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  #16 (permalink)  
Old 06-09-2012, 09:17 PM
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Quote:
Originally Posted by S10 Racer
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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  #17 (permalink)  
Old 06-09-2012, 10:47 PM
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Quote:
Originally Posted by ap72
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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Old 06-09-2012, 11:50 PM
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Quote:
Originally Posted by ap72
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 ) 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 ?

Last edited by painted jester; 06-09-2012 at 11:58 PM.
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  #19 (permalink)  
Old 06-10-2012, 01:49 AM
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Quote:
Originally Posted by DoubleVision
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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  #20 (permalink)  
Old 06-10-2012, 02:04 AM
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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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  #21 (permalink)  
Old 06-10-2012, 03:00 AM
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Quote:
Originally Posted by DoubleVision
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.
The explanation was not meant for people who already Know Rhoads , you installed them I took for granted you already knew, it was meant for people who read this like the thread starter and may not! And the rhoads lifters idle characteristics not being on the card was stated because cam company's only state stats on what they test and recommend they dont know what the idle characteristics will be if varied from. Lumpy idle covers a lot of cams and degrees of lump! The only part really pertaining to you directly was what I meant by friendlier idle. dont take offense because none was meant! Years ago cam company's even listed recommended Idle settings you dont see that much anymore if at all. I ran many cams that the recommended idle was 2000 rpm and some much higher!! I think if cam company's still listed suggested Idle many people would shy away from those cams!!! its hell setting at a stop light in traffic idling at 3000 rpm LOL I did that all through the late 60s many of us did. But I see guys installing these type of cams and then trying to idle them down and getting nothing but trouble trying to get them streetable like installing rhoads lifters! If what I wrote struck you the wrong way it wasn't meant to! Man it after 4 am Ive got to call it a night!

Jester
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Old 06-10-2012, 02:45 PM
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This thread seems to need a bit of clarification:

1. When I had the engine built for me I didn't know anything about cams. If I were to do it over today, I would not go with Thumpr.

2. My next step is a 4.11 rear end gearing.

3. I have my engine tuned JUST FINE right now, my car drives PERFECTLY as far as I know. Granted, I have had to learn EVERYTHING by myself with NO help from anyone. There is probably stuff I am missing, and I would love to have someone with real experience hang out with me for an hour or so, but regardless, this is not a "how do I tune with a thumpr" thread.

4. The intention of this thread was to ask about alternatives to the Thumpr, that would produce equal or more power, without sacrificing drivability OR performance for power. I wish to switch to a more "normal" cam where I only have to worry about [power vs drivability], not [power vs drivability vs sound].

It seems, from the responses, that a cam isn't something that can be picked so easily. I think my next task is to do some digging and get some hard numbers off of my engine so I can know for sure what I have.

Any info on methods or tools I can use to get info out of my engine myself without having to talk to the builder would be awesome. What are some decent methods for finding out your compression? What bout spring size? Opening sizes on heads? Deck height (not sure what that is)? Any help like that would be great.

I'm re-doing my intake seal tomorrow (found a very small leak on the front of the intake where I didn't RTV very well) and I can take the heads off while I'm at it if I need to.

Last edited by Zerocyde; 06-10-2012 at 03:01 PM.
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  #23 (permalink)  
Old 06-10-2012, 04:46 PM
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If you want it to idle smooth and run well at low engine rpm, and drive well overall with 2.73 gears,
put in a smaller cam with less valve overlap .

Your ignition curve is not set up correctly to run best with the thumpr
and you did not need to drill holes in the throttles.
You got some bad (limited) advice on how to tune for the thumpr cam.

Driveability is very subjective.
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Old 06-10-2012, 05:38 PM
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IMO, if your heads are the ones indicated in your link(215cc intake port volume) then you have a severe miss-match of parts.
In order to make a 350 work well with those heads you would need a cam with much more duration (higher rpm range), and with the larger cam you would need quite a bit more compression than 8.5:1.
I'm not qualified to recommend the correct cam or CR that you would need as I've never used heads with that large of a port, but I do know that your low rpm port velocity must be poor and that the cam's rpm range is too low to take advantage of the heads flow potential.
Someone else here can elaborate. I don't think anyone realized you were using heads that big. The more info you can give (without just providing links), the better they can help.
FWIW
ssmonty
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  #25 (permalink)  
Old 06-10-2012, 10:08 PM
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If you want a good cam that will work with the specs you've given, and build power right off idle to around 5800 rpm, then go with the Summit SUM-K00052. It's made by Crane and is 216/216 @.50 duration (advertised 272/272) with .454" lift.
It's an amazing cam for a street car and works well with a stock torque converter. Just a little lopey, but not like the Thumpr cams.
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Old 06-11-2012, 07:24 PM
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I'v heard good things about RV cams in a sbc like mine. I take it the RV doesn't mean it's a cam from a recreational vehicle, does it?
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Old 06-11-2012, 07:56 PM
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The name "RV" cam is pretty loosely tossed around whenever someone says they want something a little better than stock for their pickup truck. It's usually a cam with just a little more lift and duration vs. stock.
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Old 06-12-2012, 11:59 AM
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The thumpr's still produce a fair amount of power gain over stock and sound like larger cams but are designed to have very good vacuum and drive-ability and the set up is very easy. You mentioned you had low vacuum? Hows your vacuum now? I thought you had tuning problems and have been trying to tune it for a year? But you now say its running perfect now? Is this a recent thing, you getting it running perfect? I'd be interested in what you found in your tuning to solve your problems after a year ? And Im glad you figured out the problems

The R.V. cam produces more torque off idle for towing and carrying heavy loads mainly designed for trucks and recreational vehicles LOL and There are many cams much better then the R.V. for hot rods! And a few of those cams are thumpers ( for the guys that like them )



I wouldn't run an R.V. just for the reason of not having to tell some one when Im asked " what cams that, your running in the vet ?" Id have to tell em "oh its a recreational vehicle cam for when I pull my horse trailer with my vet" LOL
That was just a joke !!!! Don't take offense to it, any one out there running an R.V. run what you like!!!!

I dont understand why people cut down the thumprs most guys here in my area never ran em but say their junk!!! And now guys that installed em in their cars and like them are actually saying their running something else LOL so they arn't the brunt of every ones jokes My vet's called Thumper my wife picked the name she always loved the little rabbit in the Bamby cartoon
I get enough jokes about that from my buddys saying its on there because of the cams, and strangers at shows always ask me if Im running a thumpr cam LOL Its driving me nuts
http://www.hotrodders.com/forum/atta...id=66010&stc=1


I guess Im different then a lot of people. I pick my cam first for how I want my engine to perform and then blue print my build around the cam. But I see a lot of people build first and then pick a cam or stick a cam in without knowing the build of the engine, If I have a Strange engine Ill pop the heads check out deck, pistons, heads, gears, tire, diameter and intake characteristics, and pick a cam that matches the build. And then match an induction Intake type and carb or injection or etc, and then the converter.

Chris
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