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gimmesomeshelter Samba Member
Joined: May 08, 2004 Posts: 1468 Location: San Carlos, CA
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Posted: Wed May 14, 2008 4:37 pm Post subject: Rod choices for oldspeed engine |
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Hello-
I’m trying to figure out which connecting rods would be ‘best’ (I’m willing to pay for durability and performance, but only if I need to) for an ‘oldspeed’ engine with a 74mm Porsche crank and Okrasa heads. I would imagine that this engine will rarely see 5000 RPM.
Are Porsche 912 rods a good choice? Given my relatively low RPM ceiling, would the any of the $1000+ rods give me that much in terms of performance (low weight) or durability? Are there other rods I should consider?
Thanks,
Paul _________________ "I would rather have questions that can't be answered than answers that can't be questioned."
Richard Feynman |
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Bengt H Samba Member
Joined: September 11, 2005 Posts: 332 Location: Sweden
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Posted: Thu May 15, 2008 12:34 am Post subject: |
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I think any Porsche 356 rod will do the job, what cylinders/pistons are you going to use? |
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commercial air Samba Member
Joined: July 19, 2005 Posts: 230 Location: Driving in the crumple zone...Regina, Saskatchewan, Canada
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Posted: Thu May 15, 2008 8:15 am Post subject: |
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With the 72mm crank that I'm using, I chose to go with stock 36hp rods and ARP bolts. However, I opted to spend the money on custom JE pistons. One thing to consider is rod cap clearance past the cam lobes. I have to radius the rods to clear. The Porsche rods may have enough clearance right out of the box?
Chris _________________ Northern United Transporter Society
www.nuts.commercial-air.com |
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gimmesomeshelter Samba Member
Joined: May 08, 2004 Posts: 1468 Location: San Carlos, CA
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Posted: Thu May 15, 2008 9:31 am Post subject: |
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Hello-
At this point I'm thinking of using custom made 77mm stroker pistons. Larger pistons sound appealing, but I haven't worked out the math to see what the limits of the heads and carbs are.
Paul _________________ "I would rather have questions that can't be answered than answers that can't be questioned."
Richard Feynman |
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Bengt H Samba Member
Joined: September 11, 2005 Posts: 332 Location: Sweden
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Posted: Thu May 15, 2008 3:27 pm Post subject: |
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Porsche rods cleares the cam in original. |
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Bengt H Samba Member
Joined: September 11, 2005 Posts: 332 Location: Sweden
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Posted: Thu May 15, 2008 3:32 pm Post subject: |
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gimmesomeshelter wrote: |
Hello-
At this point I'm thinking of using custom made 77mm stroker pistons. Larger pistons sound appealing, but I haven't worked out the math to see what the limits of the heads and carbs are.
Paul |
I used Mazda 323 pistons in 77,5 mm cylinders together with Porsche crank and rod.
I dont know the limit for heads and carbs but 83mm is no problem, you can read a lot of this in the "36 hp dragracing" thread |
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77ducci Samba Beer Head
Joined: March 07, 2002 Posts: 408 Location: Gathering the Missing Parts
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Posted: Thu May 15, 2008 3:33 pm Post subject: |
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commercial air wrote: |
With the 72mm crank that I'm using, I chose to go with stock 36hp rods and ARP bolts. However, I opted to spend the money on custom JE pistons. One thing to consider is rod cap clearance past the cam lobes. I have to radius the rods to clear. The Porsche rods may have enough clearance right out of the box?
Chris |
That was my same combination 72mm crank and stock 36hp rods. I was told there is not that much that needs to be clearanced (I could be wrong) and that you could degree your cam to gain some additional clearance as well. |
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commercial air Samba Member
Joined: July 19, 2005 Posts: 230 Location: Driving in the crumple zone...Regina, Saskatchewan, Canada
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Posted: Thu May 15, 2008 11:14 pm Post subject: |
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77ducci wrote: |
commercial air wrote: |
With the 72mm crank that I'm using, I chose to go with stock 36hp rods and ARP bolts. However, I opted to spend the money on custom JE pistons. One thing to consider is rod cap clearance past the cam lobes. I have to radius the rods to clear. The Porsche rods may have enough clearance right out of the box?
Chris |
That was my same combination 72mm crank and stock 36hp rods. I was told there is not that much that needs to be clearanced (I could be wrong) and that you could degree your cam to gain some additional clearance as well. |
The ARP bolts help a lot too. The smaller multi-point head helps get past the cam. There is plenty of room in the case for a 72mm crank without clearancing. Radiusing the caps seems to do the trick to get past the lobes. I now see the benifit to using Porsche though and skipping this step all together.
