Lost low end torque

JJ's90fox · Jun 12, 2025

Hi all. I've got a 90 fox gt that has lost low end torque. My engine has stock intake manifold and cam. It has a cai, shorty headers, and brand new h-pipe and exhaust. It's never been tuned or a chip. No cel's, spark gap is good, timing at 14. I feel like I'm missing something. Any advice is welcome
And very appreciated. This is my first build. Thanks.

gkomo · Jun 12, 2025

Have you been able to check for codes?

JJ's90fox · Jun 12, 2025

Yup. No codes.

gkomo · Jun 12, 2025

So you got code 11 KOEO and 11 KOER?

JJ's90fox · Jun 12, 2025

Yes sir! On both.

gkomo · Jun 12, 2025

Ok ok, that’s about the limit of my helpfulness.

Based on your mod list, I don’t think a tune would be necessary. Computer look good? Air filter clean? MAF clean?

JJ's90fox · Jun 12, 2025

Ok thanks. Im wondering if I have too much back pressure

JJ's90fox · Jun 12, 2025

Or not enough

gkomo · Jun 12, 2025

H-pipe is catted or off-road?

When I used to swap my midpipes back and forth for smog I did notice the catted ones would have a noticeably different power feel compared to the straight piped ones. But almost like more torque on the low end, not the other way around. I got used to it after a while before swapping them back (or not).

JJ's90fox · Jun 12, 2025

Off road h pipe. Smog pump and egr delete. Into a summit racing 3 inch exhaust and hi-flo muffler.

General karthief · Jun 12, 2025

Full three inch from the headers back to the bumper?
Back pressure..... Yeah that's an interesting conversation...
What makes you think it's lost torque? Noticed this after the new pipes? Stock headers? If not what size?
Now for an opinion based on info given and some just assumed, you haven't lost torque, the bigger pipes just moved it up in the RPM range and with a stock rear gear get'n off the line is going to seem sluggish, now it needs a gear to get back to where it was on the butt dyno.

AeroCoupe · Jun 12, 2025

If it’s falling flat as the RPM’s increase it might be fuel related. Have you checked the fuel pressure?

General karthief · Jun 12, 2025

AeroCoupe said:
If it’s falling flat as the RPM’s increase it might be fuel related. Have you checked the fuel pressure?

It's the 'back pressure ' can't you tell?

AeroCoupe · Jun 13, 2025

Ha ha ha!!! What the F ever.

limp · Jun 13, 2025

So this has happened since you modded your engine??

Mustang5L5 · Jun 13, 2025

Full 3" all the way back on a stock engine might have shifted the powerband up a little higher, but it shouldn't have killed all your low end torque. How much loss are we talking? Did it happen right after the exhaust?

Had a buddy years ago who had a bone stock 1989 GT 5-spd. At the track this was a low 14 second car consistently. One day he must have sniffed some glue or something and took the entire cat-back off and switched to an off-road H-pipe. Essentially it was open exhaust with no mufflers. Car was loud and sounded like the world was coming to end. Damn thing couldn't get out of the low 15's after that.

General karthief · Jun 13, 2025

This ^^^^^^ is why research and planning is so important to a 'street' car, a 'street' car with racecar parts is more than likely to be a pooch on the street, low RPM driveability will suffer because the torque/HP has been moved up enough in the RPM range that it takes the 'street' out of the 'street car'.
My replacement stock block/heads with a E cam was only fun to drive when in the upper RPM range like 4 and 6k RPMS!! Below that it bucked, pissed and moaned and I hated driving it.

JJ's90fox · Jun 13, 2025

Thanks for all the input. The headers are 2.5 inch, h pipe is 2.5 into a 3 inch exhaust. I agree with the torque being moved up. Makes sense. It is super responsive and quick in the 3-5k rpm range. It does have stock gears. Next move is to put 3.73 in the rear. Hopefully that will help

Mustang5L5 · Jun 13, 2025

That will definitely help. Since you moved torque band up, you need gears to get up into that higher RPM range sooner;.

Noobz347 · Jun 13, 2025

JJ's90fox said:
Thanks for all the input. The headers are 2.5 inch, h pipe is 2.5 into a 3 inch exhaust.

This is what has killed your exhaust scavenging.

"Backpressure" is never an advantage. This is interwebz myth and/or an over simplification of what is going on.

You will likely see an improvement from swapping out your 3 inch pieces for 2.5 to match the rest of your system.

I've left a couple of links that may be useful:

View: https://youtu.be/DvMBbojZpII?feature=shared

View: https://youtu.be/2tZYJHtXG9s?feature=shared

Your engine and cam create an exhaust "pulse" going down the length of your exhaust. By switching to a 3 inch at the end, you have effectively terminated the pulse that helps 'vacuum' the next firing cylinder's exhaust.

Lost low end torque

Member

now i can hopefully expect to receive the shaft

Member

now i can hopefully expect to receive the shaft

Member

now i can hopefully expect to receive the shaft

Member

Member

now i can hopefully expect to receive the shaft

Member

wonder how much it would cost to ship you a pair

lube between the nut and the face. I know my lubes

wonder how much it would cost to ship you a pair

lube between the nut and the face. I know my lubes

wrap a little cheese around it and its a done

That is…until I whipped out my Bissell

wonder how much it would cost to ship you a pair

Member

That is…until I whipped out my Bissell

Stangnet Facilities Maint Tech... Er... Janitor

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