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1970 Chevelle, 396, Muncie 4spd, 4.10
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Discussion Starter · #1 · (Edited)
Hello everyone. I have finally found a block and heads. They are currently at the machine shop. The block is a 454, 4 bolt that will eventually be machined for a 496 forged rotating assembly. Heads are older 6055 aluminum Edelbrock. It will go in to a 1970 Chevelle, 4 speed Muncie (with plans for a tremec in the future) 4:10, 12 bolt
The shop and owner have been around since the 70s. The owner is very knowledgeable and has assembled hundreds of engines. However, I was surprised by a conversation we had at the shop. He was speaking highly of the big mutha thumper comp cam. Quite honestly I have not read much good on this line other than “it sounds good”. It is nice to have a nice sound but I’m more concerned on the performance within monetary reason. That’s why I will be keeping the heads that I mentioned. Anyway, what do you guys think? Is that cam good? If not what would you guys have me look at?
I believe the cam is 108 LSA. I guess that’s where the rough idle comes from. I am concerned with vacuum on the brakes. I understand this may also cause fumes in the cabin? Does that sound right?
This build will happen as money becomes available. But my first step is to get the heads set up so I need to know what cam to use.
Thanks for the help, comments and suggestions.
 

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not much of what you are saying makes any sense? Do you have any flow numbers on the heads, What are you expecting from her. what other parts are you using. BBC is different from sbc so lets get some info please
 

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There are a lot of mutha thumper cams so exactly which your mechanic is proposing would be good info. 108 LSA is an upper RPM cam it will like high compression which aluminum head’s will provide or at least cam without detonation blowing holes in the pistons. Where the world gets a bit foggier is the relationship of how much vehicle weight does the motor need to move and how stiff are the gears in the rear end. The Mutha Thumper in a 350 bolted to a 4 ton pickup with 3.08 gearing and tall tires is going to be a dog. In a 70 Chevelle with a 496 tied to a 4 speed stick and some final gears getting up toward 3.7 to 4.1 there is so much torque you’ll need a G-suit every time you crunch down on the go pedal, all at the same time it will have a real racer idle because,,,,it is!

Bogie
 

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1970 Chevelle, 396, Muncie 4spd, 4.10
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Discussion Starter · #4 ·
not much of what you are saying makes any sense? Do you have any flow numbers on the heads, What are you expecting from her. what other parts are you using. BBC is different from sbc so lets get some info please
Hey moosecountry this is what I found on another forum as far as flow numbers
Intakes/Exhausts
.100"=76/76-70
.200"=146/146-132
.300"=210/212-156
.400"=255/255-181
.500"=294/284-207
.600"=314/297-228
.700"=----/----
I was thinking a victor jr intake and 750 Holley would work well on top. But open to suggestions on that as well.
This will be my first build.
Looking to get 550 hp and 500ish torque. Not looking for a race car. Something I can drive for fun and still able to play.
 

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1970 Chevelle, 396, Muncie 4spd, 4.10
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Discussion Starter · #5 ·
There are a lot of mutha thumper cams so exactly which your mechanic is proposing would be good info. 108 LSA is an upper RPM cam it will like high compression which aluminum head’s will provide or at least cam without detonation blowing holes in the pistons. Where the world gets a bit foggier is the relationship of how much vehicle weight does the motor need to move and how stiff are the gears in the rear end. The Mutha Thumper in a 350 bolted to a 4 ton pickup with 3.08 gearing and tall tires is going to be a dog. In a 70 Chevelle with a 496 tied to a 4 speed stick and some final gears getting up toward 3.7 to 4.1 there is so much torque you’ll need a G-suit every time you crunch down on the go pedal, all at the same time it will have a real racer idle because,,,,it is!

Bogie
Thanks Bogie. It goes to show my ignorance. I was under the assumption there were only a few to choose from that had that type of grind. I’m certainly not looking for a race car, just a driver with the ability for fun at times. Not looking for high rpm either.
This will be my first build. I have not read much good on that series and thought it best to ask. Again, ignorance speaking here.
Thanks for the reply
 

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Sounds like a street car, power brakes, 4 speed Muncie/5 speed Tremec, not high RPM’s, Edelbrock heads, assume 3600 pounds and no mention of gears. So assume some where between 3.36 and 3.73. Go for a grind closer to the 375/425 horse Chevy cam. Plenty of bottom end and pleasure to drive not having to rev and slide the clutch at every stop light. I’m assuming you are adult and ride and performance is preferred over impressing the kids with sloppy idle.
 

