So I was finally able to run a compression test and I get a average of 143 psi. High of 150 low of 140. This was done in the cold so I'm sure it'll skew the numbers. It's about 45 here. Yea spring. Lol sorry it took so long though.
I also found out more on the pistons, they are a 12 cc gm performance replacement for .030 motors found in older zz4 , 383, and 350 ho blocks.

 

Based on the following:
Stroke: 3.48
Rod length: 5.7
Adv cam duration: 280
Altitude: 200 metres
Ambient temp: 45 f
Cranking compression: 145 psi
Theoretical calculated compression ratio: 8.5:1.
Using a compression ratio calculator, the above parameters combined with a piston to deck clearance of .025" (stock), a head gasket of .040 x 4.100" (best guess), a 76 cc chamber and a 12cc piston dish gets you aboput 8.2:1. Not far off the theoretical guesstamate. That nets a DCR of 6.5:1. Definitely not the stuff of legendary racing engines.
Conventional thinking is that a cam with that duration (and the calculator I use is flawed in this regard as it doesn't take into account the actual intake valve closing point) wants a SCR in the 10.5:1 range. Possibly more. That's two full points off the mark.
My best guess is that the poor flow of the stock 76cc heads combined with a less than optimal static compression ratio relative to the cam duration has produced a classic underachiever.
Without reading back through the previous three pages of dialogue, I'd say your compression test result pin points most of your low power production.
Just my observations...

 

I agree with Skinny.

It's pretty much what I said back on the 1st page post #11 or so.

7.8 to 8.5:1 compression and WAY too big of a cam.

Hate to say it, but the options are still the same as I recommend on the 1st page.. Get your compression higher with smaller CC heads, or keep the heads you have and swap to a smaller cam.. A dual pattern 204/214@.050" cam fits the bill here.

Good news is you have pretty good cylinder/piston/ring seal. Only 10 psi between low and high is good.

 

Thanks guys!
I know for sure that I'm going to do heads next winter. I'm thinking like a 58-64 cc head would fit well. Itll last through this driving season at least.

What lift cam is that one you listed? And since I have a flat tappet hydraulic cam do I need to change lifters too?

Also, another problem has raised its ugly head. I'm hoping that one of you guys can advise me on an 1406 edelborck carb iissue. I put new plugs in and within warming the car up and playing with the air fuel idle screws l, they are black and sooty. I've leaned the carb out the most I can on idle circuit using the front screws. What's another step? Seems to run fine, would they be sooty due to just idling rather than driving with a load on it? How much total timing should I run, thinking maybe not enough timing causing an issue too..

Sorry for tons of questions just picking your brains.
Thanks

 

Elgin cam and lifter set $90 #E923M .420"/.443" lift

Idling can color the plugs, go drive it around some to clean them up.. Then make a WOT pull for at least 1/8 mile, shut it down and coast to shoulder of road and pull a couple of plugs and see how they look.

With that much cam, and that low of compression it's gonna want a lot of timing. 16-18* at idle w/o vac advance hooked up. For a total of 36-40*, plus add in the vac advance on a full vac source (not ported/timed) to add in another 15* or so

Set idle mixture screws with a vac gauge to the highest vac level you can get.

If you still need to lean out the carb, then it's a simple metering rod change. Look at top of carb, to the left and right you will see a "bump" sticking up with a plate and screw on top of each "bump"

The metering rods are under those, loosen screws, flip plate to side, rods will pop up.

Before you get into that though, check and set the timing, adjust mix screws with vac gauge and take it out and run it like I said.... The 1406 is already set pretty lean from the factory

 

Thanks for the precise answer. Always enjoy a straight to the solution answer. I will play with the timing for sure, since they put a balancer with a 12 noon mark and a timing cover with a pointer at 3 o'clock, might be off a few degrees with my made to match line on balance to align to the pointer area. Can I time with vacuum gauge too? Or just by numbers?

 

Your welcome..

You can time with vac gauge, I have seen it done but myself I like knowing for sure the timing in degrees as it helps to keep track of your testing, tune, and pin point probs easier.

