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Discussion Starter · #1 ·
I have a mildly modified 327 mated to an M21 with a 4.11 rear end and some really stuffy World Products S/R heads (not even the torquers). It is running a 3863151 vintage performance cam (222/222) that makes power between 1500-5200rpm. I plan on upgrading my heads to something that can breath, and going with a 480/230 cam in the future to bring my hp up to somewhere around 350ish and the power band would move up to 1800-6500

I really enjoy driving the M21/4.11 around town, but don't take it on the highway because in my city you have to be doing at least 70 to keep up with the slow traffic, and 70mph is about 3500rpms with the M21 and 4.11. It sounds fantastic, but gets old on longer drives...not to mention I can watch my gas gauge go down on the highway.

I am going back and forth between transmission options for the future. One option is the Tremac TKX 5spd, the other is keeping the M21 and adding the Gear Vendors overdrive unit, and a third would be lowering my final drive ratio down to something like a 3.73...or even lower. The TKX seems like the pedestrian easy option. The Gear Vendors unit is really cool, but really expensive, and lowering the rear end ratio just seems like the boring way to go.

I've also thought of the idea of keeping an entire rear end with brakes and everything set up with something like a 2.73 that I could just bolt up to the car if I were going to go on a road trip.

I've used the calculators out there and I have seen the numbers, but I would like some real life feedback. Has anyone had a chance to compare any of these set ups? Can the TKX take the same kind of gear banging abuse that the muncie can? Is it as fun to drive? I really like the muncie, but I really want an overdrive.
 

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i abbused the shit outta the early tremec 3550 model i had behind the 427bbc
with the 4.11 gears and the 0.68 overdrive it was great hammering it around
then on the expressway the rpms would drop like 2000rpm
i would suggest a tremec if you want a cool trans...
they are very fun tp drive :)
 

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I put a gear vendor unit behind an M20 in a 68 last fall. Had to beat the crap out of the tunnel and notch the floor brace to make it fit. I didn’t think that was ideal. Plus the wiring is a cluster F for it.
I’d go TKX.
 

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Actually the TKX can take 600lb/ft of "gear banging abuse". I don't believe any (typical) Muncie can take anywhere near that. Its a bolt in and fits the 68-72 bodies with no mods. 64-67 not so sure (don't know what your year is). I just bought one thru Summit and am in the process of installation now.
 

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1966 Malibu, 327, Muncie, 3.55 posi
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I have tossed around your ideas too with my 327. Just not in my budget to upgrade to any newer manual or OD.
My Muncie and 3.55 combo is more highway friendly than your setup, but still not ideal. I commute to two work places on the highway; furthest being a 45 min drive. The sound of 2500 rpms isn't so bad for that length of time with a good stereo making more noise.
 

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The L79 cam that you are running is famous for a reason. Unless you are going with a roller you will be hard pressed to have a better overall street cam. I am stuck because I am number matching and can not use headers but my 68 L79 with a nice intake, 650DP, ignition and quality headers will make 400. Stock L79's run 353Hp on the dyno. I have the M21 with 3.31 gears and wished I would have installed a new M20 gear set when I rebuilt mine. M22's are just too loud for me. If originality is no concern I would install AFR 64cc "As Cast" heads, intake of your choice, same cam, get the compression up to 10.5, M20 gears with a 2.52 first gear (or 2.90) and drop the rear gear to 3.42's or 3.55's max for the street. Personally I would not install any tranny that required modifying my floor. If you are going to do a lot of highway then an overdrive should be installed. My 3.31's with 26.5 inch tires (235/60/15) runs around 2500rpm at 60mph and very tolerable.. BTW L79 cam is 1500 to 5800 power range, actually max HP for my engine is rated at 5800.
 

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I have a 67 w/BBC auto trans and the gear vender, a blast to drive with six gears. I have a 66 w/sbc 4 speed Muncie and decided to go with the Tremec TKX since the car is a stick already. The trans gearing I want is still in production so I cannot give you and information on it yet. I looked at the options available for both vehicles and believe the gear vender was the best choice for the auto trans. The Tremec IMHO is the best choice to swap for the Muncie. Both will give you what you want in the way of highway driving.
 

