MannyL Posted January 22 Report Share Posted January 22 Currently have a camed z22 and I just bought the 38 outlaw carb after seeing the 32/36 couldn’t keep the engine rpm up throttling through corners, I’ve seen people talk about running 91 octane I currently have oem high vol replacement pump and was wondering what spark plugs are recommended for the intake and exhaust sides with high octane Quote Link to comment
MannyL Posted January 22 Author Report Share Posted January 22 On a side note I still have stock exhaust header and was wondering who has a reputable long tube 4-1 header Quote Link to comment
iceman510 Posted January 22 Report Share Posted January 22 (edited) Proper spark plugs are not necessarily dependent only on octane. Proper heat range can depend on a lot of factors such as compression ratio, combustion efficiency, proper mixture, engine timing, etc. How do they look? Edited January 22 by iceman510 Quote Link to comment
datzenmike Posted January 22 Report Share Posted January 22 Stock compression engine so use the factory NGK plugs. BPR6ES for intake side. 6 is a cooler plug because it faces the hot exhaust valve. BPR5ES for the exhaust. 5 is warmer because it faces and is cooled by the intake air coming in. You don't need higher octane 91 this is a very low 8.42 compression engine with hemi head and dual plugs. It is very detonation resistant. Octane adds no power, it is a measure of resistance to igniting from excessive heat of compression mostly. A header might help in the higher rev ranges you expect but a waste on vehicles for regular use. The stock system is 'good enough'. I think the 720 uses a 2" pipe, you'll have to measure and see. Going to a 2 1/4" will increase the cross section by just over 25% (more than enough) increasing flow and reducing any 'back pressure'. If you have a catalytic converter you can eliminate it and run a turbo style muffler which is good for flow and still not annoyingly loud. A long tube header will extract more from the cylinder so it may upset your air/fuel mixture and need a jet change. Quote Link to comment
MannyL Posted January 22 Author Report Share Posted January 22 I currently have 2 1/4 all the way back from headers to a bigger exhaust chamber. Would the gains not be beneficial on 91 octane with an outlaw Weber at 3-5k rpm constantly. I have a small turbo to fab up a draw through setup if needed but I doubt with my abuse the engine will last that long Quote Link to comment
datzenmike Posted January 22 Report Share Posted January 22 What do you expect higher octane to do? Quote Link to comment
MannyL Posted January 22 Author Report Share Posted January 22 My thought is higher octane better spark more fuel more air would get me outa corners faster Quote Link to comment
datzenmike Posted January 22 Report Share Posted January 22 Again, octane is an ingredient that raises the ignition temperature of gasoline. 87 and 91 gas has the same energy in it. Higher compression allows you to extract and use more of the energy in the gasoline. Higher octane allows it to be used in a higher compression engine without it exploding from the heat caused by compression it. You can run 91 in it but it won't run any better than 87. Now if you were to raise your compression ratio you could take advantage of the higher octane rating and extract more power form your gas. Quote Link to comment
fiveoneO Posted January 26 Report Share Posted January 26 Higher octane will allow you to run more spark advance. This may or may not gain you a little bit more power. I'm not too familiar with how the timing on the 8 plug z engines works. Quote Link to comment
datzenmike Posted January 26 Report Share Posted January 26 Yes but the limiting factor is your compression ratio. If you're at 8.2 you are likely maxed out on advance already. The higher the compression the faster it burns and the faster the pressure rises and pushes down on the piston. Burn gunpowder and it fizzes and produces clouds of gas but confine it in a cardboard tube and close the ends and it explodes! Higher compression extracts more work out of gasoline however squeezing it that hard will cause it to explode from the heat of compressing it. Now this is where a higher octane comes in. It makes it harder for the gas to self ignite or ping/detonate. Going from 8.2 to 9.2 would gain maybe 3-5 hp at the power peak and from 8.2 to 10.2 perhaps 5-6 hp. It's the same gas just extracting more power more efficiently. What I would do is locate a W70 or W04 head casting from an '83-'86 Z20 powered 'Mileage Option' 720 truck. These were special small displacement Z20 engines with high compression to maximize economy. Mostly aimed at fleet operators or federal use. The combustion chambers are much smaller and would boost your compression to 9.59 and would need higher octane gas. Note the small flat areas on top and bottom of all the combustion chambers. Below... W04 head top W70 was used on the early Mileage option truck... Either should work but must have those two flat spots (quench areas) on the combustion chambers. To find a Z20 truck engine look under the passenger side hood hinge on the inner fender for the engine tag. Second line up from the bottom. Should say: ENGINE/MOTOR.... Z20(S) Quote Link to comment
Stoffregen Motorsports Posted January 29 Report Share Posted January 29 So this is a drift car? Quote Link to comment
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