Street Tunnel Camino

Randystys

Member
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Hey I'm Randy, I've been so busy digging through the posts and cross posts on tuning a tunnel ram I never noticed that there was a current forum going on, I thought this was all archived information...

My project is a frame up hot rod '66 El Camino... 383 aluminum heads, weiand tunnel 2x Holley 450, big mother thumper cam, Muncie 4 speed, 4.11 posi traction, 4 link, tubbed, lowered 4" .

I got it up and running, now in the process of dialing it in, smoothing it out best I can for the street/strip.

I don't expect a mom's car grocery getter temperment with the cam I have in there, but want better than the full blown all or nothing race mode I have now. Looking for tips and tricks and tuning.

I have lots of pictures but I guess I have to figure out how to shrink them down to 500k to load here.

(Edit: I'm going to cut and paste some previous Posts and Picsfor reference)

I have the Muther Thumper cam Grumpy says "not the best for this application"

Damn... probably explains why I'm struggling to smooth it out and get good transition...
But I thought it fit in the ranges grumpy listed in his thread:
106-109 LSA I have 107
245-300 duration i have 295
Lift is what, .500 /.490?
I have 10.5:1 flat top small chamber (I believe 64) aluminum head compression.
If that cam is the total dog, wrong ass, ain't gonna happen, ilI' pull it out and try your suggestion.
If itsi more like it'll work but there's better cams out there... Id like to work with what I have for this summer and change it out next fall...

Other Stuff I Have in and done

6.5 power valve
68 jets (might be 72)
31 squirters
50cc pumps
4160s
Mechanical secondary matched opening.
Right at the moment 850-900 rpm idle
11.4-12.6:1 f/a idle
6-8 psi idle
I have not drilled flaps yet
20* initial timing

Grumpy says "Id adjust the fuel pressure regulator to provide 5psi -5.5 psi at the carb inlet port
as a first step, and adjust the jets to get closer to about 13.5-14:1 fa ratio at idle"

So that's where we left it last week or so ago...
I should mention I'm 61 yo and I built this over the last two years as retro hotrod of what I would have built back in my high school days had I the money and the wearwithal.
I don't plan on any "serious" strip work built mostly for show(s) and cruising the bullivard so lumpy idle fits in the picture as long as I can get driveability out of it...
What I'm saying is I'm not looking for top performance on the strip. Although I might take a run down the 1320 just for grins...Photo6.jpg Photo9.jpg
 
So ended up I had 66s in for jets... I tried a set of 63s and then a set of 60s and with a little tweeking on the needles and idle screws was able to come up with a solid 13.8-13.9 F/A @ 900 rpm with good transition and drop down where I'm not afraid it'll die at the stop lights...

At 900 I'm not quite into the lopey idle of the Thumper cam, and that's ok for now... if I go much slower the bottom drops right out, goes rich (11s-12s) and blubbers and dies) so theres that.. Not sure if I want to persue a lower idle or how to go about it if I should...

Again, I understand this is not the optimal cam for a tunnel intake, but my plan is to eventually put a blower on... Is the cam you would recommend for a tunnel the same or similar as for a 6-71 -10 blower? If not... I'd like to work within the limitations of this cam in the tunnel and buy the proper cam for the blower when I change out possibly this winter...Rather than buying and switching twice...Photo 19.jpg
 
a cam for a super charged engine would be considerably different from one idealized for a tunnel ram intake, now I'm certainly not suggesting adding a supercharger to most engines, won,t make more power at least over some rpm range with a tunnel ram or N/A (non-assited ) engine cam, but you'll certainly benefit more from maximizing the components used to work with max efficiency under boost.
and ideally, a tunnel ram equipped engine would have both a tighter LSA in the 105-108 range and significantly higher compression,
usually in the 10.5:1 or a bit higher, and maximizing the exhaust scavenging and it might require more duration on the intake in relation vs the exhaust duration,
that might only have marginally more or need more duration if any more,
you'll sure run into issues with detonation much faster if you try to supercharge a high compression engine, without race octane fuel.
but that will hold true only if the duration and lift on the two cams is kept almost the same,
obviously, if you add duration and lift on the supercharged combo power tends to increase.

while a supercharged combo, would usually benefit from about 8:1 compression and a 112-116 LSA and more duration on the exhaust lobe, as you'll be dealing with significantly more exhaust gas volume on a supercharged engine and a tight LSA, will allow some boost to escape during the valve overlap.

http://garage.grumpysperformance.com/index.php?threads/semi-fool-proof-cam-sellection.82/

http://garage.grumpysperformance.co...lsa-effects-your-compression-torque-dcr.1070/

http://garage.grumpysperformance.com/index.php?threads/calculating-overlap-and-lsa-or-lca-etc.480/

http://garage.grumpysperformance.co...chevy-cams-and-a-few-similar-aftermarket.133/

http://garage.grumpysperformance.com/index.php?threads/camshaft-opinion.15053/

http://garage.grumpysperformance.co...mpression-ratios-work-better-with-boost.1894/
 
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Okay so we're talking a whole different block configuration for the blower...that changes things for the short term... Will be focusing more on taming the tunnel this year and if we don't get reasonable results by end of summer we may opt for the "optimal" tunnel cam for next year.
Put the blower on the back burner for now...
 
