thumper crap

Mr, first you need a new mechanic, the guy who told you to ditch the Autolight carb is an idiot. The shoebox carbs are excellent. You need option 3, get rid of the crap cam. We'll help you pick a new one if you want. The reason the Thumpers sound the way they do is because they have a narrow lobe displacement angle, like 106 or 107. What most of us need in an everyday street driver is 110 or 112. Fuel injected cars should have even wider LDAs. A fuel injection system would be very very unhappy with a thumper cam. LSG

 

Mr, first you need a new mechanic, the guy who told you to ditch the Autolight carb is an idiot. The shoebox carbs are excellent. You need option 3, get rid of the crap cam. We'll help you pick a new one if you want. The reason the Thumpers sound the way they do is because they have a narrow lobe displacement angle, like 106 or 107. What most of us need in an everyday street driver is 110 or 112. Fuel injected cars should have even wider LDAs. A fuel injection system would be very very unhappy with a thumper cam. LSG

i agree with this assessment. you need a new mechanic, preferably one that will build an engine based on what you need an not on what he wants.

what people have to understand is that when building an engine, they have to take a systems approach, and select parts that work together. using a cam that is designed to operate above 2500 rpm with an intake and heads designed for 1000-5000 rpm isnt going to work well.

as for fuel injection, holley makes a system that just might be perfect for you. its their new sniper system. about $1000 and it is a bolt on system, and uses the stock fuel tank. check it out.

 

++1 ^^^^

 

Dump the cam. It doesn't fit with what you've stated as the purpose of your car.
Option 2 is to build everything around that cam...... none of what you have
currently really "fits" with using that cam.
Your engine builder should be shot for installing that much cam for the level of
build you (hopefully) told him you were trying to achieve.

 

Ditch the cam 0.02

 

Definitely ditch that cam. I don't think I know anyone who has one that likes it, unless they're the type to only putter around to cruise-ins. For "normal" driving they're terrible!

The alternative is to build everything else up around the cam, but I honestly wouldn't. It won't do you a lick of good in daily driving or road trips. There are some really good cam grinds that aren't as lumpy but will run much more smoothly - they're more mild but they will fit better with your intake / heads / carb. Others will have better recommendations than I, as I've only ever run a custom grind that the PO put in my car.

 

Ditch the cam and your mechanic. The thumper cams are garbage, you don't pick a cam based on sound!

 

Either drive the car at 5,000 rpm all the time, or replace the cam.

Which sounds more reasonable ? ?


Z

 

The easiest solution? "Dumper the Thumpr" and replace with a cam that may not sounds as "cool" but actually makes power with your combination of parts. The Thumpr, in itself, isn't a BAD cam, but it needs the right combination of components to work properly.

You don't mention what you're using for pistons, but let's assume the typical flat top with 4 eyebrows like SpeedPro's L2482.

First, your move to GT-40 heads, if they're unmilled, has cost you a full point, plus, of static compression. Next, while the GT-40 head flows a bit better than, say, an E7TE, it still has exhaust flow issues attributed to port size, shape and the intrusion of the Thermactor "bump". Also, the HiPo exhaust manifolds are (in my opinion) just as good as an equal-length shorty, they aren't going to help much at higher rpms (nor will most other headers) as long as they're bolted to the unmodified GT-40's. Moving along, it sounds like you're running a stock iron Ford 4V intake and a 1.08" Autolite 4100. No help here with a cam that's expecting much more flow. Also, the stock power valve on an Autolite 4100 is going to be open at your idle vacuum, making it run really rich.

What you'll have to decide is what's more important...a car that runs well or one that sounds "cool"....

With what you're using for a combo I think I'd go with something along the lines of a Comp XE256H (you'll need new lifters, too) and call it a day.

If you want to stick with the Thumpr, then I'd say you need to invest in an intake, carburetor, cylinder heads, headers and exhaust.

Oh yeah, and don't forget, whichever route you choose, yank that distributor, send it to Glazier-Nolan, and get it recurved.

