340 camshaft question, yea another one.

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bobscuda67

bobscuda67

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Due to some great weather last weekend I have my engine stripped down ready to pull the cam.
I think I can pull it out with out removing the grill.
It has a XE 274 and it's not working, thanks Comp Cams tech line.

What I have is a 340 with a 3.58 stroke and stock rod.
It has a measured 9.9 static compression ratio.
Magnum heads with stock valve 120 seat and 300 open spring pressure. Also 1.6 roller rockers.
AirGap with a 650 carb.
Not so good is I'm using 340 exhaust manifolds with 2 1/4 inch dual system.
And a 2200 stall converter with a 3:55 rear gear. The 904 trans has a low gear set with a 26 inch tire.

I'm thinking about 4 different cams.
Lunati Voodoo 256. 8.26DCR
Lunati Voodoo 262. 8.03 DCR
Comp XE 262. 8.21 DCR
Hughes SEH 1620. 8.54 DCR
This is street only of course and the torque curve is the most important thing to me.
Should I try and keep the DCR as high as I can or is it not that important?
Does it even make any difference?
 
oh no...not this again! lol
i would think the Voodoo 262 or similar would be hard to beat for a street build.
 
You might want to consider consulting someone like Shady Dell Racing, Dwayne Porter, Bob Karakaschian, etc. and discuss with them your combo and goal. I have 3 of Bobs cams, "Stock A12", "Stock 71-440 6pack", and a stage 2 cam for a 340/416 stroker with stock heads and exhaust. All from Bob K. 340 isn't done yet, but the other 2 run excellent. When spending 300-400 on a cam combo, for a second time, call some of the racers who build engines.
 
Good point, are there other issues? Timing, valve adjustment, trans/gearing, etc. XE274 isn't that hot of cam.
 
Whats wrong with the XE274H? I run that in my 340 and it's a great cam. Good down low torque. Pulls hard past 6k rpm.

I will say this, your stall seems a little low no matter what cam you end up with. And I'd get headers, 2-1/2 exhaust, and a 750 double pumper on there.
 
Thanks all.
The converter stall is way to low and the stock exhaust isn't helping.
Slipping the trans in neutral at every stop sign gets old and the cylinder pressure is low too.
I'll never put headers on it as I have way to much invested in the manifolds and the Accurate exhaust system.
 
bobscuda67 said:
Thanks all.
The converter stall is way to low and the stock exhaust isn't helping.
Slipping the trans in neutral at every stop sign gets old and the cylinder pressure is low too.
I'll never put headers on it as I have way to much invested in the manifolds and the Accurate exhaust system.
Click to expand...

So what is wrong with the XE274H? Why are you putting the trans in neutral at the stop signs? Why is cylinder pressure so low? You should have 150PSI or more with that cam. Depending on elevation and if it really is 9.9:1 compression.
 
Cam in retarded, bad ignition timing event, too long pushrods are the things that come to mind for what described.

A leaky PCV or small vacuum leak elsewhere as well
 
Yeah Ima thinking the tune is off.
And whatever else you put into it, the tune will still be off.
And if that is so, then the new smaller cam will still be needing a tune.

Reading between the lines, it seems that your engine does not idle that well with the 274. Heck that is an easy tune. My 276/286/110 will pull down to 550 and pound pistons there as sweet as can be.
But if your TC is pumping oil, at your chosen idle speed, I can see a conflict right there. Mine's a stick,so I don't have that problem. Mine idles at 700/750 all day long.
I agree that HAVING to slip it in and out at every stoplight would get old for me in just one afternoon.

If it's not too late, we are here to help you put a tune into it.
 
bobscuda67 said:
Thanks all.
The converter stall is way to low and the stock exhaust isn't helping.
Slipping the trans in neutral at every stop sign gets old and the cylinder pressure is low too.
I'll never put headers on it as I have way to much invested in the manifolds and the Accurate exhaust system.
Click to expand...

Have you done a compression test?
 
I'd just go with a smaller cam and recheck everything before I did. The XE274 is a little large for the combo and for being docile enough for a great driver considering the described package.
But it does sound like there's more to the problem.
 
i agree...the 274 is too big for your gears and converter.
A grind with around .220 duration but keep some lift would work better
and probably get good mileage.
 
Yes, with the XE 274 the cylinder pressure is around 155 psi. About 20 pounds too low. That cam needs 165 psi to work well. My engine has a DCR of 7.87 right now and is soft down low.
The cams I listed have a earlier intake closing point and have a higher DCR.
I'm just wondering which cam I listed would work the best for me.
 
