Hey everyone,

I've recently completed my 3800 turbo build and I've hit the drag strip a couple of times. The car is performing well but there is one thing i would like to improve, launch/60 foot and building some boost at the line. As is stands im leaving the line with 0 psi at 2000 rpm and not reaching full boost until the end of 1st/begining of 2nd (4t65e-hd and factory converter). I know a higher stall converter would help some and would allow me to leave with more rpm but i was curious if there was another way (2-step or something) that would allow me to spool up more on the line so the delay is reduced. I've seen a couple comments here and there about messing with the iat sensor but i haven't found anything yet that has enough details about how it works and how its done.
Any advice would be greatly appreciated!

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Deathcon1395
RSE parts technician
1985 Fiero GT L67 3800 Turbo E85 4T65E-HD

What size turbo?

Going to need a looser converter to get up around 2800-3000 rpm to spool regardless of other tricks. Then the brakes need to be able to hold the car back as the torque increases as turbo spools. Even if you don’t make boost on the line a looser converter will flash higher and help make boost faster.

Dark horizon used nitrous to help spool his turbo, if you want to try that.

Not much available for 2-steps on stock pcm, I can’t even recommend the one I have as it was a battle to make it work, I had to send it back for modification. Other option is the MSD ignition box but it is unreliable.

IAT mod allows you to cut timing while spooling the turbo but requires pcm programming to work. Takes experimenting to find right timing, so you really need to be able to do the tuning yourself.
Search for “ iat timing mod” online, info is out there, regardless of GM platform, the idea is the same.

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10.007 @ 135.54MPH. <-- Video
Best 60' 1.42
Best mph 138.82
Billet 6262 Precision turbo, PT1001 intercooler, ST1 cam, 140lb springs, comp pushrods, HV3, stock L32 bottom end and heads.

Old M90 XP Cam time -
11.425 @115.60
1.543 60'

Nitrous is the easy "button".. I had mine setup to turn off when the boost came up to a specific point automatically.

The other option is to really upgrade the brakes with a drift style handbrake that sits on just the rear brake line so you can grab the rear significantly better than stock brake pedal will let you and you can put more throttle into it at a stop.

Hmm, interesting suggestions. I have thought about the nitrous option but im not ready to go down that road at this point. The handbrake option is interesting, I hadn't thought of that.
I'm not to sure of the size of the turbo off the top of my head, It came from an ebay turbo kit that I bought from a friend when he changed his plans. I do know that its a t4 flange, 4" inlet and 2.5" outlet on the compressor side and Its about 3" diameter outlet on the exhaust side. My brother has a SRT4 and we compared it to his AGP turbo and they were virtually the same on the inlets/outlets and mounting flange.

I like the hand brake plus converter options the best, I will most likely look at getting a higher stall converter and handbrake setup once the racing season is over up here (only one more race in 3 weeks planned for this season at the track I race at anyways).
I will also do some more reading into the IAT timing modding and see if I can figure that out, I've been successful with tuning the car all myself (with the internet and this forum's help of course!) up to this point and I'm not affraid to learn and try something new.

Thanks for the responses

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Deathcon1395
RSE parts technician
1985 Fiero GT L67 3800 Turbo E85 4T65E-HD

[This message has been edited by Deathcon1395 (edited 07-27-2022).]

The timing mod works, but its not a perfect solution. It takes some trial and error because if you arent making enough power to push the converter higher in the rpm you're probably going backwards in spool speed.

Also the converter gets to be a tough situation where you'll end up slipping and blowing through the converter when you loosen it up too much, so I never suggest running much over a 3000-3200 rated stall.

I haven't got around to reading more into the iat timing mod yet but i agree with you that it might not be worth it. From my time slips and running numbers im getting about 360-370 crank horsepower. I would describe my current "spooling" situation as sitting on the brake at about 1800-1900 rpm and once ive launched it takes most of first gear to get to full boost and as im starting 2nd i would say its at full boost from there on out. It's not a horrible delay and it makes my launches very consistent with no wheel spin or anything so it could be worse.

I was thinking about a 2500-2800rpm stall for the new converter which should be an improvement and still be very streetable, my only fear with that is breaking the input shaft in the trans but it might be ok at my current power level (only one way to find out!). I can only go so fast before I need a roll bar anyways and I'm not ready to do that yet either so the converter might be the ticket to get me to my desired 12.0 for now.

quote Originally posted by Deathcon1395: I haven't got around to reading more into the iat timing mod yet but i agree with you that it might not be worth it. From my time slips and running numbers im getting about 360-370 crank horsepower. I would describe my current "spooling" situation as sitting on the brake at about 1800-1900 rpm and once ive launched it takes most of first gear to get to full boost and as im starting 2nd i would say its at full boost from there on out. It's not a horrible delay and it makes my launches very consistent with no wheel spin or anything so it could be worse. I was thinking about a 2500-2800rpm stall for the new converter which should be an improvement and still be very streetable, my only fear with that is breaking the input shaft in the trans but it might be ok at my current power level (only one way to find out!). I can only go so fast before I need a roll bar anyways and I'm not ready to do that yet either so the converter might be the ticket to get me to my desired 12.0 for now.

e85 + a turbo this laggy should let you make well into the 500-600hp range which would be alot easier than leaving better.

quote Originally posted by darkhorizon: e85 + a turbo this laggy should let you make well into the 500-600hp range which would be alot easier than leaving better.

When did E85 become a thing in Canada? I've still never seen an E85 pump in this country.

I'm running race ethanol at the track and technically its mixed (E98 race ethanol diluted with 93 octane race gas) to E65 really but for the simplicity of things I just say e85. I have yet to see e85 at a pump up here either.

[This message has been edited by Deathcon1395 (edited 07-28-2022).]