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Discussion Starter · #1 ·
Let's say for a moment that the cons of running a thumpr cam are starting to out-weight the pros for me.

Can I get some help figuring out a cam that would produce either equal or greater power than my thumpr, but with better drivability\easier tuning?

Engine info in quote block:

Had a stock 350 sbc short-block built for me (he cleaned a block then bored and honed it to 355), with complete brand new rotating assembly and the smallest thumpr cam (flat tappet).

He chose and built the heads for me. Procomp, aluminium. I don't know the exact part number, but they are aluminium heads, 1.5 lift roller rockers. I wanna say these heads here are close but I can't be sure.

Edlebrock air game RPM intake (nascar edition).

Holley (proform) 650 double pumper.
I've been tuning it about a year now and have it running pretty decent. 18 degrees advanced with 18 mechanical (seems like both dizzys I bought, cheap one and then this nice one came already set to a small amount of mechanical advance, almost as if they know they were going in a thumpr. Unless, of course, I'm just flat out doing something wrong.)
It stinks often, and I had to drill butterfly holes in my carb, and my manifold vacuum is low. The car shakes back and forth when I try to drive at a slow idle, but that's probably just because my rear is still like, 2.73 or something highway like that. But it does sounds beautiful.

But I guess if I could get more power with the same lack of drivability\tunability, then why not?
 

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Discussion Starter · #3 ·
ap72 said:
What compression? Headers?
Headers are hooker shorties. I didn't know crap about engines when I was having the guy build it for me, but I got the impression that the compression was rather stock, 8.5 I believe. The compression tester you can buy from the parts store that plugs into a spark plug hole, will that give the actual engine compression number? I was thinking about picking up one of those anyway.

I feel like an idiot for all the stuff I didn't take note of when building this engine. I was such a newbie. In a few years when I stroke this engine out, things are gonna be different.
 

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The general consense is the thumpr cams sound good and leave a lot of power left of the table. Your not going to get a cam recommended that is going to sound "good" with a stock c/r and highway gears.

from my personal experience I ran a comp 262XE in a 73 malibu (pretty heavy car) with 2.73 gears. It ran good enough for me. Way better than the stock 2 barrel carb but far from fast. Your set up is pretty similar to my old one except I had the stock smog heads. I got 21-22mpg on the highway but mid single digits in town. That motor worked hard to get my tank rolling. The 256XE or 262XE would get you better driviblity get you somewhere in the 275-300hp range. The 262 isn't a rough idle you can tell isn't completely stock.

The compression tester gauge from the parts store tests the amount of pressure produced in the cylinder. The C/R you need to know is the volume of your cylinder with the piston at TDC (top dead center) compared to BDC(bottom dead center). Your engine builder should have told you this or wrote it down on the build sheet.
 

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You're never going to get a Thumpr to tune in a 8.5:1 motor. You should not change anything until you speak with the builder and find out exactly what you have. You need to know cylinder heads, pistons, deck height, and static CR just to start. You will most likely be better off changing something else IF you have an 8:1 motor.
 

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Your biggest problem is probably that you don't know much about engines. Which is okay because we all start somewhere.

There's a lot more to tuning than swapping jets or turning an adjustment screw. You should be able to get that to tune just fine, once you know what you're doing.

What is your initial and total timing? What springs are in the distributor? What have you done to the carb to alter the stock settings? Is it a new carb?

I wouldn't buy one more part until after you have this tuned.
 

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Your ignition timing sounds about right.

You need a smooth idling "RV type" cam with a 2.73 gear and stock compression.

I would use cam like a 252H compcam (206/206 at 0.050") or an edelbrock performer cam (204/214 at 0.050"). These cams work with stock springs.

I would avoid super fast ramp cams, like voodoo or xtreme cams. As they are more likely to go flat.
 

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Zerocyde said:
Let's say for a moment that the cons of running a thumpr cam are starting to out-weight the pros for me.

