Thread: Detonated Dreams

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Wow! That is a lot. 120-140 is more like it.

Panic time? New cam gives the same cylinder pressure. It has 4 degrees advance ground into it. Our timing gear only allows 2 degrees in either direction. Is that the answer? ....retard it the 2 degrees and see what we get?

Panic time? No. Install the cam straight up. Most Comp cams have 4 degrees advance ground into them. You can retard it two degrees if you want, but you should not have any problems with installing it straight up. I didn't, and I am running a higher DCR than you. If you are unsure, call the CompCams Cam Help tech line (800-999-0853) and ask them. I think they will tell you not to retard it. You are not going to get a good reading on your compression until everything is installed. The compression test seemed high to me, but I only take a compression test when I suspect a problem with a cylinder. DCR is a better indicator--trust it.

I'm only nervous because they read the same. Wouldn't we have liked to see a drop? It is pretty much all together except for the intake.

Not necessarily. With the valves closed on the compression stroke, it would be the same, would it not? When I stated 180 psi seemed like a lot, I have never even checked the compression on my engine. I have heard of 120-140 being acceptable for a compression check on most engines, but with the longer stroke of of a 383, more air is being compressed than a 350 or a 327, so it would naturally be higher. I am not familiar with compression test numbers on a 383, and I may have misspoken about it seeming high. I have only used a compression test to diagnose a suspected problem in a cylinder. Someone else my chime in on this with a better explanation than I can give.

Several people I have talked to have all thought that 185psi was really hi. 185 doesnt alarm me as much as the fact that the new cam showed the same number. The longer stroke would make more pressure, that makes sense, and seems to go along with why DCR would be high on my under cammed 383. But for the same reason that a differant cam is going to lower my DCR,(bleeding pressure out of the intake valve) shouldn't it also lower my cranking cylinder pressure?

Anyone have suggestions?

install a supercharger and route the belt so it turns the supercharger backwards, hence sucking out excess cylinder pressure! lol

HA HA, that's just crazy enough to work. ...better be careful, someone might think we're serious.

Let me do some checking with the resident guru on another forum.

I think from what others have posted in the past 185 is normal on a new motor.

If our gov't would just get rid of corn and heptane, we could also elliminate the word "detonation" from out fraternal vernacular!!!!!!!

So the cam works nice. Runs real hard and clean with the little bit of race gas that we had left over. After we burned through that we filled up with the best pump gas available in our area, 91 octane The base timing and fuel is set up for 93 octane. We are experiencing some knock at WOT after running hard for a few pulls. Started pulling timing back out of it so we are at about 28* with 4" vaccum from 2000-5000RPM. How far can you retard the timing before you experience drastic power loss?

The first opinion is that the cam seemed to fix the knock problem. The weather this weekend was about as hot as it ever gets around here and I'm sure the little bit of knock we experienced is a result of the low quality gas available and my lack of tuning experience. Thanks for everyone's help.

Any advice on tuning for low quality gas? does anyone make an octane booster that is actually worth a shiite?

Does your fuel injection system back off timing when it senses knock? What water temperature are you running?

The injection doesnt have a knock sensor. I can hear it very faintly tho. The water temp cruises at 175. After running it pretty hard for a few minutes it will get up to 185-193.

If it didn't ping on the race gas, I would say you need to take a little more timing out. This gas in Iowa is crap. One tank seems ok and the next is crap. Also if your at WOT, shouldn't the vaccum be closer to 0. Not enough air flow? Leaning out could be causing the ping. Just some thoughts.