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Discussion Starter · #1 ·
I have a 1980 El Camino that I will be putting a 489 BBC in with a turbo 400 trans.
Engine specs:
measured 10.2 to 1 comp 489 guts in a 454 block
Brodix aluminum race rite 270cc oval port heads
Howards hydraulic roller 282/288 229/235 @.050 .589/.601 lift on a 110 lsa
Edelbrock RPM air gap
Holley 850
2" primaries and 3" exhaust (Hooker super comp headers)
255/60R15 tires

I should have torque out the wazoo so setting up the rest of the car is where I'm a bit fuzzy. My main thing is I want to drive this thing a lot so I don't want it screaming down the road at 60mph. I had a Cutlass with the same tires and 3.42 gears and it spun 3grand @ 60mph. Of course I had a B&M 2400 stall in it and I've since learned that is a less than ideal convertor and was prone to excess slippage.
Anyway that has kind of soured me on the 3.42s. don't get me wrong, that gear was an absolute riot behind my BBC 408, but the simple task of passing somebody at highway speed would result in the tack going north of 5grand and I never downshifted. Again I'm sure convertor related, but didn't think it should tac up so quick just passing someone while still in drive. And don't get me wrong, it's not like the motor tacked up and I casually passed them, I passed them like my *** was on fire! It just seemed I ran out of RPMs if I had to pass more than one car. And on the 4-lane at 70mph the car just plain wasn't happy.

So the above statements are the reason I'm kicking around putting the 3.08 gears in the Elky. I want more road manners so to speak. lower rpms @70 will be a huge plus.
I can already hear the put an overdrive trans in it argument but I have a perfectly good turbo 400 already built to handle that 489. And this engine is costing more than expected to get right, lol.

My main concern is what are the pros and cons between the two gears with my combination?
Is it too much cam for the 3.08? ( haven't actually bought the cam yet)
Would there be a significant power loss between the two gears? I would think it could blow the tires off through first and second at will.

I'm out of my element here so any and all input will be greatly appreciated.
 

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I would also expect you to blow the tires off at will in 1st or 2nd gear, even at a 35-40 mph roll in 2nd.

cruise rpm will be down a little with the 3.08 compared to the 3.42.
about the onlty difference I think wold be all that noticable is once the tires are blazing, when you pedal it go restore traction the 3.42 have a better chance of caching it quuicker is all.

Since you aren't drag racing competetively, the lower rpm at cruise will likely be more in line with your desires.

I would not go to the expense of overdrive at this point....if you do down the road, make it a 4L80.
 

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In the 60's & 70's , even into the 80's , the 1/2 dozen vehicles I drove on the street had nothing below a 3.55 gear , none were overdrive . I don't recall there being any problem on the highway , interstate or passing , normal cruise rpm was 3000+ or- , I don't understand the issue ?
 

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Discussion Starter · #4 ·
In the 60's & 70's , even into the 80's , the 1/2 dozen vehicles I drove on the street had nothing below a 3.55 gear , none were overdrive . I don't recall there being any problem on the highway , interstate or passing , normal cruise rpm was 3000+ or- , I don't understand the issue ?
The issue is there is absolutely no reason to be spinning 3,000 rpms at cruise in a street car with that big of a motor. Small wimpy engines or over cammed engines need rpms and lower gears to operate correctly.
The 3.42s in my Cutlass were great for nutsing around but I got tired of listening to the 408 big block sing at 3 grand and higher on the road. Granted, a good part of that was the crappy convertor. Not only that, with that gearing there was already too much power for the tires to handle so the fun factor wore thin fast.
Why do you think everyone is on the AOD tranni band wagon? to lower their rpms at cruise. (plus being able to use a lower gear ratio for a better launch)
 

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Discussion Starter · #5 ·
I would also expect you to blow the tires off at will in 1st or 2nd gear, even at a 35-40 mph roll in 2nd.

cruise rpm will be down a little with the 3.08 compared to the 3.42.
about the onlty difference I think wold be all that noticable is once the tires are blazing, when you pedal it go restore traction the 3.42 have a better chance of caching it quuicker is all.

