[jazziejeff5]

Here is a list of some parts and improvements that would make a noticeable difference for a Duke rebuild:
Start at the bottom...
1. Clevite 77 tri metal bearings
2. Balanced reciprocating assembly (important!)
3. High volume oil pump (some will argue this, but it has worked for me every time)
4. High end FelPro gasket set. Has the silicone blue oil pan gasket.
5. Chevy 350 flat top pistons. They have the same compression height as the stock dish 2.5 piston (pin to piston crown distance) and the same size piston pin too. You can buy a hypereutectic 350 piston for $16!!! Compression will increase from 8.5 to a little over 9:1.
6. Moly piston rings. Better than the iron ductile units.
7. Match port the head to gaskets. The heads on these engines are pretty close, but the benefit is there still...
8. Porting the intake/ exhaust runners. This can be tricky, you can actually lose HPs. If you knock off the valve guide sharp edges and blend the guide in the bowl, this usually helps flow and doesn't mess up the runners.
9. Cam. Oregon Cam grinders have several different grinds for this engine. They are great... you can actually talk to these guys and tell them what your requirements are, they will provide you with the right cam for your application.
10. Aluminum timing gear. This replaces the phenolic gear and doesn't shred. They are slightly noisier than the stock gear, but the long life is by far a better choice
11. Roller rockers. IIRC, Chevy big block rockers are a bolt on. There are different ratios, the Oregon boys are the best for recommending ratio choice/ cam combination.
12. Stock header... This is an easy one. Cut the stock header flange off,
(it's 1 1/2" in diameter) and weld on a 2 1/2" flange. This will effectively give you a performance header for cheap.
13. 2 1/2" exhaust - a muff shop can bend up a head pipe to cat for a 2 1/2" pipe.
14. High flow 2 1/2" cat. This connects right to the pipe from the header.
15. Performance exhaust: Summit Racing® Cat-Back Exhaust Systems SUM-680031
16. If you are really going for it... a performance chip for the ECU.

These inprovements can give you an honest 120 HPs. Not much of a gain, but it makes an S10 Duke fun to drive.

Figure about $1,500 to $1,800 for everything - if you do most of the work yourself. It can be done for less if you shop around and don't go for all of the upgrades.

Hey only thing about a high volume oil pump is it draws HP believe it or not. U can use standard oil pump take it apart and do some minor clearancing and polishing and Shaffer rod hole and it will greatly improve flow and pressure

 

[jazziejeff5]

Hey only thing about a high volume oil pump is it draws HP believe it or not. U can use standard oil pump take it apart and do some minor clearancing and polishing and Shaffer rod hole and it will greatly improve flow and pressure

All this is very helpful information to follow

 

[jazziejeff5]

Some pics of parts:

Hypereutectic 350 pistons and fresh Clevite bearings:


Aluminum cam gear:


Fresh flat top 350 pistons installed in the 2.5 block


Another pic of the 350 piston:


Fresh high volume oil pump:


Here's a pic of a Pontiac 301 V8 piston. They also fit the 2.5. The 350 pistons are a better choice.


Here's a pic of the crappy crank in a 2.5. No counterweights, and made out of paper. This is why balancing is so important. The factory does a crap job balancing these POSs.


I'll post more if there is any interest.

Hey. I wish I had known about the 301 pistons or I wouldn’t have gotten Chevy pistons. The “deck hight “ I had to cut .050 off my deck. But I don’t know what kinda price difference there is on 301 pistons. I know the flat top 151 pistons are not cheap

 

[Rl6e3]

Here is a list of some parts and improvements that would make a noticeable difference for a Duke rebuild:
Start at the bottom...
1. Clevite 77 tri metal bearings
2. Balanced reciprocating assembly (important!)
3. High volume oil pump (some will argue this, but it has worked for me every time)
4. High end FelPro gasket set. Has the silicone blue oil pan gasket.
5. Chevy 350 flat top pistons. They have the same compression height as the stock dish 2.5 piston (pin to piston crown distance) and the same size piston pin too. You can buy a hypereutectic 350 piston for $16!!! Compression will increase from 8.5 to a little over 9:1.
6. Moly piston rings. Better than the iron ductile units.
7. Match port the head to gaskets. The heads on these engines are pretty close, but the benefit is there still...
8. Porting the intake/ exhaust runners. This can be tricky, you can actually lose HPs. If you knock off the valve guide sharp edges and blend the guide in the bowl, this usually helps flow and doesn't mess up the runners.
9. Cam. Oregon Cam grinders have several different grinds for this engine. They are great... you can actually talk to these guys and tell them what your requirements are, they will provide you with the right cam for your application.
10. Aluminum timing gear. This replaces the phenolic gear and doesn't shred. They are slightly noisier than the stock gear, but the long life is by far a better choice
11. Roller rockers. IIRC, Chevy big block rockers are a bolt on. There are different ratios, the Oregon boys are the best for recommending ratio choice/ cam combination.
12. Stock header... This is an easy one. Cut the stock header flange off,
(it's 1 1/2" in diameter) and weld on a 2 1/2" flange. This will effectively give you a performance header for cheap.
13. 2 1/2" exhaust - a muff shop can bend up a head pipe to cat for a 2 1/2" pipe.
14. High flow 2 1/2" cat. This connects right to the pipe from the header.
15. Performance exhaust: Summit Racing SUM-680031 Summit Racing™ Cat-Back Exhaust Systems | Summit Racing
16. If you are really going for it... a performance chip for the ECU.

