Fast 92 TB cold start issue. Pics and info
09-18-2013, 03:52 PM
#1
FormerVendor
Thread Starter
Fast 92 TB cold start issue. Pics and info I know there is already a thread about this but I thought I would start one with my findings.
Tuned a cammed 4th gen yesterday, ended up with IAC counts at 65 hot.
Would not cold start this morning even with maxed out IAC valve. Nothing would get it to start so I pulled the TB and compared it to stock. As mentioned by others, the IAC ports just do not flow enough.
Here is the air entry hole to the IAC port on the Fast92-
And here is the IAC air entry on the stock throttle body-
IAC port hole on the stock throttle body is .537in-
It is .490 on the FAST92-
Here is the port from the IAC valve to behind the throttle blade on the FAST92. Very small/restrictive-
Much like the entry, on the stock throttle body it is just a large open area after the IAC port hole. Pretty much unrestricted-
I took the FAST 92 and drilled the main IAC hole to .537, same as stock, then opened up the port leading to behind the throttle blade pretty much as much as possible. Problem with the design is there isn't much area until you start running into the sealing surface for the throttle blade.
IMO for these to be made correctly the throttle blade/shaft should be moved forward in the throttle body housing to allow for properly sized IAC ports. As it is, opening up the ports on the FAST (I did nothing to the entry port) allowed this car to fire up perfectly on cold start and that's ending up with a hot IAC count of 100.
For comparison, here is the port on a Nick Williams throttle body (which I have never had any cold start issues with). Much bigger than the FAST.
At this point I would say the IAC ports on the FAST tb are a design flaw as you will need to re-work them in order for it to function correctly.
Tuned a cammed 4th gen yesterday, ended up with IAC counts at 65 hot.
Would not cold start this morning even with maxed out IAC valve. Nothing would get it to start so I pulled the TB and compared it to stock. As mentioned by others, the IAC ports just do not flow enough.
Here is the air entry hole to the IAC port on the Fast92-
And here is the IAC air entry on the stock throttle body-
IAC port hole on the stock throttle body is .537in-
It is .490 on the FAST92-
Here is the port from the IAC valve to behind the throttle blade on the FAST92. Very small/restrictive-
Much like the entry, on the stock throttle body it is just a large open area after the IAC port hole. Pretty much unrestricted-
I took the FAST 92 and drilled the main IAC hole to .537, same as stock, then opened up the port leading to behind the throttle blade pretty much as much as possible. Problem with the design is there isn't much area until you start running into the sealing surface for the throttle blade.
IMO for these to be made correctly the throttle blade/shaft should be moved forward in the throttle body housing to allow for properly sized IAC ports. As it is, opening up the ports on the FAST (I did nothing to the entry port) allowed this car to fire up perfectly on cold start and that's ending up with a hot IAC count of 100.
For comparison, here is the port on a Nick Williams throttle body (which I have never had any cold start issues with). Much bigger than the FAST.
At this point I would say the IAC ports on the FAST tb are a design flaw as you will need to re-work them in order for it to function correctly.
12-30-2013, 11:18 AM
#2
I have an older 90mm Fast TB which has never properly idled on a cold start, does fine warm. When cold is also makes a very loud hissing from the air filter which I am told is an overworked IAC sympton.
I finally tried this yesterday. I wanted to do it in stages since I could not find a thread like this until today. Thank you for posting...I think I may need to go back and do some more but so far mine is a little better, it no longer dies when stabbing the throttle on a cold start (like low throttle rev to 2000rpm and let off instantly, I'm not an idiot redlining a cool engine).
I did not do anything to the area around the seat as I was afraid of messing it up. Might have to try drilling it like you did.
Here are the pre-cleanup pass shots of the size I ended up with (I swear it's not as sloppy as the flash makes it look).
Did you have to go back an retune once you modded the throttle body or did it just start to behave?
I finally tried this yesterday. I wanted to do it in stages since I could not find a thread like this until today. Thank you for posting...I think I may need to go back and do some more but so far mine is a little better, it no longer dies when stabbing the throttle on a cold start (like low throttle rev to 2000rpm and let off instantly, I'm not an idiot redlining a cool engine).
I did not do anything to the area around the seat as I was afraid of messing it up. Might have to try drilling it like you did.
Here are the pre-cleanup pass shots of the size I ended up with (I swear it's not as sloppy as the flash makes it look).