But a cheap speactra, mr gasket, summit, etc $8-10 chrome adjustable timing tab.... Bolts on to engine using 2 of the timing cover bolts.. You can adjust the pointer/scale to line up with your 12:00 damper.

 

Really, I had always though that those would only line up properly for the 3 o'clock ones. Figured the bolt holes would line up to accurately set for noon timing. I'll have to Def grab one, I'm maybe assuming local auto parts stores might have one too.

 

Absolutely.
I'm a fan of full manifold vacuum for timing however all lot of tuners have trouble dialing in the vacuum can. It seems they haven't got a vacuum can that pulls all of the timing in a few inches of vacuum below what the engine idles at. The problem gets more complex as the idle speed changes with changes in idle timing. Lots of guys through in the towel at this point and opt for ported vacuum. Unfortunately they miss out on the benefits of using full manifold vacuum.
I use an adjustable timing can (one which adjusts the rate of the advance) in tandem with a limiter which adjusts the amount of timing. The combination of the two makes an excellent tuning tool.
One of the best additions you can make to your ride, especially if you're going to work on the carb tune to any extent, is to invest in a wide band O2 gauge. It makes short work of dialing in the correct A/F ratios.

 

Yeah my local auto zone and advance auto parts both has the adjustable and non adjustable ones on the shelf (down the "performance" isle). I'm pretty sure it's the spectra brand

 

Your talking the vacuum can on the side of the dist right? I have thought about getting an adjustable one, just didn't want to jump head first into something I'm not sure with. So basically I'm the stock form if I were to time the car using vacuum gauge it wouldn't come out right due to the engine not pulling accurate or full potential of the amount of vacuum at idle? Or am I getting confused. The manifold port on the Edlebrock is the one below the blades right? That's where my dist (when plugging in vacuum advance) and also the vacuum gauge should be hooked up right?

I will head up to my local advanced and check out what they have. I looked on summit to find something that looked like it'll work with noon timing and didn't see much, all looked like 2oclock pointers.

 

Here's how I've done it:
Correct amount of initial timing. As Night suggests, you could easily run 18° of spark lead. I run 16°.
Vacuum advance disconnected.
Idle mixture is adjusted so as to achieve the highest manifold vacuum. It's important to note here that the throttle blades can't be open too far and expose too much of the transfer slot. This often happens to tuners who can't get enough idle speed after setting the mixture and have to crank down the idle speed screw to get enough rpm. This inevitably results in an off idle stumble. It's a good idea to remove the carb, flip it over and verify the blades are set correctly. Then make a note of the position of the idle screw so you can keep track of it as you tune.
In my case, after all of that, my engine idles at 13" of vacuum. I've adjusted my vacuum can to have all of the advance available in by 11". I also have a limiter (as noted in the link posted earlier) to keep my total vacuum advance to 10°. The vacuum advance all in about 2" below idle vacuum is a reasonable set point. It's tougher for engines that only produce about 4-6" of idle vacuum. You could be one of them with the larger cam and low compression. You still want to target about 2" below idle though.
Here's a tuning method I use for full manifold vacuum advance:
With the engine idling and the vacuum advance disconnected, I use a hand held vacuum pump (like a Mighty Vac) and apply vacuum to the vacuum can. I can then observe via a timing light how much advance is applied and how much vacuum it takes to apply it. There's a lot of going back and forth because as you add vacuum advance, the idle speed increases. You have to keep the idle speed at your particular spec and repeat the test until you get what you're after. You can now see that's it's important to know where the throttle blades are and what position the idle speed screw is in relative to the blades.
You also need to know that the mechanical advance isn't entering into the picture as the speed increases. Some distributors are set to start the advance curve just above 1000 rpm. I went so far as to tie my advance springs closed so no mechanical advance was applied during the set up.
It's time consuming but the benefits are well worth the effort.
Smoother and lower idle speeds.
Crisp throttle response.
Increased fuel economy.
Lower engine idle temps.

