Highway pulls: Sequential or non-sequential?
The Man
Joined: Aug 2001
Posts: 702
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From: Lee's Summit Mo.
Originally Posted by rynberg
I'm confused by this, because once you cross transition, the turbos are in non-seq mode until you drop back below 3k rpm (default PFC setting). I track the car regularly and am in non-seq mode the entire time on the track -- even downshifts/upshifts do not kick it out of non-seq. (Ok, I take it back -- out of the 2nd gear hairpin at Buttonwillow, it does tend to drop back out of non-seq in that one turn...)
First off, let me clarify, I'm talking about the flat spot before transition. Take your car and slam on the brakes from 125mph or so and down shift into a 90degree left hand turn with an immediate right hand sweeper. You lose much momentum from the brake and downshift, now hit the gas at 3300 rpm seq. mode------------- flat spot! You wait for the turbos to hit transition then you take off. IN NONSEQ you don't have that flat spot, even though you make less torque low, the turbos are making linear power and can accelerate the car ever so slightly better in this situation. I was referring to this 3300 to 4500-4700 rpm transition period.(highly modded exhausts and lightweight flywheel out accelerate the turbos so the transition is usually a little higher) I know they work parallel about 4500.
This also confuses me as I'm able to hit 10+ psi in first on a semi-good launch? I do suck at drag racing and my car (wasn't) modded as heavily as yours, so maybe that's part of it?
This is the issue. I have full 3 1/4" exhaust and a light flywheel. By the time the engine revs(very fast) the turbos are trying to switchover and boost so there is not enough time for the turbos to make full boost. Without the transition, there is a little more lag at the bottom but once I hit 3800 rpm I get full boost to redline which I haven't had in some time.
Cool, can't wait to see the results. Good luck on the dyno.
I hope to get my car back next week with BNR Stage 3s running sequentially on a mild streetported motor -- car will still have a hi-flow cat. I hope to get the car tuned in September after break-in and we'll see what she'll do....
First off, let me clarify, I'm talking about the flat spot before transition. Take your car and slam on the brakes from 125mph or so and down shift into a 90degree left hand turn with an immediate right hand sweeper. You lose much momentum from the brake and downshift, now hit the gas at 3300 rpm seq. mode------------- flat spot! You wait for the turbos to hit transition then you take off. IN NONSEQ you don't have that flat spot, even though you make less torque low, the turbos are making linear power and can accelerate the car ever so slightly better in this situation. I was referring to this 3300 to 4500-4700 rpm transition period.(highly modded exhausts and lightweight flywheel out accelerate the turbos so the transition is usually a little higher) I know they work parallel about 4500.
This also confuses me as I'm able to hit 10+ psi in first on a semi-good launch? I do suck at drag racing and my car (wasn't) modded as heavily as yours, so maybe that's part of it?
This is the issue. I have full 3 1/4" exhaust and a light flywheel. By the time the engine revs(very fast) the turbos are trying to switchover and boost so there is not enough time for the turbos to make full boost. Without the transition, there is a little more lag at the bottom but once I hit 3800 rpm I get full boost to redline which I haven't had in some time.
Cool, can't wait to see the results. Good luck on the dyno.
I hope to get my car back next week with BNR Stage 3s running sequentially on a mild streetported motor -- car will still have a hi-flow cat. I hope to get the car tuned in September after break-in and we'll see what she'll do....
One thing to consider as well now is how you can use the PFC to affect the transition to give it a smoother line. I've had the M2 stage 3 and when the second turbo came on line, bam, 50 rwhp in less than 500 rpms made for fun, but not fun in the curves. With the PFC, I can get the rwhp curve to have the same shape as a non-seq car with the only exception being the actual transition point dips, but the overall curve is like a single or non-seq setup.
Tim
Tim
The Man
Joined: Aug 2001
Posts: 702
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From: Lee's Summit Mo.
I agree Tim, since I run the petttit ecu I don't have that luxury of setting a transition point. I am considering going back to seq. and having Cam tune me a microtech and a switch so I can have the best of both worlds, but right now I'll have to dyno the car and make a good comparison.
