"The Mongoose" - 1 3/4" Headers To 1 7/8" Headers (447 rwhp and 431 rwtq)
Thread Starter
TECH Senior Member
iTrader: (27)
Joined: Dec 2009
Posts: 9,728
Likes: 13
From: Jefferson City, MO
"The Mongoose" - 1 3/4" Headers To 1 7/8" Headers (447 rwhp and 431 rwtq) I switched from Stainless Works 1 3/4" headers to Speed Engineering 1 7/8" headers. Below is the back to back dyno graph. The green line is with the new Speed Engineering 1 7/8" headers and the black line is with the Stainless Works 1 3/4" headers. As you can see, I gained power in the low and mid-range, but lost power up top. We attribute this to the LS6 intake with stock TB. The intake and TB just cannot provide enough air to the excellent heads and headers that are on the car. The LS6 intake does fine in the low and mid-range, but not good at all up top. I asked Kent how the car felt after the new headers were on, and he said it felt great; never heard it lay over at all. AFR was spot on. A little rich on the hit for torque, but then right to 12.7 Below is a list of modifications. Again, nothing changed but the headers.
Advanced Induction Dart/RHS CNC's 223cc heads with Brian Tooley .660 sping kit
227/235 110 LSA cam
Hardened pushrods
Speed Engineering 1 7/8" headers
Texas Speed 3" True Duals w/ SLP Loudmouth 1's
SLP Lid with custom 4x6" coupler (No MAF)
Accel 44lb/hr injectors (stock pump)
Stock M6 transmission with Monster Stage 3 clutch and Tick Master
3:42 rear gears
15" rear drag setup with 26" tall tires
On thing to note is that Kent's dyno had been dynoing extremely low. On another dyno over a year ago, with the old 1 3/4" headers, I put down 420 rwhp and 382 rwtq. Kent later figured out why the dyno was reading so low, so he made some calibration changes to get it right. The second graph is a pull we made with the new headers after the dyno calibration changes.
With Stainless Works 1 3/4" headers - 353 rwhp and 347 rwtq
With Speed Engineering 1 7/8" headers - 350 rwhp and 356 rwtq
419 rwhp and 442 rwtq
While I'm disappointed that the car did not make more HP, I did gain power through the low and mid-range. I believe that after I put on a FAST 92/92 setup, it's going to make a ton more power.
Advanced Induction Dart/RHS CNC's 223cc heads with Brian Tooley .660 sping kit
227/235 110 LSA cam
Hardened pushrods
Speed Engineering 1 7/8" headers
Texas Speed 3" True Duals w/ SLP Loudmouth 1's
SLP Lid with custom 4x6" coupler (No MAF)
Accel 44lb/hr injectors (stock pump)
Stock M6 transmission with Monster Stage 3 clutch and Tick Master
3:42 rear gears
15" rear drag setup with 26" tall tires
On thing to note is that Kent's dyno had been dynoing extremely low. On another dyno over a year ago, with the old 1 3/4" headers, I put down 420 rwhp and 382 rwtq. Kent later figured out why the dyno was reading so low, so he made some calibration changes to get it right. The second graph is a pull we made with the new headers after the dyno calibration changes.
With Stainless Works 1 3/4" headers - 353 rwhp and 347 rwtq
With Speed Engineering 1 7/8" headers - 350 rwhp and 356 rwtq
419 rwhp and 442 rwtq
While I'm disappointed that the car did not make more HP, I did gain power through the low and mid-range. I believe that after I put on a FAST 92/92 setup, it's going to make a ton more power.
Last edited by Rise of the Phoenix; Nov 28, 2016 at 12:31 PM.
The thing that bothers me is how hard it falls off from 5800 to 6400. Damn near 25hp. I really do think the intake is the main problem just seems lil aggressive on how fast it falls off.
The last corrected dyno graph. I started the hit at 2200rpm vs getting the rpm up to 3k then stabbing it.
The last corrected dyno graph. I started the hit at 2200rpm vs getting the rpm up to 3k then stabbing it.
Thread Starter
TECH Senior Member
iTrader: (27)
Joined: Dec 2009
Posts: 9,728
Likes: 13
From: Jefferson City, MO
The thing that bothers me is how hard it falls off from 5800 to 6400. Damn near 25hp. I really do think the intake is the main problem just seems lil aggressive on how fast it falls off.
The last corrected dyno graph. I started the hit at 2200rpm vs getting the rpm up to 3k then stabbing it.
The last corrected dyno graph. I started the hit at 2200rpm vs getting the rpm up to 3k then stabbing it.
What typically is the cause for a setup nosing over like that? You said it sounded good and didn't hear it lay over and the AFR and fuel pressure was good, so there was no difference between the first time you dyno'd it to the second time, other than the header change. You don't think it could be anything in the valvetrain, do you? I would think if it is, you'd have heard that or you'd see something on the graph to indicate a problem. The torque and HP curves look good; just noses off hard lower in the RPM range that it did with the smaller headers.
11 Second Club
Joined: Mar 2012
Posts: 1,541
Likes: 15
From: South Florida
I am very interested in these results.
