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Old 05-23-2004, 06:22   #1 (permalink)
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Detonation and preignition

I have a fairly worked 351 cleveland that tends to run on after turning it off.

The engine has the following: 40thou over forged pistons, worked 2V heads, 4 -1 pacemakers, 750vs holley on top of redline street torker manifold, cam specs unknown(lumpy). It had 202rwkw on dyno before the pacemakers. It runs mainly on optimax. I have been using NGK BP6FS plugs that seem to foul far too quickly. It still knocks on optimax at 12 deg initial, 30 deg total timing if it is really loaded up. If I run octane booster in it the knock goes away - but an expensive way to run.

How can I get my cleveland to run like a cleveland and not a diesel?

Would removing the PCV and running a breather help? Is this street legal?
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Old 05-23-2004, 08:17   #2 (permalink)
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Re: Detonation and preignition

Sounds like most of your problems are not enough fuel octane, that could cause the run-on. The 6FS plugs should be right for a warmed over 351, 7FS for a hottie and the 5FS for smog spec clevo's. Maybe your carb needs a tune.

Toluene makes for a cheap and great octane booster, check out: Where to buy Toluene?
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Old 05-24-2004, 01:39   #3 (permalink)
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Re: Detonation and preignition

I would try and get my hands on a smaller carb,say a 650dp. clevo,s love dp,s.you may have too much carb for your setup which may be causing the plugs to foul up>You may find the smaller carb is better at metering fuel due to the smaller venturi,s and hence will see better atomisation.borrow one off one of your mates and give it a go.Too many dudes think more carb is better but it makes em run like shit.A bit of Holley tuning knowledge would also be of great benefit(ie power valve etc).
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Old 05-24-2004, 02:17   #4 (permalink)
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Re: Detonation and preignition

Do you know what your static compression is?

If the timing is set right and the cam is on the lumpy side you shouldn't have too many problems unless your compression is through the roof... even 11:1 should be OK if your cam has a fair bit of overlap.

Have you backed off the timing until it stopped pinging? What did you have it set to when it ran OK? Have you had it dyno tuned?
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Old 05-24-2004, 05:12   #5 (permalink)
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Re: Detonation and preignition

I used to foul plugs a bit with the bp6fs, but went to 5's and it lasted longer , but since changed heads, so i dont know how much longer they lasted. The only problems is the detonation, so you probably dont want to go hotter. Pitty you dont know exact cam specs and compression.
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Old 05-24-2004, 05:36   #6 (permalink)
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Re: Detonation and preignition

Thanks for your replies.

If I can help it I would try and stay away from Octane boosters as at the moment it is a daily driver. However it was being built as a track car until some lowlife scum stole my s@#$box runaround.

russxr67 : I have a 600vs sitting in the garage that was on my old 302C. For the sake of a $5 gasket and some hose fittings I could give it a go. I've seen plenty of debate in the forum of the pros and cons of vs versus dp. I would love to learn more about holleys.

xdc351 : I backed the timing yesterday but ran out of time to finish the job. The less initial timing certainly helped the starting this morning. It is probably 1 - 2 deg too advanced at the moment. I don't know what the static compression is.

It was dyno tuned about 2 months ago. I don't know if they changed jets or power valve, however they did fix up the secondaries as they weren't opening at all. They did pick up nearly 40kW tho'!!!
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Old 05-24-2004, 06:00   #7 (permalink)
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Re: Detonation and preignition

Also try Mobil synergy. I used to run optimax in my clevo. then for some reason now it just fouls plugs for me. Swapped to synergy and the issue minimised and completely disappeared when I got the correct rated plugs.

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Old 05-26-2004, 00:20   #8 (permalink)
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Re: Detonation and preignition

Shard, you didnt mention that when you put the octaine booster in if it fixed the run on as well, which seemes to be your original complaint. so if fixed, ignore this, but if not, here's my thoughts on that topic. I'm aware that you suffer from detonation as well as running on, but ask yourself one simple question does my car detonate at idle? I'm guessing it doesnt. which makes me tend to think it might be something else like two problems possibly.
Your detonation happens when the heat and pressure inside the combustion chamber get so high so the petrol self ignites, this probley happens most under load i'm guessing, and since octaine booster helps there theres no doubt you have that problem.
But again, those pressures arnt there at idle, (timing dramaticly changes effective compression pressure when advanced). other things can cause run on or "dieseling".
First you could be running a engine at a hot temp, or could have a piece of material in your combustion chamber protruding out getting hot like a glow plug type affect, this could also cause pre ignition and might fit in with the pinging.
Or most common, is the engine dieseling simply caused by a high idle, please check this.
People with cams and hollys often drill holes in holley primary throttle plates to help in transfer slot action, check for this, together with a slightly high idle could cause problems.
True, crappy petrol can cause run on, but it would have to be really crappy and is usually accompanied with another problem like a high idle.
I used to have a mustang with a stock holly carb, the throttle plates where closed completely when the key was shut off via a anti dieseling soloniod.
It just doesnt hurt to check idle adjustments, if you need the high idle to go with the cam you might have to put a soloniod on. doesnt hurt performance,
To break it all down.. check the idle.
For the detonation problem, if your not using the car for racing now, and dont need the power, knock the total timing advance back for mellow street use.
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Old 05-26-2004, 04:31   #9 (permalink)
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Re: Detonation and preignition

My openchambered clevo used to run on if hot and idling high. Well, it used to allways be hot and idled high to run good in gear(auto). My remody, and it worked well for years was to turn car off in gear. Never again did it run on.
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Old 05-26-2004, 04:38   #10 (permalink)
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Re: Detonation and preignition

Drof,

you are correct in that it never detonated until under load. Adding the octane booster certainly cured the detonation and helped with the "run on". I have also changed plugs regularly, probably more often than the oil lately. The plugs have been dry and have carbon around most of the electrodes.

Idle speed was 1000-1100rpm, which was probably on the high side. Having taken 2deg timing out it now idles at 900-100rpm. It certainly ran better today.

As I am using it more for the street at the moment I think I'll give the 600vs a try on the weekend.
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