Compound turbo ?

[joverman]

I have a couple of questions about compound turbo's. I would love to eventually run this type of setup simply for its flexability when towing or playing, but right now its just not a possibility for me. So I just what to try to learn as much as possible.

If I understand the plumbing on the intake side it goes from the air box to the "big" turbo to the "small" turbo to the intercooler to the engine. On the exhaust side gasses run from the header/exhaust manifold to the "small" turbo to the big turbo and then exit. I realize that most systems have a wastegate/diverter that when excessive pressure builds will allow spent gasses to bypass the small turbo to help spool the bigger turbo. If all of this is correct then I understand the exhaust side pretty well but I am confused how if the small turbo is "upstream" from the big turbo when the big turbo finally starts making positive boost how does the small turbo not act as a restriction and limit boost? Does the small turbo further compress the intake charge coming from the active "big" turbo. Is there a bypass past the small turbo to the intercooler?

Also I have read on several occasions that the head gaskets on most D-Max's are good to a certain PSI (I can't remember the exact # but it seems to be around 45 or 50) with a big single charger but the heads studs and gaskets are able to hold slightly more boost(around 10-12 PSI more) with a compound system. Is there any truth to this or is it a load of bull? Is the IAT charge cooler with a compound system. I realize that this is alot of questions for a new member but any help you can give or a link that might help me understand how a compound system works I would appreciate it.

Thanks in advance.

 

[Killerbee]

Someone here will correct me if I err, but the small compression precedes the large compression.

Sometimes, aftercooling is built in to each stage. Since two smaller compressions is usually more efficient than one large one, manifold charge temp is lower with twins.

Someone else will have to reply to the head strength question, I don't understand it well enough.

 

[JoshH]

I have a couple of questions about compound turbo's. I would love to eventually run this type of setup simply for its flexability when towing or playing, but right now its just not a possibility for me. So I just what to try to learn as much as possible.

If I understand the plumbing on the intake side it goes from the air box to the "big" turbo to the "small" turbo to the intercooler to the engine. CorrectOn the exhaust side gasses run from the header/exhaust manifold to the "small" turbo to the big turbo and then exit. Correct I realize that most systems have a wastegate/diverter that when excessive pressure builds will allow spent gasses to bypass the small turbo to help spool the bigger turbo. On the MPI system there is no wastegate for the small turbo. The turbo vanes act as the wastegate and limit boost as necessary. The big turbo does have an external wastegate to limit boost created by the big turboIf all of this is correct then I understand the exhaust side pretty well but I am confused how if the small turbo is "upstream" from the big turbo when the big turbo finally starts making positive boost how does the small turbo not act as a restriction and limit boost? Does the small turbo further compress the intake charge coming from the active "big" turbo. Is there a bypass past the small turbo to the intercooler?There is no bypass around the small turbo. The small turbo is probably somewhat restrictive but not so much that it will negatively affect performance. I have a boost gauge between the two turbos and one at the engine. I can say on a race tune I will see about 28-30 psi of boost from the big turbo and 50-55 at the engine. So the small turbo does further compress the air from teh large turbo.

Also I have read on several occasions that the head gaskets on most D-Max's are good to a certain PSI (I can't remember the exact # but it seems to be around 45 or 50) with a big single charger but the heads studs and gaskets are able to hold slightly more boost(around 10-12 PSI more) with a compound system. Is there any truth to this or is it a load of bull? I don't know if a compound setup is safer for head gaskets, but I have run as much as 55 psi of boost on a 100% stock engine without any problems so far. Is the IAT charge cooler with a compound system. With an ambient air temp around 70, I see IATs of about 130 by the end of a 1/4 mile run. I realize that this is alot of questions for a new member but any help you can give or a link that might help me understand how a compound system works I would appreciate it.

Thanks in advance.

If you have any other questions, I'll answer them the best I can.