[Steve70GTO]

Originally Posted by Cliff R

+2

The cam used is a BIG player with the 455 and those heads on pump gas. It will pound like SLEDGEHAMMERS with a Comp XE262 or 268 in it and "normal" timing fuel curves.

I've had two 455's in here over 9 to 1 compression using that cam, and one used the HR version of it, XR276HR, and both pinged EVERYWHERE unless we pulled a ton of timing out of them, and ran like crap as well......FWIW.....Cliff

Thanks Cliff ... I have a feeling this is the problem. I am going to try the easy stuff first ... then if I have to change the cam ... I may just pull the whole engine and take it to Butler and have the whole thing done over.

[Cliff R]

LOTS of opinions out there on cam choices for these engines. I would avoid anything with "short seat timing" events or tight LSA's, at least if you plan on using pump fuel and have over 9 to 1 compression.

Cams with short seat timing and tight LSA's advance the intake lobe position and increase cylinder pressure. The tight LSA also narrows up the power curve, and spikes dynamic compression higher earlier in the rpm range. Both of these things will increase octane requirements all else being equal.

If you are building a 455 with pretty high compression, go with a long duration cam on a wide LSA. The higher compression offsets the loss of compression from later intake closing and longer duration. The bigger cam now comes in and makes a broader torque curve, with peak torque higher in the rpm range. This works for us as far as octane requirements.......Cliff

[Steve70GTO]

Originally Posted by PontGuy

You haven't mentioned the cam- do you know what it is? Also except for the ping does the engine run smooth? Any significant oil usage or blow-by?

My TA 455 has 5C-4 heads so should have the same size chambers. And flat top pistons, so high compression (pumps 175-180 on all cylinders). I have documentation showing it has a CC XE268 cam and if you read through threads here the cam is not recommended for this combo due to the very short seat duration. But backing down the total timing to around 30 without vacuum advance does eliminate the ping under heavy load.

You are saying your engine still pings backed all the way down to 16 deg total. Based on my experience that should not happen even with a poor cam selection. One more time- get CR readings on all cylinders to confirm the valve train is OK and a head gasket is not broken. I am having a hard time believing that A/F could cause that bad a pinging problem all by itself unless maybe it is way, way off. Still worth taking a look at due to the questionable e-carb though.

FYI my other 455 has similar size chambers and C/R, also pumps 170-180, but absolutely no ping even with an aggressive timing curve. Biggest difference is the cam has much longer seat duration.

I don't know what cam is in the motor but it sounds mild. Idles smooth at 700 rpm. I am putting a compression gauge on it today. Also a vacuum gauge and I am going to put a piston stop on it and test TDC to see if the harmonic balancer is OK.

[Steve70GTO]

Originally Posted by PontGuy

You haven't mentioned the cam- do you know what it is? Also except for the ping does the engine run smooth? Any significant oil usage or blow-by?

My TA 455 has 5C-4 heads so should have the same size chambers. And flat top pistons, so high compression (pumps 175-180 on all cylinders). I have documentation showing it has a CC XE268 cam and if you read through threads here the cam is not recommended for this combo due to the very short seat duration. But backing down the total timing to around 30 without vacuum advance does eliminate the ping under heavy load.

You are saying your engine still pings backed all the way down to 16 deg total. Based on my experience that should not happen even with a poor cam selection. One more time- get CR readings on all cylinders to confirm the valve train is OK and a head gasket is not broken. I am having a hard time believing that A/F could cause that bad a pinging problem all by itself unless maybe it is way, way off. Still worth taking a look at due to the questionable e-carb though.

FYI my other 455 has similar size chambers and C/R, also pumps 170-180, but absolutely no ping even with an aggressive timing curve. Biggest difference is the cam has much longer seat duration.

Aside from the pinging the engine runs great. No blow-by and no smoke at all.

[steve25]

That's good, now get rid of the Ping issue and it will stay a good running no oil usage motor !

[rtanner]

Originally Posted by Steve70GTO

Wow. Thanks for all the info. I am not sure how to tell the difference between 6X8 or 6X4 heads. Regardless ... I am putting 93 octane ... should not be pinging like that.

I don't think the cam has a flat lobe ... doesn't sound it.

I will put a vacuum gauge on it this weekend to see if their is a bad head gasket.

The plugs look fine. They don't look like the car is running lean.

I will get the number off the carb too.