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IMO your best bet is the TKX. It is the best of both worlds. Your get the advantage of nice performance gears in the rear and low highway rpm.
Jury is still out about no mods. IIRC someone reported some mods needed on a 72. Another with a 67 was having some difficulty. So with a few more installs we will know for sure.
 
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What about a Muncie with one of the AutoGear gearsets? There's a gearset that gives you a 2.98 first gear, I think it's the M22Z. You could re-gear your rear end to maybe 3.42 or so and get the best of both worlds, still keep you existing driveshaft, bellhousing, shifter, etc, and no hacking up your floor.
 
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Discussion Starter · #10 · (Edited)
The L79 cam that you are running is famous for a reason. Unless you are going with a roller you will be hard pressed to have a better overall street cam. I am stuck because I am number matching and can not use headers but my 68 L79 with a nice intake, 650DP, ignition and quality headers will make 400. Stock L79's run 353Hp on the dyno. I have the M21 with 3.31 gears and wished I would have installed a new M20 gear set when I rebuilt mine. M22's are just too loud for me. If originality is no concern I would install AFR 64cc "As Cast" heads, intake of your choice, same cam, get the compression up to 10.5, M20 gears with a 2.52 first gear (or 2.90) and drop the rear gear to 3.42's or 3.55's max for the street. Personally I would not install any tranny that required modifying my floor. If you are going to do a lot of highway then an overdrive should be installed. My 3.31's with 26.5 inch tires (235/60/15) runs around 2500rpm at 60mph and very tolerable.. BTW L79 cam is 1500 to 5800 power range, actually max HP for my engine is rated at 5800.

I'm just stuck between what I want this car to be...I drive it to work 2-3 times a week, which is about a 6 mile drive, and I like how snappy and go-go-go the 4.11 feels. I also like the vintage old school set up of the munice, but I also have day dreams about taking it on a long roadtrip someday, or just up to N. Georgia for the country roads. This is a 68 Malibu that was originally a 307 car with a power glide on the column. It now has the 327 and M21 with a hurst on the floor. I have no concerns about modifying the chassis if needed for the TKX or GV...whoever installed the hurst shifter absolutely butchered the transmission tunnel already. She has some rust issues, it's driver, and a car I can make what I want it to be without having to worry about butchering a numbers matching survivor. The carb I have is a Holly 600 street warrior. It has headers, and a progression ignition system. The main issue powerwise is the heads. Thanks for the heads up on the As Cast AFRs, those are about the same cost as the Floteks I was orginally looking at.

Very good insight on the L79 cam. I'll probably just leave it in there and change the heads, then look at lowering the rear end gearing...maybe...
 

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I'm just stuck between what I want this car to be...I drive it to work 2-3 times a week, which is about a 6 mile drive, and I like how snappy and go-go-go the 4.11 feels. I also like the vintage old school set up of the munice. I have no concerns about modifying the chassis as needed. This is a 68 Malibu that was originally a 307 car with a power glide on the column. It now has the 327 and M21 with a hurst on the floor. This was all done by the previous owner. She has some rust issues, it's driver, and a car I can make what I want it to be without having to worry about butchering a numbers matching survivor. The carb I have is a Holly 600 street warrior. It has headers, and a progression ignition system. I'm looking at the Flotek 180cc heads with 64cc chambers, the Floteks may not be quite as tuned-in as the AFRs, but they are a fraction of the cost.

Very good insight on the L79 cam. I'll probably just leave it in there and change the heads, then look at dropping the rear end...maybe...
The reason why I said to buy the "as cast" AFR's is they are under $1000 for both which should make your decision easier and you have a top quality manufacture. I do not know what year your 327 is but if it is pre 68 it has a small journal forged crank. If is a non L79 68 327 then it is cast so watch your high RPM's. Gears certainly make a car peppy but I only owned one 4.10 gear in my 67 Barracuda but gas was like 25 cents so who cared plus I was a kid. IMO hot gears for a primary street machine is too much and in the long run can ruin the driving experience in many situations such as you are experiencing. I prefer a 750 cfm Quadrajet over a Holley for the street and often can out perform a Holley especially a 600 cfm. One thing I can tell you is that cam needs compression and even though I am running stock 2.02 64cc heads with stock high compression forged pistons (11 to 1) I do not ever ping and if you do your mixture may be to lean. I do not prefer the M21/M22 gear set below 3.73's, however 3.55's can be OK. Although my gears are as they were built originally Chevy could have made a better choice. Once my car is above 15 mph it is very quick so never sell a L79 327 short. I may change my gear set not the Muncie to bring in the bottom end power. Remember Grumpy Jenkins beat the 426 Hemi in stock class with that little 327. Its not a 600hp BB but its a blast to drive (with gas mileage) and can get it done....
 

