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  #16 (permalink)  
Old 09-09-2008, 11:19 PM
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is this the camshaft?

If so, start by locking out the mechanical advance and set the timing at idle to 34degBTDC. (the timing does not move with rpm). Try it. If it pings, take 2deg out and try again. What's your jetting?

If you are power timing it at 3500rpm, using either stock GM advance weights and springs or the stuff from most typical advance curve kits eg Moroso), by the time you get to 5300rpm the timing is over advanced, (unless you have dissassembled the distributor and physically limited the travel of the advance pin in the slot under the advance weights.)

This cam is big enough to want a ton of initial timing at idle. Start your tuning with the mechanical advance "locked out". If its hard to start when hot install a ignition power interupt switch to disable the spark while hot cranking.
Crank 'er over, without spark 1-2-3 then throw the switch and it will fire easily when hot.

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  #17 (permalink)  
Old 09-09-2008, 11:38 PM
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This is why I'm constantly harping on building a tight squish into the motor. Changing to a thicker head gasket to lower compression will just make it worse, widening the squish.
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  #18 (permalink)  
Old 10-13-2008, 01:28 PM
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Finally fixed my problem, I simply dissassembled my distributor, and welded up the mechanical advance slot, the stock distributor gives in way too much advance. Afterwards, I gave my car a good 20 degrees of advance at idle, and it goes all the way up to 32 at around 3500 rpm. Tried the car, at first I hesitated, didn't want to make it knock, pushed it and it pulled without complaining, and throttle is more responsive. I'll have to try it out at the track sometime this week.
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  #19 (permalink)  
Old 10-13-2008, 05:22 PM
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Quote:
Originally Posted by chevy_power427
I have a 10.75:1 Compression 355 Chevy with Vortec heads. I currently use 94 octane gas with no octane booster. The car seems to knock at around 5300 rpm. What could be a solution for this. I retarded the initial timing, richened the carb slightly, knocking is a little less bad. I was thinking about colder plugs and or maybe limiting mechanical advance. Could octane booster help?? I yes, which brands are recommended.
10.75 is just plain too high for pump gas, even 94 octane. Even aluminum heads would struggle with this. You need to loose about a full ratio of static compression, actually about 1.2.

High speed detonation is extremely distructive, you need to get on this right away.

Bogie
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  #20 (permalink)  
Old 10-13-2008, 05:51 PM
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Quote:
Originally Posted by oldbogie
10.75 is just plain too high for pump gas, even 94 octane. Even aluminum heads would struggle with this. You need to loose about a full ratio of static compression, actually about 1.2.

High speed detonation is extremely distructive, you need to get on this right away.

Bogie
yep, just look at the LS7, there is no way that it can run on 87 octane with 11:1 compression... wait... er... well not under boost... you need atleast 92 octane for that... I guess it is completely possible to run up to 13:1 on pump gas- especially since it has been done.
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  #21 (permalink)  
Old 10-13-2008, 06:05 PM
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Quote:
Originally Posted by ap72
yep, just look at the LS7, there is no way that it can run on 87 octane with 11:1 compression... wait... er... well not under boost... you need atleast 92 octane for that... I guess it is completely possible to run up to 13:1 on pump gas- especially since it has been done.
He doesn't have an LS7!

Bogie
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  #22 (permalink)  
Old 10-13-2008, 06:13 PM
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Seriously, what happened is that when I rechecked my ignition timing yesterday, mechanical advance was going all the way up to 45 degrees which is way too much. At first it seemed to go to 35, but I was wrong. Now, I checked it twice, after I modified the distributor, and it stops at 32 and it wont move any further. Test drove the car until now and I consider it fixed, no pinging, no knocking and improved throttle response. I'm happy with it like this.
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  #23 (permalink)  
Old 10-13-2008, 06:31 PM
How fast is fast enough?
 
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Quote:
Originally Posted by oldbogie
He doesn't have an LS7!

Bogie

No, he doesn't but blanket statements about pump gas mandating a maximum compression of 9.55:1 are about as valid as people suggesting running locked out ignition timing on every car. It just doesn't hold water.

Suggesting a maximum DCR for an iron headed gen I chevy 350 of 9:1 on pump premium is a lot more specific and valid- though even that has a LOT of exceptions.

I just can't stand blanket rules like that, especially when there's plenty of exceptions.
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  #24 (permalink)  
Old 10-13-2008, 06:33 PM
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Quote:
Originally Posted by ap72
No, he doesn't but blanket statements about pump gas mandating a maximum compression of 9.55:1 are about as valid as people suggesting running locked out ignition timing on every car. It just doesn't hold water.

Suggesting a maximum DCR for an iron headed gen I chevy 350 of 9:1 on pump premium is a lot more specific and valid- though even that has a LOT of exceptions.