In my last car it did the same thing. Turned out the cam was installed wrong. I put in a stock ram air 3 cam and it ran MUCH better. I really don't want to do a cam swap on this.

your fising to the same thing w this car

[Steve70GTO]

OK ... I guess my friend's compression gauge was broken. I bought a new one and these are the readings I got:

1 190
2 170
3 175
4 170
5 165
6 175
7 170
8 175

#1 hole seemed to be an outlier so I tested it again and got the same thing = 190.

So ... the compression seems to be higher than I thought.

Also put on the vacuum gauge and I have 11" at idle in drive ... in neutral have 14".

When I get on the throttle it it detonates and the vacuum is around 5".

I should also mention that I still have it at 6 degrees initial and with not much advance in the distributor. 20 degrees total at 2,000 rpm, 22 degrees at 3,000 rpm.

You guys think that compression is on the high side? What would you think that comes to? over 10 to 1? 11 to 1?

With 6X heads how can the compression be so high? Would the cam grind affect the compression gauge reading?

Maybe the previous owner put in different pistons?

Whatever input you guys have would be appreciated.

[jonmachota78]

the high pressure on #1 can be caused by a colaplsed lifter in the intake, or (worst case) missing lobe, causing early closure of the intake valve. Or if your're lucky could just be that lifter is not pumped up all the way. at this point you may want to pull the driver side valve cover and start it to make sure that pushrod is spinning

[PontGuy]

Except for the 190 cylinder the numbers look very reasonable. Agree that it is worth checking the valve train to see why that one cylinder is so much higher than the others. Could very well be the cause of your problem.

Yes the cam selection will affect the readings (and tendency to ping) since compression starts when the intake valve closes. In general the higher the compression, the more duration is needed in the cam to keep it from detonating. There is a lot of science to this and I am not an expert- plenty of real experts posting here though.

[Tripower455]

Keep at it Steve! These guys will get you straightened out!

[PontGuy]

I figured some of the real experts would jump in by now but I'll take a shot with some suggestions.

First thing I would do is pull the valve cover, rotate the engine by hand and watch the rocker on the #1 intake lobe. It should "look" like the others as it cycles. If the cam lobe is going flat it is usually pretty obvious that the valve is not lifting all the way. If still not sure then you could run the engine with the valve cover off to see if the pushrod is spinning, but that makes a huge mess unless you have a spare valve cover cut or some sort of deflectors for the oil. Instead of doing that I would go ahead and pull the intake and valley pan, and take a look at the cam lobes and lifters to make sure all are OK.

Other than that one cylinder your numbers are actually a little lower than the readings on my engines. My guess is that your compression is somewhere in the 9.5 range which is right where you want to be. If you determine the existing cam is a problem there are a lot of cams that would work well with that C/R, from pretty mild to wild. So I wouldn't worry about the heads/pistons just yet.

[HWYSTR455]

If you're under 30 degrees total timing, and under 10:1 SCR, I would say it's a lean condition.

Vacuum seems low for that cam, I would first check for a vacuum leak.

Sounds like you have a vacuum gauge that you can see while driving, so if there's a vacuum at WOT, over say 4500-5000 RPM, the carb is too small. (Or the choke plate isn't open enough maybe)

PSI on the cyl, eh, one off that much may just be the conditions or way the reading was taken, and wouldn't worry too much, same with the variance, it's not enough to worry. If there was one that was like under 100psi, that would be a flag.

If it's an OE balancer, I too would suggest verifying the TDC mark.

My guess is vacuum leak and lean carb. Pull the rods and jets and check the numbers, and it's not a bad idea to refresh by going through the instruction manual and the theory of operation on the 1407, may make a light bulb come on:

http://www.summitracing.com/parts/ed...a/instructions

Plug readings may not be a valid read since it's been det-ing. First get that under control then check again.

.

[Bruce Meyer]

Originally Posted by Steve70GTO

OK ... I guess my friend's compression gauge was broken. I bought a new one and these are the readings I got:

1 190
2 170
3 175
4 170
5 165
6 175
7 170
8 175

#1 hole seemed to be an outlier so I tested it again and got the same thing = 190.

So ... the compression seems to be higher than I thought.

Also put on the vacuum gauge and I have 11" at idle in drive ... in neutral have 14".

When I get on the throttle it it detonates and the vacuum is around 5".

I should also mention that I still have it at 6 degrees initial and with not much advance in the distributor. 20 degrees total at 2,000 rpm, 22 degrees at 3,000 rpm.

You guys think that compression is on the high side? What would you think that comes to? over 10 to 1? 11 to 1?

With 6X heads how can the compression be so high? Would the cam grind affect the compression gauge reading?

