Has anyone gone from 60 mm TB BACK to stock?

[Zmanco]

I've read quite a few threads about the downsides of using too large of a throttle body. I currently run a 60mm 240SX TB with a stock intake manifold on my L28 turbo motor. Turbo is a T3/4OE, head is P90 shaved with unshrouded valves, currently running with a Schneider stage II turbo cam, good sized intercooler etc. I'm staying with 8-9 lbs boost for now as I learn to drive with the extra power. Driving is on the street and road courses - no drag racing.

 

As some have predicted, the throttle is difficult to modulate when on boost between 3500 and 7k rpm. For example, I can generate full boost above 3500 rpm with around only 50% throttle. The 2nd half of the pedal movement makes very little difference. And it's hard to modulate that much power in such a small range of throttle opening when in high-G corner.

 

I know my setup is pretty common here on hybridz so was wondering if anyone has tried both the 60mm TB as well as the stock one and can let me know how they differ in terms of throttle control? I'm considering putting the stock back on to help with driveability and wondering how much better it will be? Also wondering if dropping down to 50mm for the TB will make that much of a difference on peak power given I'm running with 2.25" intercooler piping anyway.

 

Thoughts?

[Tony D]

Make the linkage less linear to introduce deadband in the first 25% of throttle play. You end up having to move the pedal more to affect the same delta-change flow-wise.

 

You are now finding out when properly driven 'turbo lag' is not an issue in a modern turbocharger setup. Keep it above boost threshold and power is instantaneous with very little throttle position change.

 

The smaller T/B may introduce some bottlenecking between manifold and piping boost levels. Basically you will show more boost in the pipe (which affects your BOV) than you will have in the manifold. Under lower flow situations this may not be much, but under high flow high rpms this 'orifice plate' can restrict output.

 

Generally you shouldn't have a T/B with a smaller diameter than your I/C piping, and in fact slightly larger to accomodate for butterfly and throttle shaft turbulence/restriction.

 

The 50mm stocker will work, but a non-linear linkage solves tip-in jumpiness. I preferred an eccentric mounted cable actuated throttle. I think I used a nautilis-shaped cam off of a Mazda with a humongo T/B for a 2L engine. You would need non-linear with that setup!

[Zmanco]

Thanks Tony, I had been looking around for a while for an eccentric cam but haven't found one yet. And I wouldn't mind getting rid of the stock linkage (which is a bit kludgey when used in a 240z) anyway.

 

Any chance you can remember which Mazda?

 

You are now finding out when properly driven 'turbo lag' is not an issue in a modern turbocharger setup. Keep it above boost threshold and power is instantaneous with very little throttle position change.

Indeed, the throttle response once above 3k is nearly instantaneous. The challenge is modulating it so that I don't get full boost in the middle of the corner when already at the limit of traction

 

The smaller T/B may introduce some bottlenecking between manifold and piping boost levels. Basically you will show more boost in the pipe (which affects your BOV) than you will have in the manifold. Under lower flow situations this may not be much, but under high flow high rpms this 'orifice plate' can restrict output.

I expected that, but since the wastegate gets its signal directly from the intake manifold, I would expect that the turbo would just run to a slightly higher level of boost to compensate for the drop across the TB.

 

I do like your idea of an eccentric cam better though. Anyone else know of any that would bolt up to the 240sx TB?

[Bernardd]

You can also change the turbo boost reference from the intake to the turbo outlet. Are you using an electronic boost controller or a ball and spring type? The electronic bc gain can be turned down or switch to a bleed type manual boost control and the boost hit should slow down.

[Zmanco]

Right now I'm just running with a mechanical wastegate actuator which is preset to 8-9 psi. I do have a solenoid in the circuit controlled by megasquirt for boost control, but it can only increase the boost level, not reduce it. As much fun as more power is in a straight line, it only makes things worse on the track.

[2eighTZ4me]

Great - this is something I get to look forward to......

[jgkurz]

Interesting topic. My turbo L28 with a Weber 60mm TB also has a hair trigger boost response. I liken it to a two-stroke or a Porsche 930. Wait for it........wait for it........ wham! Modulating throttle on my car at peak torque is near impossible. I had RTz drive my car a while back and he had the same conclusion. I always thought these characteristics were due to having a larger turbo. My turbo is some weird custom Innovative jobby that is not ball-bearing or as efficient as a Garrett GT series but it flows well for it's size. I'd like to upgrade to a GT35R some day to see if I gain any low-end boost response. What we all really want is a nice flat torque curve. I really doubt you could make a significant improvement in throttle modulation manipulating the throttle assy. If you added an eccentric cam wouldn't you sacrifice peak torque to flatten the curve? Cool idea BTW. Adding cubic inch, improving airflow, optimizing timing and adding an efficient BB turbo are the easiest non-exotic ways in my opinion.

