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Old 08-04-2019, 09:49 PM
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Johnny99 Johnny99 is offline
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Default Engine detonation/knock

I've been fighting with this for a week now and running out of ideas.

I bought a 65 Lemans with a 455/th350 a few months ago that had been used for bracket racing but parked about 10 years ago. I had been cleaning up the car over the winter/spring in hopes for having it summer ready. That's not working so well.

drive train config when I got the car:
  • 455
  • flat top TRW pistons
  • older Edelbrock round port heads 87cc
  • Torker 2
  • Lunati solid cam 292/302 duration 550/571 lift
  • QF 850 dp carb
  • MSD billet with 6A
  • TCI 241001 Streetfighter. 3800 stall
  • 4:11 rear
  • 2" headers
  • 3" exhaust

currently the car is set up with:
  • 455
  • flat top TRW pistons
  • older Edelbrock round port heads 87cc
  • Performer RPM
  • Summit 2802 cam
  • Street Demon 750 carb
  • Points distributor
  • stock 13" convertor
  • 4:11 rear
  • 1 /8" headers
  • 2.5" exhaust


When I got the car there were holes in the headers as well. It was loud and didn't really move till it hit 4k. I didn't hear/feel any detonation. Only drove the car a few times locally.


Now that the car is together I get nasty detonation at 2500rpm. The timing is set at 12btc (had it as low as 8 btc) no vacuum advance hooked up yet . Mechanical looks to be in by 2500 for a total of 32.

93 octane is in the tank. I added a t of VP booster which should bring it to about 95 knock is still there.

The distributor I was using was a new not rebuilt Cardone with Blue Streak Points rotor and cap. Thought there might be issue with the distributor so I rebuilt the stock cast iron unit from a 66 GTO 389 that I have. No difference.

I checked the fuel pressure (Holley 110 gph). The pump is older but the pressure is consistent between 6.5 and 6.75. When turning the car off the pressure goes down to 0 pretty quickly and when I remove the gauge "T" from the fuel line the line seems to be empty. Nothing spills out. Not sure if this is normal.

I think a 750 Street Demon should be enough carb for the car. Seems people run them out of the box on big block Chevys and Mopars regularly. I'm sure it can use some tweaking but I wouldn't think it would be small enough to cause this type of issue.

My next thought is float level being too low.

Car idles great at 650 in drive and cruises ok till just over 2k accelerating. Past that and hitting 2500 I have to back right off.

I can't really read the plugs because I used the Octane booster so they are brown. They are Champion 9YC's .

I'm open to all suggestions and any help. Thanks

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Last edited by Johnny99; 08-04-2019 at 09:57 PM.
  #2  
Old 08-04-2019, 10:32 PM
tom s tom s is offline
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Do a compression test to see what it pumps.For me I have found if they pump over 180 it can be a detonation issue.Cant hurt to check.Tom

  #3  
Old 08-04-2019, 10:49 PM
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Time for Total Advance, no vac adv hose, not initial.
Total with iron head is 34 deg. i dunno about 87 cc E-heads.

  #4  
Old 08-04-2019, 11:18 PM
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Thanks. I had run the compression test previously. They all ranged from 160 to 170.

Thinking about it that was with the previous cam. I'll recheck with the new cam. The figures would have changed wouldn't they?

I've got to recheck the total advance. at least to 2500. It was under 32 I remember it being low so I didn't pay much mind to it. I didn't write down the figure

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  #5  
Old 08-05-2019, 05:56 AM
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The first thing I would try out is one step colder plugs.

Does your timing stay steady at rpms above 2000, or does it slap around?

Also what is the general range of the motors coolant temp?

Once the coolant gets to 160 after a cold start does the motor ping and or knock even at that low of a coolant temp?

Most motors with no vacuum leaks when tuned right will only need 93 Oactane once cranking pressures get to 180 psi.

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And he was not talking about 1/8 or 1/4 mile ETs!

