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Crank flex / rod angle, 86 or 88 stroke?
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-Alex77-
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PostPosted: Tue Jun 05, 2012 1:31 pm    Post subject: Crank flex / rod angle, 86 or 88 stroke? Reply with quote

cant decide which crank i will buy, 86 or 88 flanged. Always bigger isnt best. With 4" piston and cylinders cc's will be either 2789cc or 2854cc.

I will buy all T4 mains flanged scat crank, and rods 5.7" long. (DRD crank order was no success..) Rpm limited to 7000-7300rpm

Long stroke otherwise will no be problem, since i am using TF-1 case with 0.100 dropped cam line

Bad choice 88 stroke crank? Will the be significantly more flex and more rod angle? Rod ratio drops to 1.64 from 1.68.
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bugguy076
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PostPosted: Wed Jun 06, 2012 3:34 pm    Post subject: Reply with quote

What are you going to use the engine for?
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Howard 111
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PostPosted: Wed Jun 06, 2012 4:30 pm    Post subject: Reply with quote

The engine will be wider by the time you add spacers to get the correct deck height.


.
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mcmscott
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PostPosted: Wed Jun 06, 2012 5:12 pm    Post subject: Reply with quote

With an 86 or 88 x 4 inch bore and a tf-1 case, I don't think width is a concern
I don't think you would have that much more crank flex from 86 to 88.
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Tom Simon
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PostPosted: Wed Jun 06, 2012 5:18 pm    Post subject: Reply with quote

I don't think you will experience any noticeable difference (main bearing wear or case fretting) at those rpms with either stroke.

Not a high-mileage street cruiser, but I have a 96.7 bore x 88 stroke race engine in a VW mag case, no cam drop needed with 2" Chevy journal H beam steel rods, or Pauter aluminum/steel cap rods.

I've run both 86 and 88 stroke in that same engine, didn't see a remarkable difference in wear. The T4 mains really help.

The cam obviously needed clearancing, like any big stroker, the case, too. I barely ground through the top of the case in one spot, I patched it with Devcon. No big deal since that is not a high stress part of the case.

I would suggest you have the center thrust conversion done to your case and crank, if you are using a flanged crank. No one seems to be able to perform the 'split bearing' machining of the rear main bearing properly anymore. The Honda-style thrust conversion fixes that problem.
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mark tucker
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PostPosted: Wed Jun 06, 2012 5:55 pm    Post subject: Reply with quote

if I were you I would use as much stroke as posiable with drilled rod throws.longest rod you can fit,wear out that wallet.and think about using a honda size journel on the rods to get even more stroke.there is plenty of slightly used nascar shit cheep on flebay.
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-Alex77-
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PostPosted: Thu Jun 07, 2012 12:11 am    Post subject: Reply with quote

Engine will have custom made nickies and 27mm pin height JE's, so its close to stock width with 5.7" rods.

Otherwise at the will not be lot clearancae problems, due to the TF-1 case.

Is 5.7" rod too short with 88 stroke?

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modok
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PostPosted: Thu Jun 07, 2012 12:22 am    Post subject: Reply with quote

If your having trouble choosing then just make it 87mm
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PostPosted: Thu Jun 07, 2012 12:29 am    Post subject: Reply with quote

I want to see a pic of the termites that ate away the rest of his piston Very Happy
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-Alex77-
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PostPosted: Thu Jun 07, 2012 12:41 am    Post subject: Reply with quote

66brm wrote:
I want to see a pic of the termites that ate away the rest of his piston Very Happy


LOL

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Alstrup
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PostPosted: Thu Jun 07, 2012 2:19 am    Post subject: Reply with quote

With type 4 mains and those light pistons, and limited to 7500 rpm you will not see any trouble with the longer stroke. Your overlap will be better as with a 84 type 1 and Chevy rod journals.

The Scat crank is a nice piece of steel. YouŽll be glad that you stepped up from that three letter vendor.

Looking forward to hear about that beast when its done Shocked Cool

T
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yamaducci
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PostPosted: Thu Jun 07, 2012 6:13 am    Post subject: Reply with quote

I run a 90mm crank x 94mm pistons, 6 shuffle pins, 2" journals and 5.7" rods. Zero case fretting. The crank is also a full-circle crank so it's not flexing either. All the bearings are Type 1 sized. The engine is over 1" wider.
Hope this helps.
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-Alex77-
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PostPosted: Sat Jun 09, 2012 5:27 am    Post subject: Reply with quote

I wonder, if with 86mm stroke engine size is 2789cc and estimated power 250hp,

Adding 2mm stroke engine size goes to 2854cc, how much more power will more stroke give? 2-4hp?
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ALB
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PostPosted: Sat Jun 09, 2012 6:55 am    Post subject: Reply with quote

-Alex77- wrote:
I wonder, if with 86mm stroke engine size is 2789cc and estimated power 250hp,

Adding 2mm stroke engine size goes to 2854cc, how much more power will more stroke give? 2-4hp?


It's roughly a 3% increase in displacement, so that would make a power increase of 7-8hp.
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mark tucker
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PostPosted: Sat Jun 09, 2012 7:55 am    Post subject: Reply with quote

$$$ per hp.do whats bigest.if the cost is the same gofer the biger one every time. and when it breaks how do you know if it lasted a week shorter than the next size smaller or a month longer? you dont, so no need to worry.
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Jake Raby
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PostPosted: Sat Jun 09, 2012 8:20 am    Post subject: Reply with quote

The last Type 1 I have here is a combo almost exactly like you state.. Been saving parts for it since 2001 but care nothing about building it.

All new parts:

TF-1
88 Bugpack T4 main flanged crank (early good one!)
Aluminum flywheel with J&G
LN Billet rods
LN 96.9mm Nickies with custom pistons

A few other goodies. Make me an offer on it. I know what its worth but I am so done with Type 1s I want every last part off my property. I don't frequent these forums much anymore, so if interested email me at [email protected]
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Steve Arndt
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PostPosted: Sat Jun 09, 2012 1:03 pm    Post subject: Reply with quote

Alex,
What do your heads flow, and what RPM range do you want power in?
s
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-Alex77-
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PostPosted: Sat Jun 09, 2012 1:47 pm    Post subject: Reply with quote

Heads will be JPM, i dont know exact flow, but many 2300cc + engines have made over 230hp without any porting.

He made with 2387cc engine and fuelinjection 253hp at JPM dyno sweden:

http://cal-look.no/lounge/index.php/topic,12883.0.html
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PostPosted: Sun Jun 10, 2012 5:02 am    Post subject: Reply with quote

I just assembled a 87 stroke by 94mm piston with 5.7 Chevy journal rods. It all went into an Aluminum case with no issues at all. I like 86 stroke with 5.6 , 87 with 5.7 and 88 with 5.8 rods. Its all about how creative you get when you assemble.
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