 

Wow, I really wish you were local. Lol, there is a lot of awesome info there skinny z thank you. I'm going to atleast see what kind of vacuum I'm seeing at idle and go from there. Hopefully I can use your advice to its full potential. I did put more timing into the car at one point over summer and the car would heat up alot faster, I'm assuming it was to much timing. Think I set it to something like 38* all in, or something like that since my timing mark isn't exactly in correct location. To which I need to just get it marked correctly.

 

Absolutely. It might be useful to determine exactly where your TDC is although the timing tabs as suggested by Night should locate it for you.
It might also be helpful to install a timing tape to help with your tuning. Either that or invest in a dial back timing light.

 

Again I got to agree with Skinny. Everyone that plays with, works on, tunes, etc these cars or any other distributor ignition system car should have a dial back timing light. You really need to see your timing in numbers and see the full scale from idle to the maxed out timing point, and have a degreed damper, or damper cover, timing tape, or dial back light and a true tab/pointer is the only way to see that.

The main tuning tools that's a must have IMO are...
Dial back/advance timing light
Digital tach (a lot of the timing lights has this built in)
Vac gauge
Fuel pressure gauge
Compression gauge.

That's about $200 worth of tools that you will wonder how you lived with out them once you get and start using them.


Next step up would be a wide band O2 gauge.

 

I've been looking for a decent one and have come up empty. Any suggestions?


I can't imagine NOT having one.

 

Do you have a link to this dial back/advance timing light with tach? I have a timing light that I use and the marked marker on my balancer but it only goes to 12* BTDC which works for the most part.

I want to get a wide band 02 sensor but I don't have the couple of hundred dollars for one.

 

Here the timing light I have. http://www.summitracing.com/parts/ino-3568/overview/
Digital tach, Advance read out, LCD screen.

I have had mine for 12 years or so. Works great with all the ignition systems I have used it on. Points, HEI, CD (like MSD, Mallory, etc boxes)


For digital tach, all I have found was non contact laser types or multi meter types. Here is one that my buddy has
http://www.aliexpress.com/item/Autom...187967419.html

Here is another http://www.aliexpress.com/item/Autom...861216659.html

And here is a cheap harbor freight $35 one like the above http://www.harborfreight.com/lcd-aut...kit-95670.html

 

Yes yes and yes, I've been looking into all those tools for my personal collection. Heh. Just havnt had means to buy most of them. I have looked into a/f gauges and have seen this one here for the cheapest deal, it's a newer addition to summit:

http://www.summitracing.com/parts/fst-170634

I currently have a narrow band, but obviously it's not worth anything other than idle and wot I guess.
I have a dial back light, analog dial on it. Would love a digital one but the dial back has been ok for me.

 

You could try getting a timing chain that allows you to advance the cam 4* and see if that help. The sooner you close he intake valve the sooner your motor starts making compression. If your timing chain already has +4* 0 and -4* install the gear +4 and do another compression check. I like to see around 180-200 out of a motor. 145 average is low.

 

Okay, Skinny, I finally got you some actual cranking compression numbers for the combo below to enter into your database/spreadsheet. I checked the 3 easiest holes; numbers were 239 , 244, and 245 psi.
This was on a cold motor, after sitting since November, no oil sprayed into the holes, throttle open, all other plugs out, full charge on the battery.
Local barometric pressure is 29.04"Hg.
I believe you said your calculator said 230 psi; that's pretty close.

 

Holy smokes! Give me a little while and I'll reverse engineer your compression ratio.
I'll say this up front though, THAT'S what it's all about. Compression pressure is what makes an engine perform. (And we all know about your performance).
I'd like to know the cranking pressure of your daughters engine too.

 

After a 2nd calculation, yes, 230 psi is the predicted pressure. Keep in mind that the local barometric pressure isn't factored into the equation (and it really should be). I'm seeing a significant difference in performance from one day to the next depending on the pressure of the day.
Having said that, the calculator uses some basic assumption linking advertised duration to the intake valve closing point (which is something I believe we've discussed in the past). Of course, with cams that are better spec'd than the typical off the shelf grind (and given that you have a 108 LSA so I'll assume you did your research), the compression pressure results will be skewed from the calculators prediction.
Now to keep myself from making the same mistake I did in another post regarding cam timing, having a tighter LSA (108 vs 110) might close the intake a degree or two later, yes? That would account the better pressures you realize as opposed to what the calculator predicts.
At any rate, that's some mighty fine pressure you've got there and it encourages me to revisit my failed attempt at running 10.5:1 with iron heads and a 205 psi cranking pressure. I still think it's workable but will have to re-evaluate my testing procedures.