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Last edited by steve25; 08-05-2019 at 06:03 AM.
  #6  
Old 08-05-2019, 06:01 AM
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Simple problem and solution. The cam is WAY to small for that set-up, replace it with one having about 10 more degrees seat timing. Cylinder pressure (dynamic) too high, and peak torque happening too early. It's made worse by the good flowing heads and with their excellent cylinder filling abilities you aren't able to manage pump fuel in it.

I've never used that cam in a 455 and wouldn't recommend it. The smallest cam I'll put in any 455 build with have 230 @ .050". The 2802 is better suited for a 400 build with 9.5 or so compression, not a 455 with over 10 to 1 compression.

Look at the attached dyno chart. The first cam pinged and the engine is only 9.3 to 1 compression. It used #96 iron heads that were professionally ported to 250cfm (not even as good as what your using) and it pounded so hard on the dyno it required rod bearing replacement! It got nothing but a cam change, idled better, no detonation at all and made quite a bit more power..........Cliff
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73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
  #7  
Old 08-05-2019, 06:20 AM
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I went to SD Performance website yesterday, they have a calculator for several engine and other spec's. Your 455 is 10:1 or very close.....

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  #8  
Old 08-05-2019, 07:34 AM
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Based on what I'd read I was assuming compression would be around 10:1.

With a 180 stat in it it runs at about 210 at idle. Right now it's just putting along a 2k locally and wasn't getting any hotter. I'll have to check exactly what it's running at. When the car came to me it was running only a restrictor, center of the stat clipped out, and running pretty solid 180s .



According to what Cliff is saying a big part of my problem is the heads flow to well something I had wondered about. Unlike most I'm not looking to wring out peak numbers which is why I thought this cam would be a good choice. It looked similar to a 744 and with the wide LSA I thought it would help with static compression
  • Duration: 298 int./303 exh. 224 int./234 exh @50
  • Lift : 0.466 int./0.488 exh.
  • LSA: 114

Right now I'll check out the cranking compression total compression and temp tooling around at 2k just to have the numbers.

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  #9  
Old 08-05-2019, 07:50 AM
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Decent cam for a 400 build around 10 to 1 compression, WAY too small for what you are doing, which is obvious as it woln't effectively manage pump fuel at 10 to 1 or so compression and the heads are aluminum.

Years ago I built a 455 with Edelbrock round port heads (early design) and 87cc chambers. It made 505hp/551tq, with a 231/240/113 Crower (RAIV clone) cam in it. It was DONE making power at 5200rpms, clearly showing those heads wanted more camshaft. The Crower cam also has 304/316 seat timing, considerably more than your 2802 cam. So not only are you pinging, you're leaving a butt-load of power on the table with that cam.....IMHO.....Cliff

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73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
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Old 08-05-2019, 08:37 AM
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Another troubleshooting thing you can do is near empty gas tank put some race or AV. gas in it to get the right octane fuel that would work with the combo
Also how many times did you check the timing chain? at cam install degree it? Or dots?

Then figure out next step with the results

.

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Old 08-05-2019, 08:50 AM
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i agree put some racing gas in it. no mix just straight. i think even if you change the cam its safer to go with a higher octane gas. you dont want pieces of your pistons flying out your exhaust.

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Old 08-05-2019, 09:31 AM
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The timing gears were set by the dots. Verified a few times while adjusting the lifters.

Cliff is your recomendation the Crower 60919 cam? How would that work with a stock convertor and highway gears?

I'll check a few things and when done pick up some racing fuel to test. If that works I'll just run the high octane for the rest of the season. After that I'll need to close the garage door and rethink the combination.

I understand a bigger cam looks to be the answer but it's not an engine combination I think I'm interested in. I don't want a street/strip car. Running out of steam at 5200 would probably be fine. My goal is a cruiser. I think a factory style 455 might suit me just fine.

I had reservations with the EDL heads thinking they would flow too well for my needs and wasn't sure I could put something together to work around them but that doesn't seem to be the case.

