Throttle response and Low speed performance in a 440 stick.

My '68 GTX 440 stick 3.54 gear is less than impressive in terms of throttle response and low speed performance. I've experienced this in similar cars owned by friends. They are all basic garden variety 440s. Cam intake headers holleys 10 to 1 compression. The 340 stick cars I've owned seemed to have much better throttle response and low speed performance. THe cam in the GTX is a Comp. 305 Magnum. Used this cam in 440 A/body automatic. And it seemed to work much better. I'm wondering if it's cyl. pressure or duration related. Thought about dropping the intake duration down to 268 adv. and seeing if that makes a difference.Always degree the cams and try different ignition advance combinations.

Need more specifics about the combo.

Hedman 1 3/4 primary tube, Holley list 4780 Performer RPM intake 906 heads KB flat top pistons stock dist. with electronic conversion.Currently have 1 Mr Gasket spring in the dist. At idle its at full advance 34 degrees. I'm looking for someone who's had a similar experience and what changes remedied the situation. Certainly welcome thoughts and opinions.

Of you have an adjustable valvetrain, I'd strongly suggest going to a solid cam.

If that's not an option, and you're going to stick with a hyd...... I'd look at taking 20-25deg @.050 out if it.
Something along the lines of a Comp XE274 or XE275HL.

Currently stock rockers. A close friend with similar 440 with a stick difference being rpm heads roller rockers with the XE275HL. I didn't ride in his car but we were talking about it and he expressed the same feelings. I definitely respect his opinion.His car did have a 3.91 gear.His engine was also professionally built. He pulled the engine out of his '71 300 which was an automatic and put it in a "69 B body.He felt the motor definitely worked better in front of the automatic. I was thinking the same way you are about the duration. After talking with him I started to wonder about that. Going to a solid cam makes sense.

IMHO, too much cam and too big of a carb for good throttle response.

If you want really snappy throttle response, a carb with small bores will give it.

That cam, with 253@.050" duration is bound to be soggy down low with a manual transmission. It would need a high stall an auto with high stall converter and 4.10's to feel strong.

Suggest you go down 20-30 degrees... 222-235 @.050 range to get the low and mid range torque back. A

Could also try advancing the current cam a few degrees if you don't have piston to valve clearance issues.

I ran a Mopar .509 4* advanced in a low compression 440 stick car, even occasionally running it with 2.76's it wasn't objectionably bad.

Assuming you want to keep your axle?
Lighter flywheel
3.09:1 1st gear

A few things have gone through my mind. The weight of the rotating assembly and the length of the stroke. I've had 383s that had better throttle response and low speed performance. I've thought about advancing the cam. I've had good results with that in the past. It's a heavy car and I'd like to keep the 3.54 gear in it. That in itself presents a bit of a challenge. In this situation it seems like the automatic is more forgiving. Anxious to try some different things and hoping to get the chance soon.

Just curious as to how tall the rear tires are ? Ron

There are a bunch of things that can make a motor not accelerate well like to rich at part throttle, valve lifters with not enough preload or to much preload, degreeing the cam off of the exhaust lifter instead of the intake lifter , not enough advance at low RPM on the ignition timing, to cold on the heat range on the spark plugs and probably some others that aren't coming to mind right now
How tall are your rear tires now?
Is your NP 833 a 2.65 low gear set or is it the later 2.2? low gear set As already suggested using a lower first gear ratio like the stock 3.09 low gear set makes a bunch of difference on the street
Been there done that years ago when the early A body trans. where plentiful in our local SO CA junk yards
I put one of those gear sets in a friend of mines 1970 Duster 340 4 speed street race car that ended up with a set of 5.57 rear gears in the Dana 60 , you needed to be on your game on the first three gear changes in that rascal It flat hooked and book with a set of 13x30x15 drag slicks on a set of 12 inch rims
It showed a bunch of BB Chevy the tail lights on lots of occasions

Calculate the cranking compression to see how much that cam is hurting you for starters. Best off idle will be helped a great deal by coming up with a combo of cam, compression, and cam installed centerline that will be as high as the fuel you use can take.

What is your cylinder pressure? Get that first so we know what your working with.

My friend's 68 4 speed GTX w/ 3.54 drove like it was on ice in 1st gear. Small cam, fairly low cylinder pressure, good factory heads, factory spreadbore intake and matching carb. Car was a blast on the street. That being said, it really wasn't that fast at the track, so don't confuse the two, as they may or may not be the same thing.

I haven't checked the cranking compression.The rear tire is a 275/60/R15.The trans is an older 18 spline which I believe has the original 1st gear in it. I'm guilty of tuning it like my automatics.The post has opened up my mind a little more. I just have to do the homework.

The 70 and later 4 speeds has a 2.44 first.

A lot of sophisticated answers here. Why not try something real easy like bumping that timing up to 36-38 degrees. Just try it. Then work on the acceleration rich factor.

