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Discussion Starter #1
I have been searching and using the sticky threads in an attempt to educate myself, but I still have some basic questions.

What does the designator 4BT or 4BTA stand for?
What is the difference between a 4BT and a 4BTA?
Are there sub-models of the 4BT and 4BTA that make increasing performance easier?
Which engine would be the most versitile to look for?

Are all the 4bt engine blocks the same and then they have a different transmission adapter plate depending upon what kind of vehicle they came in? or do they come with different bolt patterns in their castings? I see that many of them come with a TH-400 attached, does that mean that they all come with the Chevy bolt pattern?

I don’t see them with after-coolers stock, would this help a stock motor?

Thanks for your help. Please educate me or point me to the correct link so I can get smart on this.

Sincerely,
Preston
 

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4 = 4 cylinders
B = B series engine
T = Turbocharged
A = Aftercooled


If you are out for performance a 4BTA would probably be best as it has a lower 16.5:1 compression ratio whereas the 4BT has a 17.5:1 ratio lower compression = higher boost . the best for performance would be one with the P pump next best is an A pump followed by the rotary pump (BTW nothing wrong with the rotary pump) P pump is rare.

Are all the 4bt engine blocks the same and then they have a different transmission adapter plate depending upon what kind of vehicle they came in?

YES.

or do they come with different bolt patterns in their castings? I see that many of them come with a TH-400 attached, does that mean that they all come with the Chevy bolt pattern?

see above

I don’t see them with after-coolers stock, would this help a stock motor?

they do come with aftercoolers, either water/air built into intake (removable) or air/air or one can be added to a 4BT.

Thanks for your help. Please educate me or point me to the correct link so I can get smart on this.

Sincerely,
Preston[/QUOTE]
 

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Discussion Starter #3
Thanks 66gaza!
 

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If you are out for performance a 4BTA would probably be best as it has a lower 16.5:1 compression ratio whereas the 4BT has a 17.5:1 ratio lower compression = higher boost .
Where did you find the compression ratio of the 4BTA? The spec sheets I have are strangely silent on the topic.
I do have one that lists a 4BT (CPL 0730) as 17.3:1.
 

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I may have that info in one of my manuals but I don't have that manual right here at the moment. I do however have compression ratio info from the Cummins Operations and Maintenance Manual, Industrial B3.9 and B5.9 Series.

Naturally Aspirated 18.5:1
Turbocharged Only 17.5:1
Turbocharged/Aftercooled 16.5:1
Charge Air Cooled 18:1

I'll follow up with more when I get it.

Ok, From the Cummins B series shop manual 1991-1994;

4B3.9/6B5.9 Industrial Naturally Aspirated 18.5:1
4BT3.9/6BT5.9 Industrial Turbocharged 17.5:1
4BTA3.9/6BTA5.9 Industrial Turbocharged and Aftercooled 16.5:1
B3.9/B5.9* Automotive Charge Air Cooled 17.6:1

All 91-94' Automotive Charge Air Cooled are designated as B3.9 and B5.9
 

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Where did you find the compression ratio of the 4BTA? The spec sheets I have are strangely silent on the topic.
I do have one that lists a 4BT (CPL 0730) as 17.3:1.
I got info from a "Troubleshooting and repair manual for B series engines" its in PDF document format now but its about 25meg so too big to email. as far as I can tell its the genuine thing.

Gaza
 

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Discussion Starter #7
What are the cpl numbers people have in their signatures?
 

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4 = 4 cylinders
B = B series engine
T = Turbocharged
A = Aftercooled


If you are out for performance a 4BTA would probably be best as it has a lower 16.5:1 compression ratio whereas the 4BT has a 17.5:1 ratio lower compression = higher boost . the best for performance would be one with the P pump next best is an A pump followed by the rotary pump (BTW nothing wrong with the rotary pump) P pump is rare.

Are all the 4bt engine blocks the same and then they have a different transmission adapter plate depending upon what kind of vehicle they came in?

YES.

or do they come with different bolt patterns in their castings? I see that many of them come with a TH-400 attached, does that mean that they all come with the Chevy bolt pattern?

see above

I don’t see them with after-coolers stock, would this help a stock motor?

they do come with aftercoolers, either water/air built into intake (removable) or air/air or one can be added to a 4BT.

Thanks for your help. Please educate me or point me to the correct link so I can get smart on this.

Sincerely,
Preston
[/QUOTE]

Please forgive my ignorance. Could someone explain the lower compression = higher boost comment? Does this indicate that the turbos are different according to the engine that they are installed on (4BT vs 4BTA) and if so, would the ideal set up be the biggest turbo (BTA) on the highest compression (BT) motor. Additionally, what pump are you refering to with the P, A, and rotory? Again, forgive my lack of knowledge on diesels, just learning as I go here. Thanks.
 

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Please forgive my ignorance. Could someone explain the lower compression = higher boost comment?
Engines which feature lower compression are intended to run with higher boost levels.
The lower compression is needed to reduce mechanical stress on engine parts as well as reducing NOx emissions.

However, a lower compression ratio does hurt engine efficiency. Running a higher compression engine with the same boost level will give slightly better power and economy. The tradeoffs are engine life and emissions.
 

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now the only difference in these engines would be the gasket thickness or are the pistons different? If its just the thickness of the gasket, how thick are the 4bta ones?

thanks! wow i didnt realize how old this thread is....oh well
 

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Welcome to the forum, Woodsrider,

There's a whole bunch of questions about the diesels and fortunately there's a place to find the answers. Take a look in the Tech section at the sticky titled FAQ. BobS has spent a whole bunch of time and energy organizing past threads alphabetically per subject and topic, many hours of informative reading there. There are other stickies in other sections as well.
 
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