brand of cam?
Administrator
Joined: Nov 1998
Posts: 71,112
From: Hell was full so they sent me to NJ
Re: brand of cam?
The LT1 MAF produces a frequency output. The hot wire is held a fixed number of degrees above the temp of the incoming air, and a Wheatstone bridge measures the power input required to heat the wire. The power value is converted to a variable frequency by the electronics in the sensor. The PCM contains a table of mass air flow vs. MAF frequency. The theory uses the BTU's lost from the wire as a measure of mass air flow, based on the specific heat of air (BTU/#-*F).
Given the fact that the sensor is sampling only the very tiny bit of air that actually contacts the wire and extrapolating that mass flow over the total face area of the meter, the calibration has to be based on a known flow velocity distribution over the face of the meter. The screen distributes the air more uniformly, so the sample has a known relationship to the actual air flow. If you do anything that changes the velocity distribution across the face of the meter, the calibration is affected.
The straighter the duct leading into the meter, the more uniform the flow distribution. Instrument applications generally recommend at least 10 diameter of straight duct before a hot wire meter. That would equate to about 30" of straight pipe. The LT1 doesn't have that. It's bending the air several times, within about 15-20 inches of the MAF, in a duct with changing cross-section. Change the ductwork from the way GM set it up, and you will change the calibration.
GM actually took the screen out of the C5 MAF sensor, and picked up 5HP. They were able to do that because if the symmetry of the air intake system. Using an LS1 airbox would appear to be similar, but the air is going to be fairly turbulent as it enters the box. Hard to say whether pulling the screen out of the MAF behind an LS style box would do as much harm as pulling the screen out of the MAF downstream of the stock LT1 ductwork.
Given the fact that the sensor is sampling only the very tiny bit of air that actually contacts the wire and extrapolating that mass flow over the total face area of the meter, the calibration has to be based on a known flow velocity distribution over the face of the meter. The screen distributes the air more uniformly, so the sample has a known relationship to the actual air flow. If you do anything that changes the velocity distribution across the face of the meter, the calibration is affected.
The straighter the duct leading into the meter, the more uniform the flow distribution. Instrument applications generally recommend at least 10 diameter of straight duct before a hot wire meter. That would equate to about 30" of straight pipe. The LT1 doesn't have that. It's bending the air several times, within about 15-20 inches of the MAF, in a duct with changing cross-section. Change the ductwork from the way GM set it up, and you will change the calibration.
GM actually took the screen out of the C5 MAF sensor, and picked up 5HP. They were able to do that because if the symmetry of the air intake system. Using an LS1 airbox would appear to be similar, but the air is going to be fairly turbulent as it enters the box. Hard to say whether pulling the screen out of the MAF behind an LS style box would do as much harm as pulling the screen out of the MAF downstream of the stock LT1 ductwork.
Registered User
Joined: Aug 2005
Posts: 39
From: Las Vegas
Re: brand of cam?
... ......
I dont have an LT1 but an EFI sbc that had AFR 195 heads with stealth ram intake which has been used on some LT1 cars before after its modded to fit. behavior of the cams wouldnt change no matter what its in. If the old ecms can handle it, I'm willing to bet the more modern stuff should beable to as well. I had a 383 with a big custom grind. Thats all I generally run since my builds are not typical and need custom stuff to fit the application best. Mine was sorta like a CC306 on steroids. 230/245 at .050 but 109 lsa and over .600" lift with 1.6 rockers. Tuned easily and drove exceptionally well. Sounded like a disturbed hornets nest but drove incredibley docile. It did everything I asked it to do.
Also ran a 360" motor with stealth ram and old AFR 190's which are close to L98 aluminum heads. 280xfi cam, 230/236 on a 113 lsa, .576/.570. Good cam, but mostly top end power for that small cubes and hard to control valves. Needs much stiffer springs than what was used and stiff than what COMP recommends for those cams. Go figure
Idle was rough and lopey but stable enough to daily drive in the summer and Houston traffic. 800 rpm idle or so.
Local guy ran the AI 226/234 in his 96 LT1 and it ran very well. Lower 12's at almost 116mph. Thought it was a stock head car but the car was alittle lightened. it may have been mildly ported too, hard to say but the performance seems more like a 370's whp + car which would have needed head mods.
My buddy ran a cc306 in his 95 with stock heads and ran low 12's too but it wasnt trapping more than 110-112 I dont think.
Bigger cams do not have the bottom end and require gear/converter/compression to run right.
From what you described, you definately dont want to go over 503 shelf grind. Like I said, thats what i'd run with a good tune or the GM 846/crane cam since I like alittle bigger cam in my drivers, but by no means are they THAT big to make it an undriveable cam.
Now alittle less duration and tighter LSA can also work. LT1 short runner intakes seem to like tighter LSA's. ECM should beable to handle it in closed loop but nothing wrong with an open loop tune if you have to run them.