Did you have to go back an retune once you modded the throttle body or did it just start to behave?
Last edited by thunderstruck507; 12-30-2013 at 11:31 AM.
12-30-2013, 12:59 PM
#3
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,605
Likes: 0
Received 6 Likes
on
6 Posts
I think that IAC air is not the problem, but overfueling
when cold. The cranking VE table probably is way off
post-cam and there's nothing but guesstimation for
that.
But I did find that 3/16" was too small an IAC inlet bore
on my ported & filled stock TB, and 3/8" enough to keep
airflow vs IAC counts linear (meaning the plunger is in
control). This never impacted starting, just stability,
on the stock-cam setup of the day.
when cold. The cranking VE table probably is way off
post-cam and there's nothing but guesstimation for
that.
But I did find that 3/16" was too small an IAC inlet bore
on my ported & filled stock TB, and 3/8" enough to keep
airflow vs IAC counts linear (meaning the plunger is in
control). This never impacted starting, just stability,
on the stock-cam setup of the day.
12-30-2013, 01:18 PM
#4
I will look into that as well but I have spent hours upon hours over the last year or 2 messing with it and this is the best it's gotten so far.
I fired it up on lunch cold (40*) and it busted right off and idled steady...before on a dead cold start I nearly always had to use throttle to keep it running for 20 seconds or so and then it idled poor until it warmed up more.
Any advice on the cranking VE table?
I fired it up on lunch cold (40*) and it busted right off and idled steady...before on a dead cold start I nearly always had to use throttle to keep it running for 20 seconds or so and then it idled poor until it warmed up more.
Any advice on the cranking VE table?
12-30-2013, 03:59 PM
#5
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,605
Likes: 0
Received 6 Likes
on
6 Posts
What I recall doing was, I created an Excel 'sheet
where I pasted the main and the cranking VE tables,
and set it up with scatter-plots butting the two up
visually. Then by eyeball I fitted the cranking "lines"
to follow the evident trajectory of the main "lines",
having gotten those pretty right. I'll have to crack
open the tuning laptop and see if I can find that. It's
nothing fancy but it served the need. Maybe somebody
with better Excel skills could figure out how to curve-fit,
extrapolate and auto-gen a cranking table, but I'm not
that good past the basics.
where I pasted the main and the cranking VE tables,
and set it up with scatter-plots butting the two up
visually. Then by eyeball I fitted the cranking "lines"
to follow the evident trajectory of the main "lines",
having gotten those pretty right. I'll have to crack
open the tuning laptop and see if I can find that. It's
nothing fancy but it served the need. Maybe somebody
with better Excel skills could figure out how to curve-fit,
extrapolate and auto-gen a cranking table, but I'm not
that good past the basics.
12-31-2013, 08:39 AM
#8
All I know is that I went home last night and fired the car again and for the first time since this damn intake/tb went on years ago (several dozen tunes ago and even a cam change ago) it busted right off and idled where it was supposed to in sub freezing temps and didn't hang with high rpm idle once it warmed up like it would with blade adjustments.
I am going to pull it again and do a little more now that I know I can't go too big outside of porting past the blade sealing area. Then I guess it's time to put all my idle related tune sections back to stock and tune this thing correctly. I can't even remember all the stuff I've messed with over the years trying to fix this....
Basically the same cam in my roommates car took me 1 try to get it idling perfect in all conditions (then 1 more to keep it from dying with the a/c on). The primary variable being he has a ls6 intake and I have the Fast 90mm.
I am going to pull it again and do a little more now that I know I can't go too big outside of porting past the blade sealing area. Then I guess it's time to put all my idle related tune sections back to stock and tune this thing correctly. I can't even remember all the stuff I've messed with over the years trying to fix this....
Basically the same cam in my roommates car took me 1 try to get it idling perfect in all conditions (then 1 more to keep it from dying with the a/c on). The primary variable being he has a ls6 intake and I have the Fast 90mm.
12-31-2013, 10:30 AM
#10
If I can get this sorted out fully I will be stoked.
It deters me from getting the car out at all when starting it and warming it up is a long process of: crank, hold throttle open, let off throttle super slow until it idles without surging and dying, letting it idle to warm up over 150*, turn the engine off for 30 seconds, restart and let it go through all the random idle surges and revs until it settles....THEN I can drive it.
