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I have a 400 sbc .030 over, stock heads, dual plane edelbrock intake,750 aed mechanical secondaries carb,I have the comp cams small thumper cam.the car has a muncie m20 with 3:42 rear gear.The car runs very poor,any recommendations besides swapping cams, what would be a good cam choice?​
 

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When it comes to cams part numbers or timing specs are meaningful information.

Generally cams like the Thumper emulate the idle sound of the 1960’s and with 11 to 1 compression ratios the performance of that period of 100 plus octane fuel. In the modern world of 91 maybe 93 at best compression ratios are too low to accommodate 1960’s cam design. Modern cam design uses less ramp with more duration squeezed between ramps with more lift using less overlap and earlier closing intake valve. This with aluminum heads with Ricardo chambers and flat top or D dish pistons and a tight squish/quench clearance is the way to get the burn improved and to increase detonation resistance without resorting to fuels beyond the low 90’s in octane rating.

Your 400 is going to take some rethinking of these components, whether that is a different cam or changes to the top end depends on how you want to go.

Bogie
 

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Welcome to the thumper cam disappointment club. I once had the bug mother thumper cam of the hydraulic roller version camshaft with a 350 and I had a complete engine build that was up to par minus a little bit on the compression but not enough to keep it from performing though and I had the proper stall converter and reaer gears and rpm range to make that cam work and I can tell you it was the worst decision I ever made.

I won't get into the whole story but it was in a 86 chevy s10 v8 swap and it did perform quite well but was a very pain in the rear to tune the carb I had to get it to run all the way around without any issues and get it to perform well and I did accomplish it with time and patience. The problem with those cams is they can perform but they are made more for sound vs all out performance and efficiency for a street performance cam. They have a tone of overlap, even more for the average size performance cam such as a comp extreme energy or lunati voodoo cam that is similar in size. Mine was 243/[email protected] with the 106 lsa and I had the cam for three months and it did perform and would haul my truck like you would not believe but it was not fun driving around and cruising with that thing.

The overlap was just to much and killed any mileage of course you don't expect your cake and eat it too with performance stuff to a certain degree. It was not very fun to drive with overall in different conditions vs with other cams I had. I took it out and installed a lunati voodoo cam with a more better 231/[email protected] with a bigger 110 lsa and with less overlap and better manners on the street and better performance and I could tell it had way more power with just changing the camshaft and retune my carburetor I had and it had a lot more spunk from off idle all the way to t he top and I picked up a bit of fuel mileage with it as well and believe it or not got 19 mpg highway speed of an average of 60 mph and 3000 rpm.

They can perform but other performance cams can give more power and better overall results for your build regardless of what you do with it and still give you a nice lopey sound depending on the specs and perform better at the same time. I had ported heads and all the works and still hated it.
 

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Depending on what heads your using and what compression ratio you have I would weigh the options of either one, swapping out the cam for something matching your combo you currently have look at better cylinder head options with 64cc chambers if your compression is really low to get performance but I will warn you even with 3.42 rear gears with the 4 speed tranny you still going to be a dog on the bottom end as that cam likes the higher rpm range.

I run a 3.42 rear gear ratio in my 96 chevy s10 with a turbo 350 and it has same 1 to 1 final ratio like your muncie does and I run a dart shp 377 build (4.155 bore x 3.48 stroke) and I have a way smaller cam of 220/[email protected] with a 114 lsa and my truck loves that size of a cam and runs great for cruising and an all around daily driver type of a deal and runs plenty strong to the high 5500 plus rpm range before it levels off.

I did have a bigger cam in there around the [email protected] range and it was fine as well but not as good for what I use my truck for and the thing with the bigger duration cams is they like high rpms at all times as much as possible and that cam is better with like 4.10 gears or steeper to get more from it and within the torque range those cams have. If it was me I would swap the camshaft as that would be the cheapest option to begin with and then plan for better heads down the road if you already don't have them already on your build.
 

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I've seen Thumpr cams work real nice in some rides. You need to look at the maker's recommendations, like CR, what carb they suggest, headers, gears and so on. I run a Lunati Voodoo that is a great cam, slight lope and is good in traffic. I have gears and a close to a 10:1 CR, the car flies. This is one of those things where you have to do your homework on to be happy with it.
 

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I have a 400 sbc .030 over, stock heads, dual plane edelbrock intake,750 aed mechanical secondaries carb,I have the comp cams small thumper cam.the car has a muncie m20 with 3:42 rear gear.The car runs very poor,any recommendations besides swapping cams, what would be a good cam choice?​
Get rid of the stock heads. Iron eagles were good heads. Even the best old school fuelie heads don't flow enough for a good cammed 400. Concentrate on the exhaust system. It will help a 400 more than intake, or carb. Then get some cold air into the carb. 400 likes to run hot so feed it cold air to limit detonation. I have a hydraulic roller new on the shelf. I was planning on a 400 but never got to it.
 

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Get rid of the stock heads. Iron eagles were good heads. Even the best old school fuelie heads don't flow enough for a good cammed 400. Concentrate on the exhaust system. It will help a 400 more than intake, or carb. Then get some cold air into the carb. 400 likes to run hot so feed it cold air to limit detonation. I have a hydraulic roller new on the shelf. I was planning on a 400 but never got to it.
Comp cams 12-433-8
Hydraulic roller.
 