Can I get some help figuring out a cam that would produce either equal or greater power than my thumpr, but with better drivability\easier tuning?

Engine info in quote block:



I've been tuning it about a year now and have it running pretty decent. 18 degrees advanced with 18 mechanical (seems like both dizzys I bought, cheap one and then this nice one came already set to a small amount of mechanical advance, almost as if they know they were going in a thumpr. Unless, of course, I'm just flat out doing something wrong.)
It stinks often, and I had to drill butterfly holes in my carb, and my manifold vacuum is low. The car shakes back and forth when I try to drive at a slow idle, but that's probably just because my rear is still like, 2.73 or something highway like that. But it does sounds beautiful.

But I guess if I could get more power with the same lack of drivability\tunability, then why not?
1. You may need to add a vacuum pump.

2. That cam's minimum rpm range is like 1900 so it's going to "shake" at anything below that.

Remove the cam, open lid on trash can and toss. There are alot better cams out there for your motor. Now, if you just want the nasty sound and don't care about performance or street driveability, leave the cam in, otherwise, do yourself a favor and part with it.
 

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I'm yet to figure out why people go with thumper cams? Because of the sound? That leads to a couple questions I have and they are:
1. Before the thumper existed, it wasn't known that high performance cams loped at idle?
2. When did current high performance cams stop loping at idle? Is that why so many buy thumper cams? Because the current performance cams don't lope at idle anymore?
Thumper cams are gimmicks. They are for those that can't make a high performance cam lope at idle and why they can't make them lope is because they don't know how to tune it.
 

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Do people really purposely tune their cars to lope at idle :confused: ???

If a guys going to buy a mild cam for good performance in every day driving but its lame sounding, get a thumper that matches that cams characteristics If you like the sound! advance or retard the cam to put your power were you want it. The Thumper cams do produce good power. Just not as much as they sound like they can LOL! Hell I Know guys that run hellasious cams and run Rhodes lifters to make them a little friendlier at Idle are they posers?



Most guys in the hot rod hobby I know tune em for optimum speed and performance!!! The lope is something I could do without if I could get the same power & speed out of the car!!! If you could make your car quiet with no back pressure or loss of H.P and Et would you do it now that would be a real sleeper!!!!

I never understood air conditioning on a lumpy rod ? LOL :D If any one out there could snap their fingers and have their car quiet with open headers, no lope, no vibrations, slicks that didnt hydroplane on a few drops of water, and good handling, without changing a thing would you do it? Would you feel the same pulling into the A & Ws with the other rodders that are built to the hilt and the sound and vibration can be felt in your chest and soles of your feet as they Idle buy I wouldnt!!! I put 3 1/2 gallons of 110 octane gas in my vette at $6.97.9 a gallon (it was on empty) last night to go 14 miles total distance I told the wife it was plenty and when we came home and pulled into the drive it was bellow empty :sweat: :pain: if I could just snap my fingers and run regular without a loss in power & performance I would! My wife was still going on this morning that I was lucky we didnt run out :pain: :boxing: Man wives :( !! If I could just snap my fingers :mwink: LOL !!!!!

To the guys that run thumpers all the more power to ya!! To the guys that spent 20 thousand and upwards on the engine and is a trailer queen and is affraid to get a bug on his paint job Now thats a real poser!!


LOL :D Chris
 

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I never met anyone who used Rhoads lifters to help the idle. Anytime I seen them used it was used for one of two purposes.
Those purposes was they wanted better low end torque and street manners.
The other is the cam they installed was too large for their purposes so they were using it as a band aide, but as said, Never seen anyone use them to try and get the lope out of the idle. Especially when cam companies print clearly on the cam cards what type of idle the given cam will have.
When I was in tech college we were doing the finishing touches on my instructors '56 chevy 2 door. The car was fully restored except he kept the original 265 and Powerglide on the table and installed a 350 and a TH350.
The cam was one that was given to him by a student. However when he gave him the cam he mistakenly gave him the wrong cam card and the cam was considerably bigger than my instructor wanted. He did however, like how it sounded at idle but he didn't like the lazy low end response. We installed Rhoads lifters and I told him he wouldn't like them because they tick and he likely would notice very little improvement. A week later he told me they ticked like solid lifters at idle and low end power didn't improve much. Why we installed them was because he didn't want to have to change cams. but we ended up doing so anyway.
 

