Ok so up until recently I've always thought the smaller the hotside the quicker the spool (my rx7club knowledge ). i ended up going down to florida to the nscra event down there a couple of weekends ago and talked to a few big name people in the game and they all told me that actually with a bigger hotside they see quicker spool because of the lack of exhaust restriction.

On my t70 with .96 hotside and half bridge ported motor I've noticed that turbo spool is sort of like a switch, it really doesn't start to spool hard till about 4500rpm but then it just opens up all the way and spins my tires. My question is would a 1.15 backside work to widen my power band? My logic was that it wouldn't because the .96 is smaller so it would spool quicker than the 1.15 however when talking to the guys at WWR and a few others they seemed to take that rx7club knowledge I had and turned it upside down when they told me a 1.15 would spool quicker due to the hotside allowing for more unrestricted flow.

your thoughts?

Also I was in need of a tune and ended up getting a pretty good tune from Kilo. Would putting a 1.15 housing on change the tuning enough to warrant retuning?

 

When a friend of mine spent time talking to the guys racing the C6R he asked them how much more power would they see if they removed the restrictors, they told him nothing. The car was built to optimize what they were allowed to work with, point being, a lot depends on the level of build as a whole. I say put it on there and you'll see for yourself. Yes you will need to adjust your tune. My guess is you wont see quicker response. Also as has been said many times more than just A/r will have a effect on response. A question worth asking would have been how much measured improvement was seen and how was it measured.


~S~

 

Hum, interesting. I'm guessing the biggest thing that's probably screwing with flow is the hks log manifold and undivided housing. Maybe when I get rich I'll buy a nice divided manifold and a 1.15. Heck I may even try the 1.15 right now, I've got my eye on one on ebay right now that should work fine. One interesting thing though is after some hardcore pulls and burnouts the other day I thought for sure my egts where going to be crazy with the .96 however after really getting on it I opened the hood and could actually comfortably put my hand on the turbo blanket and it was only warm to the touch. Cruising is a bit different but really whooping on it seems to cool things down, maybe the water injection pre turbo

 

Yes I would point my finger firstly at the log mani. When I ran the greddy log for a couple years with different turbos I found it made them come online more on/off then the divided I'm running now. Moving the gt3574 (.84 backside) from the log mani to the divided mani gave better ultimate response, and more linear response.

Also yes, EGTS will generally be higher in cruise because of the much leaner mixtures.

There's still tonnnes of variables regarding spool up, but I'd be willing to bet your log mani is causing alot of the lightswitch engagment you're experiencing

 

Ok was wondering if that maybe part of the problem. I guess I'll just make do with what I got for now and go from there. To bad these damn divided manifolds are so expensive, but I understand why. Until I get rich I guess I'll just have to deal with the on/off switch.

 

If you go bigger in the turbine a/r usually you should move up in the downpipe/midpipe size.

 

I've got a 4" downpipe right now then it transitions to a 3" cat-less single pipe exhaust system, should be enough right?

 

You're exhaust is fine...

Sounds like you have a lot of weak links in your system, ignition system, engine tune, and engine condition.

 

Im having the same issues with my setup.
HBP REW(on a FC)The biggest turbonetics F series exhaust wheel(a little bigger than a Qtrim)
.96AR T76 BB,Boost comes hard like a switch not in a linear fashion like when i had my Ptrim 1.15
and divided manifold,im thinking about going back to the old setup.

 

Everything on my setup is fine. brand new rebuilt motor by BDC, 2 crane hi-6 amps and 4 lx92 coils, expensive *** 11.5 spark plugs, and microtech x4 ignition box. water injection pre turbo, 850 primaries and 1600 secondaries all flow tested, tune was done by Kilo racing. Not sure what the weak link would be.

 

What manifold are you using now? sounds like you got one heck of a drag setup which really if your using it for that and have a 2step than there shouldn't be a problem. Now if you want a street setup than yeah the old setup would probably do alot better.

 

Im using a greddy non divided manifold with a 50mm hks 2 control boost(still spikes planning 2 go with a dual setup)and the car is daily driven on the street.

 

Lots of things determine your spool up characteristics!

First, let’s not confuse "hot side" sizes, there are three factors when talking about "hot sides", 1: turbine size (major OD), 2: turbine trim (major/minor OD ratio) and 3: turbine housing A/R (A/R = Area/Radius, or area of the valute opening verses radius from center of the turbine wheel).

Your turbine size should be determined by what compressor you’re running. Optimally you’re going to want to run near the same major diameters for both wheels of within a close margin. Trim will be determined by were you want your power band to be to some extent, you’re going to want to keep the area of the compressor and turbine close for optimum performance for a spool up verses power, but it can be fudged in either direction to fit your goals. A/R determines power band also and can be fudge in either direction to suite goals as well.