Since you aren't drag racing competetively, the lower rpm at cruise will likely be more in line with your desires.

I would not go to the expense of overdrive at this point....if you do down the road, make it a 4L80.
I know exactly what you mean lol. It's like the difference between roasting the tires in second vs third gear and trying to pedal out of it. In third your more likely to lose it before the tires catch again at the same road speed- been there done that lol.
If I go with the 3.08s, will the cam I chose be a bit much? Howards has a smaller hyd roller with 278/284 225/231 @.050 .567"/.578" lift 110lsa. I could time it straight up instead of 4* advanced if cylinder pressure would be an issue?
A torque convertor is another question I have. With the 3.08s and far too much torque at relatively low rpms, what kind of convertor would you use? Is say a well built 2500 stall of any benefit for this combo?
Like I said, I'm way out of my comfort zone with this build
 

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I'd have at least 2900 rpm stall, but it would be a custom converter built for the car and combination, to be tighter at partial and low throttles.
I believe you are underestimating just how much those 80 cubes and better flowing heads are going to tame up that cam, stick with it.

Down the road, if/once you get tired of blowing the tires off and want to be a little more serious about traction you can get into a programmable ignition controller and use it to control rate of rpm gain per second or tire speed
 

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Discussion Starter · #7 ·
I'd have at least 2900 rpm stall, but it would be a custom converter built for the car and combination, to be tighter at partial and low throttles.
I believe you are underestimating just how much those 80 cubes and better flowing heads are going to tame up that cam, stick with it.

Down the road, if/once you get tired of blowing the tires off and want to be a little more serious about traction you can get into a programmable ignition controller and use it to control rate of rpm gain per second or tire speed
Okay, once I get to that point I'll call convertor companies (freakshow, fti etc) and see about a nice custom made piece for my combination.

I don't know about a programmable controller, But traction is a concern of mine. Suspension upgrades are on the list.
My biggest fear with this kind of power would be flooring it at say 60mph and having the tires come unglued at say 80mph due to the torque. This fear may be totally unwarranted but I don't want to find out the hard way. Will be starting a post in the suspension category about how to hook this thing up
 

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The issue is there is absolutely no reason to be spinning 3,000 rpms at cruise in a street car with that big of a motor. Small wimpy engines or over cammed engines need rpms and lower gears to operate correctly.
The 3.42s in my Cutlass were great for nutsing around but I got tired of listening to the 408 big block sing at 3 grand and higher on the road. Granted, a good part of that was the crappy convertor. Not only that, with that gearing there was already too much power for the tires to handle so the fun factor wore thin fast.
Why do you think everyone is on the AOD tranni band wagon? to lower their rpms at cruise. (plus being able to use a lower gear ratio for a better launch)
Just pointing out that IME , there's absolutely nothing detrimental about 3000 continuous highway rpm ..Just for the record , I never have been one to jump on bandwagons or follow trends !
 

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Discussion Starter · #9 ·
Just pointing out that IME , there's absolutely nothing detrimental about 3000 continuous highway rpm ..Just for the record , I never have been one to jump on bandwagons or follow trends !
Lol! I understand and totally agree with you. I'm not much for trends either. And you are right, 3grand won't hurt an engine one bit. It's just my personal preference. We all have one.
 

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Discussion Starter · #10 ·
I would also expect you to blow the tires off at will in 1st or 2nd gear, even at a 35-40 mph roll in 2nd.

cruise rpm will be down a little with the 3.08 compared to the 3.42.
about the onlty difference I think wold be all that noticable is once the tires are blazing, when you pedal it go restore traction the 3.42 have a better chance of caching it quuicker is all.

Since you aren't drag racing competetively, the lower rpm at cruise will likely be more in line with your desires.

