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Discussion Starter #1
I'm building a 2.5 tech 4 and I'm gonna need a stronger crank than the stock one. Could someone tell me wat crank I could use with out havin to have pistons or rods made. I know the 3.0 will work but it has a 2 piece main seal. Thanks
 

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Boozebag
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Supposedly that 3.0 marine crank is your only option. I have read that with some machine work it will fit. I have never heard of any other crank that is adaptable.
Raven or Steady Eddie may be able to add info. There was also a guy from Cali that posted here. He seemed to be a guru about weird performance mods for Dukes. I don't remember his posting name...
 

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Cool, Tight, & STRONG....
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I'm building a 2.5 tech 4 and I'm gonna need a stronger crank than the stock one. Could someone tell me wat crank I could use with out havin to have pistons or rods made. I know the 3.0 will work but it has a 2 piece main seal. Thanks
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zach--

Welcome..:D..

Depending on which model of engine you have, the stock crankshaft will support the maximum RPMs the head will flow. ie. 4500 maximum RPMs @ 300 cu. ft. per minute flow.

The Crankshafts with the least flex are those with the "gear" on them, the one that runs the oil pump, IIRC.

Member M Max has a good photo of one of these cranks in his "Build" thread. You can increase the overall strength of these cranks, by cryo treatment, by some 20%.

http://en.wikipedia.org/wiki/Cryogenic_treatment

What will NOT live are the OE connecting rods. For these you should attempt to find forged rods made for a 301 cu. in. Pontiac V-8. These are a bolt in swap, many times stronger than the OE "soda straw" rods.

To top off the mix, a set of forged pistons would work out well. There was a stock sized set made by TRW that was forged right out of the box, otherwise, a set made for the Turbo 301 Pontiac V-8 may be found on eBay or at a garage sale.

With the right mix of component parts you should be good to go..:cool:..
 

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i believe some super duty cranks can be ground to stock dimension, but without the rods pistons, head, etc it's not worth it

using different stroke like from super duty, regrind chevy/marine either 153ci/181ci/3-liter cranks custom fit, needs rods and/or pistons that match to work/fit correctly
 

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Boozebag
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SE- I bought 2 harmonic balancers for a Duke. They are different diameter than the standard pulley (smaller), and are also offset towards the block more. I looked at taking the non balancer pulley and botling it to the balancer, I would have to be dead nutz on for it to rotate correctly.
Moral of story: I did not find a balancer that is a direct bolt and go to fit a Duke in a Dime. Do you know of a source that has one? :dunno:
 

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Discussion Starter #7
Alrighty thanks for the info. I've found 301 Turbo rods an pistons. How many HP is my crank good for? I'm wanting to get it aleast 120 or more.
 

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Cool, Tight, & STRONG....
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SE- I bought 2 harmonic balancers for a Duke. They are different diameter than the standard pulley (smaller), and are also offset towards the block more. I looked at taking the non balancer pulley and botling it to the balancer, I would have to be dead nutz on for it to rotate correctly.
Moral of story: I did not find a balancer that is a direct bolt and go to fit a Duke in a Dime. Do you know of a source that has one? :dunno:
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MM--

Here is a link:

http://www.fierosails.com/HarmonicBalancer.html

Dunno if it'll fit..ie..bolt right in..

The deal is this: Pontiac did make one that does fit. It was for a serpentine belt and everything. IIRC ? The vee belt S-10 motors are not covered..

Here is a link to the one made by Dorman..4.3 pounds right up front where it counts..

http://www.dormanproducts.com/carquest/p-10108-594-027.aspx

And last, but not least, here is a link to the real deal:

http://alansempireclassicautoparts.ecrater.com/p/5442735/10101369-gm-harmonic-balancer-25-engine-fiero-and-more-1987-92-all#
 

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Boozebag
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Alrighty thanks for the info. I've found 301 Turbo rods an pistons. How many HP is my crank good for? I'm wanting to get it aleast 120 or more.
BTW, I went through the rod and piston dance with the Duke I am presently building. I ended up using Chevy 350 Hypereutectic flat toppers. They have all of the same dimensions as the 2.5 pistons, though they are flat top which should give a little more compression. They were also coated. I had to go .060 overbore to clean up the cylinders!!
I have a set of standard bore 301 pistons and moly rings, they are also flat top. If you don't need to bore your Duke, I'd sell them for cheeeeeep. They are a bolt in also. (PM me if you are interested)

The 301 rods are the way to go. I used the standard Duke rods - I'm not looking for gorilla grunt from this unit. I am hoping for 110 RWHP, which will make it a good running street fighter.
BTW, check the cylinder head valve bowls. They could use some work since the valve guide bosses are fugly POSs. Just cutting the edges off and blending the bosses should offer a good improvement - particularly on the exhaust side. The middle exhaust bowls have almost 30% occlusion!!
Post pics of your build...
 