Maybe the previous owner put in different pistons?

Whatever input you guys have would be appreciated.

Did you do the compression check after the engine was fully warmed up?
The 6x4 heads have around 91-94 cc,s. If they have been milled they could be in the 80,s
Bringing comp ratio closer to 10:1.
With a small cam its going to ping.

[PontGuy]

You are getting good advice- debugging this sort of stuff is just never easy. Taking an interest since I am working through a similar situation with my TA engine.

Checking for vacuum leaks is always a good start (but I would expect idle vacuum to be a bit low with the timing pulled back a bunch.) If you have access to a known good carb that would be worth testing. And you might consider installing a wide-band gauge. I have one in the Lemans and just put one in the TA. I don't really use them much to chase the tune, but very useful for debugging carb-fuel related problems.

The high cylinder may not be an issue, but I still think its worth pulling the valve cover and watching the valve cycle. Easy to do and doesn't cost anything except a new V/C gasket. And while you are at it you can remove the rockers on #1 to keep the valves from opening and use a piston stop to confirm that your balancer mark is correct.

Not enough info on the cam and C/R to tell if that is a problem or not. Compression numbers look OK but impossible to really know for sure without pulling things apart. I wouldn't jump into a cam swap until eliminating all the other possibilities.

In my case I can get rid of the ping by backing down to 30 deg, and I know that A/F is OK, and I know that the cam is too small. What I don't know is what the actual C/R is. So I plan to pull one of the heads and check the deck height and chamber cc's before deciding on a new cam. Painful, but the cost of getting things really right.

[Steve70GTO]

I shut things down due to winter. I will be pulling the valve cover to look at the intake on #1 cylinder. I got a good feeling it is the cam and/or lifters. If that is the case then I am thinking of a cam swap to a ram air 3 grind. I want to keep the engine fairly mild. I want to go with one of the ram air 3 cams with 1.65 rockers and then port match my heads to the intake and exhaust. I would also have the heads gone over with new springs and valves if needed. I am getting the cast iron headers from RARE.

This is all going to happen if a bad cam/lifter is confirmed.

My question to you guys is which cam would you go with:

the 068 ... 288/302 duration with 410 lift

or ...

the 744 ... 301/313 duration with 410 lift

With the 1.65 rockers the lift on both go to about 470.

This motor is in a 70 GTO convertible with automatic and what I believe are 4.11 gears.

[Kenth]

With 4.11:1 gears i would consider the RAIV grind. I guess no long trips?

I´m using the #744 in my 462 w/TH400 std converter and 3.55 and it´s a torque monster.
Also, the #744 REQUIRES 125lbs valve springs@1.586" installed height.

[Steve70GTO]

Thanks for the info on the valve springs. The duration on the RAIV cam is really high. I am concerned about keeping the revs down in the 455.

[TransAm 474]

Originally Posted by Steve70GTO

Thanks for the info on the valve springs. The duration on the RAIV cam is really high. I am concerned about keeping the revs down in the 455.

The RAIV camshaft/Crower 60919 is a perfectly fine street camshaft for a high compression pump gas 455 with 6x-4 heads,it doesn't need to rev high in the big 455. Also,it is a proven "FAST" street combination by Mr. Ruggles and Mr. Hand.... makes an exceptional running street 455 in this combination and still retains good street manners. I would use that cam with Rhodes lifters,Crower 68404/68405(depending on installed height) valve springs and 1.65 rockers..... easy 430-440 HP/ 500+ lb Torque with no port work with the right carb and tune-up

Brian

[Steve70GTO]

Thanks Brian. I plan on pulling the valve cover this weekend to confirm the problem. I have been all over the map with ideas .... I even thought of getting the ram air V heads and trying to make it look "stock" and putting ram air V stickers on the hood scoops!

I guess I am not really interested in going VERY fast ... but more like keeping it Pontiac and tame. I also want it completed by June so I can enjoy the car this summer.

Thanks for all the input guys.

[Steve70GTO]

Well I pulled the valve cover and all the valves moved normally to the eye. Can this thing really detonate due to a too lean or rich carb? Maybe the cam was installed too far advanced or retarded? My next step will be to check to see if the harmonic balancer has slipped. I guess that will be the last of the diagnosis ... then I will just do a cam swap. I went through most of these steps with my last car and just did a cam swap and then the thing ran great.

I just figure that if maybe the harmonic balancer is off then I can fix that easy enough and concentrate on other stuff with the car this year and work on the engine down the line.