Fox Foxbody feeling a bit sluggish

QSACfoxbody · Feb 25, 2019

Hey guys,
I've been driving around my 1984 Mustang for a few weeks now and it just seems a bit sluggish to me. It became more evident when I took it to Irwindale speedway to see how it would do stock before adding any mods. The best it ran the 1/8th mile was 10.3 @ 63 MPH and this is on drag radials/skinnies with race star industries wheels and a semi stripped interior. My foxbody has a stock motor besides a 650 4 barrel carb with a Edelbrock performer intake and underdrive pulleys, World class T5 from a 1999, 8.8 rear end with 2.73 gears. Spark plugs were changed since I thought this was the problem and the base timing is already set at about 13-14 degrees. Had a lot of backfire at the carb when at WOT before i changed the spark plugs but now it occasionally happens when trying to accelerate. When trying to accelerate it just doesn't feel like the car is accelerating at all so I'm trying to fix any mechanical issues before actually adding mods to it. Could it also be related to the loud jolt I hear from the rear end when I go into a different gear? Any help is appreciated

TOOLOW91 · Feb 25, 2019

Well for starters those 2.73s are doing you no justice . If it’s a stock 84 motor that you just have the intake and carb on - well they were very anemic to begin with . Something tells me minus the gears you’re not far off .

General karthief · Feb 25, 2019

^^I agree with Jeff^^
Now I will give you my 2c worth: if this was a fuel injected setup I would say fix the lean backfire first but no need to in this case.
I imagine the 84 engine does not have a lot of compression compared to the FI engines we enjoy. So that said, you need a gear change and the usual heads, cam and intake swap. Then you can tune the carb.
The parts you pic must match what you want the car to do. The plan is the most important part of the build. Kinda sounds like your leaning towards a drag car so now you have to decide how fast you can afford to go.
read through this thread, https://www.stangnet.com/mustang-forums/threads/bob-cosbys-12-second-recipe.853108/ now most of it applies to the 5.0 efi cars but the suspension and clutch/trans stuff can apply to your car, then when you get to a point you will need to update the engine with higher compression, bigger heads, cam and carb, it's a sickness so start out small. The most important part will always be the plan.

JD1964 · Feb 25, 2019

Is the carb mechanical or vacuum secondaries? I ask because a non ho 302 doesnt need anything near a 650 cfm carb. Im nort saying it cant work, Im saying it does not need that much cfm capability. If you have mech secondaries and your going full throttle, it might be too much carb to get the mixture right. With vac secondaries, this might be less of a problem.

In the past I had a modded 455 olds that would pull to 6000 rpm with a 650 mech sec carb. No way a 302 needs that much, especially not a stock 302.

QSACfoxbody · Feb 25, 2019

Yea I’m already planning for 3.73 gears or 4.10 depending on which I decide since I still want to be able to street drive it. Yes this is a car meant for drag racing and a bit of street. It has a full Eibach drag spring setup with Lakewoods up front and adjustable shocks in the back.
In terms of the carb it is a Holley 650 can carb so I think it is a vacuum secondary but I can double check on that. I bought the car with this carb and intake that it has. I plan on adding nitrous to the car to get the best bang for buck since we want to swap out the motor for another ford (but that’s a secret for you guys to see in the upcoming months ) we’re just waiting on this engine to blow. Any other suggestions on best bang for buck upgrades on this carb engine?

90sickfox · Feb 25, 2019

I think its fuel related...could be a bit of timing issue too. If the balancer isn't new it may have spun. Get a cheap air fuel ratio gauge and check your fuel ratio. I picked one up from advance auto a few years ago for cheap. I had an edeljunk 600cfm carb and was able to tune it pretty dang well. Ran well...and got 26mpg on the highway at 72mph. With 373s and zspec t5.

QSACfoxbody · Feb 25, 2019

Yea I'm going to take the carb to a specialist for him to disassemble it to clean it out. Could a clog in the carb cause the occasional backfire and such a slow 1/8th mile? The previous owner seemed to have marked the 13 degrees BTDC and it's still on point. I would think my mustang would atleast be in the 9's with the drag radials, skinnies, drag suspension, interior strip, and the intake/carb setup.

QSACfoxbody · Feb 25, 2019

Of course I'm still taking the gear ratio into consideration so I'll see how it'll do with 3.73s or 4.10s which would you guys recommend for a drag/occasional street setup? I'll try to take my fuel ratio this week and I'll let you guys know. Also would the bang that I feel from the rear end after switching into another gear be a problem? Could it be a driveshaft that is too long since the trans and rear end were swapped.

90sickfox · Feb 25, 2019

Check your rear upper and lower control arms. Bad bushings or loose bolts will make a clunk noise whe changing gears. Check the u joints on the driveshaft as well. I doubt the driveshaft is too long. Easy to tell be the distance in front of the front u joint. It should be about an inch or so between the shoulder of the yoke and the transmission output seal.

QSACfoxbody · Feb 25, 2019

I'll check those out this week and see if any of those need replacing since I know the all the springs, shocks & struts needed replacing when I bought the car. I forgot to mention that the driveshaft is extremely difficult to take out and put back in we basically have to use leverage to force the driveshaft onto the rear end once the driveshaft is already in the transmission and needs to be bolted onto the rear end.

90sickfox · Feb 25, 2019

It shouldn't be hard to get in. As the rear ends drops, from jacking the car up, the driveshaft distance gets longer. If its binding with the rear dropped than it will definetly bunc when it's on the ground. Yoke should slide freely in and out if the transmission. There something wrong there buddy.

Maybe it's the wrong driveshaft and it is too long.

QSACfoxbody · Feb 25, 2019

Could a simple fix just be taking it to a specialist and shaving a bit of it at the slip yoke?

General karthief · Feb 25, 2019

QSACfoxbody said:
Could a simple fix just be taking it to a specialist and shaving a bit of it at the slip yoke?

No, if the drive shaft is too long, and it sounds that way, it will have to be shortened, it would be cut where the tube meets the yoke flange and the flange welded back, then balanced. There may be a driveshaft that fits without cutting but that would depend on rear axle housing, upper/lower control arm type and trans type. Lots of variables.

QSACfoxbody · Feb 25, 2019

Yea I'll look into an aluminum driveshaft to eliminate the process of having to shorten the current driveshaft

Fox Foxbody feeling a bit sluggish

QSACfoxbody

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TOOLOW91

If you're the village idiot what's that make me?

General karthief

wonder how much it would cost to ship you a pair

JD1964

there is enough sticking out to grab on to

QSACfoxbody

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90sickfox

Wasn't a pretty sight...and I've got big hands

QSACfoxbody

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QSACfoxbody

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90sickfox

Wasn't a pretty sight...and I've got big hands

QSACfoxbody

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90sickfox

Wasn't a pretty sight...and I've got big hands

QSACfoxbody

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General karthief

wonder how much it would cost to ship you a pair

QSACfoxbody

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Fox Foxbody feeling a bit sluggish

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If you're the village idiot what's that make me?

wonder how much it would cost to ship you a pair

there is enough sticking out to grab on to

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Wasn't a pretty sight...and I've got big hands

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Wasn't a pretty sight...and I've got big hands

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Wasn't a pretty sight...and I've got big hands

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wonder how much it would cost to ship you a pair

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