It deters me from getting the car out at all when starting it and warming it up is a long process of: crank, hold throttle open, let off throttle super slow until it idles without surging and dying, letting it idle to warm up over 150*, turn the engine off for 30 seconds, restart and let it go through all the random idle surges and revs until it settles....THEN I can drive it.
12-31-2013, 10:30 AM
#11
Funny I stumbled across this post when I was just looking around. I took about year and a half off LS stuff while I built an old mustang. Point is I've been frustrated with my setup since going 102/102. I had one of the first batches that came out in 2009. Bottom line, WOT is fantastic, but drivability sucks, especially cold starts. I've been to several rep tuners on here that couldn't figure this out in mid 2012. I had one of them ask me to drill a hole in the blade, which I did but idle would hang about 1800 and still had cold start issues. My last guy, has had it best but still not where it should be.
I absolutely hate a cold start at a cruise in or meet. pedaling the when everyone looks a me is frustrating and one of the reasons car only had 200 miles on it this year.
I opened up both sides. I left the bore alone inside the TB. I assume I need to port some more but will do this in steps.
I did a search, can someone show me the link where the other thread is?
I absolutely hate a cold start at a cruise in or meet. pedaling the when everyone looks a me is frustrating and one of the reasons car only had 200 miles on it this year.
I opened up both sides. I left the bore alone inside the TB. I assume I need to port some more but will do this in steps.
I did a search, can someone show me the link where the other thread is?
12-31-2013, 01:56 PM
#13
Couldn't wait and ported it. I did both sides and bore. All the settings left the same. Cold start was night and day difference! I ported it about twice the size it was. I've ported heads so I had an idea of what and how. May need to go a more but may just adjust the blade a pinch. First time I just touched the pedal and started and stayed running cold. Like it never did that...
12-31-2013, 10:29 PM
#15
Ha, well I had a smile but want to do some fine tuning to NOT have to even touch the gas. It also helped on a hot start but did hang a bit once. Like I said it was better but need to fine tune more.
It sucked, hated driving into a met or cruise in and cold start it!
It sucked, hated driving into a met or cruise in and cold start it!
03-18-2014, 08:56 AM
#16
After this post the temps outside began warming up here and I guess the tb didn't like that. Cold starts stayed perfect but it began idling high on a warm start and got to where it didn't want to idle down quickly coming to stops.
While I'm sure I could have messed with it more and got it back right I decided to see if the grass was greener on the other side and ordered a new tb instead. I went with the Ballistic Speed 92mm for price and have no regrets.
Everything works like a charm right out of the box so far with nothing but set screw adjustment. Cold starts are great with no surging on throttle blips and warm starts don't have idle hang. If anyone out there has one of the Fasts and doesn't have the tools or desire to alter the IAC passage (and possibly epoxy around the blade for a tighter seal) then switching TBs and proper tuning might be a better option for you.
While I'm sure I could have messed with it more and got it back right I decided to see if the grass was greener on the other side and ordered a new tb instead. I went with the Ballistic Speed 92mm for price and have no regrets.
Everything works like a charm right out of the box so far with nothing but set screw adjustment. Cold starts are great with no surging on throttle blips and warm starts don't have idle hang. If anyone out there has one of the Fasts and doesn't have the tools or desire to alter the IAC passage (and possibly epoxy around the blade for a tighter seal) then switching TBs and proper tuning might be a better option for you.
07-21-2017, 12:40 PM
#18
This are the only sizes I can find, I drilled it with a 1/2" bit but not sure what drill bit you guys used to get .537 for the IAC port hole.... I just bought a Fast 92mm tb and I'm having the same cold start issues.
1/2. - .500"
33/64 - .5469"
9/16 - .5625"
1/2. - .500"
33/64 - .5469"
9/16 - .5625"
Last edited by Ogoz23; 07-21-2017 at 01:21 PM.
07-22-2017, 08:05 AM
#19
FAST products are pretty much all half baked, **** poor QC and manufacturing.
From their original intakes with no tangs to hold the MAP sensor, to their TB's that wont start cold, to the 102MM intakes that you have to shim your cradle to fit, the customer ends up being their guinea pigs.
I cant understand why people love their generic garbage.
From their original intakes with no tangs to hold the MAP sensor, to their TB's that wont start cold, to the 102MM intakes that you have to shim your cradle to fit, the customer ends up being their guinea pigs.
I cant understand why people love their generic garbage.