pinging

stroked windsor · #1 (**permalink**) 12-10-2017, 06:48 AM

my mechanic now saying my 402w is pinging under load.. normal driving its ok. once you hit it you can hear it. 402w. AFR205 heads. HR cam from comp.XR282RF. small cam for street car.. low mid range.. he is trying different timing settings. even with 50 50 mix its still pings.. pretty bad.. next is the MED dizzy. mech.. weights springs etc.. might have to run full 110 until I can figure on what to do.. hate to pull the motor out again.maybe I should have kept the bigger cam in. 240-248-624-600-110 with this engine. new motor only 100 miles since new plus dyno pulls.. vic jr with a 950 carb.. any ideas?

olddog · #2 (**permalink**) 12-10-2017, 07:25 AM

Cam change likely increased the dynamic compression ratio. Do you know what the static compression is?

Get a wide band O2 sensor on it. Make sure you are not running too lean. At WOT the AFR should be around 12.5:1. You can go as rich as 10:1 to help with the pinging, but you would likely loose some power.

As you are already trying, retarding the timing will help. I would not be doing too much with the timing until I had the fuel correct. Typically with fuel injection people pull about 5 deg out of the timing until they get the fuel dialed in, just to stay on the safe side. They don't work on the timing until the fuel is right.

That would be my strategy here. Pull timing until is stops pining. Then make sure the fuel is correct. If you are already at 12.5:1 at WOT and your timing was pinging at say 30 deg at 3500 rpm, you can try going to 10:1. If it pings at 10:1 30 deg at 3500 rpm then you have too much compression. You would have to lower the dynamic compression with the cam or lower the static compression.

olddog · #3 (**permalink**) 12-10-2017, 07:31 AM

If it is only pinging under 3000 rpm, then you are bring the timing in too quickly.

stroked windsor · #4 (**permalink**) 12-10-2017, 08:07 AM

more over 3000 it seems. once he hit it it pings normal driving its ok

stroked windsor · #5 (**permalink**) 12-10-2017, 08:09 AM

bigger cam? like I had?

spdbrake · #6 (**permalink**) 12-10-2017, 09:27 AM

Olddog makes some good points to inspect.
A tighter LSA does increase dynamic compression and chance of knock.
But your posted LSA (new and old are the same).
The new CAM is not what I'd call milder, although its less lift, it is a bit more Lopier with more duration.
35-425-8 - Xtreme Energy

From your post it appears this started right after the Cam change?
If so your new cam may be degreed wrong for your application.

This guide may be of help.
degree it in correctly and get it to last,cam install info, | Grumpys Performance Garage

ALWAYs check what you did last...

stroked windsor · #7 (**permalink**) 12-10-2017, 09:42 AM

I don't know as I didn't drive the car with the bigger cam. just dyno..

stroked windsor · #8 (**permalink**) 12-10-2017, 09:44 AM

cam was installed by a local engine builder..and dyno.ed..

olddog · #9 (**permalink**) 12-10-2017, 10:03 AM

When the intake valve closes ABDC is what impacts dynamic compression. Advancing or retarding the cam will impact this, as well as the duration. Looks like the old cam had 10 deg more intake duration. The new cam (less duration) would have increased dynamic compression, but I haven't a clue as to how much.

The AFR and exactly where the timing is when it pings would be helpful to know. There are some guys who know a whole lot more than me on this site, but you are going to have to give them a lot of specifications and information before they can help you. I think I have pointed you in the correct directions to look. Good Luck.

stroked windsor · #10 (**permalink**) 12-10-2017, 10:10 AM

my mechanic wants to run full race gas first. not 50 50 mix.. 110 vp.. ill get back soon..

stroked windsor · #11 (**permalink**) 12-10-2017, 10:12 AM

thanks for all the help..

olddog · #12 (**permalink**) 12-10-2017, 10:26 AM

Not sure what the other cam was but it looks like it was closer to the 294. Perhaps a 5 or 6 degree change in when the intake closes. Advance or retarding the cam could make another 1-3 degree change on top of that. Here are some links to cams.

XR-294-RF-HR - intake closes at 73 ABDC
35-427-8 - Xtreme Energy

XR-288-RF-HR - intake closes at 70 ABDC
35-426-8 - Xtreme Energy

XR-282-RF-HR - intake closes at 67 ABDC
35-425-8 - Xtreme Energy

jhv48 · #13 (**permalink**) 12-10-2017, 10:31 AM

Was the cam installed with too much advance?

Three Peaks · #14 (**permalink**) 12-10-2017, 10:46 AM

I'm running the XR 294 cam on my 393 with Vic Jr heads and don't have any problems. I made sure to degree in the cam when installing.
Have you checked what your compression ratio is? Your post doesn't specify or say which pistons your are running? You need about 20CC or more of dish in your pistons to stay in the 10:5 compression area recommended for using pump gas.
Also, IMO, that is a lot of carb for a 402. A 750-780 double pumper would be plenty of carb for that engine.

Bob

stroked windsor · #15 (**permalink**) 12-10-2017, 11:38 AM

dyno didn't like the 750 with the other big cam. not sure on this one.. comp ratio is 10.5.4 58 cc heads milled. total cc is 86.probe pistons.. 98.40 on the piston. 58 for head 9.50 gasket..

stroked windsor · #16 (**permalink**) 12-10-2017, 11:40 AM

I think the cam was installed straight up..

blykins · #17 (**permalink**) 12-10-2017, 11:40 AM

Quote:

Originally Posted by spdbrake

Olddog makes some good points to inspect.
A tighter LSA does increase dynamic compression and chance of knock.
But your posted LSA (new and old are the same).
The new CAM is not what I'd call milder, although its less lift, it is a bit more Lopier with more duration.
35-425-8 - Xtreme Energy

From your post it appears this started right after the Cam change?
If so your new cam may be degreed wrong for your application.

This guide may be of help.
degree it in correctly and get it to last,cam install info, | Grumpys Performance Garage

ALWAYs check what you did last...

Although I agree the new cam change is what probably caused the issue, there's a couple of notes that need to be made here:

LSA doesn't have anything directly to do with dynamic compression ratio. It's intake closing point only. I can grind two cams, with only the LSA being different and as long as the IVC event stays the same, the DCR will stay the same.

His new cam is much milder. Smaller duration. A smaller duration changes the IVC event.

stroked windsor · #18 (**permalink**) 12-10-2017, 11:42 AM

yes it is compared to the 240 248 which I had in when new.

stroked windsor · #19 (**permalink**) 12-10-2017, 11:44 AM

motor only has 100 miles or less on it plus a bunch of dyno runs. with both cams..

blykins · #20 (**permalink**) 12-10-2017, 11:45 AM

Was it degreed?

Straight up means that the LSA equals the ICL. If your mechanic just threw it in there without degreeing, it could be further advanced than it should.

Even with it on a 106 ICL, it would be right at the limit of what I would consider do-able for pump gas.