Manifold design, plays a HUGE ROLE in spool up characteristics. The log/cast style manifolds generally have horrible flow characteristics; they are concentrated on compactness and reliability. They work less by using exhaust flow and work more so on pressure. This is why you get the on/off switch type response when using larger framed turbos. On smaller framed turbo's they tend to do ok (Think OEM applications). But with the larger framed turbo's they are so large and require X amount of energy to spool up, since you’re wasting the energy of the high velocity exhaust leaving their ports and further wasting energy by mixing the pulses from one port with another (they cancel each other out effectively) your relying on pressure to build up to get enough flow to spool it up. So this wasted energy builds and the engine starts to see boost and build more exhaust energy. This happens rapidly (though late) hence to on/off response. With a fully divided tubular exhaust manifold, you’re utilizing the high velocity exhaust pulse straight from the ports and not mixing it up with a neighboring port. This energy is used to spool the turbo up way before a log manifold because you’re not relying on pressure to build up, you’re using high velocity exhaust energy so it starts spooling sooner till either the pressure/volume is there to reach target boost (this is were normally a log will start to spool). Because it's spooling sooner it’s a more gradual "ON" boost response and more linear power output. You get quicker more gradual spool up using a well designed divided manifold and divided turbine, since the spool up is soo much quicker you can afford to go bigger A/R so you have better top end and STILL spool faster yet then a log/collected manifold. It’s a WIN WIN, you get quicker spool up, more linear power modulation, bigger top end, and lower EGTs and lower preturbine pressures.

I hope I explained it so it's understandable......

To the OP, using your collected log manifold going to a 1.15 divided turbine will kill your spool up and make your car more on/off. If you’re running a P-trim with that T70, if you want better response I'd switch over to a Q-trim and stick with the .96. Or bite the bullet and get a proper divided manifold and divided turbine. Either way, if you’re running a P-trim with that compressor, it'll be on/off-ish no matter what, just less sevear with he divided set up.

~Mike.............

 

BTW, the GReedy FC cast manifolds are even worse then the HKS FC cast. The best cast style manifolds are the HKS FD divided and XS Engineering divided (simular to the HKS FD, but no longer being made).

 

+1 to RacerXtreme7.

Honestly, if you make any chance Cameron, you may want to consider going from the 1.15 A/R to a 1.00 divided but I can't recall if that cast HKS manifold you're using is divided or not. I tried a 1.32 A/R divided turbine housing on my undivided HKS cast log manifold and it completely sucked. Went back to the 0.96 A/R. Much better.

On the flip side, I've seen a half bridge with a 1.32 A/R on a lengthy divided manifold work wonders!

B

 

BTW, both posters HondaHater and joeylyrech, your intake porting style tends to exacerbate the on/off switch type boosting also. This is due to the high over lap and exhaust diluting your intake charge till rev's come up and you get enough intake velocity to overcome the exhaust dilution. This tends to happen in a small rev range so again, more on/off type boosting. A divided tubular style manifold will help with this also for more than a couple reasons. A few reasons I mentioned in my above post, another reason would be the header style tubular manifolds will dilute your intake charge less due to better flow AND you won’t have cross contamination from the opposite ports' exhaust pulse.


~Mike..........

 

Mike's a smart guy!

 

I pretend like I know what I'm talking about and fake my intelligence extremely well.

~Mike.........

 

Fixed

Thanks Mike!!!

 

LOL! hey, it's true!

 

Damn, thank you guys for the awesome explanation, I understand now why I need a tubular manifold with my particular setup and why, in general, a tubular manifold is just the better way to go. I'm guessing in a drag race type setup this manifold is fine being that you will probably be using a 2step and launching with x amount of boost all the way down the track. But if you want real driveability with a larger frame turbo setup and even more so with a bridge setup then a tubular manifold is the way to go. Guess I've got some shopping and saving to do. Sean just checked ya'lls website. I don't see any manifold pricing?

 

For a drag only set up, long tubular divided again is the way to go, or at least long tubular. Since spool up isn't as big of a concern (so as you don't fall off boost between shifts which is gear ratio selection and matching to your engines power band) you'd simply still use the benefits of a fully divided set up because it's superior flow characteristics and just go BIGGER on the turbine side for more top end and even lower pre-turbine exhaust pressures.

Anyone running a half bridge, full bridge, semi-P-port or full P-port should really run a tubular manifold no matter what. It makes no sense to run that large intake duration and overlap then kill all those benefits with a poorly designed manifold. But sometimes money gets in the way of optimum design .


~Mike..........

 

You aren't joking about that, but really I've spent enough money on this project that really 800 bucks or so on a good manifold isn't all that big of a deal in the grand scheme of things. Of course getting it retuned after I install the new manifold is where things get a bit hairy. the only weak links to me on this car are the manifold and the masterpower turbo however I saw an 8 second first gen running a masterpower turbo without a problem so I really don't think it's all that much of a weak link at all.

 

http://cgi.ebay.com/Turbo-Exhaust-Ma...item414d2e44ee

What do you think? Good or bad manifold?

 

Actually not bad looking at all, not a typical eBay manifold but you never know about the material. I'd check with A-Spec (Sean) and Turblown (1Revvin7) first, get some quotes from those guys before you possibly waste money on a questionable product where A-Spec and Turblown have been known to build EXCELLENT manifolds and have FULL SUPPORT not to mention are forum supporters.

~Mike...........