TT 408 numbers
I grew up with those things. Was one of the first to run 10's N/A with an 86mm bore on an RS Machines sleeved block. Nobody thought i could get a HG to seal on an 86mm bore back then. Indian Head Gasket Sealer and a step cut on the block (machining deck below sleeves) sealed that sum' bitch up perfectly.
At any rate - I still stand by that you know the answer already. :-)
At any rate - I still stand by that you know the answer already. :-)
I see what your saying. So with that logic the concept of the de-stroked motor would prevail. If the 6.0 blocks with the 4.8 cranks are making 1100 on only 20lbs i wonder what an LS7 block or LS3 would make with the increase in bore size ans say 28-30lbs Also i have to ask. What made you decide to bite the bullet and move over to an LSX block?
Last edited by oscs; Apr 17, 2015 at 09:22 AM.
Find MBT and knock the motor back a couple degrees from there and you are in a perfect scenario. Find MBT on a dyno or at the track in a smaller load capacity. I.E. don't go looking for MBT at full tilt. Look for it at a smaller load level. Once found knock it back 3-4 degrees for safety then start cranking up the boost.
I still believe this is a HUGE mistake people make in tuning FI cars. The whole movement of no timing or low timing with ls motors is related to the accidental crossing of MBT and motors blowing up quickly. That's why I say just flat setting timing conservatively is a band aid for not understanding the motor.
I have seen MBT on LS cars at 19 degrees and I have seen it as low as 11 degrees. If someone is setting timing at 12 degrees conservatively and have one of these weird 11 degree MBT motors it will break. Conversely, if they have a 19 degree MBT motor, they are leaving probably 15% of their safe horsepower capability on the table.
I grew up with those things. Was one of the first to run 10's N/A with an 86mm bore on an RS Machines sleeved block. Nobody thought i could get a HG to seal on an 86mm bore back then. Indian Head Gasket Sealer and a step cut on the block (machining deck below sleeves) sealed that sum' bitch up perfectly.
At any rate - I still stand by that you know the answer already. :-)
At any rate - I still stand by that you know the answer already. :-)
The impact of Honda's on the current 28 to 40 year old car enthusiast crown can not be quantified. Iconic little cars those hatches. I still would like to build another one this day with my older guy budget and know how just to see what is possible. :-)
Timing with FI motors is all related to MBT. Once you cross MBT you are doubling cylinder pressure with every degree of timing past MBT. DOUBLING!
Find MBT and knock the motor back a couple degrees from there and you are in a perfect scenario. Find MBT on a dyno or at the track in a smaller load capacity. I.E. don't go looking for MBT at full tilt. Look for it at a smaller load level. Once found knock it back 3-4 degrees for safety then start cranking up the boost.
I still believe this is a HUGE mistake people make in tuning FI cars. The whole movement of no timing or low timing with ls motors is related to the accidental crossing of MBT and motors blowing up quickly. That's why I say just flat setting timing conservatively is a band aid for not understanding the motor.
I have seen MBT on LS cars at 19 degrees and I have seen it as low as 11 degrees. If someone is setting timing at 12 degrees conservatively and have one of these weird 11 degree MBT motors it will break. Conversely, if they have a 19 degree MBT motor, they are leaving probably 15% of their safe horsepower capability on the table.
Find MBT and knock the motor back a couple degrees from there and you are in a perfect scenario. Find MBT on a dyno or at the track in a smaller load capacity. I.E. don't go looking for MBT at full tilt. Look for it at a smaller load level. Once found knock it back 3-4 degrees for safety then start cranking up the boost.
I still believe this is a HUGE mistake people make in tuning FI cars. The whole movement of no timing or low timing with ls motors is related to the accidental crossing of MBT and motors blowing up quickly. That's why I say just flat setting timing conservatively is a band aid for not understanding the motor.
I have seen MBT on LS cars at 19 degrees and I have seen it as low as 11 degrees. If someone is setting timing at 12 degrees conservatively and have one of these weird 11 degree MBT motors it will break. Conversely, if they have a 19 degree MBT motor, they are leaving probably 15% of their safe horsepower capability on the table.
I dont think the answer is as easy as " find MBT and turn up the boost" MBT is not a constant number.
My friends laugh at me when i say i want to find another 92 Hatch SI.. maybe one day.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo Find MBT at 10lbs use that timing curve for 28lbs shifted back a degree or two.