I would not go to the expense of overdrive at this point....if you do down the road, make it a 4L80.
eric, I may have to completely rethink this gearing thing. You and I have talked in the past about my gears and rpm ranges.
I ordered 3.42 gears when I built the Cutlass many years ago along with the 2400 stall B&M convertor.
You always told me that 3000 rpms at 60 with a 26 inch tire was not right.
We chalked it up to convertor slip.
But after pulling an all nighter in my recliner I crunched numbers and did complete maps of gear ratio vs rpms at a given speed.
I have also mentioned that I run out of rpms in drive in a hurry meaning the car accelerates and so does the tach. The speedo only goes to 85 so I'm guessing here, but I feel like I hit 6000 rpms by about 105-110 mph.
According to the math, 3.42s with a 26 inch tire should be about 2652 rpms at 60 mph. I'm at 3000.
At 110 mph the math says I should be spinning 4862 rpms. I feel I'm at 6000 by then.
This would imply a seriously screwed up torque convertor.
However, if you do the math for a 3.73 gear ratio things make more sense.
With those gears rpms at 60 mph would be about 2892 rpms. Given convertor slip, 3000 rpms is not outta line.
At 110 mph the rpms would be about 5302. Again if convertor slip got worse as rpms and wind resistance rose, 6000 rpms might not be outta line. After all it is a cheap off the shelf B&M.

Another thing that now makes me think is when I put 3.42 gears in my friend's Camaro with an m20 stick. His rpms were much lower at cruise and I commented He should have gone with a 3.73 gear.

The only way to clear this up will be to pull the cover and look, so that's on the to do list.
 

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I have a similar spec cam with a little more exhaust duration in a Vortec head 350 sbc with dual quads in a big ol' GM B body 4 door. I have a 2500 stall lock up converter and I'm lucky if I got a 3.08 gear and it runs fine, has lots of pull and 2100-2200 rpm highway (70 mph) cruise and will roast the tire (peg leg for now) at will from a stop. Your cam in a 489 is not that big and will make tons of torque and should run just fine with 3.08's. It'll pull hard forever or until you run out of space.
 

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Discussion Starter · #12 ·
I have a similar spec cam with a little more exhaust duration in a Vortec head 350 sbc with dual quads in a big ol' GM B body 4 door. I have a 2500 stall lock up converter and I'm lucky if I got a 3.08 gear and it runs fine, has lots of pull and 2100-2200 rpm highway (70 mph) cruise and will roast the tire (peg leg for now) at will from a stop. Your cam in a 489 is not that big and will make tons of torque and should run just fine with 3.08's. It'll pull hard forever or until you run out of space.
That's the kind of information I was hoping to hear.
 

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Discussion Starter · #13 ·
So I dropped the cover today to look at the rear gears. The numbers on the ring gear are: 80-0366-1. Also 8620. I know 8620 is what the gears are made of, but the other number can't be found on Richmond's website. The gears are for a series 2 carrier and my posi unit is for 3.08 and numerically lower gears. I didn't want to completely tear down the rear end to get an accurate tooth count so I put a mark on the pinion yoke and the tire and rotated the tire one full turn while watching the yoke. The yoke turned just shy of 3.5 complete turns. This tells me the gears are indeed 3.42s. That tells me beyond a shadow of a doubt that the torque convertor I have is the biggest POS ever installed in a car!
At this point I'm not even sure how to process this information.
 

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It's tough to tell exactly what the rpm should be at a given speed with a higher stall convert as it may still be in its slippage point and with a high torque big block it could easily push that stall to a higher rpm. In my case with the lock up not work at one point I was taching 2500-2600 rpm or so at 70 mph and would flash easily to 3000 when I accelerated to pass or pull a decent grade. That's with a small cube sbc. Put more torque on that convertor and a 2400 rpm stall could stall at a higher rpm. A tighter convertor and taller gears might do the trick.-- I just ran the numbers and with the lock up convertor (assuming it's 1:1) I have 2.56 gears and I'm good with that, just need a LSD.
 