ARt
ARt
I'm On Polychromatic Time
Joined: Jan 2004
Posts: 263
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From: Philadelphia
I run a simplified SEQUENTIAL set-up in my black FD and at 16 psi it laid down 365 rwhp. I have driven friends' single turbo cars, an unmodded non-seq. car and ridden in modded non-sequentials, and I without a doubt prefer sequential. Many times, when racing someone on the highway from 40-60 mph to over 100, I have not even had to downshift from whatever gear I'm in to easily pull on them. I don't drag race my car, so I can't speak for the advantages/disadvantages of that. On my dyno sheets, the switch at 4500 rpm or so is barely a blip- when flooring it through the gears, my secondary kick-in is pretty damn smooth. But I have a great tuner to thank too. I autocross, and run Deals Gap and sequential is a HUGE advantage in those situations, as it is on tracks like Lime Rock, Watkins Glen etc. Long live sequential! it might be damn complex, but it's worth it!
and sequential is a HUGE advantage in those situations, as it is on tracks like Lime Rock, Watkins Glen etc. Long live sequential! it might be damn complex, but it's worth it!
I'm On Polychromatic Time
Joined: Jan 2004
Posts: 263
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From: Philadelphia
Originally Posted by rynberg
Because:
1) Running high boost on the stock twins in seq = blown twins because of the pre-spooling of the secondary.
2) Running high boost on the stock twins in seq = violent transition.
3) Running high boost on the stock twins in seq = more likelihood of problems with the control system.
1) Running high boost on the stock twins in seq = blown twins because of the pre-spooling of the secondary.
2) Running high boost on the stock twins in seq = violent transition.
3) Running high boost on the stock twins in seq = more likelihood of problems with the control system.
But I am the walking, talking, driving contradiction of all 3 of those points! My black FD still has the original, unported engine and the original sequential twins. It has 66,000 miles on it, and the only problem I've had in the two years I've owned it is the alternator going bad a couple months ago. I've autocrossed it, driven it daily through last summer, driven 750 mi. each way to Deals Gap then ran it HARD on the Dragon 7 times... and like i said in the previous post, no violent transition whatsoever. It's a beautiful thing. And for the past 11 months, I've been running over 17 psi. It can be done, but you have to be paranoid about caring for your car and who works on it. (and the previus owners too).
Lives on the Forum
Joined: Dec 2001
Posts: 14,716
Likes: 10
From: San Lorenzo, California
Originally Posted by fastcarfreak
...most people drag racing are going to be in need of that mid range power....
[QUOTEAznPhoenix]
I went from a sequential set up w/ far more mods running 13 psi to true non sesquential turbos w/ js a dp running 7 psi(due to lack of boost pill), and i can tell you this, when i ran my old fd @ 7 lbs (lack of boost pill) my new non seq fd felt js as fast or faster.
[/QUOTE]
Give me a break!
Art, your car is not "exactly" the same. You have that little DP splitter. 
Guys, there are a lot of things to consider with the seq verse non-seq setups. However, in the end, it's personal preference. There has not been one single test that actually demonstrates the concept of the FULL conversion offering more power. While it's a good theory on it, there is just no concrete evidence. If there is, someone show the test as I've yet to see it. I'm not saying the theory is wrong, but without proof it's just a theory.
What has been proven is that the sequention setup cannot deal with very high levels of boost. At that point it becomes a hindrance and THAT is the reason drag racing guys don't use sequential (as they are going for all out power). Basically, if you are planning to run anything over 15 PSI, the sequential system will most likely give you fits (as it wasn't designed for that).
Guys, there are a lot of things to consider with the seq verse non-seq setups. However, in the end, it's personal preference. There has not been one single test that actually demonstrates the concept of the FULL conversion offering more power. While it's a good theory on it, there is just no concrete evidence. If there is, someone show the test as I've yet to see it. I'm not saying the theory is wrong, but without proof it's just a theory.
What has been proven is that the sequention setup cannot deal with very high levels of boost. At that point it becomes a hindrance and THAT is the reason drag racing guys don't use sequential (as they are going for all out power). Basically, if you are planning to run anything over 15 PSI, the sequential system will most likely give you fits (as it wasn't designed for that).
DinoDude
Joined: Feb 2002
Posts: 1,170
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From: Harpers Ferry, West Virginia
[Quote-Mahjik]What has been proven is that the sequential setup cannot deal with very high levels of boost. [/quote]
What is "very high levels of boost"? I get 17-18 lbs out of my sequential system on race gas.
Simplicity is about all non-sequential has to offer.
What is "very high levels of boost"? I get 17-18 lbs out of my sequential system on race gas.
Simplicity is about all non-sequential has to offer.