Chris _________________ Northern United Transporter Society
www.nuts.commercial-air.com |
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77ducci Samba Beer Head
Joined: March 07, 2002 Posts: 408 Location: Gathering the Missing Parts
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Posted: Fri May 16, 2008 7:35 am Post subject: |
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I thought about going the Porsche rout but between the price and wanting the challenge of keeping it built out of 36hp stuff I decided to go the other way. The ARP bolts sound like a good idea though. If I keep my engine stuff I will defiantly look into that. |
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Bengt H Samba Member
Joined: September 11, 2005 Posts: 332 Location: Sweden
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Posted: Sun May 18, 2008 1:04 pm Post subject: |
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I should asked this before, 72 mm crank, what manufakturer comes that one from?? |
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77ducci Samba Beer Head
Joined: March 07, 2002 Posts: 408 Location: Gathering the Missing Parts
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Bengt H Samba Member
Joined: September 11, 2005 Posts: 332 Location: Sweden
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Posted: Tue May 20, 2008 1:09 pm Post subject: |
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Ok, I see, thanks. |
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gimmesomeshelter Samba Member
Joined: May 08, 2004 Posts: 1468 Location: San Carlos, CA
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Posted: Tue May 20, 2008 2:14 pm Post subject: |
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Hello-
I’ve done some searching and it seems that new Porsche journal rods from Bugpack run ~ $400. Given that used Porsche rod cores cost $300-500, are Porsche rods really a better choice? Are they that much stronger/lighter?
Paul _________________ "I would rather have questions that can't be answered than answers that can't be questioned."
Richard Feynman |
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justinmcallister55 Samba Member
Joined: May 11, 2008 Posts: 13 Location: Riverdale Utah
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Posted: Wed Oct 22, 2008 8:39 pm Post subject: |
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are 36hp vw rod journals the same size as a 74mm porsche crankshaft rod journal? |
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oval56 Samba Member
Joined: July 21, 2003 Posts: 1309 Location: oktoberfest maintown
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Posted: Wed Oct 22, 2008 10:00 pm Post subject: |
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justinmcallister55 wrote: |
are 36hp vw rod journals the same size as a 74mm porsche crankshaft rod journal? |
no, 36hp has 50mm, 74mm porsche 74 has 55mm _________________ www.oval56.com
1956 Oval, 2364ccm typ4
1957 Oval Ragtop 1584ccm singel port modified
1950 Hebmüller, 1584ccm okrasa modified
DBK Germany!!!!!!!!!!
www.dbkvw.com |
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gimmesomeshelter Samba Member
Joined: May 08, 2004 Posts: 1468 Location: San Carlos, CA
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Posted: Wed Oct 22, 2008 10:02 pm Post subject: |
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Hmmm. I believe Porsche rod journals are 53mm. _________________ "I would rather have questions that can't be answered than answers that can't be questioned."
Richard Feynman |
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oval56 Samba Member
Joined: July 21, 2003 Posts: 1309 Location: oktoberfest maintown
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Posted: Thu Oct 23, 2008 5:08 am Post subject: |
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gimmesomeshelter wrote: |
Hmmm. I believe Porsche rod journals are 53mm. |
sorry my foult, but 36 rods will not fit on a 356 crank
i do hat the choice or decision a year ago at my engine
also using 36hp rods on a 356 crank, next problem is the piston wich will touch the crank at BDC ... _________________ www.oval56.com
1956 Oval, 2364ccm typ4
1957 Oval Ragtop 1584ccm singel port modified
1950 Hebmüller, 1584ccm okrasa modified
DBK Germany!!!!!!!!!!
www.dbkvw.com |
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tommy-turtle Samba Member
Joined: March 07, 2002 Posts: 165 Location: roseville
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Posted: Wed Oct 29, 2008 10:41 pm Post subject: Re: Rod choices for oldspeed engine |
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gimmesomeshelter wrote: |
Hello-
I’m trying to figure out which connecting rods would be ‘best’ (I’m willing to pay for durability and performance, but only if I need to) for an ‘oldspeed’ engine with a 74mm Porsche crank and Okrasa heads. I would imagine that this engine will rarely see 5000 RPM.
Are Porsche 912 rods a good choice? Given my relatively low RPM ceiling, would the any of the $1000+ rods give me that much in terms of performance (low weight) or durability? Are there other rods I should consider?
Thanks,
Paul |
What is the differance in the rod lenth?
what is the porsch rod lenth and what is the 36 hp rod lenth. I know i can look it up in a book and might have to tomarrow, but I am just lazy tonight. |
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oval56 Samba Member
Joined: July 21, 2003 Posts: 1309 Location: oktoberfest maintown
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Posted: Fri Oct 31, 2008 7:25 am Post subject: |
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i have it not measured, but pictured
i have used a 356 crank + rods with custom bushings + stock pistons, therefore you ned 11-12mm spacer on each cylinder!
[/img] _________________ www.oval56.com
1956 Oval, 2364ccm typ4
1957 Oval Ragtop 1584ccm singel port modified
1950 Hebmüller, 1584ccm okrasa modified
DBK Germany!!!!!!!!!!
www.dbkvw.com |
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