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Old 11-11-2019, 01:13 PM   #1
Rubberduck406
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Default 400 Rod Length Advice needed

New build for a bracket car. Little M block, Callies 3.75" Compstar crank, Pro Topline 23* 210cc CNC'd heads on alcohol. 3000lb ladder bar car, transbrake, typically turned under 7000 rpm.

Haven't bought rods or pistons yet and am torn between going with a 6" rod or a 6.125" rod (either length will be a Callies Compstar). Will it be more "efficient" with the longer rod or will I even see a difference in this particular application? Shooting for 13-14:1 compression if that makes a difference.
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Old 11-11-2019, 03:43 PM   #2
ColeBalster
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Default Re: 400 Rod Length Advice needed

I really don't think you'll see a difference.

My choice would be the 6.000" simply for a little less pin height, which would leave more room for the rings/valve reliefs and have a little better stability.

I have the Wiseco "Lil Quick 16" pistons in my 18 degree 406 (4.155" x 3.75" with 6.000" rods and their recommended .043" x .043" x 3.0mm rings).
I also had them change from lateral to vertical gas ports, which they did for no charge.

They offer a hollow dome 23 degree piston in the same design. p/n K0033B3 for 4.155" x 3.75" x 6.000", and rings p/n JG7708-4155-5 .043" x .043" x 3.0mm.
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Last edited by ColeBalster; 11-11-2019 at 03:47 PM.
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Old 11-11-2019, 04:51 PM   #3
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Default Re: 400 Rod Length Advice needed

6.00 in my book, I don't care for the ring stack with longer than a 6.00 on 3.750 and above strokes.
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Old 11-11-2019, 04:59 PM   #4
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Default Re: 400 Rod Length Advice needed

I have built them both ways they seem to run good with either rod.
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Old 11-11-2019, 07:17 PM   #5
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Default Re: 400 Rod Length Advice needed

X2 ---> 6" rod, least at compromising the ring stack and .043 / .043 / 3mm ring package.
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Old 11-11-2019, 08:46 PM   #6
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Default Re: 400 Rod Length Advice needed

Me, and all my friends running a 400-type block, all use 6" rods, except for one, my buddy with a tall deck block is using a longer rod.
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Old 11-12-2019, 08:38 AM   #7
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Default Re: 400 Rod Length Advice needed

6” rod. If you’re running a vac pump, .9mm/.9mm 2.5mm ring pack. It will give you some room between the ring lands for an expansion groove.
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Old 11-12-2019, 06:01 PM   #8
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Default Re: 400 Rod Length Advice needed

Mahle makes a piston for a 6" rod that'll put me close to 14:1, they're a 1mm, 1mm, 2mm pack. Engine builder has the same piston in the older style that's a 1.5mm, 1.5mm, 3mm pack. Leaning towards the older style with the thicker rings.
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Old 11-12-2019, 06:07 PM   #9
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Default Re: 400 Rod Length Advice needed

Quote:
Originally Posted by Rubberduck406 View Post
Mahle makes a piston for a 6" rod that'll put me close to 14:1, they're a 1mm, 1mm, 2mm pack. Engine builder has the same piston in the older style that's a 1.5mm, 1.5mm, 3mm pack. Leaning towards the older style with the thicker rings.
You are here asking questions for a reason. You may want to re-think that choice. There is a reason that modern pistons have narrower rings. Just saying.
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Old 11-12-2019, 09:30 PM   #10
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Default Re: 400 Rod Length Advice needed

Quote:
Originally Posted by Rubberduck406 View Post
Mahle makes a piston for a 6" rod that'll put me close to 14:1, they're a 1mm, 1mm, 2mm pack. Engine builder has the same piston in the older style that's a 1.5mm, 1.5mm, 3mm pack. Leaning towards the older style with the thicker rings.
Use the Mahle piston with the 1mm rings you will be better off.
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Old 11-14-2019, 12:15 AM   #11
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Default Re: 400 Rod Length Advice needed

i had crower 6.125 had to run .900 base circle cam to clear with cutting on rods, callies has a XD rod with the bolts canted for more clearance to run a standard base circle cam id run a xd 6.oo rod so my valve train would be more stable with a larger base circle cam. would depend how many rpm you would like to turn for how important your cam base circle is
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Old 11-14-2019, 12:24 AM   #12
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Default Re: 400 Rod Length Advice needed

*clear with out cutting rods. and yours should live forever @ 7k rpm
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Old 11-14-2019, 10:28 PM   #13
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Default Re: 400 Rod Length Advice needed

Rod length for a bracket type engine is not critical, I would go with the 6.00" with 1.0mm, 1.0mm, 2.0mm MAHLE ring pack OR 1.2mm, 1.2mm, 3.0mm ring package.

For a high RPM maximum effort drag race engine, I would go with the longer rod. Remember though, in order to get the optimum results with the long rods, the camshaft needs to be designed to take advantage of the increased piston dwell time at TDC.
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