 

Ditch the mechanic and cam. I put a GT40P motor in my 66 with a stock Mustang 5.0 cam and 1.72 rockers. It runs great! Everybody runs a lumpy cam for what?

 

Well, I love my lumpy cam simply because it works (and makes plenty of power!)

The sound is just a bonus.

 

Some people like them lumpy.
It's a head turner on cruise night.

 

Find someone that can tune for an aggressive cam........ Factory carbs need LOT's of tweaks to be compatible as well and some just don't have the circuitry to be modified. Here's a Mutha Thumpr in a 406 SB Chev. Idles clean at 750 rpm and makes enough power to put a smile on your face. It isn't the cam choice that's a mistake but rather the total build that the cam is incompatible with. And the tuner that doesn't know how to make it work.




View My Video

 

Not sure I could apply poser to a cam that sounds healthy and properly tuned makes more power than it's smooth idle counterparts. Tuning is everything provided the build will support the cam choice. A Thumpr cam will work fine even in a fairly low static compression ration engine because of it's early intake closing. BUT, the overlap dictates a highly modified carb as well as timing far away from anything stock like. I would never assume Garlits or Muldowneys rails are posers on sound alone..............Idle characteristic is a byproduct of total build/tuning. Tuning being the key. Not many, if any, stock factory carbs are up to the task of feeding a short centered high duration cam without EXTENSIVE mods to internal feeds. Most won't support it and trying to tune a cam with those specs and a stock fuel efficient carb is a recipe for total disappointment. But, the cam isn't the problem.

 

Well let's pick the Squirrel a cam! This is fun, but I have no experience with 302's. I would guess close to stock, but from a reputable manufacturer.

 

To the OP - if you want to stick with the cam and the sound, then pull the cam out of your current engine, put it in a box, and forget about it for awhile. Put in a cam more compatible with your current setup and enjoy the car. Do some research and start stockpiling parts to go with the cam if you still want to go with it in your car. Once you got all the parts and knowledge, you can go from there.

 

With a decent re-curve on the distrib......have it all in(total advance 36* by 2000RPM) and limit the total to 36-38*. Big cams NEED a LOT of initial timing.24+ degrees won't be too much.
That will let you idle it down to under 1000RPM. Really cleans up the "snotti-ness" in the cam.
Allows you to trim down the idle on the carb. (Prolly a big issue is the transition slots are uncovered too much to make it idle.) The distrib. mod will fix this.
Advancing the cam timing might help with the problem. Advance it another 4-6* above dot-to-dot setting. I would re-curve first and see.
Nothing worng with a lumpy-*** snotty idling camshaft if you like that and don't mind the grumpiness at low speeds. Heck...its your ride!!
One thing is...you need more gear to improve its actions and use the more power it produces.
That intake sux BTW!
You AND the son-in-law need to spend a weekend with some lighter weight advance springs and timing tape and tuning tips before taking that "hound dog" on a Rt.66 cruise.
Find a real "hot rod type" mechanic and not a local-yokel sparkplug changer to guide you if you need help.
Keep the cam......just learn how to tune the new combination.
6sally6

 

With a decent re-curve on the distrib......have it all in(total advance 36* by 2000RPM) and limit the total to 36-38*. Big cams NEED a LOT of initial timing.24+ degrees won't be too much.
That will let you idle it down to under 1000RPM. Really cleans up the "snotti-ness" in the cam.
Allows you to trim down the idle on the carb. (Prolly a big issue is the transition slots are uncovered too much to make it idle.) The distrib. mod will fix this.
6sally6

I did actually give this a try. The engine wouldn't even run on less than about 15 degrees. I think I have it at somewhere between 25-30 degrees initial, and I swapped out the springs to give me the correct all in. The issue that I was having with that though, is that I still have to run the idle at about 1,200 to keep it from stalling when I put it into gear.