 

I fixed it for you The IVC event is more closely linked to ICL, but tighter LSA cams are generally installed with an earlier ICL, so your generalization of a tighter LSA closing the intake sooner is almost always correct.

 

Hey when I did my compression test I didn't have blades open and also didn't spray any oil and cold motor as well. What does that mean, my number would then be higher if I in fact did all those things?

 

Your readings were all between 140 and 150; that's pretty consistent, so I doubt spraying oil into the cylinders would affect your numbers much.
Holding the throttle open should make it read only slightly higher.

 

Which is something else the calculator doesn't take into account. The same cam, installed in a more advanced or retarded position will give different compression results.
However, as a general tool, it gives an idea as to what's what especially in a situation like the OP who hasn't all the build info needed to accurately determine the SCR or DCR.

 

If you can't enter ICL, then just fool it by entering (in my case) 103 LSA instead of 108. The erroneous exhaust events will have no bearing on the compression pressure calculation.
Or, if the program assumes some degree of advance instead of "straight up", then adjust that 103 number accordingly.

 

Hey guys, new things popping up.
so I changed from a 44ts to 45 ts plug heat range. I had car out driving around for a pretty good amount of time. Car ran fine, did alot of low rpm idling through neighborhoods (house hunting). As soon as I got it almost home I tried to get on it pretty hard and it spudderred and fell on its face. At that time, since I have a header gasket leak, I smell raw fuel pretty bad in the car. Could it be fouling now that I went to a hotter plug, I didn't get a chance to pull plug due to family plans yesterday. Maybe from to much idling cruising looking at houses. Or gap issue? Gapped them to .045.

 

No, there would be LESS chance of fouling with the hotter R45 plugs.
That gap is fine too. The plugs are not your issue.

 

Hmm, smelling raw fuel when it stumbled over itself I figured for sure it was the plugs being fouled. I've never idled/drove in low gear that long. Maybe that was my issue.
The car ran fine few nights before, pull wot pulls off line with no stumble what so ever, parked it went for long drive and now had the issue. I changed nothing.

 

I'm not saying your plugs are not fouling. I'm saying going from 44 to 45 plugs is not contributing to it.

 

Right, I gotcha. I'm going to actually have time to pull them tonight or tomorrow. Should I stay with the hotter plug? I did that since motor is low compression, figured no need for colder plug.

Side note:
I think I have a header gasket leak l, but I'm not seeing any place where it's blowing out.
Could my smell of exhaust be from my back tips being 3 inched back from the bumper of car? Maybe finding it's way into car that way?

 

Ya you could be smelling it from exhaust even though it is behind you. Check the color of your plugs. You might be on the rich side.

 

Yea I'm going to pull them and more than likely replace them. As far as exhaust I'm going to move tips further out.

 

What do you figure your "idling around in low gear" vacuum was and engine temps when you first got into after cruising about?
Consider what happens at higher engine vacuum such as would be the case with cruising in lwo gear. Very low pressure (high vacuum) in the intake tract and the fuel has little trouble staying atomized. When you stand on it, the manifold pressure rises to atmospheric (or zero vacuum if you will) and suddenly that fuel instantly turns back to liquid form and falls out of the air stream. A) The car falls on it's face with a lean stumble and B) that fuel that nows lays in puddles on the intake floor appears as that smell that your experiencing.
Bird is correct in the assessment that the move in heat range is not causing your trouble. It's more than likely the extended idle condition you put it through and then getting into it. As an experiment, try the extended cruise again but this time before you go for WOT throttle, "clear it's throat" so to speak some decent revs in neutral. Often at the track, after an extended burn-out, this procedure will help ensure (for me anyway) a clean launch.
I may be totallly off the mark in my diagnosis however the science behind the fuel dropping out of the airstream at the hit is sound. That's why we have accelerator pumps in our carbs and fuel enrichment in our EFI.

