[MerrittE]

Hey guys, I’m finally getting thing sorted for my 1967 Pontiac Firebird (91 pump gas daily summer driver with AC, power disc brakes, and enough performance for an occasional track day for fun)
Engine: Pontiac 428 stroked to 461 ci (4.25” stroke)
Heads: Edelbrock aluminum, 87cc chambers, round port
• Exhaust: Doug’s 1 7/8” round port headers
• Pistons: Forged Buttler/Ross flat top -8cc
• Compression Ratio: ~10.1:1
• Rockers: 1.5:1 roller rockers
• EFI
• Trans: 4L80E
• Tire Diameter: 27”

Rear Gear Ratio: 3.23 maybe 3.73 or?

Based on Half-inch Studs post I am probably going to use the stock converter.

Comp Cams custom grind camshaft based on Cliff’’s previous post:
• Type: Hydraulic Roller
• Duration @ .050”: 230/242
• Lobe Separation Angle (LSA) 112
Or would an off the shelf cam be better suited to what I am after?

Thanks for all the help!

[64speed]

Great combo!

[krisr]

I'm running 4.3 rear gears with a 275/60 tire but is a healthy 400 cube motor and 4L80e. I'm going to go back to 3.9 rear gears as I want the car to be even more friendly at 60mph but with your larger engine I would go 3.73 rear gears with that tire and it should be really fun to drive everywhere without crazy RPM at highway speeds.

[grivera]

My 69 bird has a 4l80e, 3.55 gear with a 26”
Tire. With a 27” tire 3.55 to 3.73 should be good. Cam specs in signature.

[Formulajones]

4L80E's have .75 overdrives and the lock up converter also helps.

Really depends on what you're shooting for.

We are running a pair of 4L80E's, both cars are over 700 hp and almost 800 ft lbs. of torque so they don't really require a bunch of rear gear anyway. I installed 3.42's in one and now installing 3.55's in the other one. That puts both cars at almost peak rpm at the finish line with that kind of power and still cruises 70-75 mph at 2200-2300 rpm on the highway. So it's a nice combo that works out really well.

The one that currently has 4.10's still cruises well enough. 65 is 2400 and I can run 26-2700 if I want to go 70+ which I've done for a few years now and it's fine. Now that 4.10's are too much for the new engine I am knocking it down to 3.55's. Not for cruising, it's because I can't get to the finish line in 3rd gear anymore lol.

Just depends on what you're looking for.

[JLMounce]

I currently run 3.31's with 26" tires behind my 465 and 4l80e combo. 75mph is about 2400 rpm or so. I think with a 27" tire I'd want a 3.55 in the rear.

That said, even with the shallow 3.31's there's so much torque that any real amount of throttle application roasts the tires. So I guess it really depends on your intended use case. If you're planning on a LOT of highway miles, I might opt for a 3.23 or there about and have really nice highway rpms. If you're more concerned about performance, I'd think I'd want either the 3.55 or 3.73 in there.

[HWYSTR455]

Yeah, I did 3.73s with my 461, and 3.42s with the 535.

I probably should have kept the 3.73s for the 535, but will run it like it is for a while and re-think it later.


.

[Half-Inch Stud]

Yes, the 455 driving the stock GM Van Gasoline converter is amazing. Try that and save the large money.

Later, after all is running, will be the decision time for an aftermarket 4L80 converter, and i bet $1 the Stock converter stays put.

230/242 cam sounds fine, but try 87 octane on street, and 89 octane on track for then aluminum heads. I did with iron heads at 9.0:1 and it played well.

[MerrittE]

So Comp spec’d the following cam for me
238/246 @.550 with 112 LSA

Any thoughts on this?

[JLMounce]

Is 122 LSA a typo meant to be 112 LSA?

What lobes did they spec?

If that's actually on a 112, it's probably a decent combo in a 461.

Here is my 465 with a comp 240/248 on 112 with QNI lobes.

https://youtube.com/shorts/1O3aU7SHp...ZKV3ChR07bG-ka

[MerrittE]

Yes that was a typo I fixed it now thanks for catching that. It’s 112 LSA.
How about vacuum for power disc brakes any concern there? I’m trying to make sure it’s as healthy as it can be while still being a good daily cruiser. I’m trying to walk that same fine line as a lot of folks where I want good power but I don’t want it to be something I don’t want to drive to the hardware store because it’s too much. The Comp guy was a bit of read from the script guy and didn’t instill a lot of confidence.

[JLMounce]

It's going to be iffy for power brakes at your altitude. My cam makes about 10" of vacuum. The previous cam I had that came in at 232/238 on 112 made about 14". Extrapolating from there you can probably expect somewhere around 12" of vacuum. If think if you want to run power brakes, you'll want to look at a dual diaphragm booster in the 8" or 9" size. The C6 corvette dual diaphragm unit that DSE sells, would be my pick.

Your other options would be manual brakes (which I run) or hydroboost.