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I can't understand why people have a hard time tuning or driving such a mild cam. If you look at the specs its not that radical. It just needs proper tuning.

I've had a few 4 bangers with cams with more than 230 duration at .050"... they really weren't a big deal to tune or drive. I have one now with a 240 cam that is running a 1406 edelbrock carb (haven't finished me IR manifold yet) and it starts up and drives just fine, even with the choke removed.


Just spend your time worrying about tuning rather than throwing away good parts.
 

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ap72 said:
I can't understand why people have a hard time tuning or driving such a mild cam. If you look at the specs its not that radical. It just needs proper tuning.

I've had a few 4 bangers with cams with more than 230 duration at .050"... they really weren't a big deal to tune or drive. I have one now with a 240 cam that is running a 1406 edelbrock carb (haven't finished me IR manifold yet) and it starts up and drives just fine, even with the choke removed.


Just spend your time worrying about tuning rather than throwing away good parts.
He's been tuning on it for a year.
 

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S10 Racer said:
He's been tuning on it for a year.
Obviously tuning it incorrectly for a year. He just needs a couple hours to tune it correctly, once he figures out how.

I know everyone here loves throwing other people's money on new parts but that cam can work just fine when tuned right.
 

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ap72 said:
Obviously tuning it incorrectly for a year. He just needs a couple hours to tune it correctly, once he figures out how.

I know everyone here loves throwing other people's money on new parts but that cam can work just fine when tuned right.
It's still a junk cam no matter how you look at it. The Thumper was all a marketing strategy that has cost a lot of people money for little return.
 

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ap72 said:
Your biggest problem is probably that you don't know much about engines. Which is okay because we all start somewhere.

There's a lot more to tuning than swapping jets or turning an adjustment screw. You should be able to get that to tune just fine, once you know what you're doing.

What is your initial and total timing? What springs are in the distributor? What have you done to the carb to alter the stock settings? Is it a new carb?

I wouldn't buy one more part until after you have this tuned.



This mans advice is to me is very sound!

The small thumper is very streetable and runs good installed straight up. And runs very well on low compression engines. you may need a little higher stall converter with the small thumper.your small street gears can be managed with smaller diameter tires to increase final drive ratio ( fooling the eng. into thinking you have higher numerical gears :mwink: ) You can set your lifters with a vacuum gauge for optimum vacuum at Idle and for more power at upper rpm set them at 0 lash. your problems are probably in your basic eng tuning, even the ohm rating on the plug wires drain HP some wires are over 1000 ohms per foot others are as low as 25 ohms you can sometimes gain up to 10 hp with a simple wire change to lower ohm same thing with plugs the right heat ranges and non resistance plugs make power, check your accelerator pumps for full squirt you may need different pump cams or their out of adjustment! You shouldn't have had to drill your throttle plates unless thats an old early style holley the later models dont need it especially with a small cam like the little thumper ( thats an old cure from the 50s & 60s) so you dont adjust past your idle slot! If the carb is older & used there was no power valve protection check or change the power valve also check your vacuum at idle and the power valve rating it may be dumping fuel early? The little thumper should have pretty good vacuum so you should check for leaks? The small thumper doesnt need much enitial advance 10 to 12 degrees is usually plenty and 34 at 2500 is usualy good but then all engines are a little different!


There are so many little things that are overlooked or taken for granted by younger mechanics, and then a big mistake is adjusting a little of this and a little of that and a little of those guessing & jumping around and pretty soon there is so much little stuff out of wack that its nearly impossible for a laymen to figure out LOL

Another big mistake is the mixing of parts bottom end cams ,top end 360 ram style intakes, too big of a carb or too small , wrong valve springs! the mixing of bottom end, mid range and top end parts will kill any gains you expected!

