How much HP?

pharmd · Oct 10, 2009

How much horsepower should I shoot for when replacing my 350 Vortec (275ish hp) with the 4BT or 6BT? I am not convinced that the 105 HP stock motor is going to do it.

On another forum, many say 400hp is no problem for a reliable 4BT. That doesn't seem true. They said run twins and one can get that easily.

Can anyone shed light on this subject for me?

Mikel · Oct 10, 2009

pharmd said:
On another forum, many say 400hp is no problem for a reliable 4BT. That doesn't seem true. They said run twins and one can get that easily.

That is VERY optimistic. It's probably the same people who claim getting 40MPG

BobS · Oct 10, 2009

Compare the torque numbers. The 105HP is around 275 FT/LB.
Personally I would never exceed 200HP on a 4BT and expect any reliability, mileage, and longevity. That's just me & your results may vary.

pharmd · Oct 10, 2009

I agree with you guys. I am having a hard time accepting that a 4bt will go like a 350 gas. I am sure ther MPG will be way better (I get 12 city/15highway now). But even 200hp seems low. Will all the torque make up for the low HP. I am asking now because this isn't something I want to find out after I have done the swap.

The best thing about the 4bt to me is the MPG. On these forums, 30 mpg seems to be more of a myth, or at least a small minority. It looks more like low twenties high teens mpg. So those same numbers seem attainable with a 6bt. I would make horsepower mods that are more efficient, and shoot for low twenties mpg in a fairly light vehicle (relatively).

It just seems to me that the 4bt would struggle to get what I am after. Of course I don't have actual experience in a 200hp 4bt so that's why I am asking around on the boards.

BobS · Oct 10, 2009

A true properly tuned and efficient 200HP Cummins B series diesel will generate an average torque range between 400 to 450 ft/lb of torque at slightly less than 2000 RPM's. As an example a 454 Chevy truck engine in 1986 was rated 230HP @ 3800 RPM and 360 ft/lb of torque at 2800 RPM's.

LReiff · Oct 10, 2009

Without being too optimistic, 250 hp is relatively easy to attain, is reliable and will out perform a 350Vortec hands down. With proper pump tuning and a twin turbo setup 20-23 mpg should be easily accomplished.

pharmd · Oct 10, 2009

What exactly would you do to get the 250HP. What mods and what turbo's?

LReiff · Oct 12, 2009

The best things I've found, a good set of injectors with the proper spray angle & pop off pressure, internal pump modifications to allow timing to advance higher with rpm increase than what factory parts allow and a well matched twin turbo setup. As stated earlier Cummins built a 250hp 4bt with an intermittent hp rating...they did not advance injection timing with rpm (not possible with the pump they used), did not use twin turbos & did not use an injector with the proper spray angle...injection timing is critical to making a high powered engine survive, as well as air flow and fuel introduction. A properly tuned 250 HP 4BT will live longer than one that is poorly tuned and only makes 100 HP.

needsdiesel · Oct 10, 2009

3/4

I have a 4bta 120hp in a 1994 K2500 chevy that used to have a 6.5 diesel in it and I am very happy with the power. I used to have a 1997 chevy k1500 with a vortec 350 and the 4bta seems from my memory to accelrate about the same if not harder. I have my fuel pin turned 90 and pump timing advanced. The 1997 vortec 350 made 320ish ftlbs and the stock 4bta makes 320ish ftlbs. My mpgs as of last figureing was 18.5 mpg might be better if I used a whole tank then figured.Agine I am very happy with the 4bta.

pharmd · Oct 10, 2009

needsdiesel: You never felt like you needed more power from the 4BT? what mods did you run? Or was it stock the whole time?

needsdiesel · Oct 10, 2009

stock

Just turned the fuel pin 90 and advanced the timing and it feels like home. I personally did not look at HP its just a number torque is everything.

Dougal · Oct 12, 2009

Peak horsepower is never a good way to compare engines.

Machman · Oct 12, 2009

As previously said, comparing peak HP doesn't really tell the whole tale..

And the short version of my "It's the torque" rant is this:

Torque x RPM / 5252 is Horsepower.

And it's the Horsepower that gets it done, even if you don't want to do the math.

The stock 105 HP 4BT usually gives more horsepower at every RPM point up to it's HP peak at around 2500 RPM than most smallblock gasser engines do at the same RPM points. (And as BobS indicated, there are even some big-block engines that don't out-power the 4BT in it's operating range!) The gasser HP peak is usually somewhere around 4000 RPM.

All other things being equal (weight, gearing, etc.) what this means is that the stock 105 HP 4BT comes off the line and out-accelerates the gasser, but once the gasser gets wound up, it will then out-accelerate the 4BT.

Now, PUT IN A PYROMETER, then twist some screws, drop in a 3200 RPM spring, add an aftercooler, and mebby a bigger turbo, and suddenly the 4BT is out-powering the smallblock up to 3200 RPM, and depending on exactly which one, might be out-powering it comparing peak to peak!

As for durability concerns.. Cummins made 4BT variants that were rated at 250 HP intermittent from the factory. If memory serves, that definition of intermittent was 250 HP for an hour, then you were to operate it at reduced power for the next 7 hours or some such. (Marine version...) So I'd say that momentary excursions into moderately higher HP numbers wouldn't be detrimental.

