Here's the specs :

4 bolts 350 to 355
ported (just cleaned the casting, no modification) 906 head with ARP 3/8 studs
Compcam 280H (268 duration 480/480lift)
+350 pushrods
1.6 valves
1.5 1.6 rocker (1.6 intake)
Edelbrocke RPM air gap
Holley DP 600CFM
MSD Streetfire
Acell 8.8MM wires
Vortec ACDELCO sparks plugs

EVERYTHING is brand new.

Engine is idling by itself but when I put it on the road it push like a 4 cylindre engine...... No strumbles, but I ear tictic like engine is detonaning on the intake (timing at 36 degres)




I've read that on the MSD street fire we can adjust vacuum advance with a Hallen key?

worn cam?

 

For those heads, that's a very poor cam choice, at best; and the rocker arm split you are using just makes it worse.

The virtue of those heads is their INTAKE flow. They have all this great intake flow from their re-designed intake ports, but the same crappy exhaust ports as any other stock heads. Therefore the CORRECT cam choice would have been one with a MUCH bigger exh lobe than intake, both in lift and duration.

You can partially work around the mistake in cam choice by swapping the 1.5 rockers to the intake and the 1.6s to the exhaust.

On the other hand, stock Vortec heads won't tolerate that much lift. The bottom of the retainers will smack into the top of the valve guides at somewhere between .460" and .480", given the variation in casting and machine work among individual heads. How far did you cut the valve guides down? If you didn't do SOMETHING about that, the noise you are hearing is probably the retainers pounding on the top of the guides, and/or the push rods bending.

Vacuum advance coesn't affect "power". It affects cruising fuel economy. That's not the problem. Leave it alone.

Start by verifying that there is no mechanical interference caused by 2 pieces of metal trying to occupy the same volume at the same time; then partially fix the extreme parts selection mismatch by swapping the rockers; and go from there.

 

Thx a lot my friend for the great response...

The head are modifed


We checked more than twice if the valve reteaner is near to hit the valve guide. No problem.

Why it would it the valve guide only when the engine is on load??

Thx I can buy a new cam but the stall is a 2400.

 

Even with a relatively poor selection of parts (not catastrophically bad, but not ideal), you should be making at LEAST 250HP, without trying too hard. That's a HEALTHY V-8, nothing like a 4cyl. Something is seriously wrong.

- How did you measure to make sure the intake retainer wasn't bottoming out? Did you compress it .530" and measure the gap between spring coils? and without a spring installed, between the retainer and valve seal?

- Try idling the car and removing the valve covers. If a rocker arm is loosening off, or a stud is pulling out (likely), you'll be able to see it while it's running. Or shut it off and run a straight edge over the studs.

- You can also use a temp gun (or the back of your hand), across your headers, and see if any of them are cooler. That's a good indication that that hole isn't firing.

- If all of those check out (but I kinda doubt they will ... ) then check ignition. Back down to 32* timing (base+mechanical). What is your vacuum advance set to? amount, & manifold or timed? Is your balancer verified to show 0* at TDC? You could be actually much lower.

- Vortec intake manifold right? Have to ask....

 

did you break in the cam to spec? Im thinking you did just making sure, did you degree it, dial in your cam? I wish ya luck, good build!

 

Thx a lot for the help !



Yep with the Compcam oil and specs.

Dial my cam?

Thx !!!

 

Back when I changed the timing cover and tab, I checked this too. Found tdc with a piston stop, and the timing tab zero missed the balancer mark by 5 degrees. Had to bend the tab quite a bit to make the zero's line up.

Then I ran myself up some timing tape in CAD, and stuck it on the balancer. Even though the zero on the tab and the tape was equal, when the balancer mark lined up with 15 advanced on the tab, the tape showed 18. I'm trusting my tape, only using the tab for the zero reference now.

 

I think Sonix has it right.

 

Pre-fire? That sounds like your timing is off. You seem to have checked the timing right, but the signs still point to it...

Far enough from the seal? Ok, try pulling your valve covers, that's easy, and running the engine with them off. Keep it at a low idle, or you'll have an oily mess everywhere. Listen for a ticking, or one that "looks funny". It might be very obvious.

Retainer - The gizmo that holds your valve spring in place. I'm not talking about the "guide plates". Those - you are right, you don't need if you have self aligning rockers.

- Vacuum timing is fairly important. Try disabling your vacuum advance and recheck your timing... Go without it for a while, set up your performance first, then you can add it back in later.

 

Both sofakingdom and sonix make very good points. I'll add a few thoughts. How's your fuel pressure? You need 4-7psi and may need to stay closer to 7. The detonation could be lean AFR. That would also explain the lack of power. Another issue you may have is reversion through the intake from insufficient exhaust valve lift or a restriction in the exhaust system. Where did you set the lifter preload? You shouldn't go over 1/2 turn on any motor that will see 6,000rpm. Are you running enough spring for those lobes? You need atleast 125lbs seat pressure and probably 350lbs minimum open pressure.

 

Or maybe overfilled with oil (power loss, not the ticking).

Might do to hook up a vacuum gauge and see what that tells you.

http://www.earlycuda.org/tech/vacuum2.htm

 

Ok here's where I'm I now.

We changed the rockers for 1.5intake, 1.6Exaust

I had timed the engine to 36* @ 3000RPM with automatic advance unplugged

So we timed it 34* @ 3500RPM TOTAL

Sparks plug are gapped 0.60 (stock for vortec heads)

So we began tuning the carb. The engine was incredibly responsive.. but after the engine reached 180* the fuel pression dropped and never wanted to go up 3PSI IDLE and the engine become lean....


