sequential turbos

sequential turbos?

I had a crazy idea to run sequential turbos. idk how but I figured I could get some throttle bodies and use them as bypass valves and make up a program that opens and closes each correspondingly based off whether the big turbo is spooled up or not. they would feed off the same manifold the smaller up top the bigger below and they could each feed into a y pipe with the throttle bodies acting as a bypass valve before it gets to the y. they could run into the same intercooler (I was hoping) but idk if I would actually lose power by not going big enough piping for the cfm of the turbo or going to big. I am worried about using too big pipe for the little turbo when it gets out the y and I think I might have to do some dumb shit like put the y at the intercooler and have the bypass valves there and another y pipe going out with more ypass valves and even more bypass valves at the end. idk I need to do more research and thats why I'm here

also, would it be easier to go carb or FI with a big turbo?

It will be easier running EFI with a turbo. Having to set up a carb and ignition system that will co-operate with a boosted engine is complex and will have limitations. EFI is all mapping and ignition/fuel delivery curves. If something falls short in fuel delivery, change the pump and injectors and retune it. Just an opinion :)

I've never gotten into programming and stand alone controllers/boards. If you are comfortable with that kind of stuff, perhaps adapting a late model variable vane turbo is within your ability. It will take up much less space and probably give much smoother performance. Also, throttle bodies won't hold up to the heat of exhaust duty. Especially so close to the manifold. If what you meant was controlling the flow of exhaust through each turbo by using a throttle body.
If you really like the idea of multi turbos, there was recently an episode on Jay Leno's Garage YouTube with a Lancia rally car from the 80's. It had , I believe, three turbos with all kinds of plumbing and waste gates to switch between the three of them. Researching that system would be a good start

OK a sequential turbo setup consists of 2 turbos, a big turbo and a small turbo. the small turbo spools and tides you over until the big turbo spools. the big turbo spools and the small one is no longer needed.

so no, I was talking about throttle bodies through the intake piping. I have never heard of intercooled exhaust... lol that's a good one. I just want them for the fact that each has a Position sensor already on it and I can get them for whatever size pipe I have. its so that one turbo doesn't backfeed into the other and work against me. every sequential turbo car I have seen has had some bypass valves on the pipe for the turbos for that reason. it also helps to ensure that each turbo is spooling correctly and that we aren't making things weird running 2 turbos at one time. 2 turbos of the same size will work, but if both a big and small turbo were to be forcing air into the same pipe the air would flow at different speeds and it would do all sorts of funny things, mainly turbulence. and that's gonna decrease volumetric efficiency in the intake. and then it is gonna be just an overall crappy motor.

i know I need an oil cooler, a bigger oil pan, I would like a 4 valve conversion kit if I can find one but I doubt I will. i could modify a 4 valve head to work with the engine...? maybe takea 4G63/4G64 head and modify them??? I know that the 4G64 came in a 16 valve SOHC version, maybe that would be easier to modify to bolt on? or maybe even a aftermarket option is offered? idk, big plans. I have the money and the ideas, I am ready to rock and roll. but for right now, I am gonna drop it in with the max duration max lift 'towing' cam and weber and header, imma cut the cat, and then imma call it 'custom'. 3 of the main mods, right there.

The G63B has a provision for an oil feed on it (by #4 exhaust port) - maybe the 4G64 has it as well (never really looked but most likely it does). Just need to modify the sump so it has a drain line from the turbo(s). Now, if you wanted to go down a strange but possibly do-able route, me and a friend looked at BMW twin cam head and compared the head gasket to the 4G54. Some milling and modifications and the head might bolt down (it will need timing chain mods and a modified timing cover but it has to be cheaper than the HKS twin cam head and easier to find...) You can then use BMW manifolds to do the rest of the work...

That's a good idea, I will look into that and compare prices.

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Originally Posted by Salteen

That's a good idea, I will look into that and compare prices.

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When I was an active member on another forum there was a member who was actually in the process of doing this modification. I never saw how much progress was made - I was mostly interested in how the timing chain and guides were being set up + how to get around the timing cover issue as I saw these as being the biggest roadblocks to successfully pulling this off.

Yeah I think if I cut up the truck just a bit i could fit stuff in it. Here is what I am talking about. It's like twin turbos but one spools faster than the other and it tides you over till the big one spools up.

Sounds like a lot more work vs a properly sized turbo, or a variable displacement/vain turbo.

Yes that's true, but those can be more expensive too. It also requires more tuning and a custom ECU given none of these trucks had that. I also had my head modified for direct injection, I have a second head I am running until I do all this. I am going MPI and DI with twin 24 lb/min injectors. So like 48 lb/min total.

Here is the diagram I forgot about.

Attachment 24416

And sequential wont require any less tuning?

Well kinda. You are setting for 2 boost levels instead of a constant tbh boost level setting, unless a variable turbo works different from what I am thinking

https://www.youtube.com/watch?v=CbdY1rymBJg

I have also been thinking about a centrifugal supercharger as well, that would be really cool (and very 80's lol)

I think a variable vane turbo or a twin scroll might the way to go. Will make it a lot simpler to set up and be able to cover the bases from low rpm to open throttle. Dash 12v engines had split pulse manifolds which worked better than stock single manifolds - they spooled up faster. Now they're developing variable vane twin scroll turbos. Welcome to turbo madness :grin:

Yeah I think I'll stick with a belt driven turbo (centrifugal supercharger) or the sequential turbo setup or maybe just a straight twin turbo setup lol. I just dumped over 4500 into everything and ots import parts so it'll take a while to be here (so they said) bit I have a head set up for DI and I have the intake on the way. In the mean time I am gonna have the 87 head (actually a 82 head) machined and put on and drive it like that

A buddy of mine wanted to do a sequential turbo setup with a different route - use a small turbo to spin up boost fast, then use the output of that turbo to spool the big turbo, like the later RX-7 s did. The small turbo was like off a 1000 CC motor so the spool up was really quick, and turbo lag would be almost non-existent.

parallel turbocharging I think is what that is called. was it adequate boost to spool the second turbo? if so I might just go that route lol

look up the late model Mazda RX-7 turbo setup.

The way pennyman is describing is usually what I've seen done when running multiple turbos. I think it is technically called "staged turbocharging." Usually looks something like this:
https://www.atsdiesel.com/product_im...2A352218-2.png