These inprovements can give you an honest 120 HPs. Not much of a gain, but it makes an S10 Duke fun to drive.

Figure about $1,500 to $1,800 for everything - if you do most of the work yourself. It can be done for less if you shop around and don't go for all of the upgrades.

Hey can u drop a link to the performance chip u use or recommend?

 

[Mad Max]

Actually, it's Moates who does the hardware to do the reprogramming
They're in Baton Rouge...

GM 1985-1995 : Moates.Net

Moates.Net : GM 1985-1995

www.moates.net

If you call them, they can help you through the process.

 

[Mad Max]

I have a new build that adds to this - if anyone is interested.
I'll post the next stage of performance for these lumps...

 

[S10Gary]

I have a new build that adds to this - if anyone is interested.
I'll post the next stage of performance for these lumps...

Im interested.

 

[Mad Max]

OK... This will be stage II.
I'll run down the whole show

 

[Mad Max]

Stage II:

Here's some more performance additions:
As soon as I install and dyno this tub, I'll post performance results.

Here's the run down -
Any Iron Duke block - prefer 1986 and later RWD for a better crank, but they are all capable. The later ones have additional structural reinforcement. Like 1990 to 1993 "A" blocks.

This build - 1988 block that was already bored .060 with 350 Small Block dish pistons.

Block -

• Sleeved block to stock 4" bore. "LA Sleeves" high nickle content sleeves for long life.
• Hot tanked and installed new cam bearings and brass freeze plugs
• Decked block for new sleeves and flat surface
• Light honed main bearing surfaces
• Checked all internals for correct clearances
• New high volume oil pump
• New 282* duration flat tappet cam (More specs soon)
• 350 Chevy Small Block coated "Claimer" pistons. 2 valve relief flat top pistons for more compression
• Eagle "I" beam 6" small block small journal 2.0" rods. Shaved big end sides to fit Iron Duke crank
• All rotating parts balanced
• 1985 Fiero 2.5 harmonic balancer. Stock was a hub.
• Glyptal internal paint to assist oil return
• Exterior painted with epoxy primer and cast iron look spray - brass plugs exposed for a "look"

 

[S10Gary]

Stage II:

Here's some more performance additions:
As soon as I install and dyno this tub, I'll post performance results.

Here's the run down -
Any Iron Duke block - prefer 1986 and later RWD for a better crank, but they are all capable. The later ones have additional structural reinforcement. Like 1990 to 1993 "A" blocks.

This build - 1988 block that was already bored .060 with 350 Small Block dish pistons.

Block -

• Sleeved block to stock 4" bore. "LA Sleeves" high nickle content sleeves for long life.
• Hot tanked and installed new cam bearings and brass freeze plugs
• Decked block for new sleeves and flat surface
• Light honed main bearing surfaces
• Checked all internals for correct clearances
• New high volume oil pump
• New 282* duration flat tappet cam (More specs soon)
• 350 Chevy Small Block coated "Claimer" pistons. 2 valve relief flat top pistons for more compression
• Eagle "I" beam 6" small block small journal 2.0" rods. Shaved big end sides to fit Iron Duke crank
• All rotating parts balanced
• 1985 Fiero 2.5 harmonic balancer. Stock was a hub.
• Glyptal internal paint to assist oil return
• Exterior painted with epoxy primer and cast iron look spray - brass plugs exposed for a "look"

nice Max. What is your timetable for dyno results?

 

[Mad Max]

^^^ Hard to say.
My job is unpredictable. If there's a natural disaster declared by the pres, I'm usually off somewhere.
If no mission, then in the next three weeks or so.
The machinist friend is sort of busy at the moment...

 

[Mad Max]

An early Duke in my 1992 S10. This came out of an '83 Jeep CJ5. It has the Chevy Small block bell housing bolt pattern, the bell housing is set up for a Ford T5 transmission.

This is the new shifter location for the Ford T5 shifter. The transmission came from an '88 Turbo T Bird.

The shifter is in a much better position for the driver. The shifter is one of those short shift "Ripper" shifter units.

I guess this info is relative to this thread since the engine that was described in the beginning is the early Duke from the Jeep.

 

[Mad Max]

A pic of an aluminum gear timing set which I replaced the original Phenolic (plastic) gear. The gear set is the same as a Chevy 250 six cylinder engine.
Look carefully between the gears. You'll see the oiling tab for the gear set. This is critical to have no blockage. It has to aim straight at the gears too.