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Intake duration 227, exhaust 241,
Intake lift.479, exhaust .465
Ls 107
18 degrees at idle,34 total @3400
Thanks
Quite a few degrees in duration between the .050 marks not crazy but pretty good. Lift is pretty moderate, working the valve train a bit but again not stuff over .5 inch. The LSA is mighty tight like a race cam. Between the long duration and the tight LSA comes a sign that this cam has a lot of overlap and most likely a late closing intake. These are things that dictate good head’s with tricky combustion chamber shapes and plenty of compression. My guess these are something you stock head’s don’t provide but to do more than guess I’d need to know the casting number of your head’s, the part number or specs of the pistons used and what machine operations were done to the block and or the head’s in terms of milling them. Then another tilt it would be the head gasket thickness.

My take away right now is wrong style cam with oldtime SMOG head’s and probably low compression pistons with big round dishes or perish the thought this ended up with “rebuilder” pistons and a standard height head deck on the block. At this point I don’t have enough configuration definition to point and grunt at specifics but the generality is too much cam and within that too tight an LSA combined with not enough compression makes your 400 a dull boy.

The Thumper cam works with lots of compression, being limited to 91-93 octane E10 fuel in most of the country a different approach needs to be taken. The modern solutions are head’s with Ricardo heart shaped chambers use pictures of the L31 Vortec chamber as a visual guide. The spark plug is moved inboard as far as the valves will allow this shortens the burn distance which is time Fast Burn in other words. The plug is positioned toward the exhaust valve to catch the induced wet flow swirl off the intake valve. The far side has a beak from the squish/quench pad projecting between the valves to inhibit intake flow out the exhaust valve during overlap. This configuration is duplicated and improved on in a host of aftermarket head’s from inexpensive Chinese imports to outta sight costly domestics cast in your choice of iron or aluminum. To the end of pistons the flat top burns best, it keeps maximum area under the squish/quench pad which eases ignition, speeds the burn and heat sinks the end burn so it doesn’t go ‘PING’. Overall these features make the fuel you burn react as if it has about 5 or 6 more octanes than it is rated at, this is called mechanical octane it is a characteristic of these heart shape chambers. Aluminum head’s will take you further into the range of mechanical octane by virtue of their faster heat removal than iron. Here it’s a requirement to pump up the compression because of the quicker heat transfer will lose power compared to iron, so you have to play into the material’s strengths in this regard. The downer side is the available head gaskets needed to cushion aluminum are thicker than shim gaskets so aluminum head’s work best with either a decked block or raised compression heigh pistons, compression height being the distance from the wrist pin center to the crown of the piston. Aftermarket head’s are available with Ricardo chambers in 64cc and 76cc chambers give or take a couple cc’s either side of these numbers, this can drive on piston selection, as I previously said a flat top burns best a round dish worst (pop ups tend to interfere with flame travel but this is a different discussion from us here) the choice of champions that gives salve to play with compression ratio while keeping the great burn characteristics of the flat top is the D dish and it’s cousin the step dish. These keep the flat where it’s needed under the chamber’s squish/quench step while moving and volume needed to trim the compression ratio under the valve pocket.

I know this is a long technical read but building engines in the 21st century isn’t like the good old days.

Within the Comp family of cams the XE series with their wider LSA and short ramps works better that the Thumper where actual performance is required rather the that 60’s sound that depends on 11 to one or greater compression ratios. My recommendation for street performance or marine short of racing is don’t use an LSA under 110 degrees. This keeps the bottom end torque up with little impact at the top end power and its friendlier if you have power brakes.

Bring you plans here before spending your had earned cash, there are quite a few guys here with a lot of knowledge that can keep you out of trouble.

Bogie
 

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Educate yourself so that you will be more prepared and question the information and recommendations from so called experts. Wonder if they are selling a bill of goods and recommending products to sell rather than the products that will produce the required results. You may have bought the most expensive parts but not the parts that produce your intended results. Going to an expert that has proven their expertise with a winning track record (David Vizzard) has the research and dyno results with years of experience is probably the most cost effective way of achieving your goals. He has amassed a significant amount of research that translated into winning results. His thousands of articles & publications is extensive.
Reading his books unlocks a lot of facts and debunks even more myths, all the while backed up with real world tested results. Let's be honest, most people don't have the time, money, and expertise to achieve the results that a lifetime researcher and engine builder has.
I found it the most cost effective to go to such experts and heed their recommendations if they will in fact release such knowledge.
Nothing sounds better than high reving engine!
 

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Many different engine combinations can produce the results you want. I had a balanced and blueprints 350 bored .040. Fuelie heads, 461X ported, 2 four barrels, ignition curved to match the comp cams 268. Turbo 400 and 3:73 posi in a 69 Camaro. I helped a buddy build a 455 Olds with just a cam and headers. Both cars were fun from a light. The Camaro reving through the gears while the 442 just ate up assault with gobs of torque. Amazing what 100 cubic Inches more does. The 442 had less engine work than the Camaro and ran with it all the way. Whoever got off the line 1st usually won.
Next is a 265 bored .060 with 11.5 compression, ( must index the plugs to avoid pistons hitting spark plugs & closing the gaps ) since the 461x heads have a low plug location, line bored, decked, crank turned and indexed with stroke corrected, 461x fuelie heads, ported, screw in studs, guide plates, victor junior with 750 holley, vacuum secondaries. A lunati cam 300 duration .500 lift, 110 LSA, 230 @ .050. Running steel shim head gaskets .Running a turbo 400 with 3500 stall and 4:56 posi. Different animal all together. It was built for high rpm since small cubes have no torque. It is fun to drive and I expected no torque at low rpms. But at 3200 on up it is a wicked beast. Just goes to show what you're after, someone has probably perfected it. You just have to find him.
 
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