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I'm starting to think about this winters project. I recently did a cam swap from a CC503 to a 219/227 .549/.565 114+3. The main reason for that swap was to eliminate bucking during low load cruising. It got rid of 90% of the bucking and now I want to get rid of the rest of it. The last piece of the puzzle I believe is my high compression. Static is 11.5:1 and dynamic at my hometown altitude of 3,000ft is 10:1 according to Wallace's online calculator. I'd like to get back to stock compression which would put dynamic somewhere around 9.1:1. I already spoke to LE and he recommended his Trick Flow heads with larger chambers to drop compression up to 1 point. He hasn't answered my follow up questions yet though:
What was the idea behind raising compression in the first place? Is it just an easy way to make more horsepower?
Is that "wrong" or unorthodox to use high compression pistons and low compression chambers?
Your compression ratio isn't going to create surge like that. Raising the compression ratio yields more power at the expense of detonation resistance. However, decreasing the factory quench height (from .075+ to .040ish) will add detonation resistance back. Both of these things result in a more efficient engine and it's possible to make more power with no ill effects here. You are only 1 point over stock which is nothing.
What you are still experiencing is cam surge. A cc503 has +3 degrees of overlap. Your current cam has -5 degrees of overlap. 8 degrees of difference isn't a whole lot considering a factory f-body cam has -27.5 degrees and b-body cam has -28.5 degrees. That is why those engines can be lugged down to 1200rpm smoothly. Is that good for a motor? Hell no. Lugging an engine is one of the worst things you can do. You're heavily loading it when there's no available power, plenty of vibration, and little oil pressure.
What rpm range are you typically driving in? Keep in mind that the factory tach is commonly wrong. Mine reads 200-400 high throughout its entire sweep. With that cam I'd keep the revs between 1750-2300.
Your compression ratio isn't going to create surge like that. Raising the compression ratio yields more power at the expense of detonation resistance. However, decreasing the factory quench height (from .075+ to .040ish) will add detonation resistance back. Both of these things result in a more efficient engine and it's possible to make more power with no ill effects here. You are only 1 point over stock which is nothing.
What you are still experiencing is cam surge. A cc503 has +3 degrees of overlap. Your current cam has -5 degrees of overlap. 8 degrees of difference isn't a whole lot considering a factory f-body cam has -27.5 degrees and b-body cam has -28.5 degrees. That is why those engines can be lugged down to 1200rpm smoothly. Is that good for a motor? Hell no. Lugging an engine is one of the worst things you can do. You're heavily loading it when there's no available power, plenty of vibration, and little oil pressure.
What rpm range are you typically driving in? Keep in mind that the factory tach is commonly wrong. Mine reads 200-400 high throughout its entire sweep. With that cam I'd keep the revs between 1750-2300.
I see, thanks for the explanation. I typically drive between 1700-2000 rpm. The bucking actually isn't bad at all, it responds well to running rich so I just have my O2 switch points a little fatter in the light load cruising areas. It's totally gone in open loop but with the amount of miles I put on this car I want my O2's. I'd rather not have to manipulate it like that though.
I wouldn't mind more detonation resistance, that's been a constant struggle since I first got this engine. I've been able to fix most of my problem areas except for one. If I'm between 2500-3500 rpm in 5th under load there will be knock retard 100% of the time. To make it go away, I had to take out so much timing that there was no power at all so I put most of it back minus a few degrees and smoothed out the spark table. I suppose if these heads give me more power and more detonation resistance and nothing else, it'd still be worth it.
IIRC the stock GM AL LT1 head gasket is .049....doubt that would make much of a change over your current .040 .
you could pull some timing and or run higher octane fuel...
There's a gas station in my town that has a bunch of different fuels. I tried their 101 unleaded once. I did notice way less frequent knock retard with that fuel but it's $10/gallon. It also made the exhaust stink.
I see, thanks for the explanation. I typically drive between 1700-2000 rpm. The bucking actually isn't bad at all, it responds well to running rich so I just have my O2 switch points a little fatter in the light load cruising areas. It's totally gone in open loop but with the amount of miles I put on this car I want my O2's. I'd rather not have to manipulate it like that though.