 

Thanks much for the responses :grin2:


So, I'm sold on a new cam. I did like the sound, but I'm certainly not married to it. Now the question is, which cam do I go with? I don't mind a little performance, but good daily driver characteristics is my primary concern. (I'll do some forum searching too, as I'm sure I'm not the first one to ask which cam is best)


Forgot to mention: the block was modified to run a hydraulic roller cam, and I'm also using a Pertronix ignition


Woodchuck - I checked the build sheet, and it has these pistons listed: Speed-Pro Hypereutectic Pistons H273CP20. Also, it has listed that the chambers were milled to 58cc to achieve a 9.4 compression ratio. Actually, here's the build sheet:

 

Looks like you're running a small base circle cam?

I would call Lunati or Comp and let them know what you want out of your car. They'll ask things like desired powerband, intended use, rear gears, transmission, etc.

From there they can recommend you a cam.

 

I really appreciate the info. At this point, if it doesn't have the lumpy idle anymore I'd be just fine with it. So long as the car idles and runs right, I'll be happy. To answer a couple of the questions though;

Looks like you're running a small base circle cam?

I would call Lunati or Comp and let them know what you want out of your car. They'll ask things like desired powerband, intended use, rear gears, transmission, etc.

From there they can recommend you a cam.

According to the sheet, it does appear to be a small base circle. Not entirely sure why the builder picked one for my engine. I've heard that they're used in stroker (which mine is slightly I guess 289 to 302) and in hydraulic roller conversions (which mine is as well) maybe one or both reasons?

If you went to the standard base roller cam, you would have to buy the link style tappets and shorter pushrods. If you had the standard base, you could just swap out the cam and reuse the tappets and push rods. I think going to flat tappet, it would be a lot cheaper then just buying a new roller cam or link tappets by themselves. You would be able to keep the existing pushrods. What are you doing for rocker arms?

By links, are you meaning the spider? When I pulled the GT40 heads from the Explorer in the junk yard, the engine builder had me grab the lifters, spider, and push rods to be reused in my engine. As far as the rocker arms, I'm pretty sure they are the stock ones that came with the GT40 heads

sorry if i missed it, but which thumpr cam?

According to the paperwork I have, it's this one: 31-600-8 - Thumpr? Retro-Fit Hydraulic Roller Camshaft

 

OP, if you like the sound and the lopeyness of the cam you have now, but want one that will work for the street, check out the comp cams 270 magnum cam. it is big enough to give you the sound and the lopey idle, but when you want the power, its there.

 

One other item, outside the box- The OP could install a set of Rhodes lifters. These reduce lift and duration at low rpm, which would effectively reduce the Thumpr to more streetable profile.

So, I'm sold on a new cam. I did like the sound, but I'm certainly not married to it. Now the question is, which cam do I go with? I don't mind a little performance, but good daily driver characteristics is my primary concern. (I'll do some forum searching too, as I'm sure I'm not the first one to ask which cam is best)

Well, daily driver is NOT what you have now. Something like the C9OZ-6250-C would be far better for that, and could still get you to 320 hp. Even the C7FE-6250-A Cobra LeMans cam would run smoother than what you have, and that's an actual racing cam.

 

One other item, outside the box- The OP could install a set of Rhodes lifters. These reduce lift and duration at low rpm, which would effectively reduce the Thumpr to more streetable profile.

Rhodes lifters seem like a good idea but I seems everyone I know that ran a set (read past tense) has them on a shelf now. You need a builder to put together the right package carb to tailpipe or buy an engineered package. I always point folks to Edelbrocks packages for a mindless solution. Folks can get better numbers with a good builder but for a bolt on consider a Performer Plus intake and cam. Its engineered to give a stock motor some extra punch and bling for a few hundred bucks while working with relatively stock gear designed for a daily driver. Give them a call and tell them your story.

Do not try to chase your tail working with that cam unless you are ready to hire an expert (not your present builder) to engineer a smile on your face. Your builder should have told you everything that would need to happen to make that cam sing - he obviously doesn't know or has you scheduled to make his boat payments this year...

rhodes lifters are an idea to make the cam more streetable, but the drawback is that rhodes tend to be noisy, sounding like a solid lifter cam at idle and low speeds. some like the sound, some dont.

