IMRC issue robbing 20+ horsepower?

[Sammy123]

Been running into an issue lately where my E85 no longer feels "strong" and actually seems to run out of breath at high rpms (even shifting at 7200 vs 7800). I thought it was the Florida heat and humidity but I went and did some dyno runs to check. Problems seem to have begun after ported intake manifold and ported throttle body were installed, but could just be a coincidence.

So my mods were as follows on a 2018 Mustang GT A10:

- JLT intake
- Texas speed headers and high flow cats 3" xpipe
- E85R straight tune and 93 dedicated tune

I made 471whp with this combo. Trap speed was 123 with full weight.

Added the below:

- 2018 OEM ported intake manifold
- 2018 OEM ported throttle body

Every day driving was fine, but I couldn't help but notice peak power seemed to have dropped. I blamed the heat/humidity and maybe bad E85. However I went through several E85 refills from quality stations that tested E82/E85, went through a cycle of 93 to clean out the gunk (if any), and back to E85 with E that tested at E88.

Trevor at PBD did my initial tune. I now have a Rob Shoemaker updated tune. I'm getting 33 degrees of timing with no knock at WOT at 7000rpms.That should be real strong but doesn't quite feel that way.

Went back to dyno and the car put down 469 hp and 465hp on back to back runs. 7th gear pulls. Similar weather conditions as prior. Trap speed is 119 in same condition/road as prior run that went 123.

Rob took a look and thinks the IMRC is possibly stuck in closed position or not opening fully. That would make me miss about 20+ hp easily according to him.

Has this occured to anyone here before? I'm not getting any check engine codes or anything. What can do to check if IMRCs are actually causing some issues or power loss?

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[Sammy123]

Both throttle body and intake manifold was ported by Brett Barber from Air Flow Solutions (AFS).

 

[BigBlue]

Both throttle body and intake manifold was ported by Brett Barber from Air Flow Solutions (AFS).

Try it with the stock TB vs the ported one. I'd bet it runs great. Stuck IMRC will throw a code fyi.

 

[BlackandBlue]

From what I understand IMRC are more for low speed idle and part throttle high load situations on the 12-1 engine. They shouldn’t cause HP loss at high Rpm. Most 15-17 changeovers lock them out.

 

[Sammy123]

Had to give up my original throttle body for a core charge refund. If I can find a spare locally I might try swapping it out. I guess 469 hp isn't that bad, I was just expecting more with the money spent on the ported manifold and tb and not a power reduction. If I had to do it all over again I would just leave the stock manifold/tb on there.

 

[Zinc03svt]

What does Brett Barber have say about it?

 

[Gurjit]

can you physically lock out the imrc for testing?

 

[TRPCANA]

A few things,

First up, 477 then dynoing 465 another day is not really a concern IMO. As im sure you know, dynos are tuning tools and even tho conditions may seem similar you cannot guarantee the same dyno results even on the same day, much less different days. 465 is still strong and wouldnt get worked up over it, dyno numbers are largely irrelevant. The trap speeds dropping may also be attributed to driver variances from run to run as well.

As im sure youve heard, that JLT intake isnt doing you any good. Lethals own car project goldmember proved this by adding mods in increments then dyno'ing and doing track runs after each mod. After a tune by itself their own 2018 A10 car made 459rwhp. After a JLT was installed they made 461. A gain of 2rwhp for $350 and the increased IATS that these open element filters see (which could have been the cause of your decrease for a dyno or run btw if your IATS were hot in the staging lane and the car pulled timing in the first part of the pass) is just not worth it, its been proven time and again stock box with a filter is just fine for NA cars.

Third, The issue is likely the TB. There is a thread ongoing right now on them and several comments report issues with the ported TBs when on some tunes, id look at the thread. I also have a 2018 A10, and i installed a few weeks ago a ported stock manifold, and im also tuned on E85. I have seen zero drop in performance or anything like you describe, the manifold is performing as it did stock. Which is what it should be doing since a ported stocker is really only worth about 5 to 7 rwhp which you likely wont feel. Bottom line id swap to the stock TB and your issues will likely resolve. Perhaps sell your JLT for funds to repurchase a stock TB. Good luck.

 

[BigBlue]

A few things,

First up, 477 then dynoing 465 another day is not really a concern IMO. As im sure you know, dynos are tuning tools and even tho conditions may seem similar you cannot guarantee the same dyno results even on the same day, much less different days. 465 is still strong and wouldnt get worked up over it, dyno numbers are largely irrelevant. The trap speeds dropping may also be attributed to driver variances from run to run as well.

As im sure youve heard, that JLT intake isnt doing you any good. Lethals own car project goldmember proved this by adding mods in increments then dyno'ing and doing track runs after each mod. After a tune by itself their own 2018 A10 car made 459rwhp. After a JLT was installed they made 461. A gain of 2rwhp for $350 and the increased IATS that these open element filters see (which could have been the cause of your decrease for a dyno or run btw if your IATS were hot in the staging lane and the car pulled timing in the first part of the pass) is just not worth it, its been proven time and again stock box with a filter is just fine for NA cars.

Third, The issue is likely the TB. There is a thread ongoing right now on them and several comments report issues with the ported TBs when on some tunes, id look at the thread. I also have a 2018 A10, and i installed a few weeks ago a ported stock manifold, and im also tuned on E85. I have seen zero drop in performance or anything like you describe, the manifold is performing as it did stock. Which is what it should be doing since a ported stocker is really only worth about 5 to 7 rwhp which you likely wont feel. Bottom line id swap to the stock TB and your issues will likely resolve. Perhaps sell your JLT for funds to repurchase a stock TB. Good luck.

This one knows for sure. Stock TB swapped out, 18+ style oem intake, retune for the MAF setup/intake vs the JLT and you will decimate the previous setup.

 

[2morrow]

I have a similar issue with my motor throwing codes for IMRC stuck open which is resulting in misfires.

Similar to OP I have a ported GT-350 IM, TB, CAI, LU47's and tunes by Rob Shoemaker @ PBD. I just clear the codes on the Ngauge as closed IMRC is mostly for low RPM driving.
I have not sensed a loss in power and I have found that the RC shaft is plastic and prone to breaking easily but not too sure how to replace that shaft(s).

Anyone have experience with either this issue and/or replacing the shafts? TIA.

 

[Bluelightning]

Had to give up my original throttle body for a core charge refund. If I can find a spare locally I might try swapping it out. I guess 469 hp isn't that bad, I was just expecting more with the money spent on the ported manifold and tb and not a power reduction. If I had to do it all over again I would just leave the stock manifold/tb on there.

I have a stock 18 TB. Shoot me a PM if you want it. I'll send it to you for the cost of shipping. Had a Stage 2 Whipple on my car, but it got totaled last week, so no need to keep stock parts for a car I no longer have sitting around. Has maybe 3K miles on it.

 

[Sammy123]

I have a stock 18 TB. Shoot me a PM if you want it. I'll send it to you for the cost of shipping. Had a Stage 2 Whipple on my car, but it got totaled last week, so no need to keep stock parts for a car I no longer have sitting around. Has maybe 3K miles on it.

PM Sent!

 

[tdstuart]

Any update on this? Curious to what you found out.

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