Cam or gears (help please)?

[toomanyhobbies]

I finished the build of my '98 2 door about a month ago. It has a new L31 with a ZZ4 cam, mid length headers, large throttle body and a black bear tune.

Overall I am really happy with the truck, except that it's entirely gutless from 55 to 70ish. It has 3.73 gears and turns about 2000 going 73. Like pedal to the floor just short of kickdown to maintain speed going up an overpass gutless. And terrible mpg to boot but it's not a daily so I am less worried about that aspect.

Anyway, my choices are to change out the cam or to go to 4.56 gears to get the rpms on the right side of where the cam wants to be. A 22% increase in gearing would result in more like 24-2500 at 75 which I think is fine in terms of annoyingness.

Tires are about 30" and rear is a G80. Stall is set to around 1500.

Looking for thoughts about the pros and cons about each option, with reliability (is a 4.56 ratio going to leave me likely to blow up driveline parts) and cost being the main considerations.

I like the way the truck runs quite a bit, but it needs to run at higher revs to make the cam work as is.

Thanks


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[Stokes1114]

I would change the gear ratio. You chose that cam for a reason. It is a decent cam. The step in ratio will help the trans and motor not "work" so hard, thus making them last longer if anything. If you have an auto I would also look into grabbing a new torque converter for a cpi 4.3 as the higher stall (around 2500ish) will help as well.

 

[L31MaxExpress]

I had that cam in a L98 aluminum head TBI 350 engine in my old G20. Was not a great running cam and not torquey at all on the bottem end. I had 3.08 gears and 28" tall tires. LT4 Hotcam builds more torque than the ZZ4 cam more quickly. I would look at an Elgin E1136. 210/215 @ .050 on a 110 lsa. The ZZ4 looks ok on paper but that long exhaust duration hurts the low-end power.

You might also be able to make some tuning changes to the transmission to make it unlock the converter and downshift more quickly with less throttle and make the ZZ4 cam more friendly. Especially if you use the 4.3 S10 converter. You will want a reman1998 4.3 S10 converter to match your trans.

I have a 1999 Tahoe with a 218/218 @ .050 flat tappet cam in a 305. 3.42 gears and 32" tall P305/50R20s. 1,700 rpm @ 70 mph, it pulls most hills in OD and gets about 22 mpg with the cruise set at 70. ALOT of it is in the tuning especially spark advance. The factory timing map barely works well with the factory cam and put more duration in it amd the timing is just too retarded.

One thing I do not understand and never have with that 305. It LOVES to be lugged down and gets its best MPG under what would seem to be a heavy load. The 350 in my Express van HATES being lugged. When the 350 is lugged down it drinks gas. I run a 4.56 gear in the Express van with a 30.6" tall tire. Turns about 2,800 rpm @ 70. I still see 18 mpg on long trips.

 

[toomanyhobbies]

Thanks. I have concluded that the tune is off so I am working on correcting that before I do anything else. There are some other running issues as well. Will report back.


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[RDF1]

I ran the numbers and it looks like if you have 3.73s and a 30" tire with a 4L60 your at 2050rpms at 70mph. Going to a 4.56 you should see 2500rpms at 70mph.
That in itself should help alot.
Running a higher stall really wont help since its locked up really.

Im on the other side of the fence.
i have 30" tires, 3.73s and a 4L80E and looking to go to a 3.23 or 3.08 gear haha. Im at 2200rpms at 70 and trying to get around 1800ish. (Turbo 5.3 setup)
I can accelerate up a hill without unlocking converter in 4th.

 

[toomanyhobbies]

I ran the numbers and it looks like if you have 3.73s and a 30" tire with a 4L60 your at 2050rpms at 70mph. Going to a 4.56 you should see 2500rpms at 70mph.
That in itself should help alot.
Running a higher stall really wont help since its locked up really.

Im on the other side of the fence.
i have 30" tires, 3.73s and a 4L80E and looking to go to a 3.23 or 3.08 gear haha. Im at 2200rpms at 70 and trying to get around 1800ish. (Turbo 5.3 setup)
I can accelerate up a hill without unlocking converter in 4th.

