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Tom Molnar rod response

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kidgrem View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kidgrem Quote  Post ReplyReply Direct Link To This Post Topic: Tom Molnar rod response
    Posted: Jun/13/2014 at 6:40pm
Since I am flipping the rods and they will be on center I should be good to.
These rods are tiny compared to the scats. Twenty one Quarters (money) lighter.


Hi Gary,

I'm not worried about our rod handling the power in a Chevy engine but this being in an AMC engine puts a whole different set of variables into the mix.  The beam offset requirements for a Chevy rod is completely different than what is needed in an AMC block.  To get the beam of the rod centered in the cylinder bore on a Chevy, the beam is moved away from the cheek of the crank and to get it centered in an AMC block it needs to be moved closer to the cheek of the crank.  While a Chevy rod will fit in your application and if you read on the internet it will be fine (there are lots of people who think they are "experts" on the forums), what really happens is the beam of the rod ends up not being under the center of the piston.  The way I explain this to people is you can balance a dinner plate on a wooden dowel but if you move the dowel off center, the plate falls off.  If the rod is not centered in the bore, the piston wants to tilt slightly on the power stroke which not only side loads the rod and over time can cause fatigue fail of the rod, it also upsets the ring seal and will cause a lower power output.  I have had people tell me when they replaced Chevy rods in their Ford blocks with a Ford correct rod that we build, they picked up as much as 30 HP.

Thank you,

Tom Molnar
Molnar Technologies



On Thu, Jun 12, 2014 at 11:56  kidgrem> wrote:
CH6000LLB8-A    Chevy Small Journal     6.000   606     7/16    2.125   0.927   0.940   1.010

I have a AMC With small journal  SBC 6.00" Scat rods with a 3.850 stroke and a 778 gram piston, ring and pin combo. 10.7 compression.
The scat rods weigh 734 grams.
The engine makes 620 HP. Will the CH6000LLB8-A handle the HP if I switch to your  lighter rod.  
How about  if I use a 200 HP shot of nitrous.
Thank`s  Gary
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tsanchez View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tsanchez Quote  Post ReplyReply Direct Link To This Post Posted: Jun/13/2014 at 6:57pm
Great then he should make a stroker rod for us then. Until then this is what we do.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dbomb Quote  Post ReplyReply Direct Link To This Post Posted: Jun/13/2014 at 9:55pm
good post both ways
rebuiling 73 amx need parts
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SKeown Quote  Post ReplyReply Direct Link To This Post Posted: Jun/13/2014 at 10:37pm
Originally posted by kidgrem kidgrem wrote:

Since I am flipping the rods and they will be on center I should be good to.
These rods are tiny compared to the scats. Twenty one Quarters (money) lighter.


Hi Gary,

I'm not worried about our rod handling the power in a Chevy engine but this being in an AMC engine puts a whole different set of variables into the mix.  The beam offset requirements for a Chevy rod is completely different than what is needed in an AMC block.  To get the beam of the rod centered in the cylinder bore on a Chevy, the beam is moved away from the cheek of the crank and to get it centered in an AMC block it needs to be moved closer to the cheek of the crank.  While a Chevy rod will fit in your application and if you read on the internet it will be fine (there are lots of people who think they are "experts" on the forums), what really happens is the beam of the rod ends up not being under the center of the piston.  The way I explain this to people is you can balance a dinner plate on a wooden dowel but if you move the dowel off center, the plate falls off.  If the rod is not centered in the bore, the piston wants to tilt slightly on the power stroke which not only side loads the rod and over time can cause fatigue fail of the rod, it also upsets the ring seal and will cause a lower power output.  I have had people tell me when they replaced Chevy rods in their Ford blocks with a Ford correct rod that we build, they picked up as much as 30 HP.

Thank you,

Tom Molnar
Molnar Technologies



On Thu, Jun 12, 2014 at 11:56  kidgrem> wrote:
CH6000LLB8-A    Chevy Small Journal     6.000   606     7/16    2.125   0.927   0.940   1.010

I have a AMC With small journal  SBC 6.00" Scat rods with a 3.850 stroke and a 778 gram piston, ring and pin combo. 10.7 compression.
The scat rods weigh 734 grams.
The engine makes 620 HP. Will the CH6000LLB8-A handle the HP if I switch to your  lighter rod.  
How about  if I use a 200 HP shot of nitrous.
Thank`s  Gary

 First off, I'm a firm believer in the need to center the rod on the wrist pin. Personally I use Carrillo Chevy LS 6" rods for 2" journals with an offset ground 3.925" stroke. With the LS rods that are center beam instead of being offset in either direction, I just have .010 removed from the chamfered side of the rods. That does a pretty good job of centering them. 

 There's a member on this forum that was breaking I-beam Lunati rods due to not having the rods centered, they were breaking just below the piston pin bore. I saw evidence of the piston canting at the top of the stroke as well as the power stroke. I was running very tight piston to head clearance and the pistons were touching on the least supported side only.

 If you have no choice other than resorting to std Chevy rods you can remove .010 from the non chamfered side, then have that side chamfered and reverse them.

 Power isn't what brakes rods, power will bend them (as in my Jr fuel dragster, back when we ran nitro instead of alcohol like today) RPM, piston weight and stroke length is what brakes rods/bolts on the exhaust stroke when there isn't any resistance to keep the piston from heading north. With good 7/16" bolts you should be okay. I have 3/8" SPS Carr bolts and my engine has seen over 7500 RPM with 515 gm pistons and a 3.925" stroke.

 



Edited by SKeown - Jun/13/2014 at 11:02pm
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Post Options Post Options   Thanks (1) Thanks(1)   Quote stickshifter Quote  Post ReplyReply Direct Link To This Post Posted: Jun/13/2014 at 10:56pm
Wink
   7.03 @ 196 mph
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kidgrem Quote  Post ReplyReply Direct Link To This Post Posted: Jun/13/2014 at 10:56pm

Gary,

Yes flipping the rod puts the beam very close to where it needs to be. I am not sure what bearing you would use to clear. The new bearings from Clevite are narrow and unchamfered but they are still close to the non chamfered side of the rod. If the crank has a fillet radius in the corner it may hit the bearing unless it is modified with a chamfer. If the crank does not have a fillet radius, it will not be as strong as one with a radius. If you are willing to go through the extra work (or pay someone else to do it) our rod will work. I would not recommend the 500 gram lightweight version.

Thank you,

Tom

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SKeown Quote  Post ReplyReply Direct Link To This Post Posted: Jun/13/2014 at 11:14pm
Originally posted by tsanchez tsanchez wrote:

Great then he should make a stroker rod for us then. Until then this is what we do.

 Tom Molnar was originally the designer for Oliver rods. 30 HP, maybe that's how I overcame you're dual carb setup? Confused 

 SKeown
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tsanchez Quote  Post ReplyReply Direct Link To This Post Posted: Jun/14/2014 at 12:08am
My pistons are full skirted, no issues there. My issue is converter
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurst390 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/14/2014 at 7:36am
Kidgrem..have you balanced that assy yet and is it internally balanced?
SC/Hurst Rambler

11.62 120

100% Street Legal
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BassBoat Quote  Post ReplyReply Direct Link To This Post Posted: Jun/14/2014 at 10:18am
When I reversed the SBC rods, had the big end chamferred to make sure they didn't get into the radius to the crank, also chamfered the rod bearings as well.  When Tom Molnar worked for K1 I bought stroker rods from him, which as far as I know are still available from K1 in 6.000 and 6.125 length, with correct offset for AMC and for use with 2.100 rod journal and 0.927 piston pin.  
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