what are the pros and cons of both?

To be honest, im not even sure what either truely mean.

 

http://www.fd3s.net/non-sequential.html

Ill save you from the flamage

 

Sequential is when one turbo is spooling between a certain amount of RPM under a defined limit, then after that limit is passed the second turbo spools. Very complicated piece of engineering.
Non-sequential is when both turbos spool at the same time.

Pros of sequential: virtually no turbo-lag, because one spools right after the other, and because the first one spools from such a low RPM.
The Cons: A lot of wires! A lot! A lot of vacuum hoses, a computer that needs to control boost on the spooling at the different times for the turbos. Basically, it's a big hassle.

Pros of non-sequential: Not so many wires of hoses, lower cost, computer doesn't need to be tuned to spool one turbo, then the other.
Cons: There may be some boost-lag, but this can be fixed with a ball-bearing turbo, which spools like right after 2000 RPM, with the Garrett GT35R being the most popular...

 

[QUOTE=Mike0071;8188493]Sequential is when one turbo is spooling between a certain amount of RPM under a defined limit, then after that limit is passed the second turbo spools. Very complicated piece of engineering.
QUOTE]

Thats how i thought it worked. Thanks for your help with everything.

 

Very nice concise description Mike. While the information is there, often it can be hard to find in a search amidst all the dross. Kind of like this post I suppose.

 

next time please search before posting something like this. considering these cars have been on the road for 15 years, you can be sure that this topic has been discussed many, many times.

 

^ Agreed.

There was just a thread about this a couple weeks ago...

In the end it's a matter of personal preference whether you keep twins or go single. And if you stick with the twins it's a choice of personal opinion as to which, Sequential or non-Sequential, is better.

Long and short of seq vs. non-seq:

Seq = primary turbo from 1krpm-4.5krpm, then primary and secondary from 4.5krpm-redline. Full rats nest.

Non-Seq = primary and secondary turbo from 4-4.5krpm until redline. Less of a rats nest.

Some people claim more power from non-seq, though power gains in this regard are questionable since it's still the same turbo's being used, at the same boost level.

 

From what ive seen and driven, the non sequentials have a smoother powerband because there is no transistion period.

but the sequentials have almost zero lag and they just pull real clean.

that said, the sequentials seem to be a dice roll in terms of how much boost you get out of the secondary.

It seems like the non sequentials get "more power" just because both turbos are spooling at the same time without that dice roll of "what am i going to get this time". There isnt anything to restrict the secondary anymore, it WILL spool at 10 psi, at stock levels.