4BT stroker

C

clarkoh

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My 48 Dodge Pilothouse project is getting a 4BT and a Ram Chassis e/w NV4500 and Dana 80. Pretty much the 6BT driveline with a 4 cylinder.

I have a crank from a 4.5QSB. The stroke is 5.39 vs. stock 4.72. I am trying to build a torque monster and would like to know if anyone has done this using a 3.9 block and 12 oops 8v head. I am leaning towards a Ross piston with the pin height .335 higher to accommodate the longer stroke and still use the stock rods. My second choice would be to open my bank account and get some longer rods from Crower or someone else? and stay with stock pin height pistons. I think the stock compression height is 2.817". My stock pistons from one of my core engines has enough room under the oil ring to move the pin that high. I know the rod stroke ratio will not be great, but the truck will see very limited drag racing and mainly cruiser/ sunny day daily driver.

Suggestions of a choice of twins and possibly a cam upgrade are welcome.:thankyou2:
 
I would reccomend contacting R&R for the longer billet rods. They don't charge extra for the added length and price is better generally. You may need to pay a one time $250 charge for an engineering fee if they never made the length you request. They will tell you upfront what lengths they have available in the Cummins rods. I would retain the stock piston if you can for better DD use and keeping the cost down. Sounds like a cool project keep us posted and welcome to Compd.

Chris
 
Forged pistons will be a no go for a street application, and you will need a shorter rod if you use the stock pin placement.
 
We can help you with the camshaft, we do many regrinds for Cummins.

Just give us a call.
 
I'd run a stock piston with a 14mm top ring land, deck plate it ~.500 allowing the TRL to protrude into the deck plate and keeping the top ring in the block. Make rods the correct length, around .200 longer than stock.


Did they make and 4.2ish bore 4b blocks? 4.250 bore would allow for a much shorter piston.
 
ISB vs QSB

SuperSonic said:
I thought all the qsb4.5's were rear gear train?
Click to expand...
I have 2 new cranks from 4.5QSB engines. They are front gear train. I have heard the ISB's were rear gear. and would be useless for my application.

Sticking with a P pump from one of my core engines. And a nice set of twins. Any suggestions on turbos for my twins? I have had a suggestion to run an HX30 over a larger atmospheric turbo. A waste gate would be necessary on the smaller turbo.

And thanks for the quick replies.
 
Hmmm Deck plates

9724VF350 said:
I'd run a stock piston with a 14mm top ring land, deck plate it ~.500 allowing the TRL to protrude into the deck plate and keeping the top ring in the block. Make rods the correct length, around .200 longer than stock.


Did they make and 4.2ish bore 4b blocks? 4.250 bore would allow for a much shorter piston.
Click to expand...

This is the first I have heard about deck plates. That would allow some better rod stroke ratios and allow the stock pin height to be used. What would be a source for the plates? I have machined my own honing plates from billet aluminum. I probably could whip up a .500 thick plate. That would probably work better than stacking 10 head gaskets!

I assume that a deck plate would have to be installed, torqued down using a honing plate and the whole 9 yards bored and honed to match. Would the plate have a head gasket on each surface? How would the top ring deal with passing over that transition between the bore of the block and the bore of the plate? Or do we add sleeves that tie it all into one nice smooth bore? Hmmm. The plot thickens.:evil

Relatively speaking, pistons are inexpensive, especially compared to steel rods. If I used a custom piston, some consideration could be made to optimizing the bowl to match the injector pattern better?? Is it worth the effort and expense?

I am not sure about the 4.2 bore 4B? Did they use that 6.7 configuration to make 4.5liter engines?

Thanks
 
Cranks

I uploaded 3 pictures of the old and new cranks side by side. Longer stroke, same front snout, same rear flange and same firing order. I actually wanted to check to make sure I was not ripped off.

If anyone is interested, there are more of these on Ebay. Buy it now for five hundred, but the guy will take offers. I offered 10% less and its a deal.
 

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This is the first I have heard about deck plates. That would allow some better rod stroke ratios and allow the stock pin height to be used. What would be a source for the plates? I have machined my own honing plates from billet aluminum. I probably could whip up a .500 thick plate. That would probably work better than stacking 10 head gaskets!
Click to expand...

Can't say that I've seen any advertised for a 4B, I'd probably make my own.

I assume that a deck plate would have to be installed, torqued down using a honing plate and the whole 9 yards bored and honed to match. Would the plate have a head gasket on each surface? How would the top ring deal with passing over that transition between the bore of the block and the bore of the plate? Or do we add sleeves that tie it all into one nice smooth bore? Hmmm. The plot thickens.:evil
Click to expand...