The 70 and later 4 speeds has a 2.44 first. [/quote]
Not true Only the T/A and AAR Cuda 4 speed cars had the close ratio stock in 1970, all 1971 and later 4 speed cars had them until Corporate decided to go to the NP833 O.D. trannys in what ever year that was

2264Ply-- can you expand a little on "low speed performance" in terms of RPM?

Are we talking 2000 or 3000 rpm or something else altogether. Are you talking about the engine actually lugging? At what RPM?

Is there an RPM where you powerband comes on and the engine starts to pull fine? If so, what RPM?

Not true Only the T/A and AAR Cuda 4 speed cars had the close ratio stock in 1970, all 1971 and later 4 speed cars had them until Corporate decided to go to the NP833 O.D. trannys in what ever year that was [/quote]


My point is there never was a 2.2 first gear 833. Ever. Look at what I quoted.

This is like asking how to adjust a blower belt because the motor seems to surge.

Bolt on stockish street car with a raceish cam. Seems straight forward and predictable to me. Who put that cam in and why? I didn’t see porting mentioned and if you are expecting to turn higher rpm with a cam like that I’d think you’d use 1 7/8 headers. Just looks like a mismatched cam and nothing more. I wouldn’t bother advancing that one.

Current cam is definitely to big 253@.050 I think the XE275HL would be much better with its 231@.050 I think you can make the current carb work with a good tune.

Even advancing the current cam wont help much IMO, that cam doesn't come into its torque peak until about 4300 RPM Its going to be lazy below that. A first gear swap will help, but more work then changing the cam. IMO, change the cam.

A 275/60/15 is a tall tire,try a 295/50/15 it will be a bit shorter and help gearing but you may need wider wheels. I agree on checking cranking compression and either advancing the cam if possible or a milder stick as suggested.

Yea, ditch your wheels and tires to go from 275/60's to 295/50's.

Good Lord.

A shorter tire was my main point from a gearing aspect,but you probably knew that

that tire change would be the same as changing to a 3.73 gear - it would help some but probably not as much as you'd hope. only a 5.18% change.

Bump the timing up to 38° and it'll wake up. My dad's road runner has 3.54 gears, hemi 4 speed, and a 10:1 440 w/ the 509/292 cam w/ 6 pack induction. It is a blast on the street and will roast the 275-60 tires. Has much better driveability than I expected it to have. I even put the cam in straight up instead of 4° advanced like most do. Timing is locked out at 38°.

I know my combo is a bit differn't with Indy EZ heads but my engine screams from 2000-5000 and my passengers are looking for something to hold onto I have a 3.54 gear and 2.66 low gear 4-speed with 29" tall tires. I've got a Performer RPM,Quickfuel 1050 4150 carb, Firecore distributor set at 24* base and 34* total all in at 2200. The cam is a very mild solid Comp grind XTQ series with 1.5 rockers. I just touch the pedal and the tires are smokin

Gus

Lot of good suggestions here!
If you can borrow shorter tires, do it!
Same with smaller carburetor, easy to swap with a 4 spd. no kick down to fool with!
My first 440 four speed swap felt "lazy"
A buddy loaned me a small AFB, really woke the car up on the street.
I had been running a Holley 800 double pumper.
Definitely check your cranking pressure, just do the easier cylinders!
Try advancing the cam, and check compression again before you put it all back together.
Of course I'm assuming you've got safe valve to piston clearance.
My car had the 2.47 first with a 3.55 rear, 245/60 tire.

Interesting thread. How much do you drive the car and where? Freeway? Just to cruise nights? Sounds like a bit much on the cam side to me. I've also heard the 3.54 gear wasn't a great performer down low for cars not set up to overcome the gear. I think changing tires to the 295/60 will help the pep, but I don't think you will like it if you drive it any significant distances.

All good recommendations here but they are stuff to try and band aid a problem of wrong combo of parts. Carb is not too big ,timing is safe where it is at , gear is good street gear, tires are not too big. cam is wrong!!! probably wants more compression and port work to utilize that cam. change cam to one that fits the rest of your combo better and you will be happy.

Without the OP providing more info about the cars powerband vs what he's looking for, the biggest (by far) problem with it not performing the way he wants is....

THE CAM IS TOO BIG.

Agreed.

We need a vid?

How does the car run when wide open?

Where have you been brother, Lots of input and some questions to help. But you've been I guess.

Don't worry about the rotating assembly or stroke length.

That's the Hard stuff to fix. Even with the best tune the 253*@ .050 cam is going to be a dog below 3500RPM, with a stick, Well unless you dump the clutch and let her rip.

With a high stall vert automatic you can make it work. IMO, a smaller cam change.

But it looks like you've decided to bow out of this thread.

If your tunes fine, Cam change is your Best bet.

Rotating assembly, stroke length. Shouldn't even be in the mix of thoughts for your fix.

This.^^

Simple. Cam's too big for what you want to have for other parts, and how you're driving it. Simple parts mismatch.