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Rod choices for oldspeed engine
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gimmesomeshelter
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PostPosted: Wed May 14, 2008 4:37 pm    Post subject: Rod choices for oldspeed engine Reply with quote

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
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Bengt H
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PostPosted: Thu May 15, 2008 12:34 am    Post subject: Reply with quote

I think any Porsche 356 rod will do the job, what cylinders/pistons are you going to use?
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commercial air
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PostPosted: Thu May 15, 2008 8:15 am    Post subject: Reply with quote

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
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gimmesomeshelter
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PostPosted: Thu May 15, 2008 9:31 am    Post subject: Reply with quote

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
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Bengt H
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PostPosted: Thu May 15, 2008 3:27 pm    Post subject: Reply with quote

Porsche rods cleares the cam in original.
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Bengt H
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PostPosted: Thu May 15, 2008 3:32 pm    Post subject: Reply with quote

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 Wink
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77ducci
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PostPosted: Thu May 15, 2008 3:33 pm    Post subject: Reply with quote

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
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PostPosted: Thu May 15, 2008 11:14 pm    Post subject: Reply with quote

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.

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77ducci
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PostPosted: Fri May 16, 2008 7:35 am    Post subject: Reply with quote

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
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PostPosted: Sun May 18, 2008 1:04 pm    Post subject: Reply with quote

I should asked this before, 72 mm crank, what manufakturer comes that one from??
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77ducci
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PostPosted: Sun May 18, 2008 8:11 pm    Post subject: Reply with quote

Good stock 36hp welded from DPR. Here was my engine before I traded off my oval.

http://www.thesamba.com/vw/classifieds/detail.php?id=610230
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Bengt H
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PostPosted: Tue May 20, 2008 1:09 pm    Post subject: Reply with quote

Ok, I see, thanks.
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gimmesomeshelter
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PostPosted: Tue May 20, 2008 2:14 pm    Post subject: Reply with quote

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
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justinmcallister55
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PostPosted: Wed Oct 22, 2008 8:39 pm    Post subject: Reply with quote

are 36hp vw rod journals the same size as a 74mm porsche crankshaft rod journal?
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oval56
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PostPosted: Wed Oct 22, 2008 10:00 pm    Post subject: Reply with quote

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
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gimmesomeshelter
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PostPosted: Wed Oct 22, 2008 10:02 pm    Post subject: Reply with quote

Hmmm. I believe Porsche rod journals are 53mm.
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oval56
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PostPosted: Thu Oct 23, 2008 5:08 am    Post subject: Reply with quote

gimmesomeshelter wrote:
Hmmm. I believe Porsche rod journals are 53mm.


sorry my foult, but 36 rods will not fit on a 356 crank Smile


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 ...
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1950 Hebmüller, 1584ccm okrasa modified

DBK Germany!!!!!!!!!!
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tommy-turtle
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PostPosted: Wed Oct 29, 2008 10:41 pm    Post subject: Re: Rod choices for oldspeed engine Reply with quote

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
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PostPosted: Fri Oct 31, 2008 7:25 am    Post subject: Reply with quote

i have it not measured, but pictured Smile

i have used a 356 crank + rods with custom bushings + stock pistons, therefore you ned 11-12mm spacer on each cylinder!

Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.
[/img]
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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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