So the 1 7/8 made more power everywhere up to about 5520rpm. Then as the curve flattens out it begins to drop just after 5880.
I wouldn't think the ls6 manifold is to blame for this. The only place the intake & exhaust are even tied is the 11 degrees of overlap. Which if more flow is present with the 1 7/8 headers, at higher rpm, it would just help out a little more.
Do the new headers have tuned length primaries? Were the old headers tuned length?
As stated losing almost 25hp up top. No good unless you're only revving to 5600. Right now, from the info, if all else was the same between pulls, I would feel it to be the headers fault.
A fast intake will make more power. I just don't feel it will fix what happened here.
So the 1 7/8 made more power everywhere up to about 5520rpm. Then as the curve flattens out it begins to drop just after 5880.
I wouldn't think the ls6 manifold is to blame for this. The only place the intake & exhaust are even tied is the 11 degrees of overlap. Which if more flow is present with the 1 7/8 headers, at higher rpm, it would just help out a little more.
Do the new headers have tuned length primaries? Were the old headers tuned length?
As stated losing almost 25hp up top. No good unless you're only revving to 5600. Right now, from the info, if all else was the same between pulls, I would feel it to be the headers fault.
A fast intake will make more power. I just don't feel it will fix what happened here.
Last edited by SoFla01SSLookinstok; Apr 26, 2016 at 01:58 PM.
1 year ago it was 420hp and 382tq now its 419hp and 442tq after the dyno got calibrated. So your telling me you gained 60tq from a header change ? i'm more interested in that than you losing 25hp....
419/442 was from a different dyno with the old headers. I've been very confused as to what happened here as well and which numbers are which. Those numbers should just be left out of this if the current dyno (which is the same as the very first one) is going to be used.
11 Second Club
Joined: Mar 2012
Posts: 1,541
Likes: 15
From: South Florida
True. I believe that would be comparing two different dynos. Also, with the different calibrations here: at first the max #'s, 1 7/8, were 355tq/349hp. Then after a calibration it's 442tq/419hp. A hp/tq spread from 6 to 23?
Last edited by SoFla01SSLookinstok; Apr 26, 2016 at 02:18 PM.
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
I think it goes like this...
Dyno 1 original: With Stainless Works 1 3/4" headers - 353 rwhp and 347 rwtq
Dyno 2: With Stainless Works 1 3/4" headers - 419 rwhp and 442 rwtq
Dyno 1 recent: With Speed Engineering 1 7/8" headers - 350 rwhp and 356 rwtq
OP - If I'm wrong about this, please let me know and I'll delete my post. Just hoping to clarify since I was struggling with this as well
we just want you to get this figured out and be happy with it!
Dyno 1 original: With Stainless Works 1 3/4" headers - 353 rwhp and 347 rwtq
Dyno 2: With Stainless Works 1 3/4" headers - 419 rwhp and 442 rwtq
Dyno 1 recent: With Speed Engineering 1 7/8" headers - 350 rwhp and 356 rwtq
OP - If I'm wrong about this, please let me know and I'll delete my post. Just hoping to clarify since I was struggling with this as well
we just want you to get this figured out and be happy with it!
Originally Posted by Rise of the Phoenix
The second graph is a pull we made with the new headers after the dyno calibration changes.
Thread Starter
TECH Senior Member
iTrader: (27)
Joined: Dec 2009
Posts: 9,728
Likes: 13
From: Jefferson City, MO
With Stainless Works 1 3/4" headers - 353 rwhp and 347 rwtq (on Kent's Mustang Dyno)
With Speed Engineering 1 7/8" headers - 350 rwhp and 356 rwtq (on Kent's Mustang Dyno)
The last graph where the car made 419 rwhp and 442 rwtq was on Kent's Mustang Dyno, but he made changes to the dyno's calibration, as the way it was calibrated before was not right. It had something to do with the weight of the rollers or something like that.
When the car made 420 rwhp and 382 rwtq (old header setup), that was about 2 years ago on a DynoJet located down at the Lake of the Ozarks.
With Speed Engineering 1 7/8" headers - 350 rwhp and 356 rwtq (on Kent's Mustang Dyno)
The last graph where the car made 419 rwhp and 442 rwtq was on Kent's Mustang Dyno, but he made changes to the dyno's calibration, as the way it was calibrated before was not right. It had something to do with the weight of the rollers or something like that.
When the car made 420 rwhp and 382 rwtq (old header setup), that was about 2 years ago on a DynoJet located down at the Lake of the Ozarks.
Thread Starter
TECH Senior Member
iTrader: (27)
Joined: Dec 2009
Posts: 9,728
Likes: 13
From: Jefferson City, MO
Yes, KCS, that is correct. Kent can weigh on more regarding the dyno recalibration. Every single car that had been on his dyno prior to him recalibrating it was way down on power. I'm talking like around 100 HP/TQ down.
KCS, by looking at things, what do you think? Why such a drastic loss up above 6,000 RPM's with the new headers?
KCS, by looking at things, what do you think? Why such a drastic loss up above 6,000 RPM's with the new headers?
