Cummins question 4bt

[smalltruckbigcid]

the vehicle is a 95 2500 super cab. Has a very tired 6.5 in it right now. What would be the power difference between the 4bt and a 6.5? I thought a warmed up 4bt would make about 200 hp. so how much does it make and can it be turned up?
George

 

[AJMBLAZER]

Lemme go find a thread over on www.SteelSoldiers.com that just mentioned a lot of info about these...

http://www.steelsoldiers.com/index.php?name=PNphpBB2&file=viewtopic&t=18511

Lots of good info there.

 

[BKinzey]

The link to 4btswaps in the SteelSoldiers thread should supply you with the info you need

200hp seems doable, 300hp is possible with money and shortened life expectation

 

[MaxPF]

the vehicle is a 95 2500 super cab. Has a very tired 6.5 in it right now. What would be the power difference between the 4bt and a 6.5? I thought a warmed up 4bt would make about 200 hp. so how much does it make and can it be turned up?
George

A stock 6.5 turbo already makes 195HP. The 4BTA (turbocharged aftercooled) makes around 130HP IIRC. 250HP is easily achieved from either engine. Both engines can make similar power figures depending on mods. The difference is that the Cummins has less than 2/3rd's the displacement of the 6.5, so it won't have as much bottom end before the turbo spools. It also has less of an RPM range. It should theoretically get better mileage though, but how much better depends on how the 6.5 is built. Finally, the 6.5 is relatively smooth and quieter, while the 4BT shakes like a 9.0 earthquake and makes more noise than a busted chainsaw

If you really don't want to put another 6.5 in for some reason and you're dead set on a Cummins, then a 6BT would probably be a better choice. It doesn't shake as much and it will make way more grunt than a 4BT. Your 3/4 ton frame should handle the extra weight fine, although you will probably need heavier springs (or torsion bars if it is 4WD).

 

[rjfguitar]

I completely disagree, the torque curve of the B series, regardless if it's the 4 or 6 cylinder version, is much more aggressive than the GM 6.5. If a guy matches the HP a 6.5 makes, with a 4BT, the B series should build more torque quicker and come in harder than a 6.5 could even hope for.

 

[MaxPF]

I completely disagree, the torque curve of the B series, regardless if it's the 4 or 6 cylinder version, is much more aggressive than the GM 6.5. If a guy matches the HP a 6.5 makes, with a 4BT, the B series should build more torque quicker and come in harder than a 6.5 could even hope for.

You noticed I said "before the turbo spools". The torque rise is mainly a matter of fueling curve - the pumps on 6.x motors are deliberately detuned to minimize smoke, and that hurts the torque. Crank the fuel and it is a better matchup. The 6.2/6.5 also benefits from an extra 1100RPM of powerband which allows you to hold a gear longer, as well as run a lower rear end gear (although I wouldn't since fuel economy would suffer).

I'm not knocking the 4bt at all - I am simply pointing out that it may not be the most tractable powerplant. The 6BT or another 6.5 would be much better IMO.

 

[rjfguitar]

The 6.5 spins up above 4,000RPM's????

sure stock is governed at 2600 or so....but where's the fun in that?

 

[MaxPF]

The 6.5 spins up above 4,000RPM's????

sure stock is governed at 2600 or so....but where's the fun in that?

Oh, I know you can mod the governor. But all the dyno sheets I have seen shows TQ (and HP) falling like a rock above the stock governed speed. Maybe they needed higher pop injectors and/or more pump timing? Anyway, there must be a reason why Cummins limited the RPMs to 2500 or so

 

[DEMON44]

..........valve springs.


if you upgrade valve springs, you can turn those speeds no problem. I had my VP$$ fueling to 4000rpm. with a smarty race tune. you can get a 4000 GSK for the VE rotary or the p-7100.

 

[rjfguitar]

Oh, I know you can mod the governor. But all the dyno sheets I have seen shows TQ (and HP) falling like a rock above the stock governed speed. Maybe they needed higher pop injectors and/or more pump timing? Anyway, there must be a reason why Cummins limited the RPMs to 2600 or so

In stock applications I don't think Cummins felt that they needed to rev much past 2600rpm's.

As far as the power curve, IIRC.... the bigger GSK kits help to make the powerband wider. Yes, power starts to drop off at 3600rpms or so, but you are still making good power at 3300, as to where stock the power curve starts dropping at 2700 on a motor governed at 3200.

It also depends on the setup of the motors. Giant twins, different cam, huge injectors, etc.... equates to upper RPM performance. Not really streetable anyway.

 

[MaxPF]

In stock applications I don't think Cummins felt that they needed to rev much past 2600rpm's.

As far as the power curve, IIRC.... the bigger GSK kits help to make the powerband wider. Yes, power starts to drop off at 3600rpms or so, but you are still making good power at 3300, as to where stock the power curve starts dropping at 2700 on a motor governed at 3200.

It also depends on the setup of the motors. Giant twins, different cam, huge injectors, etc.... equates to upper RPM performance. Not really streetable anyway.

Interesting I figured Cummins didn't like a bunch of heavy parts on the end of a 4.7" stroke crank slinging around at high RPMs

It seems I remember reading something in some Cummins literature about a destructive harmonic occurring in the 6B's in the high 4000 RPM range... Have you heard about that?