LT4 Dyno not good
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Racer
Joined: Sep 2005
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LT4 Dyno not good
So dynoed the LT4 on a Dynojet and it only pulled 289 rwhp WITH K&N open air filter AND Corsa Exhaust. That comes out to like 319 hp total or so....something cant be right. It has 122k miles on it but still shouldnt be that much hp loss right? Especially since the car has been kept in great condition. Do you think it could be a simple tune up issue? Where should I start checking first? It just feels sluggish in my opinion....its like some days the car just takes off and other days its alot slower. Plus if I take off into high RPMS and let off it back-fires loud, running rich in my opinion. Can you guys give me pointers into finding out whats wrong and why im losing so much hp?
Last edited by Achilleus07; May 11, 2006 at 09:51 AM.
Team Owner
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From: Athens AL
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Needs a tuneup, plugs/wires/fuel filter first, then check for cat clogging.
Might want to check your fuel pressure readings as well.
Might want to check your fuel pressure readings as well.
Last edited by vader86; May 11, 2006 at 09:57 AM.
Melting Slicks
Joined: May 2001
Posts: 3,014
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From: Raleigh, NC
Welcome to the real world man, lol.
What kind of dyno were you on? I assume it's a dynojet 240C?
The numbers are a bit low, but I doubt there is any serous horsepower left in it. You might be able to pick up ~10 RWHP from a tune up, but I wouldn't hold my breath.
Most of the LT4's I have actually witnessed on the dyno make 300 RWHP +/- 10 HP. You'll see lot's of people claiming higher numbers than that on the internet, but that's the Internet.
How does it run at the track? Maybe the dyno was reading low?
What kind of dyno were you on? I assume it's a dynojet 240C?
The numbers are a bit low, but I doubt there is any serous horsepower left in it. You might be able to pick up ~10 RWHP from a tune up, but I wouldn't hold my breath.
Most of the LT4's I have actually witnessed on the dyno make 300 RWHP +/- 10 HP. You'll see lot's of people claiming higher numbers than that on the internet, but that's the Internet.
How does it run at the track? Maybe the dyno was reading low?
Le Mans Master
Joined: Jan 2003
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From: Portland Oregon
Originally Posted by Achilleus07
So dynoed the LT4 on a Dynojet and it only pulled 289 rwhp WITH K&N open air filter AND Corsa Exhaust. That comes out to like 319 hp total or so....something cant be right. It has 122k miles on it but still shouldnt be that much hp loss right? Especially since the car has been kept in great condition. Do you think it could be a simple tune up issue? Where should I start checking first? It just feels sluggish in my opinion....its like some days the car just takes off and other days its alot slower. Plus if I take off into high RPMS and let off it back-fires loud, running rich in my opinion. Can you guys give me pointers into finding out whats wrong and why im losing so much hp?
Melting Slicks
Joined: Dec 2001
Posts: 2,437
Likes: 1
From: Gainesville Fl
Originally Posted by Achilleus07
So dynoed the LT4 on a Dynojet and it only pulled 289 rwhp WITH K&N open air filter AND Corsa Exhaust. That comes out to like 319 hp total or so....something cant be right. It has 122k miles on it but still shouldnt be that much hp loss right? Especially since the car has been kept in great condition. Do you think it could be a simple tune up issue? Where should I start checking first? It just feels sluggish in my opinion....its like some days the car just takes off and other days its alot slower. Plus if I take off into high RPMS and let off it back-fires loud, running rich in my opinion. Can you guys give me pointers into finding out whats wrong and why im losing so much hp?
What was ur AF ratio? my LT4 dynoed a lot lower than i wanted with all the mods i have but i was also running waaaay rich on one cylinder so i htink that was costing me a lot of power. as others have said i would look into replacing the plugs, wires, fuel filter, and check the cats for being clogged.
Thread Starter
Racer
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Actually might be cat clogging....actually my right cat has been rattling and blowing out ceramic...that started after they dyno. It rattled loud for awhile and I blew it all out...or thought I did. Then it started again 2 days ago....so I blew out more. The A/F ratio was equal when it was dynoed. I couldnt say it was rich or lean...it was pretty middle road. The weird part was it got up top on the dyno sheet and then freaking jumps up and down like a lightning storm 5 hp up, 5 down, 5 up, 5 down. I will try to get a scan when I get home tonight. I ordered my EM headers and new Hi-flow cats 2 weeks ago....so whenever I get those the cat problem is fixed, wires are sitting at home, plus a fuel filter....so I will get all that done soon. then as for the dyno-tune or chip order...I really havent decided what to do yet.
Last edited by Achilleus07; May 11, 2006 at 11:13 AM.
Melting Slicks
Joined: Sep 2003
Posts: 2,270
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From: N. Babylon NY
Hi,
Sorry to hijack thread-but my 1992 (LT1) with 100,000 miles all stock except for Borla muffers dyno'd at 273hp and 305tq. This was on a Dynojet (STD). SAE was at 266hp and 297tq.
Whats the difference between STD and SAE?
Thanks,
Steven
Sorry to hijack thread-but my 1992 (LT1) with 100,000 miles all stock except for Borla muffers dyno'd at 273hp and 305tq. This was on a Dynojet (STD). SAE was at 266hp and 297tq.