Don't drill holes in the carb's throttle plates! There is another (better) way.
I don't see that you are running a PCV valve, which besides it's main function of getting rid of the blowby vapors in the crankcase, it is a controlled vacuum leak. That vacuum leak actually helps engines with lumpy camshafts because the engine needs more AIR (not fuel) at idle. When you raise the idle with the adjusting screw on the carb(s) - 2 in your case, you end up taking the carb off of it's idle circuit and into the transition circuit. And that leads to even more fuel being added to the mixture - everything you don't want.
If you get an adjustable air valve and screw into the rear port normally used for power brakes on one of your carbs, you now will have an adjustable vacuum leak - the same as drilling the throttle plates. Use it to smooth out your idle while keeping your carbs working from the idle circuit at idle.
adjustable air bleed valve 3.jpg
 

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That would be handy to have but I don't have any ports below the plates on my carbs... I actually had to drill and tap a nipple in the manifold just below the carb to get a vacuum reading... I have nothing for power brakes or pcv vacuum...
 
Okay so I have a few miles on it now and have had a chance to tweak a few things to get it to smooth out run right idle good etc...
I went from 66 to 60 on main jets to get 13.8-14.2 f/a at idle without going lean at WOT...
Good strong idle, and transition with no load.,.but when cruising at speed and stomping the throttle she goes rich and stumbles a bit..
Powervalves were changed from 9.5 to 6.5s
Should I go one more step down in jets to say a 56 ?
Or do I tweak the circuit screws in a quarter turn or two ? They're out about one and a quarter across the board now..
 
Id certainly try several power valve swaps as a first step,
and keep accurate records of the results with each change.
a couple hours spent reading and testing the results of changes made will prove highly beneficial,
use of reliable and consistent fuel pressure,
with a return line style regulator and properly set carb float levels,
and fuel pressure at the carb inlet ports is mandatory.

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volumetric.gif

FuelFlowDiagram02a1.jpg

http://garage.grumpysperformance.com/index.php?threads/holley-carb-power-valves.1639/


http://garage.grumpysperformance.com/index.php?threads/carb-tuning-info-and-links.109/

http://garage.grumpysperformance.com/index.php?threads/is-backpressure-hurting-your-combo.495/

http://garage.grumpysperformance.com/index.php?threads/setting-up-your-fuel-system.211/

http://garage.grumpysperformance.com/index.php?threads/spark-plug-info.202/

http://garage.grumpysperformance.com/index.php?threads/reading-plugs.5428/
As you make changes take accurate notes of the results, achieved,
you should see a pattern develop as you make changes that you can use as a partial guide
don,t forget accelerator pump cam changes may be helpful


http://garage.grumpysperformance.com/index.php?threads/holley-jet-chart-size-and-area-of-jets.15869/

http://garage.grumpysperformance.com/index.php?threads/holley-accelerator-pumps-cams.1790/

http://garage.grumpysperformance.com/index.php?threads/holley-jet-chart-size-and-area-of-jets.15869/

even changes to the throttle linkage ratios and spring tension may help
http://garage.grumpysperformance.com/index.php?threads/holley-jet-chart-size-and-area-of-jets.15869/

changes to accelerator fuel pumps and boosters and squirters?
http://garage.grumpysperformance.com/index.php?threads/holley-annular-vs-down-leg-boosters.5229/

http://garage.grumpysperformance.com/index.php?threads/holley-jet-chart-size-and-area-of-jets.15869/
 
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Off the top...
I do have the 50 cc pumps and they have their own specific ramps..
I went from I believe 27 to 30 on the squirters...
Should I try going up or down on the power valves ? Or won't we know until we see results ?
I'm thinking we want to go up in number...
 
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So if I'm reading this correctly, it looks like I want to go down in number so the valve doesn't open up so soon until closer to WOT...
I'll start with that direction and track results...
 
yes let us know what you change and the result you see.
 
Ok so I took out the 6.5s and put in 4.5 power valves no other changes....
It was noticeably better, not great or perfect but but better...
It still stumbles when I get on from cruising speed, but not so bad as I have to get off it and back on it like before... And A/F is more in the low 12.8-13.2 rather than 12.2-12.6...

