Wats the difference between these 2 turbo configurations?

 

Purely speaking, series != sequential.

Series would imply that one turbo stops at a certain rpm, and another engages from that point on. I guess over a very broad rpm range you could acheive maximum torque, however at the transition there will be a weaker spot as the first turbo loses efficiency or the second turbo is running too low to get maximum efficiency. I don't think this is a common setup, if anyone uses it at all.

Parallel is exactly as it sounds - two turbos working together through the same rpm range. Generally this is done because two smaller turbos spool faster than one larger turbo capable of the same flow. The downside is more complexity, weight, and cost than a single. The stock 300ZX I believe has this setup.

The stock FD is sequential - it is a primary turbo working alone until 4500rpm, then the second turbo engages in parallel and both work together above 4500rpm. It provides a smoothly increasing power through the whole rpm range, but the piping and control system is very complex. Some people convert to parallel (non-sequential) operation for simplicity sake.

Dave

 

very well said... i went to non-seq just for simplicitys sake, it cleans up the bay alot.

 

but is it true that running parallel gives you more turbo lag, but more power at peak?

 

...and i stayed sequential b/c i love the way it feels

tastes great. less filling. j/k

 

Once the second turbo comes online, they are both the same (two turbos are two . So, the difference is really only before 4500 rpms.

 

And it is sort of important to power an 80 cubic inch engine down low so that it gets to higher revs quicker.

 

So why would anyone even think of converting to non-seq (parallel) if the only "benefit" you would see, is actually an increase in turbo lag? i.e. up to 4500 now, instead of 3000

 

Two reasons really:

1. To simplify the engine area (ie no more troubleshooting sequential control problems).
2. Some road racing guys find the lack of the transition more predictable when driving on the track.

Basically, non-seq moves the low end power into the midrange. So, with non-seq, you'll have more power during the sequential transition area, but sequential will have more power in the lower area. The high area is the same.

 

SERIES has the output of one compressor feeding the inlet of another compressor, with the 2nd turbo boosting the boost of the first. This is done in diesel "tractor pull" competition engines for some mega boost.

PARALLEL has turbos sharing the avaiable exhaust gases, and each pumps out boosted air to the intake manifold at the same time. Nisaan 300z and Mitsu 3000 GT v6's were good examples.

SEQUENTIAL is a special version of PARALLEL where all exh gasses initially feed just one turbo, and the other is essentially locked out. This provides great low end performance, but has a complicated control system that is hard to troubleshoot, vs just simple PARALLEL. The FD and last Supra Turbo are examples. Porsche did it decades ago.

 

Well, I guess to make things simple, a some guys will go parallel. If you think about it though, it's not like either turbo is running at more boost, so 7000 rpm sequesntial at wot and 7000 rpm parallel at wot isn't making any difference in power, but let's say you're at 3000 rpm and go wot. The sequential turbo will kick in with the primary going only first, so since it's only one turbo, it will begin to spool up quicker, while with the parallel, both turbos are trying to spool up at the same time, so you're not accelerating as fast at first. But when the parallel starts going, you have 2 turbos that are starting to come alive at the same time, so it feels like you are going faster (ideally because you're getting to a speed from a slower starting point). Think of it as an xy chart, with x being the rpm, and y being the horsepower, with the sequential twins, the power is more linear across the chart, where as the parallel is more of an exponential curve, kind of like the plot below (note that this is not an accurate plot cause I just drew these, not an actual dyno plot). Since the power is coming on faster at a later rpm, the prallel setup feels like it's giving more power because it's more of a kick in the pants.

 

I personally don't completely like my current parallel set-up.... yes it is more balanced for track driving, but, you always have to be in the upper part of the power-band to keep momentum, however, if you slip up and drop below the operating RPM of the turbo's in parallel, hooo buddy, you're losing time at the track!! NOOO!!!! Anything with a lot of shifting/low gear work, sequential or a mild BB is a good thing.

 

That's riiiight! mmmm!

 

I am very new to RX-7's and turbo's. I am about to purchase a 93 that has been switched to a non-sequential. I think i want to switch it back to sequential. How much work does this involve? How much would it cost? Does anyone know any good shops in Philly to get work done??

 

Depends if they did a 'full' non-sequential or a 'poor mans' non-sequential. In the full nonseqential conversion, the turbo manifolds get welded and modified. I don't know how un-doable that is, but you can replace the turbos and manifold for a few hundred bucks. The poor mans is a solenoid and vacuum hose modification, so if you replace the missing solenoids and buy some vacuum hose you can do it for probably under $100. If the guy has the old parts, maybe for free.

Dave

 

Again, for everyone that says with parallel you don't get boost till 4500 rpm's is clearly doing something wrong. If you do full non-seq you get boost well before that. Most people go parallel becuase they're sick of dealing with sequential problems. If your seq system works perfectly and always has there's probably no reason to go parallel unless you're preparing for a single turbo in the near future then you can have most of the hard work done in advance...

 

Umm, read the thread again. No one said that.

 

A proper full non-seq conversion also has a little more top end power due to removeal of some parts that cause more exhaust back presssure, and intake turbulance.

You know better that that Mahjilk.

 

That's the "theory", however, there has been no proof showing that. If you have the proof Chuck, show it as I would be interested in seeing it as well (and actually "apples to apples" comparison).

 

Nobody is going to spend money to dyno the difference, that is why it has not been proved. But common tunning experience says that reducing exhaust turbulence and back pressure will help a little. Removing the turbo control gate and port matching the #2 ports will help.

Somethings do not need proving to know that they work. Science said that bumble bees could not fly for many years even thought it could be seen.

I have not seen anyone prove that B10EGV plugs work better than BUR9EQs at high boost but we know they do.

Why have most of the senior experineced members left or not participate anymore, they are fed up with this same metallity of BS.

 

Chuck, that's a load of bullsh*t.

If you have facts, point them out. If not, post the truth which is "it's theory". The question isn't whether or not reducing exhaust turbulence will help in overall power gains, the question is how much turbulence does the control gate actually provide when using the poor mans conversion. The next question is how much of a measureable gain does the removal provide.

I know someone who did both (poor man and full) back to back and noticed no difference on the butt dyno. I would wager the dyno difference would either subtle or nothing.

There are tons of tests out there demonstrating the usefulness of spark plugs in certain situations. While they may not be RX-7 specific, they do the benefits.

This is the same reason we have people passing down the same WRONG information as there are no facts to back up the claims. One person says something, and if he sounds like he knows what he's talking about, people just fall in line and quote the same garbage to everyone else.

 

So you only accept some of the data that goes with your beliefs.
Checking your history, I do not see much innovation from you on the forums.
But you sure are a moderartor!

 

Chuck,

I've never claimed to know it all when it comes to these cars or any cars for that matter. There are many people on this forum that know more than me, and many that know less.

I speak about what I have experience with... i.e. you don't see me telling people how to program their PFC's just because "I read about it". In this case, what limited experience I've had with the non-seq (with a friend) has shown that the full conversion yields no noticeable results better than the poor mans. Not to say there isn't any gain at all, but so far not enough to justify the extra work involved.

Interesting as I asked you to show proof for your comments (as I would really like to know for sure as well) and all you can do is attack my character. So, when all else fails, flame? This is exactly the time of moderation this forum needs.

Chuck, if this is the kind of help we can expect from moderators on this forum, why don't you just leave?

 

I am resigning as of today because of this forum is now too RICER and has too many people like you and Jim Lab.

 

Thanks Chuck, you are already making this a better place.