Running high octane racing fuel in low compression engines is a mistake. I saw a boy that put 130 octane and 4 cans of booster in his car thinking it would be faster it was like diesel fuel LOL it wouldn't run we had to drain the tank & flush the lines( some people think high octane is more explosive then regular) but its the opposite. High octane has a lower flash point then regular as a matter of fact kerosene has a higher octane then gas.

Chris

I typed this yesterday around noon its 2am now, and could'nt post it till now ? :confused:
 

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DoubleVision said:
I never met anyone who used Rhoads lifters to help the idle. Anytime I seen them used it was used for one of two purposes.
Those purposes was they wanted better low end torque and street manners.
The other is the cam they installed was too large for their purposes so they were using it as a band aide, but as said, Never seen anyone use them to try and get the lope out of the idle. Especially when cam companies print clearly on the cam cards what type of idle the given cam will have.
When I was in tech college we were doing the finishing touches on my instructors '56 chevy 2 door. The car was fully restored except he kept the original 265 and Powerglide on the table and installed a 350 and a TH350.
The cam was one that was given to him by a student. However when he gave him the cam he mistakenly gave him the wrong cam card and the cam was considerably bigger than my instructor wanted. He did however, like how it sounded at idle but he didn't like the lazy low end response. We installed Rhoads lifters and I told him he wouldn't like them because they tick and he likely would notice very little improvement. A week later he told me they ticked like solid lifters at idle and low end power didn't improve much. Why we installed them was because he didn't want to have to change cams. but we ended up doing so anyway.


Doublevision: I said a little friendlier at idle! Any one that ever used em knows Rhodes actually reduce the lift of the valve at idle and then off idle as oil pressure builds with rpm the lift increases to max valve lift and the main complaint when people I knew change their lifters over to rhoads is "my cam doesnt sound quite as good?" at idle, But the tires quit chirping when I put it in gear !! and I can run a little slower idle without the engine bogging or loading up and off idle response is a little better! (FRIENDLIER) Once the rhoads lifters pump up depending on oil pressure and rpm the street manners are gone because your at max lift , then when you slow and oil pressure drops and rpm slows the lifters bleed off (collapse) to a point reducing valve lift.

I didnt recomend them to the gentleman that started this thread. Ive never used em myself but I have installed a few sets for customers through the years And I dont recommend them to anyone and most cam company's dont recommend them and I never saw a cam card say what idle characteristic a specific cam would have running rhoads lifters!!!
Most large hyd cam's lash is set from 0 to .004" and tap, street strip hyd. are usually set at 1/4 turn and milder and stock hyds are set at 1/2 to 3/4 turns. the slight taping of rhoads lifters is hardly noticeable with the performance exhaust noise on most performance cars or hot rods and a lot quieter then solids! Any one that sets lifters with an engine running knows that idle vacuum changes as lifter lash is changed!

Run the mild or stock cams 1/2 to 3/4 turn on the street and 0 or .001" lash at the track its an old race trick.

Your experience with rhoads is not uncommon most people dont see much difference once a little past idle especially with high volume and pressure oil pumps and no restricter's.

Jester
 

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I know how Rhoads lifters work jester. They tap at idle as mentioned and it's no mystery to why, to me it was self explanitory. As it used to say in the 80's magazines on Rhoads lifters ads which was "The tap you hear at idle means they're working"
I wasn't referring to how a given cam would sound with Rhoads lifters. I was referring to cam cards that arrive with the cam and the basic cam and standard lifters set up. I used to have a crane "economaster" cam, and on the card it said "strong midrange torque, lopey idle"
I surely wouldn't think any cam company would print on the card how the cam worked with Rhoads lifters because I know no cam company would ever recommend them.
 
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