 

Bird and skinny, thank you!
After the low throttle cruising I did take it on freeway with almost wot throttle bursts no issues, just had the problem when was 1st gear wot after the freeway trot. Revs freely and fine too, but under load had that issue. I did not clear it out though, assuming that cleans plugs too, before doing wot pull. Think I need to change plugs? Or they will self clean with few revs?

 

In my experience it's more a matter of clearing the intake of the fuel that's dropped out and stabilizing the mixture ratio. Remember my thinking here is not that you're fouling the plugs with fuel but rather starving the cylinder for a proper mixture.
It's all just speculation as you've no indication of your A/F ratio. If you want to tune effectively with your carb, you should really consider the addition of a wide band O2 sensor. That and a dash mounted vacuum gauge. You'll learn a lot about your engine with those additions.
In the meantime, pull out a plug like Impalla suggests and report back (with pictures if possible). It'll be difficult to comment on anything other than what coloured them prior as any extended idling will remove whatever traces of a WOT throttle or cruise rpm might have put on them.

 

Maybe not a rich foul eh? Looking like it was a lean condition maybe. I did turn my regulator down a little bit, but I wot drove it with no issues before Sundays issues. Maybe it was just a case of not clearing it out first?

 

That plug is not fouled at all. The insulator would be covered with deposits to be fouled. It's nice and clean.

 

Carburetored engines can sometimes behave in odd and unpredictable ways.
That you describe never have done any extended "idling cruise" might point towards an odd set conditions where going to WOT just wasn't going to happen.
If you've adjusted your idle mixture to get the highest vacuum/idle speed and you have no stumble when you first crack open the throttles to pull away (part throttle) then is it's safe to say that your A/F mixture is reasonable and the carb blades aren't opened too far at idle speed. This might point to a combination of manifold heat and the vacuum you were seeing while "house hunting" and driving around slowly.
Keep on testing and cruising.
Plugs look good although by your account you haven't got many miles on them. If you're really curious try to duplicate your extended idle cruise but this time instead of going to WOT, shut it off and pull a plug. My bet is they'll look ok but you never know.
By the way, what kind of ignition timing do you have? Initial, total mechanical, vacuum (ported or unported source)...

 

I will give you a definate answer to timing either tonight or tomorrow. I "know" what the timing is, but I wanna double check before handing any bad data over to you. I did today use piston stop method to make sure that the mark I was using on balancer was in fact TDC, it was right on money. So I'll confirm what total, initial, mechanical timing is. I know that my vacuum is hooked up under blades of carb, so unported.

 

Your plug looks a little black to me just on the rich side. I agree with skinny a wide band is a great tool to have combined with a vacuum gage. I just ordered a wide band the other day for my car. I have to wait though on the vacuum gage cuz I just messed my car up and have to fix it I think I paid $160 for the wide band from AEM. It will take a lot of guessing out of tuning.

 

Plugs look good. Not fouled at all.

Heres a few little tips and tricks for you.

The ground strap of plug can be used to read heat range and timing.

The base ring of plug (part that ground strap is welded to) can be used to read jetting.

Look for color change on the ground strap, if the color changes closer to the welded on place, plug is too hot.

If color changes closer to the open end of strap, plug is too cold

Color should change at the half point


Look at the base ring of plug for blackness. You want 1 full turn of light colored soot for perfect jetting.

Max power would be alittle leaner than that.. Like 3/4 to 7/8 of a fuel turn of light soot, but run risk of running too lean.

If there is spots of heavy build up of soot, of dry soot on the top ring, jetting is too rich.

Do not look at the porcelin to read jetting!

The porcelin only will tell you of preignition/detonation which will show up as tiny black or silver specs/flakes on the porcelin


For timing look at the ground strap, at the base ring for a carbon mark. The carbon mark should be flush with the threads. If fruther down on the threads you have too much timing.

If higher up on the strap the timing is too retarded.

about 1/16" movement of carbon mark = 1 degree of timing.