With your given numbers, the cam appears to be in at 108.
Advancing it 3 degrees might pull the Dcr up to 8.0@160psi
That would get you a pretty good comparison to your other choices. Depending on your Squish, iron heads and over 8.0Dcr, might require a high octane to run, without detonation.IMO, 8.0Dcr might require 91 to survive. That means from your choices, only the 262Voodoo might work, and it might even work on less than 91. But check it out; you can easily retime your current cam to make that number. So swapping cams basically your time and money, and the engines power, would sorta be wasted? Poor wording but you get the idea.
So really verifying the current installed centerline,and/or advancing it several degrees is what I would be doing SECOND.I mean it's 3 or 4 hours to find out if your engine will accept 8.0Dcr
Really it's the 2200TC that is killing your off-the-line grunt, and that should be the FIRST to go ;and then the tune. That cam should easily idle down at 650in gear.
I have had great fun with a 2800.In a teener even, with a Dcr around 7.0. The same tranny and gears as you have, and it would light up both rear tires. Now I'm not quite sure what tires were on there, but I'm thinking they were 255/60-15s( that was in the early 2000s). They might have been a tad bigger,but I just can't remember.
 
AJ/FormS said:
With your given numbers, the cam appears to be in at 108.
Advancing it 3 degrees might pull the Dcr up to 8.0@160psi
That would get you a pretty good comparison to your other choices. Depending on your Squish, iron heads and over 8.0Dcr, might require a high octane to run, without detonation.IMO, 8.0Dcr might require 91 to survive. That means from your choices, only the 262Voodoo might work, and it might even work on less than 91. But check it out; you can easily retime your current cam to make that number. So swapping cams basically your time and money, and the engines power, would sorta be wasted? Poor wording but you get the idea.
So really verifying the current installed centerline,and/or advancing it several degrees is what I would be doing SECOND.I mean it's 3 or 4 hours to find out if your engine will accept 8.0Dcr
Really it's the 2200TC that is killing your off-the-line grunt, and that should be the FIRST to go ;and then the tune. That cam should easily idle down at 650in gear.
I have had great fun with a 2800.In a teener even, with a Dcr around 7.0. The same tranny and gears as you have, and it would light up both rear tires. Now I'm not quite sure what tires were on there, but I'm thinking they were 255/60-15s( that was in the early 2000s). They might have been a tad bigger,but I just can't remember.
Click to expand...

I have the cam out now. But when I installed it, in 2014, I remember it was dot to dot and it was at 106. Right at the cards spec.
The engine idled at 850 in park with 15 inches of vacuum and would just about stall in drive. Of course the magnum heads are closed chamber and with a zero deck and .038 head gasket the squish is near ideal.
The converter does suck and I might change it this spring if I can physically do it. I can get under it but I can't get back up.
 
bobscuda67 said:
I have the cam out now. But when I installed it, in 2014, I remember it was dot to dot and it was at 106. Right at the cards spec.
The engine idled at 850 in park with 15 inches of vacuum and would just about stall in drive. Of course the magnum heads are closed chamber and with a zero deck and .038 head gasket the squish is near ideal.
The converter does suck and I might change it this spring if I can physically do it. I can get under it but I can't get back up.
Click to expand...


If your T-port sync is correct,and the idle timing is between 12 and 16 degrees, AND the idle speed is in excess of 700ish; then something is wrong.The engine is likely pulling air in somewhere other than the carb. And that air has no fuel in it. So the engine is looking for an excuse to stall.A sudden decrease of airflow past the idle discharge ports might be all it takes.So even though the TC might seem to be the culprit, the reality is that it might just be the sudden drop in fuel supply,due to an already lean idle mixture.
So, I just can't stress this enough;that the T-port sync has to be correct, and the in-gear idle speed has to be low enough, so that the TC is not chomping at the bit. Then if it still wants to stall the TC is just too tight. I can see no reason why that that cam should not idle at 650 in gear with the correct idle-tune. I'm pretty sure I could get down to 600/650 in gear and happy to be there.
All too-often a fella might crank 20/25 degrees of idle-timing into it (for some unknown reason,lol),and then has to back the idle screw way out to get a slow enough idle speed. This puts the T-port sync so far out that the engine will do just what you describe, for lack of fuel flow when the airspeed drops.

The following test Assumes that the T-port sync and idle-timing are correct, and that the idle speed is about 750 in neutral, or a little less;
Jack up the rear and secure on jack stands. Warm up the engine. stick it in manual low, and let the tires spin up. As soon as the engine stabilizes, slowly start breaking the wheels to a stop. If the engine stalls, or wants to, buy a new TC. If the engine accepts this, put it into neutral. Apply the brakes hard, and put it in low. If the engine stalls or wants to, it's probably cuz the TC is too tight, and the airspeed drop through the carb was too abrupt. Lower the idle speed and try again.If lowering the idle speed doesn't work, crank in more idle-timing, and try again.. If it still stalls, buy a new TC.
But I'm still wondering why you chose an 850 idle-speed. The 15 inches of vacuum says to me that she could idle a lot slower. However, if that is the speed it took to prevent a stall when going into gear, with a correct T-port sync and idle-timing, then that is added proof that either the engine is pulling in dry air somewhere,or the TC is just too tight.
So once again we are at a crossroads; is it the idle tune, or is it the TC?
The idle-tune is by far the cheapest and easiest to prove.
If you put a smaller cam in there, it will have more idle torque, so it may pull that tight TC. But if you again try the same idle-tune that is currently in it, it is every bit as likely to stall.
 