 

Rhodes lifters seem like a good idea but I seems everyone I know that ran a set (read past tense) has them on a shelf now. You need a builder to put together the right package carb to tailpipe or buy an engineered package. I always point folks to Edelbrocks packages for a mindless solution. Folks can get better numbers with a good builder but for a bolt on consider a Performer Plus intake and cam. Its engineered to give a stock motor some extra punch and bling for a few hundred bucks while working with relatively stock gear designed for a daily driver. Give them a call and tell them your story.

Do not try to chase your tail working with that cam unless you are ready to hire an expert (not your present builder) to engineer a smile on your face. Your builder should have told you everything that would need to happen to make that cam sing - he obviously doesn't know or has you scheduled to make his boat payments this year...

 

The modern version of the HiPo cam is one to consider. It will idle at 800 rpm all day without a hiccup. And pull evenly to 6,000 too. Every cam with more power at higher rpm is a trade off, it will have less power down low. Even the HiPo cam doesn't have the same low rpm torque as a stock A code cam does, but it's way closer than what the OP has now. The HiPo cam will provide more low end torque than most aftermarket cams too.

It's just another alternative to consider. Ask yourself what type of driving will I really do ? Chances are u would very satisfied with the power curve and drivability that a HiPo type cam would offer.

Z

 

FYI, my 91, 5.0 cam specs are .444" I&E, 276° I @ .006" ~ 219° @ .050" and 266° E @ .006", 211° @ .050" and LSA as I measured 114.5°. The 89 & up have 10° more then the intake, not a typo. With the 1.72" rockers my lift is .477". Duration will be very slightly increased with the 1.72 rockers. The 85 to 88 cams have the same duration on I&E, 211°.

Just saying the car runs pretty well even with the 2.8 gears. IMO, it doesn't matter if you go flat or roller tappet. Both styles are going to run pretty much the same until you start to get around the 280° advertised range. Up to that the flat tappet will probably have the edge.

Too bad you have the reduced base circle cam. Standard base circle cams are a lot more common and used cams are plentiful at reasonable prices. You can reuse the old roller tappets without any problems. It may be more cost effective to use a flat tappet cam in your case if you decide to change the cam. I'd stick with either 110° or 112° LSA. The 110° will work well with everything and give you that slightly lumpy idle. A lot of guys like the Comp Cams H260 style with 110°.

If you went to the standard base roller cam, you would have to buy the link style tappets and shorter pushrods. If you had the standard base, you could just swap out the cam and reuse the tappets and push rods. I think going to flat tappet, it would be a lot cheaper then just buying a new roller cam or link tappets by themselves. You would be able to keep the existing pushrods. What are you doing for rocker arms?

 

Well.......you do have good compression and a multi-angle valve job.
AND an A/T(I missed that part at first!) Keep in mind that sweet rumpity-rump/snotty idle comes more from a tight LSA than big duration. 108*LSA with a 215-218* duration might get you in the "ballpark". Not too rad(IMHO) but still run like heck and sounds pretty sweet too.
I've "heard" a lot of negative things about Rhoades lifters and good.
We built a dirt tracker years ago with A/T and 108*LSA and it would idle in gear OK!
Check Isky camshafts(Summit carrys them) gond on 108* LSA's
6sally6

 

sorry if i missed it, but which thumpr cam?

 

This one. 31-600-8 - Thumpr? Retro-Fit Hydraulic Roller Camshaft

 

The rationale behind a reduced base circle cam is that roller lifters can be used in non-roller block lifter bores, typically with the stock "spider" (lifter locator) bolted in place to holes drilled and tapped in the lifter valley. The roller lifters need to be "located" or fixed into place so they can't rotate like a traditional lifter since that would put the roller off kilter on the cam lobe.

Link bar (an actual bar or link connects two lifters together so neither can rotate) are used with standard base circle cams in non-roller blocks as the roller lifters will be too far out of the lifter bores for the "spider" to work.