I wouldn't mind more detonation resistance, that's been a constant struggle since I first got this engine. I've been able to fix most of my problem areas except for one. If I'm between 2500-3500 rpm in 5th under load there will be knock retard 100% of the time. To make it go away, I had to take out so much timing that there was no power at all so I put most of it back minus a few degrees and smoothed out the spark table. I suppose if these heads give me more power and more detonation resistance and nothing else, it'd still be worth it.
I'd work on the tune, not just spark but fueling and fuel timing. You also need to address the o2 delay and target mv at certain rpms. I have 11.8:1 scr and a lot more overlap with no surge. The timing tables look funky (double hump) but my fueling tables look pretty normal for my cam.
I did notice a big difference in driveability with matching the injector delays to my new injectors. If you are running different injectors and haven't changed the delay, I'd start there. Then adjust the timing and fuel curves accordingly. With overlap, at lower rpm you'll have fuel going straight through the engine and out the exhaust; you'll need to account for that. So you'll want to richen it up. I run speed density. Maybe start there with a speed density tune, then once it's running smooth re-enable the maf and tune only the maf.
Another thing to look at is individual injector trims. I used an ir thermometer gun and balanced the individual primary header temps by adjusting the individual injector trims at idle.
I'd work on the tune, not just spark but fueling and fuel timing. You also need to address the o2 delay and target mv at certain rpms. I have 11.8:1 scr and a lot more overlap with no surge. The timing tables look funky (double hump) but my fueling tables look pretty normal for my cam.
I did notice a big difference in driveability with matching the injector delays to my new injectors. If you are running different injectors and haven't changed the delay, I'd start there. Then adjust the timing and fuel curves accordingly. With overlap, at lower rpm you'll have fuel going straight through the engine and out the exhaust; you'll need to account for that. So you'll want to richen it up. I run speed density. Maybe start there with a speed density tune, then once it's running smooth re-enable the maf and tune only the maf.
Another thing to look at is individual injector trims. I used an ir thermometer gun and balanced the individual primary header temps by adjusting the individual injector trims at idle.
This assumes you are 1994+.
With the 503 the adjustment that made the most difference was injecting fuel onto an open intake valve. I didn't like the idea of sacrificing atomization though. With this new can that doesn't have overlap, would adjusting fuel timing make any difference? I figure with stock fuel timing, the fuel is sitting on the valve long enough already.
I couldn't find any good info on how to tune O2 delay so I just added something like 20% for my mid length headers. I'm also 24x using an LS1 PCM so I can't adjust the injectors individually. I have the car set to run different afr's in different driving conditions though. More rich with light throttle cruising, back to 14.7 on the highway, lean for decel to balance out the rich cruise.
What do you mean by "double hump" in the spark table? This is what mine looks like:
I'll probably get Lloyd's intake port work and his Trick Flows with compression down to 10.5-10.8. I like the sound of detonation resistance. Any idea what kind of power bump I can expect going from stock heads with "bowl and slight runner porting" to these Trick Flows with lower compression?
With the 503 the adjustment that made the most difference was injecting fuel onto an open intake valve. I didn't like the idea of sacrificing atomization though. With this new can that doesn't have overlap, would adjusting fuel timing make any difference? I figure with stock fuel timing, the fuel is sitting on the valve long enough already.
I couldn't find any good info on how to tune O2 delay so I just added something like 20% for my mid length headers. I'm also 24x using an LS1 PCM so I can't adjust the injectors individually. I have the car set to run different afr's in different driving conditions though. More rich with light throttle cruising, back to 14.7 on the highway, lean for decel to balance out the rich cruise.
What do you mean by "double hump" in the spark table? This is what mine looks like:
I'll probably get Lloyd's intake port work and his Trick Flows with compression down to 10.5-10.8. I like the sound of detonation resistance. Any idea what kind of power bump I can expect going from stock heads with "bowl and slight runner porting" to these Trick Flows with lower compression?
I'm talking about injector voltage delay, not injector timing. The voltage delay is matched to the injectors.
As far as power difference. I'm not sure. You could try a desk top dyno. Worked heads should make more power than stock. Higher SCR lets you run more overlap, get higher efficiency, and gain some low end torque back (that you lose with more overlap). Personally I'd keep the higher scr, but with the higher flowing heads.
07-11-2017, 04:24 PM
New heads to lower compression 