I dont have an LT1 but an EFI sbc that had AFR 195 heads with stealth ram intake which has been used on some LT1 cars before after its modded to fit. behavior of the cams wouldnt change no matter what its in. If the old ecms can handle it, I'm willing to bet the more modern stuff should beable to as well. I had a 383 with a big custom grind. Thats all I generally run since my builds are not typical and need custom stuff to fit the application best. Mine was sorta like a CC306 on steroids. 230/245 at .050 but 109 lsa and over .600" lift with 1.6 rockers. Tuned easily and drove exceptionally well. Sounded like a disturbed hornets nest but drove incredibley docile. It did everything I asked it to do.
Also ran a 360" motor with stealth ram and old AFR 190's which are close to L98 aluminum heads. 280xfi cam, 230/236 on a 113 lsa, .576/.570. Good cam, but mostly top end power for that small cubes and hard to control valves. Needs much stiffer springs than what was used and stiff than what COMP recommends for those cams. Go figure
Idle was rough and lopey but stable enough to daily drive in the summer and Houston traffic. 800 rpm idle or so. Local guy ran the AI 226/234 in his 96 LT1 and it ran very well. Lower 12's at almost 116mph. Thought it was a stock head car but the car was alittle lightened. it may have been mildly ported too, hard to say but the performance seems more like a 370's whp + car which would have needed head mods.
My buddy ran a cc306 in his 95 with stock heads and ran low 12's too but it wasnt trapping more than 110-112 I dont think.
Bigger cams do not have the bottom end and require gear/converter/compression to run right.
From what you described, you definately dont want to go over 503 shelf grind. Like I said, thats what i'd run with a good tune or the GM 846/crane cam since I like alittle bigger cam in my drivers, but by no means are they THAT big to make it an undriveable cam.
Now alittle less duration and tighter LSA can also work. LT1 short runner intakes seem to like tighter LSA's. ECM should beable to handle it in closed loop but nothing wrong with an open loop tune if you have to run them.
Well the issue with the LT1 PCM is it controls the trans shift points also. So will it shift at lower rpm or even shift at all if rpm is low?
That and the EGR is solenoid metered by the PCM so it can become a smog test problem for NOx - please don't ask how i know this.
Another sad limitation is that short runner intake. Eldebrock has an improved intake but i suspect is nothing like the bolt on improvement the Lingenfelter Super Ram is/was.
Thx for sharing Orr,
cardo0
Administrator
Joined: Nov 1998
Posts: 71,112
From: Hell was full so they sent me to NJ
Re: brand of cam?
You could swap out the "sad" LT1 intake (2.8" runner) for an L98 intake (21" runner). You would see a bit more torque with the L98 around 3,000 RPM, but the engine would run out of power at 4,000 RPM. It's a matter of personal preference, and how you plan to use the engine. The LT1 design serves it's purpose well for an engine in stock form.
You could also spend $460 on the Edelbrock LT1 intake to increase the runner length to 3.2". Here's the conclusion GM High Tech Performance reached after comparing the factory intake to the Edelbrock:
You could also spend $460 on the Edelbrock LT1 intake to increase the runner length to 3.2". Here's the conclusion GM High Tech Performance reached after comparing the factory intake to the Edelbrock:
Conclusion
The factory LT1 intake manifold is clearly a well-designed piece, and hard to beat when paired with the stock heads. Despite being more efficient and higher flowing, as indicated by the leaning out of the air/fuel ratio with the addition of the intake (and 52mm throttle body) and its ability to make similar power with a much smaller plenum volume, the Edelbrock intake did not manage significant enough improvement over the factory manifold to warrant its $460 price tag if it is to be the only change. However, most likely this is only because with the larger runners the mismatch from the manifold to the heads becomes significantly increased, causing a restriction.
The factory LT1 intake manifold is clearly a well-designed piece, and hard to beat when paired with the stock heads. Despite being more efficient and higher flowing, as indicated by the leaning out of the air/fuel ratio with the addition of the intake (and 52mm throttle body) and its ability to make similar power with a much smaller plenum volume, the Edelbrock intake did not manage significant enough improvement over the factory manifold to warrant its $460 price tag if it is to be the only change. However, most likely this is only because with the larger runners the mismatch from the manifold to the heads becomes significantly increased, causing a restriction.
Registered User
Joined: Aug 2005
Posts: 39
From: Las Vegas
Re: brand of cam?
Let me qualify that. For a low rpm short cammed engine turning a 4L60E auto and 3.23 rear gears the stock manifold is not a complimentary piece - the longer the runners the better in this case. Now for a large cammed hi rpm engine driving a M6 then yes the stock intake makes a great combo.
Maybe u would have some insight on high compression and the EGR control affecting NOx Mr. RamAir? What do run for a cam and compression ratio in your 383"?
Just wanting to learn,
cardo
Registered User
Joined: Sep 2001
Posts: 4,152
From: Woodstown, NJ
Re: brand of cam?
