351W how can I tell if I have the correct stall converter I have a C4 trans

[MikeKC130J]

I did the 351W swap, my question is.
How do I know if I have the right stall converter? I feel like I should have more Grunt when I take off from the stop light?
If I remember I think I have an 1800 stall converter.
Or could it be my 3:50 gears I have 32x12 tires
It just seems a little weak.
Any help is appreciated
Mike.

 

[blubuckaroo]

I think the biggest obstacle you're facing is the C4 tranny itself. Its first and second gear are just too high. The 1st gear is 2.46, compared to the standard three speed's 2.99 which is pretty high too.
I ran into the same issue. With considerable engine mods and 32" tires, the off-the-line performance was still really poopy. I ended up changing the axle ratios to compensate. That made the low end performance right, but at the expense of highway performance.
I ended up going to an overdrive tranny, but something you might consider, is keeping your 3.50 gears and having a low-ratio gear set installed in the tranny. That would improve your low speed performance and keep the highway performance, and auto tranny drivability you have now.
I can't even tell you if a low geared planetary set is available for a C4, but someone here might be able to help.

 

[Z Bronco]

I have a 351W with a C4 transmission riding on 35's with 4.10/11s in the diffs. I have a lower first gear kit of 2.90 in 1st gear and a lower 2nd gear as well. This combo has worked well for me as it is like having 4.88s in the differential for first gear, 4.56 for 2nd gear. and the 4.11 for 3rd gear which allows me to drive freeway speeds as well as creepy crawl. I do have a low stall speed convertor which I love off road (gives some compression braking for an automatic), and multiplies the torque nicely. However, a higher stall speed will launch you better, but is not as good for rocks. My kit was from A1 transmission in California and was put in in 1996. This set up has worked very well for me.

 

[bronconut73]

The lower geared planetaries are available from Summit and Jegs, in fact...
It's hotrod stuff but should work for us.
The only reason I didn't do this was I was afraid of the big difference between 2nd and 3rd...But it sounds like it's working for Z.

 

[Broncobowsher]

3.50 gears are whats hurting you. You are abusing the convertor with the lack of gear. Since you are working the convertor so hard is what is making you think the convertor needs changing when it is really the gearing that is hurting you.

 

[MikeKC130J]

3.50 gears are whats hurting you. You are abusing the convertor with the lack of gear. Since you are working the convertor so hard is what is making you think the convertor needs changing when it is really the gearing that is hurting you.

What gear selection do you suggest?

 

[DJs74]

I did the 351W swap, my question is.
How do I know if I have the right stall converter? I feel like I should have more Grunt when I take off from the stop light?
If I remember I think I have an 1800 stall converter.
Or could it be my 3:50 gears I have 32x12 tires
It just seems a little weak.
Any help is appreciated
Mike.

Torque converter selection is usually best decided based on the power band range of your motor... in particularly using the camshaft specifications.
For example, a motor with a power range of 1500 to 5500 RPM would probably like a stock type converter with a stall rating just inside of the 1500... say 1800 to 2000 stall.
A motor with a 3500 - 8500 RPM range will need a converter of 4000-ish stall rating. Basically, you want the converter to start working simultaneously with the power being made - not before and not too far in
As mentioned by others, you might be experiencing some sluggishness based on your gearing / tire size combination. Engine power could be a contributing factor but generally speaking, lower gears will overcome low power and sluggish launches.
If you have some safe property to play (meaning not in a public parking lot where the law will get you) and want to try the gear theory, put your transfer case on low lock and see how well it takes off. There are a lot of members on here that have experimented, discussed and can probably help you pick a good gear for your tire size if you are considering a gear change.


DJs74

 

[jckkys]

My combination is close to Mikes and the performance is excellent. 31' tires help a little and the 351 is a stock '86 5.8 4V HO. So the cam is a mild flat tappet with good low end torque. Is the 351 used in the swap built for high RPM HP?

 

[MikeKC130J]

My combination is close to Mikes and the performance is excellent. 31' tires help a little and the 351 is a stock '86 5.8 4V HO. So the cam is a mild flat tappet with good low end torque. Is the 351 used in the swap built for high RPM HP?

no she is built for low end tq

 

[Tiko433]

I have a 302 mid cam , Eddy Preformer 4B . Motor is a little tired , C4 , 33x12.50 with 3.50 gears. . The trans is fresh , I did a stock stall converter which is lower then 1800 . I'm not saying my truck will smoke the tires from a stand still but it definitely would not be considered sluggish. If you built the motor for low end I would think would want a converter close to the stock stall speed.
One thing I would definitely check is the kick down . I know some guys have stated it's not needed but my opinion it makes a night and day difference in performance. I'm using a cable style, it can be adjusted. Just something the check .

 

[DJs74]

What gear selection do you suggest?

The attached file shows different combinations of tires sizes / gear ratios and rates them based on gas mileage. This might help you decide which one is right for you


DJs74

 

[Broncobowsher]

Why look at peak torque? That number only matters when the engine is at full throttle. At part throttle the torque curve is completely different. My daily driver makes peak torque at about 4000 RPM. But that is nowhere near my highway cruising speed (unless towing a trailer up a mountain and pretty much full throttle to make the power I need to get up the mountain).

Small block ford in stock to mild form runs down the highway best in the low to mid 2000 RPM range. The more load, the higher the RPM should be.

 

[blubuckaroo]

What gear selection do you suggest?

To properly select your gear ratio for highway, you need to know the RPM where your particular engine makes its maximum torque.
Then you decide the speed you will be cruising at. Select a gear ratio from a tire/gear ratio chart or calculator to put your RPM in that range.

Don't just use your tire diameter for this. You need to use the effective tire diameter. That's measured from the center of the wheel to the ground (with the vehicle weight on it) multiplied times 2. Some tires reduce the effective diameter quite a bit with the vehicle's weight on it.

Now, that's the right way to select gear sets for highway. But most of us don't have access to a dyno to find out what our particular torque curve is.

If your engine is unmodified, you can use the factory specs.
According to the Chilton's chart, factory 302s make their maximum torque between 2000 and 2600 RPM, depending on years. 351Ws produced their maximum torque between 1400 and 1800 RPM.

So basically you're on your own to make a selection that performs well for your own use. Just remember, the gear ratio you select will affect both the highway and stop and go performance of your car.

 

[jckkys]

If your Bronco isn't performing well, it may be a tuning issue, that's a lot cheaper and easier fix, than new gears. The torque converter stall speed changes with the low end torque of the engine. The 300 IL6 with the same converter has a stall that's about 100 RPM higher than the 302. If Ford offered the 300 in EBs, a lot less EB owners would wand another engine to swap in. They are a far better truck engine than the 302. Broncobowsher is right about the inappropriate focus on full throttle torque performance. In every day driving we rarely use full throttle. Full throttle HP is an even less useful. The important consideration is part throttle low RPM power. This is often called drive abillity, but to many it's seat of the pants power. HP between 1500-3000 RPM, while maintaining more than 10" Hg intake vacuum, would be a more useful tool, to quantify drive abillity.

 

[MikeKC130J]

If your Bronco isn't performing well, it may be a tuning issue, that's a lot cheaper and easier fix, than new gears. .

Thanks for the info, I'll check the timing and see how much vacuum I have.
Mike