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  #16 (permalink)  
Old 02-10-2013, 01:34 PM
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You'd be better served by getting a timing box that allows adjusting the timing a bit +/- as required, from the drivers seat. Rather than playing with the gasket. The fuel quality in the tank and the day-conditions will be the factors.

Just preset the dash timing dial in the middle of its range, and set the engine timing with a light.
Now you got convienient effective on the fly +/- spark timing adjustment.
Now you can adjust for different fuels, without lifting the hood.

cold air induction "ram air" will help. Hot air will not help.

I avoid recommending a true 11:1 cr for the street as most people will not watch the conditions and tune that close.
They just want to get in, turn the key and rug it. Its too close to the edge for most people. 91 and 94 are not the same.

You really got to watch just how aggressive the vacuum advance is. go easy for when the engine is hot.
Conditions and fuel will change and you need to stay on top of that with true 11:1cr.
Like said,, and very very true ... "64cc" is not always 64cc.

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Old 02-13-2013, 12:53 PM
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I found in the building process that there is a great variation in the compression ratio calculators available because of the assumptions they have to make and liability issues. I found that when I calculated manually all the dimensions of my engine, my actual compression ratio was nearly a point lower than the calculator.
Also, you can reduce the dynamic compression ratio by retarding the cam. I can't say I remember how much but it does help.
In 1962, Chevrolet sold 425 HP 409s with 12.5 to 1 compression. The cars were shipped from the factory with 2 head gaskets each side to lower the compression a point or so. I remember that cause I had one.
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Old 02-13-2013, 04:34 PM
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I have a V-8 Chevy Vega with the early LT-1, 11.6:1 flat top forged pistons and a .010 quench (pistons stick out of the deck by .030, Felpro permatorque gasket .040 compressed). I run 91 octane (California) with timing set at 26 degrees (locked) and approximately 14 degrees vacuum advance. I shift at 8,000 rpm's with a Sig Erson Hi-Flow I hydraulic cam, ported and polished heads (2.02/1.60 iron heads right now), and it runs just fine. The tight quench makes the burn happen faster because of turbulence in the combustion chamber, so the mechanical timing cannot exceed 28 degrees. If you have any doubts about how this can work, check with Doug Roe (chief head design and intake manifold research engineer with Chevrolet for 17 years, now retired). This engine makes over 500 horsepower and gets 11 mpg with a 700R4, 3,000 rpm stall, and narrowed 12 bolt rear (3.08:1) with posi and Camaro suspension and brakes, 14 inch tires/rims (26 inch diameter). Line bore your engine first, then shot peen and resize rods, then buy, polish, and balance pistons (I used TRW forged flat tops), and then and only then deck the block for the quench. Pistons should stick out of the block between .020 and .030 with a .040 (compressed) head gasket. Any tighter and the rod stretch will let the pistons touch the heads. Any looser (less quench) and you lose torque. All quench benefits are lost if the piston to head clearance is greater than .030 inch. Gas mileage goes up, torque and horsepower almost double with the .010 inch piston to head clearance. Just don't make a mistake in machining. I use an HEI distributor with Pro-Comp's multiple spark discharge box. It does the same thing as a Digital MSD, but is way more reliable and 1/3 the cost.
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Old 02-13-2013, 04:45 PM
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8,k RPM & .010quench