When the car had became cold ( less than 130) the fuel pump wanted to put 6PSI at IDLE.. then the engine reached 180* pump didn't want to shoot more than 2PSI and didn,t go up with more RPM on the engine.

I also fit a temporary fuel line...

ATM, I have buy a new Holley 110GPH mecanical fuel pump, fuel lines, fittings, gaskets.

We will see


Thx for the help.

Oh and the compression test gave me 125 on all piston and the piston leak test was good on every piston.

 

125 is rather low, but the consistency is more important.

 

Vapor lock issue? Mine used to suffer badly; a makeshift heatshield between the fuel line and manifold mostly sorted it.

 

Since you are in Europe and don't say what units you have 125 compressions of, I'll defer judgment on whether that's "good" or not.

However, with that cam, the reading on a gauge will be MUCH lower than it would be with, say, a stock cam.

Timing should be about 34° @ 3000 "total"; and the vacuum advance should then give about 12 - 15° more when plugged back in. With that cam, I'd aim for a timing curve that started at about 18 - 20° at idle, increasing to 34° starting at about 1200 RPM and reaching 34° by about 2800 RPM; and then the vac adv on top of that, as mentioned.

 

I just got the pump.... we will see !

 

Do you have a return style pump? Are you pressurizing your intake line (pump in tank or in line as well?). I'm not sure if vapor lock would show up as a lower pressure, wouldn't the pressure stay the same, but the medium in the line would be a vapor rather than a liquid?
However the temperature related fuel pressure seems to be a good giveaway. Lets see what the pump does, that's a really easy swap.

 

Good point, not sure either, I never measured the pressure in the vapor locked condition.

In this case, is the pressure being measured at the carb inlet, or before the mech pump?

 

Vapor lock will show as reduced pressure because the pump is trying to pressurize vapor. I would certainly use a pump with a bypass return(three port pump) or just use an inline filter after the pump with a vapor return. This allows the pump to constantly move fuel through the lines to prevent heat soak and resulting vapor lock. Also, route lines away from the exhaust. Be sure, of course, that your line from the tank is atleast 3/8" with no restrictions.

 

ok valve where not correctly adjusted , I also changed the old pump for a brand new one (holley)


But I have !AGAIN! a problem....

Do i need to adjust the amount of vacuum on the canister of my Streetfire Hei distributor???

When we buy it does it have the screw closed ?

We timed the distributor at 34* 3500RPM with vacuum advance plugged.

but it seems that I can give a lot more advance and the car run better :S

 

I don't know how many times I can say this or how many different ways there are to say it:

You should have about 36° of advance at high RPM WITH THE VACUUM ADVANCE DISCONNECTED.

With the cam you have, you should probably have about 20° at idle WITH THE VACUUM ADVANCE DISCONNECTED; the timing should begin to advance basically as soon as it comes off idle, say, at 1200 RPM; and it should reach the full 36° described above by around 2800 - 3000 RPM.

Vacuum advance should be set up to give about 12 - 15° IN ADDITION TO the above 36°. It should be active at any realistic cruising vacuum, and should drop out when vacuum drops to a point where a significant power demand is indicated. Its purpose is to improve cruising efficiency, not power output. It can probably be tuned by observing for spark knock.

Vac adv can be connected to either "ported" vacuum (active only when the throttle blades are moved off idle), or "full" vacuum (exposed to vacuum regardless of throttle position). Experiment; this is a tuning selection, not a "do it this way no matter what" type of thing.

If the engine runs better with more (or less) advance, GIVE IT WHAT IT WANTS. The engine does not read books, post on the Internet, look at timing marks, or any of that. Don't outsmart yourself. Remember: IF IT RUNS GOOD, IT IS GOOD.

Can't help you with how the particular distributor you have, comes from the factory. Turn the screw and see what happens. If you like it, turn it some more. If you don't, turn it back, and then a little more. Repeat until no further improvement can be obtained. It's called TUNING.

 

Can I try 34* at 3000RPM without advance and not plugged it until I get tuned by a professional?

 

What's that?

Sure, you can try 34° instead of 36°. Then you can go back and add the missing 2° later.

If your dist didn't come with a selection of springs and weights to calibrate it, get this kit right here.

http://www.summitracing.com/parts/CRN-99601-1/

It will have everything you need to tune your curve.

I'd suggest, to make it easiest, that you FIRST determine WITH ABOLUTELY POSITIVE ACCURACY that your timing mark is exactly in time with the motor (i.e. reads 0° when the #1 or #6 piston is EXACTLY at TDC, as determined by some independent ACCURATE method such as a piston stop); and then, if the mark is off, make a new one at 0°; and add marks at 10°, 20°, 30°, 40°, and 50° BTDC, so you don't have to use a "dial-back" timing light since those are NOTORIOUS for being INACCURATE.

Using this instrumentation and the kit, set your advance curve up as I described: 18 - 20° of "static" timing, centrifugal advance starting at about 1200 RPM, bringing the "total" timing to 36° (or 34° if you want to leave some room for further improvement later) at 3000 RPM; and set the vacuum advance to give 12 - 15° on top of that, set to drop out as soon as the vacuum starts to drop in response to engine load. Vac adv is strictly for cruising, and should disengage itself for "power" operating conditions.

In case I didn't mention it, ACCURACY is important in this procedure.

Not sure where "a professional" would fit into all this...