Chev133

hi, I have a DBW NW102 on my 08 Silverado 403ci. im having the normal down low drivability problems. (rpms bouncing, hunting, hanging etc.) im from Australia, Holden released a Monaro a few years back with a 427 LS based engine it has a DBW TB with a hole in the throttle blade. has anyone out there tried this mod ?

ctd

iTrader: (1)

No reason to drill a hole in the blade of DBW, the ECU controls the blade. No details in your profile so I can't offer anything else.

Slowhawk

iTrader: (12)

You need to change a lot of idle tables to get the 102mm to work correctly on that computer.

soundengineer

iTrader: (16)

actually, theres plenty of reasons to drill a hole in the TB blade....
the hole allows you to retain a better idle and off idle throttle response.

the bigger TB requires a lot of changes to the tune to get it to respond the same as stock...and even then, its not the same.
the biggest issue is that now you have changed the physical surface area of the space that air passes by when the blade moves...

think of it as a square number...
it might be a change from a 90mm to a 102mm...which is only 12mm...but thats a change in 144 square mm(12^2).

you can recover that 144sq mm by drilling a hole equivelant in size, and retain the throttle response down in the low rpm and just off idle...

you basically get back the proper air velocity needed for lower rpm throttle response.

Chev133

that's what I thought, If Holden went to the trouble of drilling a hole in the blade they would have done it for a reason. the 427 Monaro was released as a road car to be used on the road. it would have had to meet all the Australian design rules as well. I tried a mail order tune without success. its get a dyno tune today.

ctd

iTrader: (1)

So is your idea to get the blade to a near closed position, that is what the ECU is going to do as you increase the hole size correct?

My little experience with the 102 DBW TB's is to go the other way with the scalar rather than the traditional calculation. Then the adaptive routines, cracker & follower fall into place much easier. I've no issue's that the OP is bringing forward.

I'm always trying to find way's to improve the tune which is my interest in this topic.

soundengineer

iTrader: (16)

the idea is to get the airflow curve back to similar to what it is with the stock TB....
think of it as an exponential as I explained earlier....
if its looking for a 90mm circle to open, and as you open that space gets exponentially bigger, then when you go to a 102, you've just made huge jumps instead of small jumps in airflow...(think Volume of a circle....)
if you have a 3.5" circle, you have (2 * pi * radius) an area of roughly 11 square inches
Jump up to a 4" circle, and you get 12.5 square inches.....
so a half of an inch in Diameter made a 1.5" difference in space...

when you get to looking at the blad profile opening, suddenly the difference between open 10% and open 11% on a 102mm TB is more like the difference between 10% and 13% on a 90mm TB....
3% doesnt seem like much...but its a lot when it comes to airflow and throttle response characteristics...

Chev133

so do you think the hole should end up being 12mm ? I might get my tuner to start with a 3mm hole first then go up from there after each test. the mods I have done are 403ci, cnc ported heads, 224r comp cam 112 lsa, lsxrt inlet, volant cia, full length headers, 10.8 comp. our premium fuel here is 98 octane.

ctd

iTrader: (1)

What tuning software is your tuner using?

I doubt that any hole in your blade will magically correct issue's outlined in your original post. Now that you have explained your combination it should start, idle, return to idle rolling or not with tuning.

Or if it as simple as drilling a hole I'm listening

Chev133

I'll find out what software he has. I have efi live. I have tried a mail tune from Patrick g but that was worse. What I don't understand is the cam is very mild & no one can get it running well. Everyone says they can but when it comes to the crunch they can't. I'm thinking of puting the 5.3 back in.

ctd

iTrader: (1)

If I understand your cam spec 224/224 112 LSA correctly you have 0* overlap. Tuners dream & you should have near perfect manners.

I'm HPT so I can't help other than suggest posting up a log screen shot of the issue's with the pids related to your tune.

Can you find a different Manifold & TB set up to try, even stock? I Rx'd a brand new ported Fast 102 with damaged o'rings as shown, was very frustrated trying to tune a 243/247 114+2. I don't know how the damaged o'rings where affecting the tune but the car would pitch you out the drivers window below 2k rpm. The cam was a bad choice & I had already changed out before finding the o'ring issue. My current cam is 235/243 114+5, it runs decently, no issue's as you describe with yours.

Chev133

I've heard of people damaging the seals when they fit the manifolds. if you sit the manifold on the heads then drag it even 1/2 a inch you will damage the seals. I don't know how to post the log as im not that good with computers. I got it back from getting it dyno tuned yesterday. he said he doesn't think it can get much better because of the combination im using. (tb, maf ect) I think he just hasn't got the experience with ls2`s. it is better, but if you drive along in say 2nd & take your foot off the pedal to slow down for a corner, it will shift into 3rd & it stalled once. & it still is a little rough around the edges.

Chev133

my tuner uses hp tuner.

ctd

iTrader: (1)

Those seals are internal in the Fast, nothing to do with installation of the manifold on the motor.

Chev133

Was the lsxrt inlet you used taken apart & ported before you got it?