 

-John

Edited June 2, 2010 by jgkurz

[ZR8ED]

I don't think that the throttle body would make much of a difference, but I will tell you how I solved this exact problem. Nail it in 3rd..boost comes on, then wham! the car is sideways at full boost. I then free'd up the exhaust with a mandrelbent 3" system, and the boost came on earlier and smoother, without that harsh spike in power. It had a 2.5" system before, with no serious restriction other than the pipe diameter. No other mods between tests.

 

Though I do understand what you mean by throttle position, anything past 1/3 throttle, and it is at full boost. A flat power curve doesn't help that. Take a look at my power/torque curve. Not huge power, but pretty flat looking from my experience. Putting in a stiff return spring on the pedal will give more pedal effort, which can make it easier to control the modulation.

 

[yetterben]

Holy balls with a cable it was like this for me as well. no pedal effort plus t04e equals what control.

[Zmanco]

I suppose the better solution would be an electric boost control actuator that could be controlled by Megasquirt. MS2/Extra has a table to limit the max boost as determined by engine rpm and throttle position. But right now, the only way it works is by bleeding off pressure to the mechanical actuator which allows it be increased above 8 psi, not decreased which is what I need in this case.

 

Anyone with metal working skills think they could make an eccentric cam for the 240sx TB for use with a throttle cable? It might not be the perfect solution, but it seems like it would help.

[Tony D]

You guys are complaining that boost comes on in a turbo car when you touch the throttle?

Normally the issue guys whine about is pushing the throttle and NOT getting boost for a while...

 

There appears to be a mixup in what people are offerering for solutions, some sound as if they are trying to combat a boost threshold hard on-boost response to MODULATION ON BOOST.

 

They are TWO VERY DIFFERENT THINGS.

 

My issue was that in a specific corner, 2nd gear was too low to take through the corner due to both RPM at exit and power porduced. 3rd gear was too high so I would onset boost going halfway through the corner with the typical problems.

 

I added a wing for traction which allowed me to come in lugging the engine in third but onset boost and exit hard without traction problems.

 

His issue would be akin to my 2nd gear entry: On boost, any sort of lifting will loose boost and reapplication is difficult due to radical delta throttle change from the oversized t/b. The answer is to give less throttle change per linear movement of the pedal. Dumb it down, null it out for the first 25 to 35% of throttle pedal travel. This is the SAME issue N/A engines have with a 60 or 65mm body. Because they have relatively low power outputs it's not as big a deal. With a turbo and the power it makes, the difference between 5 and 10% throttle opening can be tremendous.

 

Either repositioning the linkage arms for angle (take a look at Derek's Lingage alteration on his home-cast ITB's for the exact same issue and resolution in a mechanical linkage scenario), or adding a progressive cam (like an eccentric) which deadens out the first 35% of throttle cable movement is a very simple solution. You will end up now moving the throttle pedal to say 50% opening, or even 65% before making any appreciable throttle plate angle change. The Mazda 626 or 929 has to be the car I got it off of, the thing was a twin 45mm barrel throttle body with a KIDNEY-BEAN shaped throttle quadrant. First half of the throttle pedal play really does VERY little to those plates, and this is where 85%+ of your driving is done.

 

Go past that point, and the throttle is basically an on-off switch. As it should be. The JDM ZX Throttle Bodies with two plates are similar. You can almost be 'floorboarded' at 75% throttle, and the primary barrel is all the way open, then depress the throttle the next (last) 1/4 of the way, and you get full flow to the engine.

 

Either basic triginometry to alter you linkages similar to Derek's Solution, or dilligent searching for a cam will deaden out your pedal fine. Most of the Japanese T/B's out there use a standard size shaft and flat cut where they attach to the exterior, so with flipping and flopping or even some screws through it to the quadrant you have you can get this altered response. I put these quadrants onto SU's so I could cable actuate them...you can fit them to another T/B! Even if it rotates the 'wrong way' you can always move the cable or flop the quadrant and make it work. "Spatial Visualisation Skills" come into play here...

 

Good Luck.

 

P.S. Sticky Tires and Aerodynamic Aids work wonders. They did for me on a 'slow' 65mph corner those 265's stopped lighting up when I put the whale tail on the back of the car. 370# at 100 still extrapolates back to 240#...weight which I don't actually carry, but which keeps my back end glued down in sweepers. There IS a reason that Turbo Carreras first came out with those tails (and not the duck tails they had for oil coolers, either!) WHALE TAILS were for traction (and the occasional place to put that humongo oil cooler...) 2 Birds, one stone. Clever those Germans...

[Zmanco]

You guys are complaining that boost comes on in a turbo car when you touch the throttle?

Normally the issue guys whine about is pushing the throttle and NOT getting boost for a while...

