do all the measuring.

 

[750H.P.V6]

I think Dave Roland mistakenly quoted the stock deck height as 9.240" in a recent post. That is probably where the confusion came in. Jeremy is right that the deck height should be just over 9.500". If memory serves me correctly I think it is 9.525" on a '86-87 block and 9.540" on the earlier blocks. You more than likely want to take a little off the deck to make sure it is flat and square. At that point you can have the machinist verify the actual #. If you do want 9.5 to I compression I'd still suggest going with a stock length rod and order up a custom piston with a smaller dish.

Neal

 

[ShaunDonWe2]

lol compression isn't just some shoot from the hip thing . You have to know your deck hight . And you adjust the variables to get the compression you want . So I would have your machinest measure the DH and the cylinder head CCs . From those numbers you adjust your head gasket thickness to achieve your compression goal. If you can't get there with the head gasket u can then look at different piston dish volumes and port out your heads to get more CCs . But it definitely isn't something to just guess .

True! I just got my block back from the machine shop I gotta look to see what he wrote on my receipt I'm pretty sure that number was off. Just gathering info so I'll know where to start on this build


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[ShaunDonWe2]

If you have a 109 block, your deck height from factory is a little over 9.5". If you're at 9.240, there was a lot of material removed. I don't think a 6.5" rod would be an option. Just stick to stock stroke stock rod and an off the shelf piston and rings. Put the money you save on machine work towards cylinder heads and a roller cam.

And as mentioned above, let your machinist do all the measuring.

Thank you, Ive got heads and a smaller roller cam which I want to upgrade to something a Lil bigger. I appreciate the advice and replies as I am still learning certain things


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[TURBOELKY]

Thank you, Ive got heads and a smaller roller cam which I want to upgrade to something a Lil bigger. I appreciate the advice and replies as I am still learning certain things


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We're all always learning around here
Tons of info on this forum and members like Neal, they know their stuff

 

[ShaunDonWe2]

We're all always learning around here
Tons of info on this forum and members like Neal, they know their stuff

Greatly appreciated [emoji817]


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[earlbrown]

I wanted to try for an higher compression 9:5:1 or maybe higher. I have a gn1 aluminum heads and my deck height is 9.240 I think, also plan on using 0.60 cometics. I don't know where compression would be just trying something new.


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If you're wanting to run gaskets that thick I'd stick with composite gaskets unless you've done ALL the nessessary machining.


In order to run Cometics effectively, you HAVE to deck the block SMOOTH SMOOTH SMOOTH, and same with the heads. Studs are also highly recommend. In my case I fillet the gaskets open, copper coat the hell of of them. Smear Yamabond around the water ports, then toss a GM seal tab in the waterjacket.

That method has allowed me to seal so well I could bust Federal Mogul pistons at the drop of a hat with no leakage.


If your deck and heads aren't machined and machined right (by somebody that gives a crap about their work), it just flat out won't work.

 

[gunzandgearz]

If you know what compression your shooting for and you've already had the block work done your kind of going backwards.The way to go about it is to cc the cylinder head chamber, then measure the deck height either with a 12 inch dial caliper or have your machinest measure it for you.These are the variables that you have to know,now you can get the exact compression ratio and quench area(I shoot for .040 on this with every engine I build)although.035 to.045 will get you right there.the rest of the measurements rod length,piston deck height,valve reliefs or dish volume ,and head gasket compressed thickness can all be gotten from the manufacturer and from here it's just a math formula.Remember what earl said about getting a good machinest as good ones are getting tough to find these days.Good luck with your project.