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From what I know about the Thumpr cam series, the main focus is on a lumpy idle, with little concern about drivability or performance. I know the GM cams are older tech with slower ramps, but they are probably easier on the valve train. You do have to keep in mind those cams required higher compression which today's pump gasoline may not handle. But maybe there are some modern versions that will let you get by with 92 octane. For example, GMPP did exactly that -- a modern update on an old school SBC performance cam for newer crate 350s. They changed the duration and LSA from 222/222 with 114 LSA to 212/222 with 112 LSA. Correct me if I'm wrong, gurus. :)
 

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I like narrow lobe centers for street car, gives broader torque and only give up HP up high, where I don't really care

496 with 230/240 duration, 108 lca and as much lift as you can get---use hyd roller for all bbc
 

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thank you good show for the numbers
not surprising the flow numbers are not great
To get 550 hp you will need a moderate camshaft a small camshaft wont get you there
I recommend a 950 on the jr
Do you know basic blue printing techniques or is your builder well versed in racing engines?
WE have a square body here with a 489, Vic jr heads and vic jr intake, 950 Holley hydraulic roller cam
10:1 cr medium tube headers (1 7/8)
After a few engine sessions it delivered 560 hp and 580 torque

I dont think you will achieve that much with those heads
Also because of the flow numbers you supplied expect to add around 10º to the exhaust side
In order to get your hp figure over 550 I see moving the torque curve higher which may or may
not be good for your application.
Back to you so you can comment and maybe explain use in finer detail?
 

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I’ll share my combo similar to your “New Build”.
Drive train is 5 speed Tremec and rear end 3.7 gears. Guessing 3500 pounds. Engine is a Chevy 427 bored .030, heads are Edelbrock aluminum oval port w 2.25 intake and 1.88 exhaust. Single Quick Fuel (leaned out) single plane Wiend. HEI ignition. Compression is 11:1 using replacement Corvette L71 (435 horse) dome pistons. Tight quench area. Edelbrock flat tappet cam shaft with spec:
292° Intake/302° Exhaust
Duration @ .050''218° Intake/228° Exhaust
Lift @ Valve.500'' Intake/.500'' Exhaust
Lift @ Cam.295'' Intake/.295'' Exhaust
Lobe Separation Angle114°
Intake Centerline109°
Intake Timing @ .050"Open 0° ATDC
Close 38° ABDC
Exhaust Timing @ .050"Open 53° BBDC
Close 5° BTDC
Vacuum @ 850 RPM Idle14-15
So nothing that shakes the earth but drivable w/power brakes and steering. I have it running on 91 pump gas (without corn juice when available). Runs cool. I like the power and response.
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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While I think there are better performance grinds out there, the "thumper" cams do fit some applications pretty well. From the information we do have, your builder knows his stuff.

Most of what I have seen and read concerning that line of cams tells me it may be among the most misused cams out there. The way they are advertised sells them by the pallet. People were over camming their engines before that line of cams and are doing it even more now. The guy with a stock 350, stock torque converter, 3.08 gears and huge tires is unhappy with this cam. He tells the whole world they are junk, this goes on until enough people come to the conclusion that a wide intake/exhaust split and narrow lobe separation are "the devil." Somewhere the original guy is still running 16 second 1/4 mile times. He has a different mismatched combination but isn't running his mouth about it.

Here's some insight into what your builder knows. We could go on for pages, but here's the general broad strokes version....

The need and amount of extra duration (compared to the intake duration) comes from the efficiency of the exhaust port (once again compared to the intake port). The general rule is the exhaust flow 75% of the intake flow is single pattern cam territory. For every 1% less you add 1.5 degrees to the exhaust duration. Your numbers suggest about a 70% intake to exhaust ratio. So figure 5% less than our 75% is 5%. Add 1.5 degrees per 1%, you have 7.5 degrees. So, in an ideal situation we are looking for at least 8 degrees on the split.

The duration numbers in general work with the desired RPM range and must be supported by the appropriate compression ration.

Valve lift is determined by how the heads flow at a certain amount of lift. Some are all done by .500, some .600 and so on. Your heads very likely go beyond the .600 mark. The thumper cams leave power on the table with the lower valve lifts but the lobes are nicer to valvetrain. In a street car, a lot of folks would trade some of that power for easier operation. Everything is a trade off. There is no free lunch.

The big block Chevrolet is one of, if not THE most, undervalved engines of the muscle car era. Consider a 2.02" valve feeding a 302, 327 or 350. A 2.19" or 2.25" valve feeding a 454 or 496 has a greater burden. A couple of ways to help that out is by #1 opening the intake valve sooner to give it more time and/or #2 increasing the overlap (when both intake and exhaust valves are open) to allow the exhaust scavenging to help "pull in" the intake charge. Overlap is more than just a choppy idle.

This is a basic look at it. There are plenty of variables outside a "by the numbers" look. I assume your builder is considering the Comp 227/[email protected]" roller. It will work well in your build! I don't know about power brakes with it though. Might be good with your displacement.