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Alrighty thanks for the info. I've found 301 Turbo rods an pistons. How many HP is my crank good for? I'm wanting to get it aleast 120 or more.
===
zach--

I don't know about the HP..the flow through the head is the limiting factor.

A percentage figure is a doable thing: 120 HP is equal to 20% gain (for a motor rated at 100 HP) BUT..the OE crank, modified for strength, will handle it with the good parts installed. It (by itself) won't make even one HP over stock, but it will live.

Back in the day, Pontiac made a cast iron Super Duty 4 cylinder head that was a damn near bolt on, and IT flowed right out of the box..:cool:..if you could locate one of those heads..my oh my..:eek:..here is the OE part number:

#347056 (I have it written down on a card in my wallet--JUST IN CASE--)
 

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Boozebag
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This is the crank SE was talking about:
 

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Discussion Starter #13
Alrighty I'll look into the heads. When I tore it apart I found out it was bored over .40. I'll post some pics of it. I'm mainly concerned about the head. I've read that there is a super duty aluminum head that they made few of. Is there anybody making them aftermarket
 

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zach--

The SD 4 head that I posted about is a cast iron head that uses all of the flow properties of the aluminum head with none of the hassles. Like gasket leakage, head warpage, etc. The alloy head was/is more of race only application, IMHO..

The 40 over engine that you have now is 10 over the maximum safe overbore limit.
 

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Discussion Starter #15
So wat do u suggest with it being bored that much. I was kinda scared to but I read on here that a Guy bored his 40 an it was fine.
 

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In 86/87 Hot Rod Magazine said 140hp or so up to 5000rpm stock bottom end, and that durability at 180hp was questionable. BTW rods and pistons were equally mentioned for failure. They also did a 205hp super duty. Looks like the parts list for both at http://www.gafiero.org/docs/IronDukeBuild.pdf , and other stuff not from article looking mostly from Fiero perspective http://www.gafiero.org/docs.shtml. And supposed Fisher and Fluidamper sell high performance balancers for the Iron Duke/Tech IV but no mention of number or different fitments.

If not bad worn clean it up, ridge ream, hone, and put in appropriately sized rings and bearings, or ridge ream and put still ringed piston back in same bore. Boring it out won't increase the durability of the block any.
 

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Discussion Starter #17
Alrighty I figured it would be ok I honed it an it cleaned up pretty good so I'm gonna put 350 flat tops an 301 forged Rods in it. I'm gonna do a little porting on the head. Any suggestions on valve springs and rockers. Roller rockers maybe?
 

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Boozebag
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Alrighty I figured it would be ok I honed it an it cleaned up pretty good so I'm gonna put 350 flat tops an 301 forged Rods in it. I'm gonna do a little porting on the head. Any suggestions on valve springs and rockers. Roller rockers maybe?
Big block Chevy roller rockers work on Dukes, but the valve cover won't fit. For the gain in HPs you will get, I don't think it is a cost effective mod.
I think porting the head will give you some free HPs. The intake/exhaust ports are pretty close to gasket size from the factory.
The improvements would be best in the valve bowl area. The main areas that would benefit are the valve guide bosses. They were factory machined without regard to flow. You'll see what I mean when you take the valves out of the head. If you blend the bosses and reshape them slightly, it should improve flow.
BTW, I have a SD aluminum head and 2 intakes. One is a 4 bbl and the other is a Holley 2 bbl style.
Here is the 2 bbl:

You can't use this on a stock head, the ports are WAY bigger.
Unless you run a performance cam, changing valve springs is not going to make any difference. Even of you run a mild cam, springs won't make much of a difference.
Remember, this is not a good engine to rev. The head design isn't that great for flow.
 

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Discussion Starter #19
I wasn't sure about the rockers. I'm gonna put a mild cam in it but I'm not sure wat yet.
That intake is a pretty cool set up but the Clifford one is like 400 dollars an I don't really think its worth that
 

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Boozebag
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Clifford may be expensive, but they are one of the very few out there that make anything for the 2.5 (aside from GM).
You also have to realize that GM revised the 2.5 intake ports 3 times over the production run of the RWD engine. This means that you have to find an intake specific to the head you have (or are going to use).
Here's a pic of what I mean...

This is an earlier manifold with a later gasket superimposed on the intake side.
Big difference, no?
How about this one...

A sort of rare Holley unit. These are obsolete now.
 
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