Upgraded to 75 atmo, same mph at track. Thoughts?

Rubenk

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Long story short, I upgraded to an RCD 75 atmo and didnt gain any MPH at the drag strip.


Longer version: I've been running my truck at the drag strip after almost every set of mods just to track progress. I managed a 12.8@106mph on stock turbos fuel and front suspension. Eventually went 4-linked with an RCD 75mm and truck progressively got slower each outing to the track. I started watching rail pressure and it was dropping to around 22k. Figured injection pump/HPFP was tired after 180k original miles. I did put a fuel PSI gauge on the fuel cooler test port and it was holding 4 PSI at WOT, with the LPFP being internally regulated to 3psi it seemed good to me. So I decided a new HPFP was in order.

Last weekend I installed a new reman HPFP. Ran at the track yesterday with new Nitto 420(was previously on 33" AT's) and while I got my best time ever(12.55), my MPH was only back up to 106mph. Watched rail pressure and it held 24,500-25k the whole run. But boost is only maxing around 44PSI. On the street i've seen 52psi. Several guys helped me look for boost leaks, I built 10PSI while they looked and could not find anything. No obvious boost or exhaust leaks(downpipe leaks a small bit, but shouldnt matter?).

List of mods:
Studded with OEM gaskets
SDP Ceramic coated up-pipes
SDP 4" ceramic coated downpipe
Ceramic coated OEM 6.4 manifolds
Rudy's Diesel CAC pipe
No Limit Intake
RCD 75mm stock-appearing atmo
New OEM HPFP

BTS Built 5r
PMF Front 4-link
PMF Rear bars
Bull**** removed
MPD CCV re-route, vented to atmo

I dont have a wastegate yet, but am working through that with a vendor. Ordered a kit and couldnt get it to fit. Will be going on ASAP.

Along with a host of OEM replacement parts fairly recent and along with stud job 40k ago.

Truck runs great, and with the new turbo it felt alot stronger on the street. I was very disappointed and surprised when it ran 2-3mph slower at my first outing after the turbo, and only returned to factory MPH with new HPFP. If I didnt know any better, and hadnt been tracking progress i'd be thrilled. But unfortunately i've been keeping track. Truck weighs in at 7600lbs, am I expecting too much for my mods? Is something still wrong that I need to track down? I'm thinking about a new low pressure fuel system, as i'll need it for dual fuelers eventually anyways.

So whats next, LPFP, injectors, dual fuelers? 59HP turbo?
 
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ckrueg

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The lower boost sounds like it could be the issue. We're you able to hit 50+lbs of boost after going to the track? Also how was the smoke and egts. A 75 mm atmo should gain at least 50 hp over stock. I know one guy with just a 72 ran something like a 12.2 at 109 with a ccsb.
 

tbsimmons

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What was the DA between the compared runs? It plays a HUGE role in MPH.
When I did bigger chargers, my boost dropped some towing the fiver. I used to be in the bottom 40's towing on a tow tune before the chargers and after I am in the mid high 30's with more power though.
I did up pipes and manifolds though. I equate that to less resistance, which is what boost pressure is anyway.
 
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Rubenk

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I'll try and post the DAs for each later. I know it affects performance, but that much?

Just not sure what to look at next, without shotgunning more parts at it.
 

Rubenk

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The lower boost sounds like it could be the issue. We're you able to hit 50+lbs of boost after going to the track? Also how was the smoke and egts. A 75 mm atmo should gain at least 50 hp over stock. I know one guy with just a 72 ran something like a 12.2 at 109 with a ccsb.

Smoke totally cleans up after launch I believe. EGTs around 1400-1500. Before new turbo was 1700+, so I know it has more air.
 

tbsimmons

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DA has a big impact on HP. When I was drag racing the DA swing could be 1500'. Which for a NA car is a lot of power drop not only MPH but also ET. Turbo cars are a little less but not much actually.
 

madman1234509

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Humidity, altitude, temperature all play a roll. Does a 4link weigh more than stock radius arms? Along with traction bars. Those alone will net you better times if you're launching it better, but they may also add weight.

Another thing, you're stock fuel. Not sure what guys have run in the past on stock fuel with a 75mm, but low to mid 12s are probably all you're going to get on stock fuel/injectors. Go to the track on a cooler, crisp evening or day and give it a go.
 

Rubenk

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Thanks fellas. I understand stock fuel can only do so much, just want to make sure its running properly before I mask it by throwing a bunch horsepower at it and hoping for the best!
 

madman1234509

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I'd ask around about your boost level. Again, I have no experience with a 75mm atmo, but maybe someone will chime in with honest boost numbers with one and stock fuel. Check for boost and exhaust leaks if you suspect it
 

Rmartin-97

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My 72mm makes 50psi of boost. But I think you have a larger than stock turbine wheel which would cause ur boost to be lower. But on stock fuel I ran 12.2 @ 108.8. Weighing 7980 pounds.
 

Rubenk

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My 72mm makes 50psi of boost. But I think you have a larger than stock turbine wheel which would cause ur boost to be lower. But on stock fuel I ran 12.2 @ 108.8. Weighing 7980 pounds.

This kind of info is what made me go for the 75 when it popped up for sale recently. Figured I could at least get a 12.2 out of mine @ 7600lbs.

Did you have any other significant upgrades at the time? 59HP Turbo?
 

Rmartin-97

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This kind of info is what made me go for the 75 when it popped up for sale recently. Figured I could at least get a 12.2 out of mine @ 7600lbs.

Did you have any other significant upgrades at the time? 59HP Turbo?

Still have stock hp turbo. No other stuff out of the ordinary. Just ******** tunes ported intake that's about it.
 

drunk on diesel

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a clogged intercooler could cause it, but I wouldn't say there's much chance that your intercooler is clogged

if it's as swampy/muggy up there as it is here, I'd check your density altitudes between the runs before you start pulling your hair out
 

sootie

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a clogged intercooler could cause it, but I wouldn't say there's much chance that your intercooler is clogged

if it's as swampy/muggy up there as it is here, I'd check your density altitudes between the runs before you start pulling your hair out

Webb06 had a similar issue and it was his aftermarket intercooler.
 

Rubenk

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Pulled the truck last night, and while the stress on an engine is a little different, still neat to see.

Video is of the minimaxx and you can see everything seems good, except for boost a little low. https://youtu.be/Z3LFOpJlw-s
 

Rubenk

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Had a chance to run against Jcain's 6.7. He dynoed 661hp at Scheids. He is on 37s(I'm 32s) and is about 1000lbs heavier. We were dead even until very top end I'd barely start pulling away.

Really doesn't seem like I'm making the right power.
 

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