Engine/Transmission (1998.5 - 2002) BD Twins, No better than single. Why?

[Blacksdieselhp]

I' bought a truck that had a set of BD twins on it . They suck on this truck. They only boost 55 psi with the wastegate plugged. And egt's are HOT. Just wandering what the point of having these twins are. A single turbo can do better than these things. They don't even spool quicker than a single. Is there something wrong with my setup or is this normal? I had a set of twins that I built using an HX-35 and HT3B and they were awesome. Spooled decent, cooled egt's way down and were very very strong. They made 70 psi. But I was just curious if this is normal for the BD twins. Thanks

 

[PC12Driver]

From what I understand, you want the top turbo to wastegate. If you try and stuff all the exhaust drive pressure through the top turbo, 1) your drive pressures will be out of sight and 2) the top turbo will be way out of its efficiency range on the high side (overdriven and blowing hot air). The 'gate needs to open once the small turbo reaches it's max efficiency (35-40psi), and then the excess drive pressure bypasses it and blows into the big turbo to get it spooling. That way each turbo stays in the bottom end of it's efficiency range and blows relatively cooler, denser air for a given psi reading.



BD is pretty vocal about not messing with the wastegate on their setup. Let it do its thing and let the turbo's share the load.



Also, twins will always spool slower than the smallest turbo due to the drag created by the big turbo on the bottom end.

 

[Blacksdieselhp]

I'm aware of everything you said, but these things are just crap. I ran them with the wastegate hooked up and they really sucked then. 45 psi was all they would do. I just plugged it to see if they could offer more pressure. For what these things cost, they should be a Lot better. I'm sure glad I didn't pay for them. I mean, an HTB2, B1 or Bell USB will do more than these twins. I put my Bell on and the truck is a lot stronger. It runs just a little cooler, but the power gain is worth the swap and it spooled better. I thought that was the point of twins in the first place. To spool better than a big single, to run cooler and to offer as much or more power. I just don't understand why they even put this setup on the market. Piers setup is far better. But I do like the BD transmission. Its awesome. I'll definately be going back to an HX-35/HT3B setup. I really appreciate your input though. Thanks

 

[Jim Fulmer]

From what I understand, you want the top turbo to wastegate. If you try and stuff all the exhaust drive pressure through the top turbo, 1) your drive pressures will be out of sight and 2) the top turbo will be way out of its efficiency range on the high side (overdriven and blowing hot air). The 'gate needs to open once the small turbo reaches it's max efficiency (35-40psi), and then the excess drive pressure bypasses it and blows into the big turbo to get it spooling. That way each turbo stays in the bottom end of it's efficiency range and blows relatively cooler, denser air for a given psi reading.



No bragging rights here but I proved that 2 years ago going from a non gated to a gated in the hot pipe, works well and drives the big charger harder... ..... better map!



BOTW, a 35/3B is real hard to beat!



Jim