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1987-1991 Parley with regards to your 1987 to 1991 Bonneville, Olds 88 or Buick Le Sabre Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 01-17-2005, 05:12 AM   #81
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Yeah generally you can run 10:1 with pump gas, although not generally 87. But here'* the kicker, there is a LOT more to octane needs than just compression ratio. Such as cam overlap, MBT, flame propigation, combustion chamber design, piston design and others. Cam overlap affects whats called "effective compression ratio" as opposed to "static compression ratio." Because most cams have a few degrees where both the intake and exhaust valve are open, it changes the amount of air that is actually compressed 'effectively' lowering the compression ratio. I'm not gonna go into classroom mode, but you get the idea. Its not "Well he does so I can" becuase you may find you need premium at 9.5 while an integra can get away with regular at 9.2. Just food for thought I guess....
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Old 01-17-2005, 09:01 AM   #82
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Yeah, I know the basics of cams.. but.. do you think, with everything in stock form and a 10:1 compression ratio [remember, this is a 16 year old car, and the car may not have the best seal anymore] would I need to run more than 87 octane? This is the biggest thing in the decision for how much I want to remove..


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Old 01-17-2005, 09:13 AM   #83
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i would only go .020 if you go anymore you start running in to more issues
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Old 01-17-2005, 09:23 AM   #84
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Err..man...imho if like $2 extra a tank is gonna break your bank, stay away from this 'mod'.

That aside, no I don't think you can go from 8.5 to 10 and maintain 87octane....You really need to set it in your mind that you may benefit from higher octane gas if you're going to raise the compression. They really go hand in hand. If GM did their job the engine is using the maximum potential of the low-grade gas. You can probably go up some and still use 87, but betcha the PCM is gonna pull timing - negating any gains. How high on 87....My wild guess? 9.0:1 ...but who knows.
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Old 01-17-2005, 10:14 AM   #85
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Quote:
Originally Posted by GAMEOVER
i would only go .020 if you go anymore you start running in to more issues
You may be right. I still need to measure the clearance I have from valves to piston top, and also account for red line runs, that stretch the bearings [anyone have a figure on that?]. If I only have .050" clearance from valves to piston, then I may forget this mod.. because I am afraid the piston will stretch that much. I am going to see if my hood 'll pop [car = frozen shut], and if I can, bring the front cylinder head out, and measure the valve clearance. I am hoping that there will be plenty.

I kinda had a brainstorm just a second ago... the cam lobe lift.. is .250" intake, .255" exhaust.. does that mean the valve opens .250" ? Or is there a change in lift through the valvetrain? The piston tops have a slight dip in them, which is right where the valves are. So, technically, that is probably .1" and I have .4" from closed valve, to bottom of head gasket. These are all estimates, I am still kinda playing with numbers right now. Sorry for the rambling... When I am typing, thinking, and excited all about the same thing.. I don't make the most sense.

It'* not that the $2 extra a tank is going to kill me, but I know this car will only rest when I am sleeping.. so I may go through a tank of gas every day or two. Which $2 extra will be a big deal then. But.. I could just run 89, because when just going around town, I don't need 100% of my power.. so retarding timing wouldn't really matter much to me.

Also, I still don't know how much clearance I will have.. so I don't know what my end compression will be, or what I really want it to be.

Questions for this post:
- Is the camshaft lobe lift how much the valves actually open
- How much does this piston stretch at 5200 rpm? Or, what may be a good figure to leave as spacing for it. "How much slack."


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Old 01-17-2005, 02:49 PM   #86
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I was afraid that it being 1.6xCam lift. I did a little better measuring, by measuring not straight but at the angle the valves sit at. This leaves me with .47-.49" clearance.. on the heads. I just went out to the car, although I cannot keep the hood up, and it'* snowing pretty bad, I was able to measure the dish in the piston. If the piston sits where it does [just below the block], then I have probably up to .35-.40" clearance. But, if the piston sits flush with the block, then I have .25-.30" clearance in the dish. Also measuring out, the valves sit in that dish, and not on the outer part that sits higher. My guess.. roughly I will have .8" clearance from valves to piston top. This is rounding off, and using averages, so of course it'* not the most accurate. But even the smallest average isn't under .7" clearance. So, if .408" is the most valve movement I will see, and .72" clearance is the smallest, I will still have .294" clearacne. Which, even with .085" removed, I would still have .209" play to allow for piston stretch. And that is using minimum and maximum figures, to be on the saftest side possible.