Whats the difference between STD and SAE?
Thanks,
Steven
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Race Director
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I was just at the C4 meet at Bowling Green. I saw 3 stock LT-4's on the dyno. 297 rwhp/299rwhp/308rwhp. There were the average of 3 pulls. I was impressed. These cars were stock!!!!!!!!!!!!!!!
Motors are under rated!
Motors are under rated!
Intermediate
Joined: Jul 2004
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Originally Posted by Achilleus07
So dynoed the LT4 on a Dynojet and it only pulled 289 rwhp WITH K&N open air filter AND Corsa Exhaust. That comes out to like 319 hp total or so....something cant be right. It has 122k miles on it but still shouldnt be that much hp loss right? Especially since the car has been kept in great condition. Do you think it could be a simple tune up issue? Where should I start checking first? It just feels sluggish in my opinion....its like some days the car just takes off and other days its alot slower. Plus if I take off into high RPMS and let off it back-fires loud, running rich in my opinion. Can you guys give me pointers into finding out whats wrong and why im losing so much hp?
Melting Slicks
Joined: Mar 2003
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From: Toronto ONTARIO
The car can be kept in great condition, but with 122k miles not everything on the motor can stay that way. Im betting theres a huge loss just from a need of tune. Not custom prom tune i mean just maintenance. it could be something very small like a sensor causing a loss in hp. Try your plugs/wires, maybe check your tps to make sure you are getting wot, o2 sensors could be clogged, cats too maybe?
good luck !
good luck !
Melting Slicks
Joined: Dec 2001
Posts: 2,437
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From: Gainesville Fl
Originally Posted by 88BlackZ-51
I was just at the C4 meet at Bowling Green. I saw 3 stock LT-4's on the dyno. 297 rwhp/299rwhp/308rwhp. There were the average of 3 pulls. I was impressed. These cars were stock!!!!!!!!!!!!!!!
Motors are under rated!
Motors are under rated!
Thread Starter
Racer
Joined: Sep 2005
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Originally Posted by Bluewasp
My stock LT4 put down 292rwhp. Dynojet.
Corsa exhaust uses 2.5 inch pipes? If so that is part of the problem. Stock is 2 3/4
Corsa exhaust uses 2.5 inch pipes? If so that is part of the problem. Stock is 2 3/4
Really, I didnt know that. Where did you find the specs for that?
Burning Brakes
Joined: Jul 2005
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From: Gainesville, FL
Originally Posted by Achilleus07
Really, I didnt know that. Where did you find the specs for that?
EDIT: - also note that his rwhp rating was only 3rwhp more - even on the same day/ air conditions - the same car can pull a difference of 3rwhp on a dyno...
Last edited by 4REGT4; May 15, 2006 at 09:54 AM.
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From: Manassas VA
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Originally Posted by Achilleus07
Really, I didnt know that. Where did you find the specs for that?
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Might not seem like a big deal but every little bit matters. I've seen, with my own eyes, stock LT4s dyno in the low 290 rwhp range. You are not that far off. Do a tune up, replace the O2 sensors as other forum members have suggested.
Last edited by Bluewasp; May 15, 2006 at 09:52 AM.
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From: Manassas VA
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St. Jude Donor '14
Originally Posted by 4REGT4
Well.... he is probably right and wrong... I don't know about the LT4 exhaust - but the stock LT1 exhaust goes from 2.75" down to 2.5" in the resonator - back to 2.75" - then RIGHT before the mufflers goes all the way down to 2.25" - ... I've changed mine since those measurements, but the LT1 certainly does not have 2.75" piping all the way through (despite what others may say)... IF the LT4 has the same exhaust pattern I couldn't imagine a full 2.5" Corsa system causing ANY problem on a stock LT4...
EDIT: - also note that his rwhp rating was only 3rwhp more - even on the same day/ air conditions - the same car can pull a difference of 3rwhp on a dyno...
EDIT: - also note that his rwhp rating was only 3rwhp more - even on the same day/ air conditions - the same car can pull a difference of 3rwhp on a dyno...
In any case going from 2 3/4 to 2.5 will make a difference. I gained 12rwhp by going from 2 3/4 to 3 inch with a 383. Granted a 383 would benefit more then a 350 but every little bit helps.
You know if you put your car on another dyno the numbers will be different. time slips hold more weight then dyno numbers.
290rwhp is around 330flywheel. LT4 are rated from GM with 330HP
Last edited by Bluewasp; May 15, 2006 at 12:10 PM.
Thread Starter
Racer
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Actually I did read alot of posts that say 2.75" stock...I have the exhaust sitting at home too I can check. I think im going to switch to a B&B 3" system regardless. I should have done that from the start with an LT4.
Drifting
Joined: Oct 2005
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From: Angier nc
a lot of good advice given here.i would go the tuneup route first.cover all the basics(plugs,wires,fuel filter,cats,sensors).all of these need to be up to snuff so you can get a true baseline.then change the exhaust if you want.that's the only way to know if it was a restriction anyway.no matter how fast i go it always needs "just one more thing".