And if you're needing continuous output of over 250 HP for more than 1 hour in 8 in an automotive application, well..

PGW · Oct 12, 2009

Machman said:
As for durability concerns.. Cummins made 4BT variants that were rated at 250 HP intermittent from the factory. If memory serves, that definition of intermittent was 250 HP for an hour, then you were to operate it at reduced power for the next 7 hours or some such. (Marine version...) So I'd say that momentary excursions into moderately higher HP numbers wouldn't be detrimental.

And if you're needing continuous output of over 250 HP for more than 1 hour in 8 in an automotive application, well..

I'll add to your discussion.

The marine 4BTA-250 makes 490 ft lbs at peak torque, and the rated rpm at 250hp is 3000. Only 1 of every 8 hours can be the HO rpm, the other 7 have to be atleast 200 rpm below. This is also in marine applications where the poor motor always feels like it's going uphill.

Also, you can definitely feel the difference in torque vs horsepower on the road. I've driven a 24valve before, and when you hit the throttle, it just goes, while a gasser must wind up first.

pharmd · Oct 12, 2009

Lreiff: How hard is it to tune all the parts you mentioned. What would be a good twin turbo combination? And lastly, are you talking about a P-pump when you are mentioning the timing modifications? Also, is this assuming there is an intercooler? If not, how much benefit can I get from adding one? Also, can you elaborate on the aftercooler? Where does it go in relation to the intercooler? Last but not least, what is a general price for all the mods so I can figure that into my budget?

Machman/PGW: I have only driven 1st hand a Mercedes 240D, which although is a great car, is also a very poor example of diesel "power". I have been turned onto diesels since then, and can only imagine what a properly tuned powerful diesel would feel like. I did experience a Dodge mid 90's Cummins Blowing my doors off like I was standing still on the highway...

Thanks for the info.

LReiff · Oct 12, 2009

pharmd said:
Lreiff: How hard is it to tune all the parts you mentioned. What would be a good twin turbo combination? And lastly, are you talking about a P-pump when you are mentioning the timing modifications? Also, is this assuming there is an intercooler? If not, how much benefit can I get from adding one? Also, can you elaborate on the aftercooler? Where does it go in relation to the intercooler? Last but not least, what is a general price for all the mods so I can figure that into my budget?

If you are looking for fuel mileage a P-Pump is out of the question because they have fixed injection timing, they are more suited for all out power. The VE pump will do way better for fuel economy because of it's capability to advance injection timing with rpms, however the max power they will make is around 250-275HP. At power levels like this you will need an intercooler and the engine mounted aftercooler becomes useless. If you want pricing and specifics call me and I would be glad to explain everything. I can be reached at 717-993-4200 from 9am-7pm est.

pharmd · Oct 12, 2009

Also, am I sacrificing all the mileage benefits of the 4BT by doind all these mods? The MPG seems like the main reason to swap this motor. The size issue isn't that important to me.

jlk5269 · Oct 12, 2009

milage

You can still get milage with a well tuned 4bt, mods can even improve milage, which is not usually the case for a gasoline engine. Jeremy

nexxussian · Oct 12, 2009

Without some form of charge cooling I would not expect the engine to survive the attempt for such a specific power (speaking of the 3.9).

The JWAC I've seen cools the charge air some, at the higher power settings, I would consider it as a minimum starting point and try to go better from there, either with an air to air setup, or a water to air setup (that doesn't use already hot engine coolant for the 'cooling' fluid).

dillenger1 · Oct 12, 2009

are they taking out shims behind the timing adavance piston?allowing faster advance.The vw guys switch springs to.theres a green spring that suspose to be the :nuke:

br455 · Oct 13, 2009

Dude you need to heed the advice about torque. There is a famous quote
"Hoersepower sells cars, Torque wins races". I have a turboed Buick 455 and it "only" makes 517HP but it puts 647ftlbs of torque on the ground at 2800 RPM. It screams, I mean pulls like a freight train. Anyway torque is king.
Thanks
Brent

reverendd · Oct 13, 2009

If your concerned at all, a 6bt with just a bit of a tune and you'll be worrying about breaking drive train stuff, something TORQUE (even with the 4bt) tends to do and you can drag around a vortec chevy truck as far as you'd like. Probably a bit more available and mileage isn't all that much different? Just an opinion of course, worth what you paid for it...

That said, it's heavier and may require a bit more finesse getting it in there.

Regards,

Rev. D.

khaoskustoms · Oct 13, 2009

I just made a a 2000km round trip with my 4bt powered Dakota. The truck dynoed over 200hp to the wheels, runs 15.0's in the 1/4 and the best tank of fuel I got was 9.45lts per 100kms or 25mpg. The worst tank was 11lts per 100kms or 21mpg. (Thats the difference between cruising at 105kph at 1800 rpm and pushing it at 125-130kph at 2100-2200rpm.) The 4bt compared to the old 318, well, it's not even a comparison. Alot of the big hills the 318 would downshift into 3rd and the 4bt just powers up in o/d with the converter locked. I love it!!!!

Stephen

How much HP?

Our Vendors

Top Contributors this Month

Recommended Communities