Geeze, everyone here takes everything so personal.
Let me qualify that. For a low rpm short cammed engine turning a 4L60E auto and 3.23 rear gears the stock manifold is not a complimentary piece - the longer the runners the better in this case. Now for a large cammed hi rpm engine driving a M6 then yes the stock intake makes a great combo.
Maybe u would have some insight on high compression and the EGR control affecting NOx Mr. RamAir? What do run for a cam and compression ratio in your 383"?
Just wanting to learn,
cardo
Let me qualify that. For a low rpm short cammed engine turning a 4L60E auto and 3.23 rear gears the stock manifold is not a complimentary piece - the longer the runners the better in this case. Now for a large cammed hi rpm engine driving a M6 then yes the stock intake makes a great combo.
Maybe u would have some insight on high compression and the EGR control affecting NOx Mr. RamAir? What do run for a cam and compression ratio in your 383"?
Just wanting to learn,
cardo
It's obvious you're fairly new to this forum and "wanting to learn." Perhaps you should revise your learning methods and contribute with quality thought-out posts.
I don't bitch about other posters very often but when you spout half bad/half good overcomplicated info on a forum which I have frequented for a long time and helped build with CORRECT unbiased info it's hard not to say anything about it.
But to (respectfully) answer your question...
The 383 I have built runs at 12.5:1 compression. Cam is a 237/242 .604"/.598" on 1.6 rockers with a 107.9 LS. Considering tightening the overlap increases the amount of natural EGR (the factory LT4 engine and production cam didn't even have an EGR valve) emissions isn't a concern.
Registered User
Joined: Aug 2005
Posts: 39
From: Las Vegas
Re: brand of cam?
My intent to irritate? Google searches and skimmed internet articles when i quote Smokey Y., D. Vizard, John Lingenfelter from their own books? Nothing is worth the effort with you as i can see that now. I don't attack anyone here with labels, personal attacks or accusations. The truth hurts and you and your little click here are in pain to say the least. Something as simple as intake runner length becomes inadequate no matter how many times i try to explain it tells me how self righteous those are that attack me at any/every opportunity rather than have anything to share or to provide advice.
This conversation is going no where but at least now i know what i am dealing with. And no this isn't your personal forum - it is owned and operated by Internet Brands. Maybe you need to review their rules and your agreement.
cardo0
This conversation is going no where but at least now i know what i am dealing with. And no this isn't your personal forum - it is owned and operated by Internet Brands. Maybe you need to review their rules and your agreement.
cardo0
Admin Emeritus
Joined: Dec 1997
Posts: 11,157
From: Nashville, TN area
Re: brand of cam?
At the suggestion of others, I have reviewed this thread.
First of all, we have a very, very smart group of people here and a tremendous amount of experience and countless successful track times to prove it (all of which I am thankful). All of the engine building books and articles in the world cannot compare to the collective knowledge here simply because as every expert engine builder will tell you, books are only a guide and will never compare to real-world experience. Every car is different, every build is different, and every builder is different. Those variables are things a book or article can never capture.
I get uncomfortable when I have to step in between to sides and have to assess things for the greater good of the continued flow of comradery here. As I did, I discovered that it was summed up best here:
Those who are new here should respect the knowledge of those who aren't. Those who are veterans here do not have the responsibility to defend their knowledge that is already proven through trial and error and not schooling others. It is okay to question for the sake of learning, but a challenge and contradiction isn't always received well. The intent is to share knowledge and not prove and disprove. That is what Internet Brands puts myself and the rest of the staff here in charge of encouraging.
I'd like to ask everyone to keep that in mind moving forward.
First of all, we have a very, very smart group of people here and a tremendous amount of experience and countless successful track times to prove it (all of which I am thankful). All of the engine building books and articles in the world cannot compare to the collective knowledge here simply because as every expert engine builder will tell you, books are only a guide and will never compare to real-world experience. Every car is different, every build is different, and every builder is different. Those variables are things a book or article can never capture.
I get uncomfortable when I have to step in between to sides and have to assess things for the greater good of the continued flow of comradery here. As I did, I discovered that it was summed up best here:
I am sorry you took my post as personal, because I obviously didn't. I'm not here to continuously argue what I think is wrong and what I think is right, just to share what I've learned over the years in REAL LIFE experience, through trial and error, not through Google searches and skimmed internet articles. Judging from your (multiple) previous posts you seem to have a hard time dealing with that by your obvious intent to irritate. I've been here for a long time and have seen members with attitude like you come and go. If you don't change how you respond to other people's experience then you're probably not going to fit in around here.
It's obvious you're fairly new to this forum and "wanting to learn." Perhaps you should revise your learning methods and contribute with quality thought-out posts.
It's obvious you're fairly new to this forum and "wanting to learn." Perhaps you should revise your learning methods and contribute with quality thought-out posts.
I'd like to ask everyone to keep that in mind moving forward.
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