From a drivability standpoint, I think you'll be nicely surprised. My setup drives as smoothly and as docile as you want, but as soon as you put your foot into it, it's an animal. A lot of that I do attribute to the TSP converter I had built for it.

I think you're looking at the stock converter, which is fine, it may be a bit over-coupled at low speeds, but I don't think it's going to be an issue with the amount of torque you're going to be making.

[yellow1098]

I am running a 4L80 with 4.10’s and on the highway I'm at 70-75 mph at about 2700-2800 rpm, 60-65 mph is at about 2400-2500 rpm. I haven’t had any problems at all in that range.

My engine is also a 461 with a 248/254 cam at 112

I’m running a 3800 lock up converter which is probably not enough but pushing 680hp it help a lot like others had said get through the traps in 3rd.

Also…my stock brake booster and master work just fine but I’m running any road courses or anything haha

[Formulajones]

Mine is setup like that and cruises in the rpm range you posted with 4.10's. actually drives nice like that but unfortunately it does not get to the end of the 1/4 in 3rd at my hp level. Steve at Hughes that built my 4l80e and converter told me he didn't want me to lock the converter at full throttle and it would be iffy if I tried to use 4th. Meaning he knows people that do it with his trans and most of the time get away with it but 4th in a 4l80 uses a single clutch/plate setup that isnt meant to hold a ton of HP. Since I was at a private track rental and out of gear at the 1000 ft mark I started using 4th. All was fine but I will say it's not ideal in a drag race situation because it pulls the motor down so much it basically kills the run.
For instance in 3rd I was banging the rev limiter at 1000 ft. I kept my foot in it anyway and ran out the back. Went 11.10 at 121 mph.
Next pass I used 4th for the last 320 feet or so and only picked up 1 mph. Went 10.90 @ 122. Using overdrive at the strip isn't ideal obviously and you can even hear it lug down in videos I shot, which is why I'm Knocking the 4.10's down to 3.55's. I sent video to Steve and talked about the converter as well. He wants to loosen it since it only flashed to 2200 and said 3.55's would be perfect for my setup. I'm making 786/772 HP and TQ so I just dont need the 4.10's anymore and it's why i said early on the gear ratio is dependent more on the engine combo if you're worried about 1/4 mile racing and not so much cruise rpm. The overdrive is just an added bonus. Problem is this stuff takes a ton of testing and time. I'll have to swap the 3.55's and test again with the tight converter first and log flash rpm at the starting line because the gear change will affect the flash rpm and how the converter acts on gear changes. Then Steve will determine if and how much the converter needs restalled or reconfigured. Then reinstall that and test yet again. We are shooting for a converter that flashes around 2800-3000 because the engine is already making over 700 ft lbs at 2700 so I just don't need or want a ton of converter in it.
I say all this because this becomes a game of testing and changing parts. How much are you willing to do and how much money do you want to spend? How good do you want it to run? Every combo is going to be different.

[yellow1098]

That’s interesting info Formula…..which cam are you running in your setup?

So by changing from 4.10 to the 3.55’ it kept you from going into 4th during the run? When i went to the 4.10 I was thinking that’s what that would do for me haha

I’m currently trying to go through the testing also with optimizing my setup but the gear change is a huge pain with the breakin process where they want you to get 500 miles before racing after every change

[Formulajones]

I'm in the middle of all this at the moment. Changing to 3.55's now. Yes those will allow me to finish the quarter in 3rd. Knowing what the car does and the math figured in should put me around 5500 or so at 125+ in the quarter depending on how the converter reacts. I'm trying to keep it at 5800 or less. With 4.10' it was on the 6200 limiter at 1000 foot cones.

Cam is a decent size hydraulic roller. Off the top of my head it's 260@ .050 and around .650 lift.

[yellow1098]

Im thinking I am around the same about 6200-6400 where mine is shifting which might be alittle to high….but I do have some huge 340cfm heads and probably not enough cam for them

These are all the tuning things I’m working on now myself

I will have to check my Holley for what gear im getting into and when as I do have transmission control in the terminator

What size and kind of converter are you running?

Thanks and sorry or all the questions

[Formulajones]

I have been running Hughes converters. Currently what they refer to as a 265mm which I believe is a 10.5"

Steve purposely set it up tight for me, mainly because it's easier to go in and loosen one than it is to go back in and tighten one, knowing I'd likely be pulling it back out for a restall as I dial in the car. Plus I like them a little on the snug side anyway even if it sacrifices a little 60 foot.

[yellow1098]

I will check out those converters formula……what stall are you running on it?

Also….what are guys doing as far as break in goes when you swap gears? 500 miles is suggested but on our cars that seems like a big ask…..

Should be good info for the OP also

[JLMounce]

When I broke in my gears I did a light drive to bring everything up to temperature, then let the car cool completely. Did one more of those followed by a heavy drive and cool cycle. Then I sent it.