98 Vortec 350 - comp ratio

[Redneckgeriatric]

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.

several folks played with those squish grooves years ago.i cut some too, didnt hurt, but was no proof that is helped as i recall. it was kinda considered as something to try. best advice i can give is to round the edges on the grooves to not create hot edges. about the same time, pent roof was all the rage, that had about the same conclusions. compression and timing nightmares were introduced into the equation and almost no one wanted to play with the $$ to prove theory. i quit keeping up with that, but a buddy does atv stuff. he worked on a kawasaki v-twin that came from factory with pent roof and big compression. worked well, until he bought into the hype of pretty packaging, internet hyperbole and "performance kit"! it always sucked after that. so take all that with a grain of salt.

 

[Erik the Awful]

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.

There's a difference between ensuring all your fuel is burned and "moving" heat from the combustion chamber to the exhaust pipe. Also, too high an EGT is a thing.

http://blog.innovatemotorsports.com/afr-vs-egt-gauges-when-to-tune-with-one-the-other-and-both/
"It’s also important to recognize that peak EGT readings don’t necessarily coincide with maximum stress on the engine. More mechanical energy being extracted from the combustion process for a certain volume of fuel being burned means less energy headed out the exhaust, and it’s well known that peak power is almost always found on the rich side of stoichiometry, which will read cooler than peak EGT."

 

[L31MaxExpress]

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.

Dynamic compression ratio will always be lower than static. RPM is not part of the calculations.

 

[L31MaxExpress]

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

With the Ramjet cam you will get detonation at ~9.6:1 with decent quench. I had to run 93 just to run the stock timing map. To get real power out of the combination I had to run E85.

 

[CW73]

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)

I ran the LT1 cam with stock compression or maybe even less due to aftermarket head gaskets. I used the suburban for towing... so it wasn't near 10:1. I had shorty headers, 2 to 1 Flowmaster, 3 inch tailpipe and K&N intake. It ran strong , pulled great and sounded good. I put 93 in it a few times and couldn't tell any difference in performance. Just my personal experience with that setup. My 98 C1500 with higher compression, Lt4 cam, 1.6 Scorpion rocker and many other mods is apart due to a deer altercation... but when it's back together I'll run 87 and see if its pulling timing. I towed a utility trailer with 2 large shop doors back from Dallas (about 3hrs) on 87. Felt fine, no audible detonation. The 10 in converter kinda make towing suck though lol. Again, just my personal experience. Different vehicles.. different combinations.. different outcomes.

 

[Schurkey]

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.

It would be worth your time to look at the articles posted by "The Old One" Larry Widmer in regards to his company's combustion research (Endyn, EnergyDynamics)
http://www.theoldone.com/articles/default.asp

Specifically, page 3 of this series from way back in 1985:
http://www.theoldone.com/articles/Hot_Rod-The_Soft_Head_1.jpg
http://www.theoldone.com/articles/Hot_Rod-The_Soft_Head_2.jpg
http://www.theoldone.com/articles/Hot_Rod-The_Soft_Head_3.jpg

I'll grant that Widmer has generated his share of controversy.

To my way of thinking, sans turbocharger, almost all the energy that goes out the exhaust port as heat, is wasted. Ideally, that heat should have pushed the piston down.

Some of the exhaust energy goes out the port as velocity, (and, yeah, velocity and heat are interconnected) the velocity energy can be used to scavenge the chamber.

As for marking the exhaust with crayon, and then seeing where it discolored or melted, I think we can safely say that the science of exhaust tuning is far more complex than seeing where some random marker stops melting. I've heard this referenced to tire crayons, actual calibrated temp-sensing crayons, and cheap home-improvement-store paint pens. None of it makes sense.

Dynamic compression ratio will always be lower than static. RPM is not part of the calculations.

Define "dynamic compression". "Dynamic compression" is generally calculated without RPM as a variable. Calculating actual compression pressure with the engine operating, would require an input for "ram tuning". Measuring actual compression pressure at various engine speeds would include "ram tuning".

Given enough ram tuning, I can see "true" dynamic compression being higher than static compression.

 

[L31MaxExpress]

Define "dynamic compression". "Dynamic compression" is generally calculated without RPM as a variable. Calculating actual compression pressure with the engine operating, would require an input for "ram tuning". Measuring actual compression pressure at various engine speeds would include "ram tuning".

Given enough ram tuning, I can see "true" dynamic compression being higher than static compression.

You are not likely to see 100% VE on a street small block unless it has a blower or turbo. I think a well moded TPI can get close where the runners are tuned for peak resonance but I think most of them even fall short.

 

[Christian Steffen]

To my way of thinking, sans turbocharger, almost all the energy that goes out the exhaust port as heat, is wasted. Ideally, that heat should have pushed the piston down.

^^This. Scavenging is important but forcing the piston down is more important. Engines are heat pumps, dumping heat to the atmosphere means lower thermodynamic efficiency.

 

[Redneckgeriatric]

looks like i got it started. yep, keep in mind, that i gave some thought provoking answers concerning someones questions or arguments about timing. not adressing individual posts.

note i said back in the day about the crayons. this was the only science avaulable then. folks still said they had a 3/4 race cam for crying out loud. far from port probes and the ability to measure 3/5/8 gasses and their affects on velocities today.

we didnt have weather stations either. but some things remain true, as heat in exhaust carries more air speed and sometimes less timing makes more power.

i guess next we will be decyphering the magical formula to mixing nitro? joe smith said ya keep adding it till the motor blows, and then back off a smidgen. lol

something simple like discussing low HP street machines can escalate quickly to magical numbers and cause and effect of making power. keeping it real for daily driver reliable vehicle is pretty much, just let the engine make the power it was designed to make, and where it was designed to make it. but thats no fun, especially when talking on the internet.

 

[Erik the Awful]

No worries. I wasn't trying to call you out, but I think we need to be as accurate as we can in discussing these things.

Speaking of nitro, Hot Rod had a really good article many years ago on The Surfers and how they owned the nitro drags through a solid application of hot rod ingenuity and a knowledge of chemistry. They ran the same Hilborn fuel injection setup as everyone else, but secretly drilled their own nozzles for better atomization. Their motor sounded nastier than everyone else's, and when a competitor asked how much gas they were mixing with their nitro, they played dumb, saying, "You're supposed to mix it?"