I just can't stand blanket rules like that, especially when there's plenty of exceptions.

It's not a blanket statement the subject of the blog is a 355 with Vortec heads. Start at the beginning next time.

Bogie
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  #25 (permalink)  
Old 10-13-2008, 06:42 PM
How fast is fast enough?
 
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well... again a lot of people are running with 11:1 on Vortec heads (2 VR pistons @ zero deck with heads milled to clean them up) on 355's and they run just fine on 92...

I'm trying really hard to not just say that you're obviously wrong, because in general people do stick with 10:1 or below on Vortec heads... but again that's not a rule, and there's plenty of proven builds to show it.

The only reason i know this is because I'm working on a very simmilar build for a toy of mine- a Vortec 357 with 11:1 and a nice solid flat tappet cam.
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  #26 (permalink)  
Old 10-13-2008, 06:44 PM
How fast is fast enough?
 
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As far as the remedy for the ping... What kind of exhaust set up do you have? I'm hoping large tube diameter headers with 3" duals and race mufflers... Its pretty much required for your build up.
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  #27 (permalink)  
Old 10-13-2008, 06:56 PM
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ap72...Just because there are a few or 1 vortec headed engines with 11:1 runnin on 92 does not make bogie wrong bout the "blanket statements".

What are the specifics on how it runs...whats sacrificed to make it run right?

Engine builds have been done over and over the "9.5 - 10:1 rule" is there for a reason.
How can you say it's flat out wrong? Are these reputable engine builders?
Even if you had a website somewhere i wouldnt believe it...guys like to add inches to fish they catch.
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  #28 (permalink)  
Old 10-13-2008, 07:14 PM
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Quote:
Originally Posted by DeathRattle
ap72...Just because there are a few or 1 vortec headed engines with 11:1 runnin on 92 does not make bogie wrong bout the "blanket statements".

What are the specifics on how it runs...whats sacrificed to make it run right?

Engine builds have been done over and over the "9.5 - 10:1 rule" is there for a reason.
How can you say it's flat out wrong? Are these reputable engine builders?
Even if you had a website somewhere i wouldnt believe it...guys like to add inches to fish they catch.
Actaully, it only takes one test to disprove a theory... so it does make the statement wrong. And the 9.5:1 rule used to be a 8:1 rule in the days of flathead Fords, or a 9:1 rule for aircooled VW's- yet both of these engines are now being built with higher compression... It seems that none of the compression rules have ever held... interesting...

Now, there are certianly limitations as to how much temp and pressure a fuel can take before it self ignites, but these limits are continously being pushed back.

And the 11:1 on Vortecs is not somethign that's only been done once, a good google search will pull up lots of examples.

and the 9.5:1 rule is for people who randomly pick parts out of catalogs and slap them together- there's usually so much not working righ that you need cushion room to make up for a bad build... Or if you want to stick an RV cam in it and tow a boat you need lower compression. But with a free flowing exhaust, a non restrctive intake, proper engine building procedures, and a well tuned fuel and ignition curve 11:1 on Vortec's with pump premium is almost a text book build.
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  #29 (permalink)  
Old 10-13-2008, 08:28 PM
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Quote:
Originally Posted by ap72
Actaully, it only takes one test to disprove a theory... so it does make the statement wrong. And the 9.5:1 rule used to be a 8:1 rule in the days of flathead Fords, or a 9:1 rule for aircooled VW's- yet both of these engines are now being built with higher compression... It seems that none of the compression rules have ever held... interesting...

Now, there are certianly limitations as to how much temp and pressure a fuel can take before it self ignites, but these limits are continously being pushed back.

And the 11:1 on Vortecs is not somethign that's only been done once, a good google search will pull up lots of examples.

and the 9.5:1 rule is for people who randomly pick parts out of catalogs and slap them together- there's usually so much not working righ that you need cushion room to make up for a bad build... Or if you want to stick an RV cam in it and tow a boat you need lower compression. But with a free flowing exhaust, a non restrctive intake, proper engine building procedures, and a well tuned fuel and ignition curve 11:1 on Vortec's with pump premium is almost a text book build.
Which text book?
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  #30 (permalink)  
Old 10-14-2008, 05:41 AM
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Quote:
Originally Posted by ssmonty
Never heard of an engine knocking at that high of an RPM. I would think that the cylinder charge turbulence, lack of time for heating of unburned fuel, and lack of time for excessive pressure build up would eliminate knock before RPMs got that high.
If its detonation, it would occur at a lot lower rpm than that I believe. If your mechanical advance is all in at say 2400rpm, thats closer to where the rpm knocking would start, probably less, then drop off as rpm increased.
I'm no expert.JMO
ssmonty
Sometimes you cant hear it knocking at high rpms due the engine and exhaust noise, but it happens!
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