Initial thought is find a set of large chamber iron heads to bring the compression ratio down or maybe dished pistons and chose a cam from there. then again that could just be frustration talking : )

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Last edited by Johnny99; 08-05-2019 at 10:01 AM.
  #13  
Old 08-06-2019, 07:51 AM
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Since you say the motor was built before you got the car for bracket racing, and since you say it still knocks with 95 octane or so fuel , I might question if those heads are not the 72 CC heads and not the 87s you where told they where, or they have been milled some.

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
  #14  
Old 08-06-2019, 08:28 AM
TAQuest TAQuest is offline
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Needs to come apart anyway. All that detonation, probably a lot before you even bought it, broke out the lands between the piston rings. That on it's own makes a noise. Had a 428 just like that. Years of abuse before I bought it.

Save the block by tearing it down instead of quick fixes. Lots of nice parts to work with if you don't let it get worse.

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Old 08-06-2019, 09:21 AM
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"Cliff is your recomendation the Crower 60919 cam? How would that work with a stock convertor and highway gears?"

Not really recommending anything, just pointing out that a 455 with aluminum heads will run fine on pump gas. My last 455 was 10.48 to 1, the current engine 11.3, and both have zero issues anyplace and dead solid reliable on currently available pump fuel.

You just didn't put enough camshaft it that engine for the compression, not to mention it's not taking any advantage of the head flow available. You'd have made just as much power with a set of 6X-8 heads on it and that cam, and it wouldn't be pinging either.....IMHO......Cliff

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73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
  #16  
Old 08-06-2019, 09:22 AM
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He would know by now due to oil smoke and low compression if the Pistons where cast and had cracked out the ring lands in a cylinder or two.

Ask me how I know this maylay, lol!

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
  #17  
Old 08-06-2019, 09:26 AM
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We run champion 7YC’s in Mopars that run a lot of cylinder pressure. If your tuning what you have I would start there.. I think steve25 already mentioned try a colder heat range. The 9YC was the stock plug in a 340 mopar. Colder than that we switch to NGK. We don’t generally run champions in our Pontiacs.

Tuning what you have my next suggestion since you have a solid cam would be tighten the intake lash .004. Or tighten the intake as far as you safely can, then try it. If it helps but needs more help loosen the exh lash. If both things help it a sign the cam is wants more advance.

I would try those things before you switch cams, unless your past to point of no return and ready to make serious changes.


Last edited by Jay S; 08-06-2019 at 09:27 AM. Reason: Error
  #18  
Old 08-06-2019, 11:08 AM
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Tuning what you have my next suggestion since you have a solid cam would be tighten the intake lash .004. Or tighten the intake as far as you safely can, then try it. If it helps but needs more help loosen the exh lash. If both things help it a sign the cam is wants more advance.

hey Jay, the solid has now been switched with a Summit 2802.

For a cruiser with the 2802 cam 6X-8 head is the way to go. I have the Summit 2802 in a 462 motor in my 69 GTO with 3:23 gears, just wanted a strong street car.

But then another approach, the 041 cam with the current heads should be just a mild as other combo.

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Old 08-06-2019, 11:37 AM
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Sorry I missed the paragraph with the 2802. Needed to work on my speed reading...


If your still running that 9YC, I suggest you go colder. I have had 9yc’s in 318’s with 8-8.5 scr and the 2801 Pontiac equivalent cam. My 10+ scr sbmopar are 7YC. Just to warn you, 9yc is not all that cold. Do not overlook the simple stuff...

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Old 08-06-2019, 01:56 PM
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160-170 on a compression test with that lunati solid cam sounds like well over 11 static compression. I know it sounds like you should have 10. But IRC that particular cam you started with and did the CT on generally has a 106 LSA if it was a box cam and not custom on the lsa. I don’t recall a 10:1 4.25 stroke engine that tight of an lsa with that much duration pumping that much compression? Maybe someone else has. That amount of overlap usually torpedos compression test, some 12:1 engines have a hard time making it to 180 with that much overlap. If the solid cam was pumping 170 your in for a challenge with these smaller cams.

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