Thread Starter
TECH Senior Member
iTrader: (27)
Joined: Dec 2009
Posts: 9,728
Likes: 13
From: Jefferson City, MO
I don't think there is an issue with the new headers. There's lots of guys making big power with the Speed Engineering headers. Like another guy stated, the quality of the headers were great. The Speed Engineering headers have the velocity spike in the collector, while the Stainless Works headers did not. Also, the Stainless Works collector is 2.5" while the Speed Engineering collectors are 3".
11 Second Club
Joined: Mar 2012
Posts: 1,541
Likes: 15
From: South Florida
I don't think there is an issue with the new headers. There's lots of guys making big power with the Speed Engineering headers. Like another guy stated, the quality of the headers were great. The Speed Engineering headers have the velocity spike in the collector, while the Stainless Works headers did not. Also, the Stainless Works collector is 2.5" while the Speed Engineering collectors are 3".
First I think I should apologize to you & Kent. None of my posts are to bash you guys or anything like that. One of the things that made me a pretty good technician is always wanting to find the root/cause of a problem. There has to be a reason for this. I would really like to find out what is was. I actually just met someone, over the weekend, that was speaking very highly of the collector design. If you look at say a kooks header, I think, at the beginning of the collector, there is a small ring & then it opens back up to say 3" or whatever. Merge style. He was saying a lot about this. I notice this on some custom race car headers also.
Another thing is that I want 1 7/8 headers now too. As your swap didn't produce what we normally expect. I'm definitely interested why. Good luck man.
Last edited by SoFla01SSLookinstok; Apr 27, 2016 at 07:46 PM.
Thread Starter
TECH Senior Member
iTrader: (27)
Joined: Dec 2009
Posts: 9,728
Likes: 13
From: Jefferson City, MO
No need to apologize. I'd love to figure out what is going on too. I 100% honestly thought I'd pick up power everywhere, and that the power-band would carry further than it did with the 1 3/4" headers. If it's truly the intake/TB, then I'm good with that and I'll just buy a FAST 92/92 setup. What has me wondering now is if I get the FAST 92/92 setup, will the car make more power with the 1 7/8" Speed Engineering headers that are on the car now, or will it make more with my old 1 3/4" Stainless Works headers?
With Stainless Works 1 3/4" headers - 353 rwhp and 347 rwtq (on Kent's Mustang Dyno)
With Speed Engineering 1 7/8" headers - 350 rwhp and 356 rwtq (on Kent's Mustang Dyno)
The last graph where the car made 419 rwhp and 442 rwtq was on Kent's Mustang Dyno, but he made changes to the dyno's calibration, as the way it was calibrated before was not right. It had something to do with the weight of the rollers or something like that.
When the car made 420 rwhp and 382 rwtq (old header setup), that was about 2 years ago on a DynoJet located down at the Lake of the Ozarks.
With Speed Engineering 1 7/8" headers - 350 rwhp and 356 rwtq (on Kent's Mustang Dyno)
The last graph where the car made 419 rwhp and 442 rwtq was on Kent's Mustang Dyno, but he made changes to the dyno's calibration, as the way it was calibrated before was not right. It had something to do with the weight of the rollers or something like that.
When the car made 420 rwhp and 382 rwtq (old header setup), that was about 2 years ago on a DynoJet located down at the Lake of the Ozarks.
Yes, KCS, that is correct. Kent can weigh on more regarding the dyno recalibration. Every single car that had been on his dyno prior to him recalibrating it was way down on power. I'm talking like around 100 HP/TQ down.
KCS, by looking at things, what do you think? Why such a drastic loss up above 6,000 RPM's with the new headers?
KCS, by looking at things, what do you think? Why such a drastic loss up above 6,000 RPM's with the new headers?
The gains you made are nice. You certainly didn't help the peak numbers much, but I think all that torque you gained in the midrange all the way up to about 5800RPM is excellent. If it were my combo and I was hunting more top end, I would try regarding the cam about 2 degrees and see what the later IVC would do.
Thread Starter
TECH Senior Member
iTrader: (27)
Joined: Dec 2009
Posts: 9,728
Likes: 13
From: Jefferson City, MO
"The Mongoose" - 1 3/4" Headers To 1 7/8" Headers Thanks KCS. If I remember right, the cam was actually more advanced than the specs. It was something like a 109 or 108 LSA as opposed to the advertised 110 LSA. I think that would help to retard the cam at least 2 degrees..
Last edited by Rise of the Phoenix; Apr 26, 2016 at 07:41 PM.
TECH Addict
Joined: Aug 2005
Posts: 2,305
Likes: 126
From: Monroe,NY
Do you think you may be losing spark on the top end? Just something to think about since you said your fuel was fine. By any chance did you see what your fuel pressure was at high rpm?
Just throwing out ideas.
Just throwing out ideas.
Thread Starter
TECH Senior Member
iTrader: (27)
Joined: Dec 2009
Posts: 9,728
Likes: 13
From: Jefferson City, MO
Fuel pressure was 67 psi. Not sure about losing spark. Wouldn't the graph get wavy when there is a loss of spark? It has TR5 plugs in it with MSD wires. Plugs and wires have less than 5,000 miles on them.