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Here is a good idea to help you decide without having to make any changes. You say you’ve used an rpm calculator. So figure out what rpm you will be running at highway speed with the overdrive trans alone and also with any rear gear changes alone. Then go out and run those rpm’s for say ten minutes at a time on a quiet highway. See how you like the ride at those different rpm ranges. Then you’ll know.
 

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again, great insight. thank you.

It's a 327 out of 69 impala, so it is not the small journal and I don't think it was an L79. The highest I've run it is up to 6000.
The last year of the L79 was 68 and was available in the Vette, Nova and Chevelle. All others were large journal cast and 6000 RPM is certainly not an issue at that rpm. Rule of thumb with most machinist is after 400HP you would start thinking about going to forged. With the shorter 3.25' stroke of the 327 that helps keep the piston speed down in comparison to the longer stroke 350 or 383 etc.. In 69 and 70 the 350/350 (hydraulic cam) and the LT1's 350/360 Camaro and 350/370 Vette were all 4 bolt main blocks with solid lifter cam and a 6500 redline. I believe the 350/350 had a 6000 redline as did all L82's 350's in 73 and 74. The entire bottom end was forged in all engines listed above to provide for longer life since they had to provide a warranty for the yahoo's like us beating them up. These cars were designed to run hard and I had a lot of fun doing so.
 

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I really enjoy driving the M21/4.11 around town, but don't take it on the highway because in my city you have to be doing at least 70 to keep up with the slow traffic, and 70mph is about 3500rpms with the M21 and 4.11. It sounds fantastic, but gets old on longer drives...not to mention I can watch my gas gauge go down on the highway.
I'm putting a TKX in my 67. Iit makes your car quieter and it will get much better mileage.
The .68 OD gear turns your 4:11 into a 2:78.
And out of the choices you mentioned, it offers the most resale value.
I think most people would pay $3000+ more for a car with a good OD trans.
 

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I went with the TK600 for my 70 SS BBC. I thought about the Gearvendors unit. I think it’s a bit less expensive than thevTK600. My stock tranny was the M20 and very good. My 12 bolt posi rear is 3:31 so not terribly low. I want to take my car on the highway to out of town car shows so high revs aren’t fun. Right now, I’m turning 2400 rpm at 80 mph in 5th gear. If I had gone with Gearvendors, I think I’d be running around 2850 rpm. My cost for the Silver Star TK600 ended up being around $3800. I did have to modify the transmission tunnel to get an additional 3/4” of clearance. Not included in the cost so far was the new CenterForce clutch around $360 to go from 10 spline to 26 spline. It’s alsonessary to “center” the bellhousing to less than 0.005”, as well as 0.004“ parallelism.

Gearvendors unit is bullet proof up to around 1200 HP so it’s a solid choice. I may well go with that option for my 67 GTO with a TH400, 3.55 rear. You’re running a 4.11, and unless you get 30” tall tires, you will always be facing high revs. Good for the 1/4 mile but not for highway trave. Good luck, I hope you find a good solutio.
 

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The GV is great. I have an automatic but on a stick I would keep it simple and just go with the new Tremec 5 speed it essentially accomplishes the same thing and your shifting anyway. I leave the GV in automatic most of the times so it acts like a 4 speed automatic. With a stick it is just easier to just put in 5th. Plus the GV is very strong (made for Winnebegos) so the weak part is your muncie and the Tremec is way stronger than muncie so you get a hole trans strength upgrade to boot.
 

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Actually the TKX can take 600lb/ft of "gear banging abuse". I don't believe any (typical) Muncie can take anywhere near that. Its a bolt in and fits the 68-72 bodies with no mods. 64-67 not so sure (don't know what your year is). I just bought one thru Summit and am in the process of installation now.
I am close to making a purchase. Just curious why Summit?
 
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