This is the gear on the cam (it's pressed on) with the thrust and retainer flange installed. The flange is the same as a Chevy 250 six cylinder also. The cam is a flat tappet unit. The newer engines had roller cams. You can use a flat tappet cam in the later engines with the correct length push rods. The earlier blocks are not set up for a roller cam though.

A shot of the harmonic balancer from an 85 Pontiac Fiero 2.5.
The balancer is smaller than the S10 hub/pulley. I tapped the three holes with a 12mm x 1.25 tap. The holes line up perfectly with the stock (larger) S10 pulley and the belt alignment happens to line up also... Coincidence?

Oops... a piston from another Duke I rebuilt. This is a stock piston. Big dish, yes?

 

[Mad Max]

Really nothing to do with this thread, just another crazy engine I built 10 years ago.
Still on the engine stand, ready to go into another S10.
1983 Buick 3.8 V6 with mad internals. Check out the crazy induction... Carbs are from a Porsche 911.

 

[Mad Max]

Stage II
GM made several cylinder heads for these engines. The early heads were not cross flow.
They had the intake and exhaust manifolds on the same side of the head. (1977 to 1979)
The next generation had a cross flow head and had large rectangular exhaust ports. It also had a carb in Jeeps and AMC vehicles. Some GMs had primitive TBI. (1980 to 1983)
The following editions had round exhaust ports and all were TBI. The intake manifold bolt pattern changed also. (1984 to 1989)
The last issue was a "D" port on the exhaust side. They were small ports - apparently for velocity. These engines made the most power... A whole 110 horsies. (1990 to 1993)

I chose a 1988 version with round ports.

Cylinder head -

• Install new valve seats for hardness
• Shave .025" for flatness and compression
• Valve guides reamed for thicker Olds valve stems
• Valve guides cut to accept improved valve seals
• Olds 350 intake valves which have a larger than stock valve head. The stems are thicker and longer too. Stock 2.5 valve head diameter = 1.720". Olds 350 = 1.875"
• Olds exhaust valves - same as stock size. Stems are thicker and longer
• Chevy small block Z28 valve springs. Better seat pressure and inexpensive.
• Olds keepers and retainers
• Open intake ports under the intake valve head for the bigger valves
• Match ports and blend bowl under valves.
• Blend valve guide bosses to remove sharp edges
• Drill and tap rocker studs to 7/16" to accept ARP Chevy big block screw in studs
• Comp Cams Chevy big block stainless roller rockers. 1.72 to 1 rocker ratio
• Custom length 3/8" push rods
• 3/8" push rod guide plates

I hope it's worth it...

 

[S10Gary]

Stage II
GM made several cylinder heads for these engines. The early heads were not cross flow.
They had the intake and exhaust manifolds on the same side of the head. (1977 to 1979)
The next generation had a cross flow head and had large rectangular exhaust ports. It also had a carb in Jeeps and AMC vehicles. Some GMs had primitive TBI. (1980 to 1983)
The following editions had round exhaust ports and all were TBI. The intake manifold bolt pattern changed also. (1984 to 1989)
The last issue was a "D" port on the exhaust side. They were small ports - apparently for velocity. These engines made the most power... A whole 110 horsies. (1990 to 1993)

I chose a 1988 version with round ports.

Cylinder head -

• Install new valve seats for hardness
• Shave .025" for flatness and compression
• Valve guides reamed for thicker Olds valve stems
• Valve guides cut to accept improved valve seals
• Olds 350 intake valves which have a larger than stock valve head. The stems are thicker and longer too. Stock 2.5 valve head diameter = 1.720". Olds 350 = 1.875"
• Olds exhaust valves - same as stock size. Stems are thicker and longer
• Chevy small block Z28 valve springs. Better seat pressure and inexpensive.
• Olds keepers and retainers
• Open intake ports under the intake valve head for the bigger valves
• Match ports and blend bowl under valves.
• Blend valve guide bosses to remove sharp edges
• Drill and tap rocker studs to 7/16" to accept ARP Chevy big block screw in studs
• Comp Cams Chevy big block stainless roller rockers. 1.72 to 1 rocker ratio
• Custom length 3/8" push rods
• 3/8" push rod guide plates

I hope it's worth it...

If nothing else it will be the absolute coolest 2.5 ever to exist! I predict the power will be much higher than what you are expecting or even hoping for. You will be setting a new standard for whats possible with the venerable Iron Duke 2.5

 

[Mad Max]

Actually, I've built several of these lumps.
Each one is a little more radical than the last one.
I'll post some pix of the '83 2.5 I built a while ago.
It's got a 4 barrel intake and everything else I described earlier.
I have a few different distributors and intake manifolds, as well as an expensive Clifford header and modified stock exhaust manifolds to connect to a large exhaust system.
I'll be posting more about that shortly.