Quote:
Originally Posted by barry425 View Post
I have a V-8 Chevy Vega with the early LT-1, 11.6:1 flat top forged pistons and a .010 quench (pistons stick out of the deck by .030, Felpro permatorque gasket .040 compressed). I run 91 octane (California) with timing set at 26 degrees (locked) and approximately 14 degrees vacuum advance. I shift at 8,000 rpm's with a Sig Erson Hi-Flow I hydraulic cam, ported and polished heads (2.02/1.60 iron heads right now), and it runs just fine. The tight quench makes the burn happen faster because of turbulence in the combustion chamber, so the mechanical timing cannot exceed 28 degrees. If you have any doubts about how this can work, check with Doug Roe (chief head design and intake manifold research engineer with Chevrolet for 17 years, now retired). This engine makes over 500 horsepower and gets 11 mpg with a 700R4, 3,000 rpm stall, and narrowed 12 bolt rear (3.08:1) with posi and Camaro suspension and brakes, 14 inch tires/rims (26 inch diameter). Line bore your engine first, then shot peen and resize rods, then buy, polish, and balance pistons (I used TRW forged flat tops), and then and only then deck the block for the quench. Pistons should stick out of the block between .020 and .030 with a .040 (compressed) head gasket. Any tighter and the rod stretch will let the pistons touch the heads. Any looser (less quench) and you lose torque. All quench benefits are lost if the piston to head clearance is greater than .030 inch. Gas mileage goes up, torque and horsepower almost double with the .010 inch piston to head clearance. Just don't make a mistake in machining. I use an HEI distributor with Pro-Comp's multiple spark discharge box. It does the same thing as a Digital MSD, but is way more reliable and 1/3 the cost.

Ive used the Sig Erson high flow II cam and it was done a 6500 rpm.

Do you have a video of your car.I would really like to learn these secrets
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Old 02-13-2013, 05:02 PM
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Hi Vinniekq2,
I've heard from several sources, one being Robbie at California High Performance, that the Sig High Flow II is junk and that the High Flow I outperforms it. I shift at 8,000 rpm because of fear! It shows no signs of shutting off even at that high rpm. I don't have a blanket and don't want to cut my feet off if something should let go.
Let me know where you are and I might be able to phone you and answer any questions you may have. I kept all the receipts for my engine and can help you build yours. In fact, if you are in southern California, I'll help you build it. I've been doing this for over 40 years (off and on) and have a lot of experience with high performance street engines and suspensions.
Barry
P.S. I have photos, but no videos.

Last edited by barry425; 02-13-2013 at 05:03 PM. Reason: add info
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Old 02-13-2013, 05:53 PM
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[QUOTE=F-BIRD'88;1644857]You'd be better served by getting a timing box that allows adjusting the timing a bit +/- as required, from the drivers seat. Rather than playing with the gasket. The fuel quality in the tank and the day-conditions will be the factors.

Just preset the dash timing dial in the middle of its range, and set the engine timing with a light.
Now you got convienient effective on the fly +/- spark timing adjustment.
Now you can adjust for different fuels, without lifting the hood.

X2 I Use that MSD Timing box and it works great.
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Old 02-13-2013, 06:02 PM
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barry425
I live directly north in Canada
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Old 02-13-2013, 08:49 PM
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Hi Barry 425,
I live WAY down south, in AUS.
I've always read that quench benefits are lost by .060" (OMG!... Der!) and are an avid fan of tight quench.
I run .035" in my 11.48:1 sbc 355 on 98octane RON (AUS ) which equates to roughly 92oct USA, with 34deg locked out.
I feel that a tight quench is extremely important for the reasons that you mentioned, but 10 thou! and 26deg, that's interesting, you got MY attention! Maybe I'll tighten mine up some! LOL!!
Is carbon build up a concern? I guess not if it sees 8000 regularly.

This should surely be 'food for thought' for the OP.

Btw Vinnie, your vette sounds ' great ' in the vid! , is that straight out of the collectors?


Duke
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  #24 (permalink)  
Old 02-13-2013, 09:00 PM
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thinwhiteduke,that sound is out the mufflers,,,,Im using 3 inch short turbos.thanks,
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Old 02-14-2013, 12:49 AM
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Here in California, we only get 91 octane. 100 octane is available at maybe 3 or 4 stations in L.A. and Orange Counties combined, but it costs 9-10 dollars a gallon. I'm retired, so that is too rich for my budget. My compression ratio was calculated using a plexiglass plate and burette on each combustion chamber, piston eyebrow (valve relief), head gasket, and cylinder. It is a true 11.6:1 and the combustion chambers are polished so no carbon has a chance to build up. Also, because the quench is so tight, no burning takes place in the quench area and so no carbon would build up there even if the chambers were not polished.
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Old 02-14-2013, 04:18 AM
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The over tight quench clearance is not what is allowing it to live at 11.6:1

Its the 28deg BTDC spark timng which is about 6-8 less than what the engine really needs. fill it up with a 110 unleaded and give it the spark advance it wants and you will see the difference.

