I tested my car yesterday and notice a lag between 2000rpm to 3000rpm with JWT 700bb.

as you can see from the dyno chart...how do I minimize the lag....I got Borla exhaust, could this be the problem ?
or more tuning is required.

https://my350z.com/forum/forced-induction/266773-thanks-to-vrt-i-can-now-joint-a-500whp-club.html

 

Looks like lag to me. Do you have straight pipes? Get the EVOTT exhaust. It sounds similar to borla, but has much bigger piping. Its quiet too (like borla). The APS 2.5'' exhaust is another quiet exhaust (if thats what your looking for). They both flow VERY well. You will need a retune after the exhaust. You'll make more power as well as get afaster spool.

 

Eh . . . . it takes time for the Turbos to reach full boost. That's what lag is.

 

is the exhaust the problem ? sorry i am asking becasue I am still new to all this turbo things. will the stand alone HKS F CON help ?

 

Having a larger exhaust will make for less backpressure behind the turbine. Back pressure= equals opposing force to the way that you want the turbine to spin hence lag. However, I don't think this is entirely your problem. You are using the larger 700bb turbos if I am not mistaken which means they take more to spool up. I think that if your exhaust was restrictive enough to cause lag at such a low RPM it would have to be stock. At that RPM you are really not pumping out that much gas especially compared to 4500rpms to redline. With that in mind you have two things I can think of that are causing lag.... big turbos, not enough exhaust gas at that RPM to spool them similar to the smaller turbos.

Even still I think that is a reasonable RPM to have lag without sacrificing fun and drivability.

 

depending on what gear that was done in, it'll show up differently.

if the run was done in 5th gear, the turbo would actually spool up sooner than if it was dynoed in 4th gear and the charts would look slightly different. The 5th gear pull would look nicer than a 4th gear pull because the turbo will be fully spooled earlier

it looks to me that the JWT 700bb turbos don't even think of getting started until you're at least at 3250 rpms
Maybe a different exhaust or boost controller would help some


What're you're technically seeing on the dynochart isn't really lag, it's "boost response"

the only way you can test or log the lag is with a timer after going full throttle and and log the hundredths of seconds between the instant your foot reaches full throttle and the instant the turbos give you positive boost. The amount of lag is going to be different at different rpms ranges, but above 4500 rpms, it's going to be almost instant for most turbos available on the Z to catch up with what your foot is doing where they give you even the slightest positive boost

 

^^^
True since a turbo is load based and there is a higher load at an earlier rpm as the gears go up.

 

^+1. I dont think the exhaust is the only factor, but it is a major factor. How do I know? In turboed cars with a severely limiting exhaust, the torque number is almost always higher than HP.
It wont hurt yoursetup to get a bigger exhaust. I can garantee you'll pick up power and loose some lag. The efficiency of any turbine is proportianal to the pressure gradient across the turbine. Increased efficiencey= more power, less lag. Also, heat is carried away from the engine faster, so lower temps ect. Its all good news .

 

no lag in 5th gear....btw 5th gear got busted during dyno....usaully get lag in 1,2nd and little in 3rd.

this forum is very informative, thank you for all inputs.

 

How long does 1st, 2nd and 3rd gear REALLY last?! hehe

 

somethings different with your setup vs VRT's other 700bb cars where the graph has a broader area. I've never heard VRT or anyone complain about lag with the JWT kit - 700bb or not

 

Test pipes or cats?

 

Enjoy that beautiful car...I wouldn't change a thing...

M

 

Michael, good to hear from you , just like what you recomended to me before, a new exhaust sytem. The car is awsome and it's so fun to drive. Big smile on my face every time I hit 3rd gear.

Good luck tomorrow.

 

not for long because the car is going back to the dealer to get new tranny and they better do it with no cost to me because it's still cover under warranty.

 

EVOTT exhaust Only exhaust I'd recomend for FI. Or APS 2.5''. Low key, does the job right, fits perfect.

 

good luck on the tranny under warrenty. It's worth a shot to try

 

if the exhaust were the cause, I would guess that you'll get the flatline on a higher rpm range. backpressure would give you a tini burst of torque on the lower range, no? bb700 supposedly only have 300rpm lag to that of the 530, but I think there might be more... I'd change out the stock cats and the tiny exhaust you got, just for good measure, cuz they don't belong with your turbo.

 

I agree with this guy

 

A boost controller might help. The internal wastegates may be creeping open which would make boost come on later/slower. By routing the wastegate to the atmosphere rather than to the intake via a boost controller, the wastegate will stay fully closed till it's time to let off steam.

The 700BBs are not that big (slightly smaller than the APS standard turbos I recall) so lag should not be an issue.

(I presume you're using the SS box that comes with the JWT kit)