What's equivalent (power-wise) to a thumpr? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 06-08-2012, 06:04 PM
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What's equivalent (power-wise) to a thumpr?

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:

Quote:
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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Old 06-08-2012, 06:11 PM
How fast is fast enough?
 
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What compression? Headers?
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Old 06-09-2012, 02:01 AM
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Quote:
Originally Posted by ap72
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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Old 06-09-2012, 04:19 AM
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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.

Last edited by sam_bo3; 06-09-2012 at 04:27 AM.
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Old 06-09-2012, 05:36 AM
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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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Old 06-09-2012, 06:46 AM
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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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Old 06-09-2012, 07:00 AM
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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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Old 06-09-2012, 08:55 AM
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Quote:
Originally Posted by Zerocyde
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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Old 06-09-2012, 11:49 AM
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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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Old 06-09-2012, 12:17 PM
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thumper is like a rear spoiler on a street car....poser
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Old 06-09-2012, 12:28 PM
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Quote:
Originally Posted by geezer69
thumper is like a rear spoiler on a street car....poser
Or racin' stripes, dual exhaust & hood scoop on a GEO Metro.
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Old 06-09-2012, 02:06 PM
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Do people really purposely tune their cars to lope at idle ???

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 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 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 Man wives !! If I could just snap my fingers 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 Chris

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Old 06-09-2012, 03:17 PM
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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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Old 06-09-2012, 05:52 PM
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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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Old 06-09-2012, 09:04 PM
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Quote:
Originally Posted by ap72
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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