Running it with retarded spark is allowing you to do it but is no where near optimum for a 23deg head SBC.

I used to run 12.65:1 on pump gas with 28 to 29deg BTDC timing.
I employed all the tricks too. .033" net quench. (.018" deck .015" gasket) hand smoothed edges etc etc.
ran ok but not near how good it ran with 36deg timing and 110 octane unleaded.
Like night and day.

The lack of spark advance is the only thing that is allowing it to live.
and you are giving up some power. There is no free lunch.

LT-1 motors had a forged dome piston and 64cc heads.

Flat tops gives less than 11.60 in a 355.
with a flat top and 64cc heads you are 10.60:1 with .030" quench

According to Joe Sherman, there he says there is a big difference in real actual knock resistantce between the 'different brands of "91 octane" gas, there. Some of them really stink.
California only mandates the advertized octane cannot be more than 91.
Nobody said the actual fuel octane has to match the label on the pump.
It just has to be labled and sold as 91 octane. You are pretty much running the same stuff we get.

Anybody can stop the knock by retarding the timing. Your timing is retarded. 28deg is not normal for that motor.

Last edited by F-BIRD'88; 02-14-2013 at 04:23 AM.
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Old 02-14-2013, 08:41 AM
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Quote:
Originally Posted by Landshark928 View Post
I am running 11:1 with aluminium heads and a .043" quench on 91 Octane, 93 when I can get it. No issues. Cam is a little bigger at 253*@0.050" and 110LSA. I run 36*total timing in by 3000rpms. I use vac advance to add 8* more under cruise.

Read your plugs and add timing a little at a time.
When you say "read the plugs". If a guy is looking for signs of detonation what appearance will the plug have?
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Old 02-14-2013, 09:32 AM
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Quote:
Originally Posted by prostcelica View Post
When you say "read the plugs". If a guy is looking for signs of detonation what appearance will the plug have?
If you catch it early it looks like small specks of black or grey "pepper". If you see some, back off timing a bit.

When extreme or prolonged it can start to melt the strap and tip.

This one has gone too far too long.



You can also change the spark plug heat range to help fight off detonation. But it's a compromise at best.
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Old 02-14-2013, 11:51 AM
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Hi F-Bird'88,
You didn't read my blog, apparently. I'm running a negative deck (pistons stick out of the block) and my quench is not .033, but .010 piston to head clearance. Since you are not acquainted with Doug Roe's engineering, I would not expect you to understand.
The gas in California is regulated more than other states. We even have different blends mandated for summer and winter. The octane is calculated by: research+motor/2=octane
I've already tried 100 octane gas ($9 per gallon) with Moroso Octane Boost and advanced timing. No good. It pings like crazy because the tight quench makes the fuel burn faster in the combustion chamber.
By the way, when a flat top piston sticks out of the block, your factory calculations for compression ratio go out the window.
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Old 02-14-2013, 01:09 PM
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Generally speaking the lower the quench area the more forced lateral acceleration and turbulence of the charge gas. Leads to quicker more complete burns. Proximity of the piston to head also allows for a little more heat removal from the piston. Less is better up to the point of interference...

The reason most go .035 to .045 is to get a nice benefit with a nice safety margin. Also the increased gains are less measurable from .035 to .025... diminishing return.

At 0.010" quench most engines will leave piston marks on the heads. How much rock does your piston have? How many rpms are we turning? How strong are your connecting rods? Lots of variables. Recommended quench ratings keep things safe and easy while still getting a nice benefit. Even pro engine builders rarely go below .025" quench. In fact going to low can actually cause charge gas to be trapped in the ring land area instead of the squish area, leading to unburnt fuel, lost power and increased emissions. Chasing that last 5HP and 10FTLB is not worth it to most Hotrodders.

Doug Roe could afford to strip and rebuild his Vega after every race. A little piston kiss was not a concern like it would be a for a street car.
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