Thanks. This is what I thought in terms of gearing. However today I did an other highway trip and it ran at 2400 at 74, and if I hit the gas it would go to 2900 and pick up steam. At one point it felt like the converter locked and I was at 2100 but it was only for a few seconds of 30 miles on the highway.

When I got off the highway it basically ran like crap. I put it in neutral coasting at 3 mph and it chased around between 900-1600 in idle. In gear it idles well at 950, then goes to 1100, then drops to 700 and shakes and struggles. Gets progressively worse to a point when run slow.

I think it's possible I have a TC problem and a tune problem as well. I will have the code reader/programmer from the tuner when I get back in town after the 4th.

I also think if it was running correctly, the problems I posted about may not exist. We will see.


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[89GMCJOHN]

Food for thought I remember running across this Hot Rod article ...about the ZZ4 crate engine they tested ....

"Disappointing Baseline
368.6 lb-ft @ 3,200 rpm
314.1 hp @ 5,300 rpm
GM rates the ZZ4 at 418 lb-ft at 3,600 rpm and 355 hp at 5,400 rpm. But when equipped with parts similar to those recommended in the current GM Performance Parts catalog-including an HEI distributor, the as-delivered low-profile aluminum intake manifold, and Holley 770-cfm vacuum-secondary carburetor-we saw just 314 hp and 369 lb-ft. "

a zz4 is a full 10:1 compression as well if I recall so that cam likes compression apparently so it doesnt feel soggy .....

Sounds like your tune to me ..BUT if your tune turns out to be correct you may want to try a simple experiment -turn off your lockup and try driving it on those same hills that gave you trouble looking at your rpm and how it feels at each cruising rpm without overdrive engaged kicking down etc ..... then play with this calculator to get you where you need to be gear wise ...

https://www.randysworldwide.com/calculators/rpm/ FWIW .

 

[RDF1]

Try this one. That randys world wide doesnt have transmission gear ratio defined unless the Ford AOD is a 0.70 4th gear ratio like the 4L60E.


https://spicerparts.com/calculators/transmission-ratio-rpm-calculator




Edit: Just found the AOD listed has a 0.67 4th gear. So pretty dang close.

 

[L31MaxExpress]

I ran the numbers and it looks like if you have 3.73s and a 30" tire with a 4L60 your at 2050rpms at 70mph. Going to a 4.56 you should see 2500rpms at 70mph.
That in itself should help alot.
Running a higher stall really wont help since its locked up really.

Im on the other side of the fence.
i have 30" tires, 3.73s and a 4L80E and looking to go to a 3.23 or 3.08 gear haha. Im at 2200rpms at 70 and trying to get around 1800ish. (Turbo 5.3 setup)
I can accelerate up a hill without unlocking converter in 4th.

That will make that setup a DOG even with a turbo. 2,200-2,600 rpm is perfect cruise RPM for a LS.

 

[RDF1]

Yikes, id hate to have it running 2600. My other turbo truck (6.0 LQ4) ran 1950@70 and it was perfect. Towed like a diesel too.
Could pull 8000# at 70 and never had to unlock the converter in 4th on the hills. It would 60' in the 1.9s with all terrains and run low 12s @5100#.

Its been years since i messed with the older Small Blocks, but i remember that they felt like they had more torque down low but ran out of steam pretty fast.
From what ive gathered the ZZ4 Cam doesnt like to be chugging at lower RPMS even tho it has a -9.5* overlap.

Just thought about it, but do you have a way to look at the live data? Wondering if its picking up any Knock and pulling alot of timing out at the lower Rpms making it weak?

Got a buddy at work with a S10 that is fighting Knock sensor issues. He couldnt pull a small hill in 4th with the converter locked, and 2nd would scream but barely pull the hill. Looked at it with a scanner and it was pulling 10-12* timing on heavy load/low rpms.