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Low end torque question

3K views 36 replies 8 participants last post by  dave1968 
#1 ·
I lost my low end torque and I think I know why but would like to hear some suggestions from all of you. I installed AFR 165cc on a stock block, stock cam. Scorpion 1.6 Roller rockers, a new upper and lower intake, sorry it's the Edelbrock knock off, (I'm married and lucky to have done the heads) and a 76mm Mass Air housing for 19lb injectors. Could the stock throttle body be the issue with the lack of low end torque? anything over 3,500 rpms and the car is like a rocket.
 
#2 ·
My best guess would be the combination of larger ports on the heads+intake would be the cause of the loss. Those are really breathing mods and net you upper RPM horsepower at a noticeable loss down low.

This is my experience with the S191 4.6 motor anyways.
 
#4 ·
165cc isn't that big and kinda doubt it's the manifold either. Check things that would affect a/f ratio or timing curve.
 
#10 ·
With a stock cam the engine reaches peak torque at 3200 rpm. An overly
large throttle body will kill throttle response. I have found that a 65 mm throttle
body is close to ideal with what you have. You don't want to slow the velocity
of the air coming in.Using an MAF larger than the TB is a good thing.IMO a set of
3.55's for the street is the best bang for the buck. It will really wake up your
car. Try this, pull the vacuum line off the fuel pressure regulator and plug it.
Take it for a ride and see if you feel any increase in performance. If you do then
you might benefit from an adjustable FPR. This will allow you to increase the
pressure as needed.
 
#17 ·
Wasn't gonna, I'married and poor too.
You should still be able to spin the tires... Play with fuel pressure and timing. Pull a spark plug and look at it. Is it wet? Is it white? I'd tell the wife that the car isn't safe to drive w out larger injectors, pump, and a tune..


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#18 ·
After installing the Holley Systemax II intake, I also noticed a slight loss of low end, but not enough to bother me. The Holley's powerband is from 2000rpm to 6500 so I figured that under 2000 would be noticeable. Sorry, I'm married and had the money!! :wink: I'm not sure what your intake is rated at (like mentioned above). I would definitely upgrade your throttle body to whatever the intake port size is - the stocker is like 58mm and is a choke point, at least 24lb injectors with matching MAF (or tune) and at least a 195lph fuel pump. I didn't upgrade my fuel pressure regulator and it's working fine. When you upgrade the gears, it just may give you the kick in the pants your car needs as well.
 
#19 · (Edited)
There's no need for an adjustable fuel regulator if one gets a tune. The TB is a choke point somewhat but not enough to make a feel of the pants difference. I'm pretty sure his air/fuel ratio is poor (way more air and not enough fuel) causing a lot of power to be left on the table and not an ideal condition to be running around beating on it.
Edit- He has this intake http://www.americanmuscle.com/typhoon-manifold-8695-satin.html#productInfo

It doesn't give an advertised operating range but it does say, "improved low end torque." I think though operates similar to the edelbrock performer which has an advertised max power at 5,500. So I don't think he's running around w a mismatched combo, just a poor tune.

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#20 ·
I'll have to bump up the pressure a lb at time to see if it makes it any better. I don't beat on the car, I just drive it like I stole it lol no seriously it's a daily driver at the moment I do drive fast on the highway but I ddon' go crazy in town slamming gears and won't take it to the track. I can check the plugs they have maybe 1500 miles on them, that's when I changed everything thing out including all the sensors on the intake and O2's.
 
#25 ·
No I don't think the combo would make me lose the torque, I don't put too much belief in advertising. AFR advertises almost 100hp gain on stock block I'd be happy with 50hp with the combo. I believe I need to upgrade the throttle body to get rid of the restriction the stocker could be causing. I will have to play with fuel pressure too. If I weren't waiting to close on a house I would just spend the money right now for the throttle body and get a dyno tune. The car is equipped with SCT eliminator chip that I'm not using because it's worse when in use
 
#27 ·
have you checked to ensure your throttle body is opening all the way?
the AFR heads likely have a smaller combustion chamber, which would have increased your compression, not decreased it as mentioned elsewhere. The larger head/intake ports are on the other side of the valves and do not effect compression ratio. Even if you have the pedestal version the chambers are 60cc... stock heads are typically 61-64cc. And, a 165cc port is not going to kill velocity... it's pretty common for ported GT40's and GT40ps to get up handy to 165cc's and those combos are known to roast the rears from idle.
A larger TB is not going to hurt velocity... your intake and head intake port will determine that. Having said that, I doubt a new TB is going to find your low end, unless of course the TB you currently have is not fully opening.
I have a pretty wild combo, and, am running stock fuel pressure. I would advise larger injectors and pump but doubt that is what is hanging up the low end... could be wrong but these cars run pretty lean from the factory at low rpm and full throttle.
Are you running Ford coil/dizzy/cap/rotor? If it's anything aftermarket, you may want to consider swapping Ford equipment back in.
Are all your grounds solid?
What is your timing set at? TPS? Plug gap?
While I doubt anyone one of those things may be the culprit, it could be a combination of a few or all that is effecting you.
 
#28 ·
Timing was just bumped yesterday to 14 from 12, the tps was rechecked yesterday . 864, bumped up fuel pressure to 40 psi. It feels a little better but I know there's more to gain somewhere. Dizzy, coil, cap, rotor and plugs are all Motorcraft. The plug gap is .54. The throttle is opening all the way. I notice more power when lightly on the throttle. I need to get my gears in as soon as I can
 
#30 ·
Apples and oranges kinda but after I added my blower the base pull on the dyno was only 240 hp from 223. It was supper lean and after tuning it ended up w over 300. I don't think I'd be running around hitting redline until I had my a/f ratio checked out.


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