Thread Starter
Junior Member
Joined: Mar 2005
Posts: 24
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From: X
this was a highway question only, not drag racing or auto-x.
I pretty much just do highway pulls with friends and was wondering which would be best just for highway purposes, not to start a sequential debate.
I pretty much just do highway pulls with friends and was wondering which would be best just for highway purposes, not to start a sequential debate.
I'm getting ready to go full non-sequential over here.
Why? Like every six months some stupid hose breaks or a solenoid goes bad and then my car is gutless. My lastest prob. As of two weeks ago my primary is really, really laggy and highest boost (on the primary) is 5 psi. Secondary is at 10 psi. After 4500 RPM even though the boost gauge reads 10, the car is still slower as I know my primary is not working to potential. Bah I'm sick of it. Simplify... Besides I seem to have right criteria for the fastest spool time: aftermarket SMIC, CAI, DP, MP (just need an exhaust)
My theory on those who think that the non-seq cars have more ponies up top is because on stock sequential cars the boost pattern is 10-8-10-8. While obviously in non-seq it's 10 (assuming stock boost) all the way till redline.
Why? Like every six months some stupid hose breaks or a solenoid goes bad and then my car is gutless. My lastest prob. As of two weeks ago my primary is really, really laggy and highest boost (on the primary) is 5 psi. Secondary is at 10 psi. After 4500 RPM even though the boost gauge reads 10, the car is still slower as I know my primary is not working to potential. Bah I'm sick of it. Simplify... Besides I seem to have right criteria for the fastest spool time: aftermarket SMIC, CAI, DP, MP (just need an exhaust)
My theory on those who think that the non-seq cars have more ponies up top is because on stock sequential cars the boost pattern is 10-8-10-8. While obviously in non-seq it's 10 (assuming stock boost) all the way till redline.
Last edited by Montego; Aug 12, 2005 at 01:12 PM.
Originally Posted by tcb100
What is "very high levels of boost"? I get 17-18 lbs out of my sequential system on race gas.
Simplicity is about all non-sequential has to offer.
Simplicity is about all non-sequential has to offer.
The seconadary part was always fine with the higher levels of boost on the seq setup; as rynberg pointed out, after 4500 rpms they are the same. It's been the primary and transition area that people have had a problem with....
Originally Posted by A.W.O.L
I pretty much just do highway pulls with friends and was wondering which would be best just for highway purposes, not to start a sequential debate.
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Joined: Dec 2001
Posts: 14,716
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From: San Lorenzo, California
Originally Posted by montego
My theory on those who think that the non-seq cars have more ponies up top is because on stock sequential cars the boost pattern is 10-8-10-8. While obviously in non-seq it's 10 (assuming stock boost) all the way till redline.
If a stock sequential car's pattern is 10-8-10-8, then it will also roll off up top when going non-sequential. THERE IS NO DIFFERENCE BETWEEN THE TWO SETUPS ABOVE 4500 RPM! I'm failing to see why people aren't getting that!
ha ha that I didn't know.
So what happens at 6500 RPMS that causes the boost to drop back to 8? In the sequential set up I it's obvious it was designed that way. 8 psi transition, 8 psi past 6500 RPMs. But in a non-seq car no more dip in transition but what component causes the dip at 6500?
So what happens at 6500 RPMS that causes the boost to drop back to 8? In the sequential set up I it's obvious it was designed that way. 8 psi transition, 8 psi past 6500 RPMs. But in a non-seq car no more dip in transition but what component causes the dip at 6500?
Originally Posted by montego
ha ha that I didn't know.
So what happens at 6500 RPMS that causes the boost to drop back to 8? In the sequential set up I it's obvious it was designed that way. 8 psi transition, 8 psi past 6500 RPMs. But in a non-seq car no more dip in transition but what component causes the dip at 6500?
So what happens at 6500 RPMS that causes the boost to drop back to 8? In the sequential set up I it's obvious it was designed that way. 8 psi transition, 8 psi past 6500 RPMs. But in a non-seq car no more dip in transition but what component causes the dip at 6500?
Racecar - Formula 2000
Joined: Sep 2002
Posts: 4,029
Likes: 367
From: Bath, OH
Originally Posted by Mahjik
Just lack of exhaust flow. Opening up the exhaust allows the car to hold boost to redline.
Originally Posted by DaveW
Also restricted intake flow... Opening the intake also improves high RPM boost.
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