Well, I think jrs3800 has defined that 87 Octane is safe for 9:1. Perhaps 89 would be fine for 10:1? Oh well, I know for a fact I will find out the hard way.


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Old 01-17-2005, 03:23 PM   #87
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Well, that may be a different engine, but Compression is Compression, and 87 Octane is 87 Octane. Well, for the most part.

You know what, this was all a dream, it'* amazing I went from just pulling the intake, to pulling the heads, to porting the heads, to now decking the heads! Where will it end? Probably here, because I think I have maxed out the power that can be made with what I am capable/feel comfortable doing.

The upped compression, IMO will make a HUGE difference. The 'numb' feeling in the upper RPM Range will decrease [I hope] a lot. I also think the bottom end power will increase. Unfortunately it won't move the power band up.. which I would love to have happen, but I have made a promise to myself that I am not digging into the engine anymore. Once this is done, I am done as far as the engine is concerned. I am not going to make this car a strip car, but a daily driver that has some good power, good fuel economy, and good looks . I may have a little high expectations for what will happen, but I hope I won't be disappointed.

Let'* just cross our fingers that it doesn't cost more than $150 [the decking that is].


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Old 01-17-2005, 09:13 PM   #88
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Quote:
Originally Posted by jr's3800
Dr. Jay,

correct me if I'm wrong here...

OSG, If memory serves you need to look at totall lift at the valve... You have 1.6 ratio rockers... so .250 on the cam would be .400 at the valve, and .255 would be .408 at the valve...

Dr. Jay is this correct?
You're absolutely right. Generally though cams are rated using a 1.5 or 1.6 ratio. If you see "Valve Lift" its using a rocker ratio, if you see "Max Cam Lift" you multiply it by the rocker ratio to get actual valve lift.

Quote:
Originally Posted by opensourceguy
Well, that may be a different engine, but Compression is Compression, and 87 Octane is 87 Octane. Well, for the most part.
This is exactly what I've been saying is NOT the case.
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Old 01-17-2005, 09:52 PM   #89
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I emailed my dad [hell in itself].. I basically updated him on the process, and what I have all done. And, I got this email back

Quote:
- I think the clearances I have seen or heard of are in the 0.010-0.020 level. Now that would be for a fresh engine. In the case of a 150K mile engine I would go a little more
- too high of a compression ratio will be a problem with detonation/pinging. Although you can find many engines today that run 10.5:1 ratios, they have a different camshaft overlap. I was looking at a higher compression ration for the Ford P/U (10.5:1) and I would have required a much more aggressive camshaft. The issue is static vs dynamic pressures. Think of 2 identical engines 10.5 CR, one with a high torque cam and the other with a high RPM cam. At 2000 RPM, the 1 cam would have the valves closed earlier in the compression stroke resulting in a higher pressure build. The high RPM cam has more overlap and longer duration for opening...this results in the valve taking longer to close...hence part of the compression stroke has the valve open...i.e., no compression building until the valves are closed. This is the difference between static and dynamic compression ratios. The calculated compression ratio is based on the valve being closed
- the real key is how much can be cut off without creating a situation where the material on the head is compromised. If there is not enough material, the head could leak, be susceptible to cracking, or more likely, susceptible to warping.
- have you considered a thinner head gasket.
I think he may be implying that shaving .085" is too much to remove, and it may compromise the structural integrity of the Heads. Do I have anything to worry about? Or does he not want me to have a car faster than this .

I think he is also implying that my cam may be perfect for this compression boost. Or, that maybe it will be too much.. the static/dynamic question. I don't know how much duration my cam has, but my guess because it is a low RPM power maker it doesn't have much.

The detonation thing he is suggesting was over the 87/89 octane question I asked him.


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Old 01-17-2005, 10:26 PM   #90
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Quote:
Originally Posted by jr's3800
If I remember right the .250 intake and .255 exahust is listed as Lobe lift so .400 and .408 should be valve lift..

So .388 or .389 lobe lift should be .620 at the valve... Holy cow... Does GM make em like that.. I know my friends 3.0 has always had a bit of a lumpy idle... Screams when you floor it... That little 3.0 shocked me the first time around..

Like I said though, I'll have to dig into the lift a little more and see what comes up..
mmm, .258" sounds more like a cam they'd put in stock and thats what .388" valve lift would be at the lobe with 1.5 rockers, .242" with 1.6. Maybe you read it wrong? Otherwise, thats one heck of a cam from the factory!
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