98 Vortec 350 - comp ratio

[Diptenkrom]

You can run 87 or 89 with just decking the heads to true them up and the .030 gaskets. My 98 has had the heads decked .010 and .015 steel gaskets and have ran 87 with no problem but I normally try to run 91 due to tune. As far as the cam, I would go with the Ramjet because of the weight of a 4wd suburban. You can run that cam with stock springs and tune. The hot cam will move torque up higher in the rpm range. I run the hot cam with 1.6 rockers in my 98 C1500 with 4:10s, a 4l80 and a 3000 stall 10 in converter.

so i should be able to run the ramjet cam, with stock springs and retainers, just new lifters, and minimal head decking with cometic .030 MLS and be good with a little extra power. the thing is here,that i am trying to do this with as little downtime as possible, and pulling the whole motor to get the block decked will increase time and money by a lot. i'm not looking to compete at anything, just have a bit more power for doing what suburbans were meant for, hauling and towing!

 

[Redneckgeriatric]

Hard to say what octane rating will be required, IF THE KNOCK SENSOR IS PULLING TIMING to prevent detonation.

You'd have to connect a scan tool, and watch the knock sensor/ignition retard data. It's entirely possible to run an engine that "needs" 93 octane on 87, if the computer is pulling timing like mad, and the vehicle is lightly loaded. Doesn't make it right.

amen. well said. amazes me to hear about these higher octane "tunes". i see reference to chips that require higher octane and colder thermostats, and i laugh. are they shooting for open loop all the time? is the chip fried to turn off the timing retard, so they demand higher octane?
are there any real tuners (a human with data log and dyno skills) ? why dont folks build the engine to run on pump gas 87 with ethanol to make more power and capable of being tuned for best performance?

 

[L31MaxExpress]

amen. well said. amazes me to hear about these higher octane "tunes". i see reference to chips that require higher octane and colder thermostats, and i laugh. are they shooting for open loop all the time? is the chip fried to turn off the timing retard, so they demand higher octane?
are there any real tuners (a human with data log and dyno skills) ? why dont folks build the engine to run on pump gas 87 with ethanol to make more power and capable of being tuned for best performance?

Because higher compression ratio and more timing to use higher octane offers a fuel mileage increase that cancels out the hogher cost at the pump and offers more power.

My Infiniti M56S was 12:1 and it ran best on 93 octane.

My 383 in my Express van is 11:1 and runs on 89 running empty and 91+ towing. Really wakes up on E85 though.

Running a colder thermostat does not mean open loop all the time. Just means the heads run cooler and the intake charge stays cooler. Both of which mean more power.

 

[L31MaxExpress]

so i should be able to run the ramjet cam, with stock springs and retainers, just new lifters, and minimal head decking with cometic .030 MLS and be good with a little extra power. the thing is here,that i am trying to do this with as little downtime as possible, and pulling the whole motor to get the block decked will increase time and money by a lot. i'm not looking to compete at anything, just have a bit more power for doing what suburbans were meant for, hauling and towing!

You will need to run good gas when towing with the Ramjet cam.

 

[Redneckgeriatric]

Because higher compression ratio and more timing to use higher octane offers a fuel mileage increase that cancels out the hogher cost at the pump and offers more power.

My Infiniti M56S was 12:1 and it ran best on 93 octane.

My 383 in my Express van is 11:1 and runs on 89 running empty and 91+ towing. Really wakes up on E85 though.

Running a colder thermostat does not mean open loop all the time. Just means the heads run cooler and the intake charge stays cooler. Both of which mean more power.

i have heard all that before, but there are builds (and proper tunes) that make more VE on everyday pump gas. lower octane can and will make more power. higher octane is used to control the detonation that is present in poor builds/tunes. what if you could run low octane /fast exploding fuel and have no detonation?
yes, more timing moves more heat to the heads, less timing moves more heat to the exhaust where it is needed to help speed the exhaust flow. it is a balance that is made at the drawing table and again at the dyno. and finally with data logs and side of the road tuning to find those crevaces in the tune that were missed or skipped while tuning on the dyno.

just thinking out loud.

 

[Mark Gilbert]

If you haven't heard of "Singh Grooves" it is another twist to get you thinking. If I built more engines I would think about trying them on one of them.

 

[Erik the Awful]

i have heard all that before, but there are builds (and proper tunes) that make more VE on everyday pump gas. lower octane can and will make more power. higher octane is used to control the detonation that is present in poor builds/tunes. what if you could run low octane /fast exploding fuel and have no detonation?
yes, more timing moves more heat to the heads, less timing moves more heat to the exhaust where it is needed to help speed the exhaust flow. it is a balance that is made at the drawing table and again at the dyno. and finally with data logs and side of the road tuning to find those crevaces in the tune that were missed or skipped while tuning on the dyno.

just thinking out loud.

I have some issues with what you said, but I'm not going to say your wrong, just that I have a different understanding of how octane and compression interrelate.