Off the line WOT, through the gears is clear 14.2 a/f ...pulls hard

Idle seems to be running a little rich now so a little low, I didn't touch it yet just an observation...

So I'm thinking try 2.5 power valves, adjust the idle again and see what we got ?
 
Ok sounds good, I have the brown ones in there now so I'll try the green ones two steps down...
I can change those external, and then if if needed I ordered a set of 3.5s to sweeten the deal...
 
So all I changed was the brown cam to the green cam which is two steps down...
That didn't work, I noticed brown cam pumps from the start right off idle... green cam has a gap before pumping, looks like after blades pass transition slots...

Now I go lean at transition... From 3000 rpm up is good because that's when the cam is pumping... But from 2000 rpm goes totally lean 18a/f ... Because cam hasn't engaged yet.

Thinking of going back to brown... going smaller on squirters so I don't hit it with such a dump of fuel...
And maybe drilling plates 1/16" and resetting metering block so I'm leaner off idle/transition when I punch the throttle ??

Other option might be to stay with green cam and go back up in power valve to fill in the gap...if that makes sense ??

Open to direction...
 
Seems to me you need to start with getting the idle correct. That includes getting the throttle
plates set so there is 0.020" of the transition slot visible. Every circuit builds on the previous
circuit, they transition from one circuit to the next, so there is some overlap.

To get the correct idle rpm with the .020" transition slot opening and the Idle Fuel Ratio screws
out 1-1/2 to 2 turns, you could drill and tap the Idle Feed Restrictor (IFR) passages and put in
your own jets. Be sure to measure what you have now before drilling. I used drill bits for this
since I had to buy them anyway to make my jets.

To read about drilling the IFR start reading at the link below and continue thru the next page:
http://garage.grumpysperformance.co...gine-project-dart-shp.3814/page-87#post-46393

Another good source:
http://motorsportsvillage.com/forum/viewtopic.php?f=6&t=9717
http://garage.grumpysperformance.com/index.php?threads/tuning-a-tbucket-dart-400-cuin-engine.11433/
 
Ok as far as my idle, prior to this last cam change...
I could adjust it to 900-1000 rpm with 13.9-14 a/f but as soon as I turned idle speed screws (plate stop) slower to 800 a/f loaded up to 11-12 and choked out, even with mixture screws 1/2 to 1 turn out..
I had the carbs off to change the cams and checked the slots...had almost 1/8" showing when it was running 900 idle and 14 af...1 1/2 turns out...
Obviously too much slot...
But when I close them they go rich.
That's what leads me towards drilling the plates for air rather than drilling jets which would make it even more rich...
Am I missing something here ?
 
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I had the carbs off to change the cams and checked the slots...had almost 1/8" showing when it was running 900 idle and 14 af...1 1/2 turns out...
Obviously too much slot...
Yes you are right, that is way too much T-Slot showing below the throttle plate. You don't have
any transition from idle to the main circuit, causing it to stubble.

But when I close them they go rich.
That's what leads me towards drilling the plates for air rather than drilling jets which would make it even more rich...
Am I missing something here ?
Setting up for installing different size jets that you make for the Idle Fuel Restrictor (IFR) will
allow you to adjust it leaner by going to a smaller orifice. Did you read the links above ?

I went from the original orifice size of .035" to .024" for my IFR.

You most likely will need to buy some brass set screws and some numbered drill bit sizes. I bought
these drill bits, they go from #61 to #80 or .039" to 0135".

Don't let me talk you into doing something that you are not comfortable with, proceed at your own risk !!!

https://www.amazon.com/100-Pc-Micro...ds=mini+drill+bit+set&qid=1596992147&sr=8-153

FP02_MeteringBlockNomenclature.jpg upload_2020-8-9_12-1-29.png
FP03_SemiComplete_5747.jpg

Keep a log of everything you do! Always include what you changed FROM and changed TO in each entry. That
way you don't have to scan the text above later on trying to figure out what is was before the change.
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DO NOT DRILL THE THROTTLE PLATES!
Your engine is telling you that it needs more air, but not more fuel. This is common when using a performance camshaft.
Just like throttle body injection has an IAB (Idle Air Bleed), you can accomplish the same with an adjustable vacuum leak.
Use one of these screwed into the rear power brake port at the back of the carb and dial up the amount of bypass air required.
Don't believe me? You can test it for yourself by opening up any unused approx. 1/8 - 3/16" diameter vacuum port or hose.
You set your idle speed screw for the proper amount of transition slot showing - and leave it there. Then use the adjustable air bleed to set your idle speed.
air bleed.jpg
 
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