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[airman]

Mostly knock is caused by carbon build up in chambers [raising compression ratio] and on valves [leaning the air flow] from not vigorously exercising the engine WEEKLY!

Elaborate on this please. How _vigorously_ one should exercise the engine?

[Q45tech]

A 10.2 CR engine needs to run at speed ...........those that do 80 mph continuous interstate runs for an hour a week should be fine.Anything above 2500 rpm.A bad situation is a crank and 15 minutes of slow traffic, then a shut off. The absolute worst case: cranking the car and only driving 5 minutes or less.

We are lucky [in some ways] as traffic around Atlanta can run 80 mph [not in rush hour which is most of the day] but on weekends.

You can always drive in 2nd gear [5,200 rpm @70 mph] and blow it out for 2-3 minutes by alternating WOT and closed.

[maxnix]

Or drive it in first gear at 55 mph while it is redlining, like elwesso!

No wonder his mileage sucks.

[Q45tech]

278 HP would be 139 pounds of gas x 1.15% extra richness = 160 pounds per hour or 160/6.2= 25.8 gallons per hour........0.4297 gallons per minute.........0.43 x @2.00=86 cents per minute vs say 8.5-9 cents minute at a normal 60-65 mph cruise. netting 77 cents rounded down to 75 cents for the fraction of time you let off.

Notice I said 2-3 minutes or $1.50-$2.25 extra per week for a magic tune up..............even less than BG44k per application which should be added once per month if your gas is really yucky.

Bet you never though that your Q cost 23 cents per minute [gas plus maint/repairs] Plus fixed depreciation and insurance to drive on the highway.......probably 50-60 cents per minute/mile.

[ScottJackson]

My take on this all... 10.5:1 compression with aluminum heads and a relatively small bore means that 87 octane should be fine. The only time you'll lose power is WOT. If you want to have the most power available at WOT, use premium. Carbon buildup in the chamber not only raises the compression ratio, but absorbs heat and promotes detonation. My 89 camaro with 4.020" bore, iron heads, and 10.4:1 does need premium for any full throttle. If I know I'm going to be interstate cruising with it and won't be opening it up, 87 works great.

[Q45tech]

Till you miscalculate and pass a car and face a semi headon......oh you said interstate driving.

Or you take a summer trip when it's 100F driving thru S. Georgia with AC on.

Mostly the problem is lack of maintenance [plugs, deposits, restricted air flow making the already lean cruise really lean for a second in low speed tip in throttle.

Saving $4-$4.40 on a 8 hour interstate trip maybe significant to some...........only trying it will tell you what to do on your car.You can always refill at 4 hours and make most of the problems start to go away.

The air velocity thru the valves is much higher on a 2 valve V8 at 2,000 rpm than on a 4 valve engine..........32valve V8 have a hard time cruising at 60 mph [2,000 rpm] other wise you would see much low diff gearing like in US V8 which can amble/lug along at 1600 rpm [Corvette].............32valve have very little swirl/tumble till 3,000 rpm.

The Q 2-1.5" intake valve have a combined area of 3.534 square inches vs single 1.94" [350 chevy] 2.956 square inches.

Try a set of these $6,000 heads on your IROC:http://www.ronsraceshop.com/co...B.php

[Q45tech]

Most knocking pinging on a Q occurs at 1500-2500 rpm not at higher rpm, when the advance is already retarded from the 44 degrees necessary to provide good efficiency under low VE conditions.

Really a ecu time delay caused from the time it takes for MAF voltage to reflect changes and the long distance from the chambers to the MAF.The plenum air is elastic a couple of rpms worth is stored plus 2 more rpms worth out to the MAF........more modern designs have a closer MAF and of course a faster ecu that can anticipate these sudden throttle transitions.......from the rate of change [degrees per millisec] of the throttle. Current drive by wire slows the sudden changes making tip in knock nonexistent!

At 2,000 rpm cruise the air is traveling thru the 3" MAF at about 11-12 Ft/sec, at 4,000 rpm WOT the air is moving 108 feet per second. 125 fs at 6,000 rpm WOT.

[ScottJackson]

Oh yes, the 32V SBC heads... I know the old Dominion 32V sbc heads had issues with valve guide wear, I wonder if those do too. At any rate, I don't like chevies. I built one because they're cheap to modify. In keeping with that theme, sure, I'll put in the cheap gas for cruise interstate. What's the valve area for a stock 4 barrel ford 351Cleveland? 2.19" diameter intake, 1.71" exhaust...?

[Q45tech]

2.19"?[ 2.041, 2.045, and 2.195] = 3.767 square inches......

I would hope a 351c with the racing valves would flow more than a 274 cubic street engine............6% more isn't much but we are disregarding cams and lift.

What really counts in the curtain area.