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I have a similar spec cam with a little more exhaust duration in a Vortec head 350 sbc with dual quads in a big ol' GM B body 4 door. I have a 2500 stall lock up converter and I'm lucky if I got a 3.08 gear and it runs fine, has lots of pull and 2100-2200 rpm highway (70 mph) cruise and will roast the tire (peg leg for now) at will from a stop. Your cam in a 489 is not that big and will make tons of torque and should run just fine with 3.08's. It'll pull hard forever or until you run out of space.
B body axle might be hard to find a posi, depends on the year. If it's an 8.5 then the 2.56, 2.42 and 2.29 are a unique carrier that only fits those gear ratios
 

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B body axle might be hard to find a posi, depends on the year. If it's an 8.5 then the 2.56, 2.42 and 2.29 are a unique carrier that only fits those gear ratios
I am lucky enough to have the robust 7.5" diff in my bucket of bolts. I have a line on a 8.5 out of a wagon but the 7.5 will do till it blows up!
 

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In the 60's & 70's , even into the 80's , the 1/2 dozen vehicles I drove on the street had nothing below a 3.55 gear , none were overdrive . I don't recall there being any problem on the highway , interstate or passing , normal cruise rpm was 3000+ or- , I don't understand the issue ?
Lower engine RPM equals longer engine life and better fuel mileage. I’d go with the 3.08 gears. They were standard in gym pickups in late 70s and for some years beyond
 

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Lower engine RPM equals longer engine life and better fuel mileage. I’d go with the 3.08 gears. They were standard in gym pickups in late 70s and for some years beyond
Depends entirely on the engine & its projected use .
Perhaps in what I refer to as " suburbanites trucks" generally not in 3/4 ton & up work trucks .
 

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Depends entirely on the engine & its projected use .
Perhaps in what I refer to as " suburbanites trucks" generally not in 3/4 ton & up work trucks .
Yep. Could be ordered as high as 4:10. and 3:73 was not uncommon 3:73 in my 98 Silverado 1500. But it has L460E transmission. In 3rd speed which is 1 to 1 it turns 3000 rpm @ 60. I ordered my 78 K10 with 2:76 rear gear and 4 speed manual transmission. Never regretted it. 21 mpg after I rejetted the Quadrajet to .065 primary jets. I could run over 70 mph in 3rd gear and stay under 4000 rpm. Never had any shortage of power even pulling a camper. I knew guys with 3:73 rear gear that couldn’t get more than 13 mpg in identical truck. 350 engine. I had the speedometer needle upside down and hadn’t hit 4500 rpm Ran out of straight road. It would have gone faster. 2100 rpm @ 70 mph. Same as my 98 Silverado. So I guess I basically had the same as an overdrive transmission with 3:73 rear gear. I had rebuild the engine with .060 overbore and flattop pistons. Stock cam and heads which limited top rpm but the small valve heads yielded lots of bottom end torque. Was an absolute stump puller in low range. But I’ve gotten off topic. Back on topic, it’s all up to what he wants to accomplish with his vehicle. I’m done now.
 

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Discussion Starter · #20 ·
Yep. Could be ordered as high as 4:10. and 3:73 was not uncommon 3:73 in my 98 Silverado 1500. But it has L460E transmission. In 3rd speed which is 1 to 1 it turns 3000 rpm @ 60. I ordered my 78 K10 with 2:76 rear gear and 4 speed manual transmission. Never regretted it. 21 mpg after I rejetted the Quadrajet to .065 primary jets. I could run over 70 mph in 3rd gear and stay under 4000 rpm. Never had any shortage of power even pulling a camper. I knew guys with 3:73 rear gear that couldn’t get more than 13 mpg in identical truck. 350 engine. I had the speedometer needle upside down and hadn’t hit 4500 rpm Ran out of straight road. It would have gone faster. 2100 rpm @ 70 mph. Same as my 98 Silverado. So I guess I basically had the same as an overdrive transmission with 3:73 rear gear. I had rebuild the engine with .060 overbore and flattop pistons. Stock cam and heads which limited top rpm but the small valve heads yielded lots of bottom end torque. Was an absolute stump puller in low range. But I’ve gotten off topic. Back on topic, it’s all up to what he wants to accomplish with his vehicle. I’m done now.
Let's remember guys, this is an El Camino, not a full size work truck. The 489 is built with STREET in mind, not drag racing.
After much debate I feel the 3.08s will serve my needs quite well. Combine all this with a proper "tight" stall convertor and the grin factor should be huge.
And hopefully without killing me on fuel.
 
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