I'm a shade tree mechanic. Most of the folks here and your builder know far more than I do. I'm just sharing what I think I know!
 

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Discussion Starter · #12 ·
Wow! Very good information guys.
The knowledge in this forum is incredible. I am glad to be a member. And very happy that you guys are willing to help a newbie.
I do apologize. I edited the post before I submitted but for some reason it didn’t save. My computer skills are on par with my engine building skills.
I did update to show I am currently running 4:10 gears with the intent to put a tremec in as money becomes available. Just to be clear this will just be a driver, will never see the track. It currently has a 396 in it and just looking to have more hp for fun. As well as take it a little further from home, hence the tremec. Also just have an itch to build an engine. I have been trying to educate myself reading, watching videos and talking to folks like I find here. And just when I think I know enough to ask an intelligent question I realize I have more studying to do. Lol.
I am very fortunate though. I have a friend that has built many engines. In fact he worked at the machine shop I have referred to earlier. He will be helping me with the build. He is a small block ford (largely) guy and that is why I was asking the original question. Certainly not to question his ability, he is very sharp.
Yes. The machine shop has built hundreds of race engines. A big portion of those were dirt track small block. But certainly has plenty of experience in bbc as well. Maybe I should listen more to what his experience says. Rather than question him due to what I read on the internet.
Again everyone thank you for the information.
 

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which tremec are you planning to use? There are a couple choices for O/D ratios.
A 496 with 4.1 rear gears? Yikes, you need to rev to take advantage of the gears.
You will need an O/D ratio that will drop rpm enough to enjoy driving at speed. I have a TKO
600 with .82 5th and 3.50 rear gears. 60 mph nets 2050 rpm

Give me your tire size and lets work out a good choice for you. What does the car weigh?
I think 525 hp 580 pounds torque might be your answer. Yet again questions to you.
 

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Discussion Starter · #15 ·
which tremec are you planning to use? There are a couple choices for O/D ratios.
A 496 with 4.1 rear gears? Yikes, you need to rev to take advantage of the gears.
You will need an O/D ratio that will drop rpm enough to enjoy driving at speed. I have a TKO
600 with .82 5th and 3.50 rear gears. 60 mph nets 2050 rpm

Give me your tire size and lets work out a good choice for you. What does the car weigh?
I think 525 hp 580 pounds torque might be your answer. Yet again questions to you.
The tires are 275-60-15. I have done a few of those charts for a general idea. I was looking at the tkx. It is rated up to 600 hp/tq. I helped a friend install one in his 70. Seems to be straight forward without tunnel work. Best I can tell I would still be around 73-75mph at 2500 rpm. That is with the close ratio and .68 5th gear. However, I will be putting another gear set in soon. The pinion is whining now. I was thinking 3.73. That would put me at 80 ish at 2500. Which would be all I need to go a little farther from home. I think if I went any higher I may have to change the carrier. Does that sound right to you?
 

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Quoting: “That is with the close ratio and .68 5th gear. However, I will be putting another gear set in soon. The pinion is whining now. I was thinking 3.73.”

That is an excellent combination even 3.55 with the low 1st gear would be good. Running down the interstate at 80 MPH will be no issue and you could keep up with traffic without emptying the tank so soon.
 

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Discussion Starter · #17 ·
Quoting: “That is with the close ratio and .68 5th gear. However, I will be putting another gear set in soon. The pinion is whining now. I was thinking 3.73.”

That is an excellent combination even 3.55 with the low 1st gear would be good. Running down the interstate at 80 MPH will be no issue and you could keep up with traffic without emptying the tank so soon.
Hey Nomad thanks for responding. Is it true that I would need to change the carrier with 3:55? Would I have to do that with 3:73? Or would it depend on the “class” of carrier? Not sure that is the correct term. I haven’t opened it up so I am uncertain what exactly is in there.
Thanks
 

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Depends but generally the 3.73 and higher work. And the 4.11 and lower work. Some of the ultra high ratio such as 2.56…I don’t know.

Do the revolution count with chalk mark. Be position fussy between 3.55 & 3.73. Also 3.55 & 3.36 as it can be a guess otherwise. Most have a tag or in the case of Chevy a notched disk denoted ratio via chart to match notch.
 

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The 12 bolt rear end in your Chevelle had one of 3 carriers based on the gear ratio. Each "series" had a different deck height to accommodate the varying thickness of the ring gear. 2-series 2.76 and numerically lower. 3-series 2.76 to 3.73. 4-series 3.90 and numerically higher.

Some gear manufacturers make a thicker ring gear to run numerically higher gear ratios on a shorter deck height carrier. A popular example would be a 4.10 ratio on a 3 series carrier. It adds weight doing it that way but scores of people are doing it without any trouble.

Figure out what you have and go from there. This car is going to be A LOT of fun to drive!
 
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