 

There appears to be a mixup in what people are offerering for solutions, some sound as if they are trying to combat a boost threshold hard on-boost response to MODULATION ON BOOST.

 

They are TWO VERY DIFFERENT THINGS.

 

Tony, I understand that these are two different issues and in my case, I am only concerned with modulating boost when I'm well past the boost threshold. I have a ZX 5 speed with 4.11 diff so as long as I'm not lazy with shifting, it's easy to find a gear where there's boost right NOW.

 

I'll take a walk around the pick n pull some time and see what can find for throttle cams. It's been a while since I read Derek's thread on his linkage so I'll re-read that as well.

 

I've been thinking of adding a rear spoiler, but not as big as the wing you describe. Hence I don't think it would add enough downforce to really solve my problem, although I expect it could help.

[Tony D]

Not you zmanco, the others... I was trying to point out some solutions were pertaining to one phenomenon totally unrelated to what you asked about, and will muddy the water when people read the thread thinking (confusing them) all the 'solutions' offered are applicable to your originally stated issue.

 

Though the irony if someone complaining that they get 'instant' boost should not be lost on the myriad of people who are continually complaining about 'lag' or 'mushy' boost characteristics.

 

"Drive it right, and you won't have that problem." The corollary to that would then be "Then you will have an on-boost throttle modulation issue..."

Edited June 4, 2010 by Tony D

[Zmanco]

"Drive it right, and you won't have that problem." The corollary to that would then be "Then you will have an on-boost throttle modulation issue..."

LOL, I've got a track day tomorrow which will be the first event with new Techno Toy Tuning front LCA and TC pieces and the extra camber and caster they bring up front. Frankly I'm a little nervous because I expect to have more FRONT grip than I'm used to, as well as more power that's difficult to modulate and can overwhelm rear grip. That could be a recipe for less-than-graceful cornering. I'll know a lot more in 24 hours.

[jgkurz]

Though the irony if someone complaining that they get 'instant' boost should not be lost on the myriad of people who are continually complaining about 'lag' or 'mushy' boost characteristics.

 

That's what I was alluding to in my above post. I personally wouldn't want to sacrifice tire burning torque for a lesser but flat torque curve unless I did not have to make a sacrifice. I participated in a track day a while back and set the boost on "kill". The car was a handful and had huge peaky power on boost. I blew a boost pipe off during one of my sessions and the car suddenly had a flat torque curve. Not nearly as exciting. I've tried to build a fun and fast car but there are always sacrifices when asking so much from our little Datsuns.

[Tony D]

My wife refused to drive my Turbo "Shark Car" because it had 'a gas pedal that was an on-off switch'...

 

I tend to believe it was more because of a 9# flywheel and 350+ ft-lbs of torque that hooked up pretty well through 265's out back (replace every 8K miles, every second set of rears, replace fronts as well...)

 

I didn't think it was a hair trigger, but to be honest a BIG wing on the back made the car stick far better. At Autocrosses it was a total joke unless driven really brutally (jerk, toss, mash, BOOST!) Then again, my boost threshold for 17# was 1700 rpms.

 

And I had 6 45mm throttle bodies opening simultaneously. What was the problem here, a single 60mm vs single 50mm on a plenum?

 

Like I said, this CAN be tamed by geometry or cam selection. I did it on my car, that's when I went from 15# to 9# on the flywheel!

Edited June 4, 2010 by Tony D

[johnc]

http://www.paragon-products.com/product_p/welt_tc-400.htm

[HowlerMonkey]

The stock linkage gives the pedal much less authority at the beginning of the travel and much more authority as the throttle is opened more.

 

I am quite fond of how it works.

 

When using the same articulation of the linkage, I notice no difference in response between the 50 and the 60.

 

Perhaps the people noting too much response at low throttle openings have swapped the stock linkage "throttle curve" with a truly linear cable....which opens the throttle "faster" than the stock linkage at the beginning of the throttle movement.

 

The porsche 944 has a pretty progressive throttle cam and may be a source for a more driver friendly curve.

 

I remembered this because I worked with Al Collins at autothority to make a linear cam for quicker throttle response on the 944 back in 1985.

Edited June 5, 2010 by HowlerMonkey

[Zmanco]

http://www.paragon-products.com/product_p/welt_tc-400.htm

John, forgive me if this is a stupid question, but that cam doesn't look eccentric. How would it help?

[Zmanco]

I had the car out on a road course this weekend and what felt too sensitive on the street was just right on the track. I suspect it was because most corners on this track are 3rd gear with entry speeds between 50 and 70 mph, so even full boost (8 psi) wasn't affecting the chassis balance too much. There was one 2nd gear corner hairpin at the top of a crest and I had to be careful to avoid wheel spin accelerating out.