********
You are a little rich.
Plug heat range looks to be right on
Can't see the back side of strap for carbon mark for timing

 

Night rider. That is awesome info. I'll yank them back out tomorrow and take a pic of the back of plug so you can see the back of the strap. I've never heard of it broke down like that, most say to read porcelain . Being new to carb timing I'm new to all this.
More info to come tomorrow

 

My question is: Based on reading plugs, a what point in the engine cycle are you actually reading? If you make a WOT pass, kill the ignition and then pull a plug, I get it. You're going to look at the plug after a WOT pass.
However, if you've got a pile of mixed driving, then idle along to a stop and pull a plug, what are you looking at?
We all know from tuning carbs, that an A/F ratio can be all over the map. Just watch your wide band gauge as you drive around. Mine is from 11.5:1 to 17:1 depending on whether on the throttle half way, all the way or coasting from 5000 rpm.
Plug reading, I will admit, is something I don't do other than perhaps pulling a plug for a look and seeing something that's obviously not right.
Having said all of that, I will check my own plugs (as I'm in the middle of a major tuning thrash....go figure) and will try and correlate what Night has offered compared to what I'm getting from my data logger. The heat range aspect is particulary interesting to me as that's something a data logger or wide band can't tell you.

 

Your welcome. Yeah I was taught that method of reading plugs many years ago (in fact I was a child when I was 1st told that info). I have used it ever since then to jet and time by and has always worked for me. I get pretty close to the same results doing it that away as jetting for max trap speed at track or using a 02 sensor and a/f gauge.

The big diff though is you can ONLY see/tune one thing, where with the wide band 02 a/f gauge you can see and adjust your idle, cruise and WOT jetting.

The only true way to read the plugs for jetting is by making a WOT pass, shut engine down, coast to a stop, pull a plug and read it and adjust as needed.

Because if you read the plugs after you have been tooling around, it could show you are rich, then you run and swap out jets and now it's right, but at WOT it needs more fuel and now you run lean at WOT.

Keep in mind each circuit of the carb can be adjusted independent of each other.

If you are rich idling you don't change jets.. You tune the idle circuit.
Same goes with the primary and secondary circuits.

The edelbrock carb you have metering rods that has a stepped design, step up springs, prim. jets and sec. jets

The step up springs are what moves the metering rods up and down. They are rated by inchs HG vac.

The metering rods fits down into the prim. jets. Under light load, high vac, cruise the biggest part of rod is in the jet limiting the amount of fuel going through

As you increase the load, the vac level drops, and the step up springs lifts the metering rod up, so now the smallest part of rod is in the jet and the amount of fuel that can pass through is not as limited

As you go WOT, the metering rods are up, and the air valve opens for the sec. side of carb and you get fuel through the sec. jets as well.

This is not a full detailed log on how the carb works, just the basics to give you some idea on how you can change each circuit

They make 5 diff step up springs (3" hg, 4" hg, 5"hg, 7" hg, 8" hg)
Around 20 diff jet sizes
Around 30 diff metering rod sizes/combos

 

Sweet, thanks.
So if I have low vacuum already due to larger cam, if I continue to have issues, should I be thinking of a spring change to one that takes less vacuum to spring open.
I'm going to yank the plug again for strap image in a few.

 

Am I seeing this right. Carbon mark is way at the tip almost, means not enough timing?

 

I can't see the timing carbon mark on the plug on the right, but on the one on the left it looks like mark is up higher than the threads.. So that would mean your timing is too retarded... Measure the space from carbon mark and 1st thread at very top.. Add X amount of timing based on the 1/16" = 1 degree.

You are correct on the step up springs.. Step up springs pretty much does the same thing as a power valve in a holley carb and is tuned in pretty much the same way.

Check your idle vac in gear (after getting timing and air fuel mixture screws set right) and half of that reading is the spring or power valve you need.

If you have 10" hg vac you would use 5" hg step up springs or power valve.

This is one of the main reasons I swapped over to a holley HP carb on my new engine combo. My setup only idles at 3-4" of vac and edelbrock don't have a 1.5 or 2" spring.