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My timing is set at 16* initial, mechanical is 18* at 3400 and the vac can is 14* at 14 inches. I have it connected to manifold vacuum so it had 21* total at idle.
I have been looking at the stock 340 cam for my car, I'd be fine with that.
 
bobscuda67 said:
My timing is set at 16* initial, mechanical is 18* at 3400 and the vac can is 14* at 14 inches. I have it connected to manifold vacuum so it had 21* total at idle.
I have been looking at the stock 340 cam for my car, I'd be fine with that.
Click to expand...

There it is
The 21 at idle is killing it. Put that Vcan back on the spatk-port, the 274 is waaaay too small a cam to be able to run that way.
When you remove the vcan the idle speed will drop, then when you put it into gear, there won't be as sudden nor as huge an airflo decrease through the carb nor will there be a sudden drop out of timing due to the Vcan backing off when the manifold vacuum drops.
That's probably the biggest contributor to your problem.
If you remove the carb right now and flip it over you will probably see the T-ports as good as covered, and SHAZZAM that is the problem! That is exactly what I've been talking about. Now go look! If I'm right, put that 274 back in!

Now heres the deal with the factory 340 cam, listen carefully; IT WILL NOT MAKE ONE SINGLE BIT OF DIFFERENCE
And here's why. Your 274/110 cam in at 106* has an ICA of 63*, and
the 340 cam is 268/114 in at 110 has an ICA of 64*
Exactly 1 degree later, so the idle torque is likely to be exactly the same! Now the 340 cam will idle slightly smoother on account of the overlap is only 44*.
But sliding one in there will make ZERO idle difference.
 
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The transfer slots are a square looking at the bottom of the carb. Had to drill holes in the throttle plates to get it there on a Edelbrock 650.
And yes the idle was at 850 to keep it from stalling when put into gear. I know the converter is a large part of the problem. I did the jack stand test last summer and you called it. The engine wanted to stall when coming to a stop.
 
OH JEEPERS, get rid of those holes!OOps wait

OK heres what is happening
With the Vcan hooked to fulltime vacuum, it is pulling in; 21 less 14 initial equals 7 degrees right? When you put it into gear, manifold vacuum drops. This causes perhaps all of those extra 7* to disappear, depending on how fast vand how low the vacuum drops. Now the engine is trying to idle on the 14*. But the loss of the say 4 to 7 also means the rpm just dropped down too!
At the same time,the engine is pulling air through those holes. That air should be traveling past the idle discharge ports, and getting loaded up with fuel. But it's not, is it? Check your idle mixture screws. They should be at about 1.5 turns out from lightly seated. If they are out at say 3 turns, then you need more T-port exposure. See those mixture screws are there to augment the transfers. The transfers are your low-speed fuel delivery system. The mixture screws are just there for idle enrichment compensation. When airflow drops past the transfers,the fuel flow slows down and if there's not enough,between that and the sudden loss of the Vcan timing, the engine complains right quick.
So we have to figure out a better way to give the engine the air it is craving.Holes through the plate can work, but IMO the 274 cam should not require that. So the next question is :Are you running a PCV system? The PCV is your idle-air bypass, so it must be there. The carb was designed for it to be there.
So where did you drill the holes and how big are they?
 
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my point was exactly that your cam is like a stock 340 cam, and the 340 converter was around what you have
 
There are TWO ways to control your idle speed; Throttle opening and timing. But no matter which you use, the engine wants the right amount of fuel.
To illustrate this, I have run engines with empty carb bowls, by spritzing fuel down the barrels and holding the throttle open. I have also started engines with no carb on them at all, again, with a spritzer. If you have ever started a flooded engine by flooring it, you have done a similar trick.
On an idling engine, you can grab the dizzy and pull a lot of timing into it. And the more you give it the higher the rpm climbs,until the engine complains about too much. And you can dial quite a bit out, before you have to compensate with throttle opening, and eventually it will not be enough timing.
Your task is to find the sweet spot. And the starting point is to get the T-port sync right. Once the sync is pretty close, you only have timing and bypass air to work with.
It looks to me, that you know all about this. But it seems the tune is not quite right. Once the Sync is set, you must not vary the rpm much with the curb idle screw. The idle speed must be set with timing and bypass air. Did I just echo that? And I think this is where your tune is failing; well that and the 7* timing drop-out.
So it's unfortunate that the cam is already out
 
You have 16 initial and 14 in the can hooked to manifold vavuum?

If that's the case the car is likely getting 14* of timing pulled out when it goes in gear. Just a guess the engine would want at least 20 initial BEFORE any vacuum can timing was in play.

No way should that engine idle at 850 and die when put in gear if it has 16+ initial timing. Nor should the carb need bypass holes drilled in the plates. IMO, the camshaft is NOT your problem.
 
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