Use 2 head gaskets, the top ring will not come to the transition, the area above the top ring is all that will protrude into the deck plate.

Relatively speaking, pistons are inexpensive, especially compared to steel rods. If I used a custom piston, some consideration could be made to optimizing the bowl to match the injector pattern better?? Is it worth the effort and expense?
Click to expand...

A custom piston will not last in your application. The top ring lands do not have steel inserts like the OEM pistons do. For what you are doing I would rather have a custom rod. If a piston needs replaced, or you want to try different bowl shapes, compression ratio's ect, it's handy to have off the shelf parts.

I am not sure about the 4.2 bore 4B? Did they use that 6.7 configuration to make 4.5liter engines?
Click to expand...

I'm not sure if they ever used that bore in a 4b.
 
You do realize that a 3.9 block has a shorter deck height than a 4.5, right?
I believe it's a ~ 1/2" difference.

The QSB-110C 4.5, as used in Military GLG Telehandlers, utilized a VP-30 electronically controlled injection pump.
As equipped in said Telehandler, it also used an H30W turbo with a 12cm exhaust housing, mounted on top of the manifold and also had an air compressor mounted below the injection pump.
It utilized an SAE 3 belhousing and was also equipped with a 22-SI alternator.

This engine also used the "typical" front gear train timing components, along with a 2-valve per cylinder arrangement.
Bore size is the same as the 3.9, but the stroke has been significantly increased.

Mark.
 
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Thanks for information.
What material should I use for my deck plate?

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While searching for deck plates I saw an image of a BHJ head bolt alignment plate. The shot shows a tap being located and aligned by drill bushing which is located and aligned by the plate. I am guessing this is used to tap the engine block for bigger head bolts/studs. Has anyone used one?

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Steel is the most common, though that is normally in a competition application where heat cycles and expansion and contraction are quite a bit different than your application.

I would probably consider a good grade of ductile iron.
 
Piston Information

I cleaned one of the pistons pulled from a core 3.9. It has a bowl that is undercut, creating a lip around the top edge of the bowl. The number cast inside is 102039. Does that translate to a Cummins part no.?

Would it be advisable to use aluminum rods? Since the majority of the running will be on the street? Not sure the big end would clear everything? On my gas engines we usually notched the bottom of the cylinders so the big end could miss them. And what about the proximity to the cam?

Thanks again for the feedback. I am excited just thinking this might work, without the expense of a 4.5 block.:rockwoot:
 
clarkoh said:
I cleaned one of the pistons pulled from a core 3.9. It has a bowl that is undercut, creating a lip around the top edge of the bowl. The number cast inside is 102039. Does that translate to a Cummins part no.?

Would it be advisable to use aluminum rods? Since the majority of the running will be on the street? Not sure the big end would clear everything? On my gas engines we usually notched the bottom of the cylinders so the big end could miss them. And what about the proximity to the cam?

Thanks again for the feedback. I am excited just thinking this might work, without the expense of a 4.5 block.:rockwoot:
Click to expand...

The number will be 4 digits stamped in the top, regardless I would personally go away from that bowl design. I would use what some refer to as the "marine" bowl. There is several different compression ratio's available and since your crank will increase compression you'll have 3 or 4 higher ratio's to choose from.

Aluminum rods are not a good idea for you. Longevity may be a issue and physical size will be a problem. You'll get to the cam before you get to the bottom of the bore's, timed flats can be machined on the cam for the rods to clear if necessary.
 
Ok. Great stuff. I found a source for the ductile iron plate. Not cheap. Going to use longer rod and about 0.500 thick plate.
Now, the $64,000 question. What compression ratio should I end up with? Based on a conservative set of twins and still looking for drivesbility on street.

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Your common piston options with a 14mm top ring land are going to put you at about 17.5:1, 19:1, or 20:1.

Since you have compression to spare, I would probably cut some shallow valve reliefs (around .060) just to give you some camshaft options.

Or, if you really want to get at it, deck .060-.080 off the head to unshroud the valves and increase low lift flow, and cut around .120-.150 valve reliefs to make everything fit.
 
Is there a sticky with piston dimensions? In my case, I need the distance from the top of the piston to the ring land. Plus the usual bowl volume, compression height, etc.
Ordered a 3/4" thick piece of ductile iron plate and a set of 0.200" kind Cunningham rods. Have to get one if my blocks bored and cleaned. I have a line on a surfacing machine with capacity to do blocks, heads and deck plates. I can use it, but might buy it.

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