Octane is simply the fuel's resistance to knocking, and a higher octane tends to burn slower. Fuel burns, but if it's compressed to where it self-ignites (explodes), you get detonation. Higher compression ratios can cause fuel to self-ignite, unless it has a higher octane. The more you compress the air fuel mixture, the more power you can extract from the burn, and the more advance you run means more time the expanding gases can exert force on the piston before the exhaust valve opens. Too much advance and your gases are reaching peak pressure before TDC (simplified explanation). I don't agree with your statement on heat in the exhaust. More heat in the exhaust means the gases are trying to expand back through the exhaust valve, hindering your exhaust flow.

I will say that given a set timing advance and a set compression ratio that is compatible with a lower octane, a lower octane fuel will make more power than a higher octane, but that is because the fuel is slightly more gasoline and less additives. As soon as you start running more compression or advance the higher octane produces more power.

 

[Diptenkrom]

I have some issues with what you said, but I'm not going to say your wrong, just that I have a different understanding of how octane and compression interrelate.

Octane is simply the fuel's resistance to knocking, and a higher octane tends to burn slower. Fuel burns, but if it's compressed to where it self-ignites (explodes), you get detonation. Higher compression ratios can cause fuel to self-ignite, unless it has a higher octane. The more you compress the air fuel mixture, the more power you can extract from the burn, and the more advance you run means more time the expanding gases can exert force on the piston before the exhaust valve opens. Too much advance and your gases are reaching peak pressure before TDC (simplified explanation). I don't agree with your statement on heat in the exhaust. More heat in the exhaust means the gases are trying to expand back through the exhaust valve, hindering your exhaust flow.

I will say that given a set timing advance and a set compression ratio that is compatible with a lower octane, a lower octane fuel will make more power than a higher octane, but that is because the fuel is slightly more gasoline and less additives. As soon as you start running more compression or advance the higher octane produces more power.

all of this i understand, it is why my Audi TT 1.8T runs on premium fuel only. turbo is basically a pressure adder, and a heat adder at once, and with low octane fuel you will blow up the motor from detonation in a hurry. Also I come from the "import world," where everything is high compression unless it is turbo and most of my cars have required at least 89 octane due to that. I WANT to add compression, to add power, but i do not want to have to fill up the 42 gallon tank with 93 octane. if you make a "quality tune" on a 12:1 compression engine that runs on 87, it will be a slug as the timing will have to be super retarded to even stay alive with any throttle. If I can run 10:1 compression and 87 or 89 then that is ideal. i am not trying to push the limits, but increase the baseline a bit.

on another note, to get back on topic, i have made the decision to install the RamJet cam (14097395) and 1.6 ratio roller tip rockers with beehive springs and comp retainers for the clearance, the driveability, fuel economy, and the flat torque curve. the rest of the equation is - do i just get the heads checked and surfaced with a valve job, or do i deck at all? goal remember is about 300hp

 

[CW73]

so i should be able to run the ramjet cam, with stock springs and retainers, just new lifters, and minimal head decking with cometic .030 MLS and be good with a little extra power. the thing is here,that i am trying to do this with as little downtime as possible, and pulling the whole motor to get the block decked will increase time and money by a lot. i'm not looking to compete at anything, just have a bit more power for doing what suburbans were meant for, hauling and towing!

Yes sir, I ran a stock LT1 cam in my 98 C2500 Suburban.. stock springs, retainers and reused the roller lifters. Stock tune on 87. PCM didn't pull timing. (LT1 cam is just a tiny bit more lift and intake duration than the Ramjet cam)

 

[Redneckgeriatric]

I have some issues with what you said, but I'm not going to say your wrong, just that I have a different understanding of how octane and compression interrelate.

Octane is simply the fuel's resistance to knocking, and a higher octane tends to burn slower. Fuel burns, but if it's compressed to where it self-ignites (explodes), you get detonation. Higher compression ratios can cause fuel to self-ignite, unless it has a higher octane. The more you compress the air fuel mixture, the more power you can extract from the burn, and the more advance you run means more time the expanding gases can exert force on the piston before the exhaust valve opens. Too much advance and your gases are reaching peak pressure before TDC (simplified explanation). I don't agree with your statement on heat in the exhaust. More heat in the exhaust means the gases are trying to expand back through the exhaust valve, hindering your exhaust flow.

I will say that given a set timing advance and a set compression ratio that is compatible with a lower octane, a lower octane fuel will make more power than a higher octane, but that is because the fuel is slightly more gasoline and less additives. As soon as you start running more compression or advance the higher octane produces more power.

taking camshaft into consideration, at what rpm does dynamic compression equal static, and at that point, what would a properly tuned engines fuel and timing tables looklike?

tuning with exhaust heat is real. EGT kept as high as possible without damaging components because hot air is fast air. heat wrap is used to keep heat in the pipe, because a cold spot will slow air and cause turbulance. an old hot rod and race track tuning trick was to mark exhaust pipe with crayon, or wax. the point that the marker stopped melting is where you cut the pipe off. maybe ask the turbo guys about EGT and power.