In theory, MBT shifts related to load and engine speed. In practical application I only see it shift dramatically related to engine speed across and load related to engine speed. However, Peak Load vs Peak Load variances - I hardly ever see deltas in MBT. Example: Let's say 10lbs peak compared to 28lbs peak I don't see a big difference in MBT. If you hit MBT at 10lbs or cross over your motor has a better chance of survival. If you try the same at 28lbs as a hypothetical situation, it will grenade should you cross it.
Find MBT at 10lbs use that timing curve for 28lbs shifted back a degree or two.
Find MBT at 10lbs use that timing curve for 28lbs shifted back a degree or two.
You are confusing me with the statement "using the curve" and "finding MBT" my understanding is that MBT is a specified number. If you found this number and applied it at 10lbs I would say at 28lbs that number should be much smaller. I mean my timing curve at 10 vs 28 is very different. Correct me if I'm wrong or missing something. I am trying to learn.
Yes timing curve could vary between 10lbs and 28lbs depending on fuel.
Let's say 28lbs and 48lbs with a 4G63 motor as an example since so few people run 48lbs on an LS motor. Fuel is E85.
At 28lbs your timing retard by boost is already all the way out. Find MBT at at peak load with 28lbs of load as the example.
Use the same timing curve now for your 48lb boost curve. I bet you would find MBT didn't shift much if at all. Make sense?
Peak load of 10lbs vs Peak Load of 28lbs was used as dramatic swing example.
Yes timing curve could vary between 10lbs and 28lbs depending on fuel.
Let's say 28lbs and 48lbs with a 4G63 motor as an example since so few people run 48lbs on an LS motor. Fuel is E85.
At 28lbs your timing retard by boost is already all the way out. Find MBT at at peak load with 28lbs of load as the example.
Use the same timing curve now for your 48lb boost curve. I bet you would find MBT didn't shift much if at all. Make sense?
Yes timing curve could vary between 10lbs and 28lbs depending on fuel.
Let's say 28lbs and 48lbs with a 4G63 motor as an example since so few people run 48lbs on an LS motor. Fuel is E85.
At 28lbs your timing retard by boost is already all the way out. Find MBT at at peak load with 28lbs of load as the example.
Use the same timing curve now for your 48lb boost curve. I bet you would find MBT didn't shift much if at all. Make sense?
Peak load of 10lbs vs Peak Load of 28lbs was used as dramatic swing example.
Yes timing curve could vary between 10lbs and 28lbs depending on fuel.
Let's say 28lbs and 48lbs with a 4G63 motor as an example since so few people run 48lbs on an LS motor. Fuel is E85.
At 28lbs your timing retard by boost is already all the way out. Find MBT at at peak load with 28lbs of load as the example.
Use the same timing curve now for your 48lb boost curve. I bet you would find MBT didn't shift much if at all. Make sense?
Yes timing curve could vary between 10lbs and 28lbs depending on fuel.
Let's say 28lbs and 48lbs with a 4G63 motor as an example since so few people run 48lbs on an LS motor. Fuel is E85.
At 28lbs your timing retard by boost is already all the way out. Find MBT at at peak load with 28lbs of load as the example.
Use the same timing curve now for your 48lb boost curve. I bet you would find MBT didn't shift much if at all. Make sense?
I don't see how that could be remotely true. The speed of this flame front depends on the AF mixture and density. More dense the mixture, the faster the flame front travels, requiring less lead. Assuming the AFR ratios are correct, 28lbs will require more lead than 48lbs at a given RPM point. MBT would also vary widely with RPM. Damn near impossible to find true MBT across the rev/load range for the average tuner... or tune anywhere near it IMO.
Load and MBT are more fixed in my view. Load and Rev range don't have to be variable.
If 28lbs is peak boost on one pull and 48lbs peak boost on the next pull. The time elapsed between 28lbs and 48lbs is damn near instantaneous. Meaning peak load of 48lbs will occur at nearly the same rev as the 28lbs on the previous pull.
The timing figure used at 28lbs won't change much for 48lbs as it related to MBT. In summary -
MBT vs. RPM - Yes, flexes
MBT vs. Varrying Peak Loads - Not a big shift, which is why finding MBT, so long as the peak load occurs at similar rpm from pull to pull, is safer and easier. These are of course my experiences. If you have other's I love to hear differing opinions and learn more.
Cross MBT and cylinder pressure doubles for Each degree past it. It's when **** breaks quickly and it varies wildly from set up to set up.
Nothing against Erik, but I have a ton more faith in my engine builder than him. Thats not to say supporting the cylinders wouldn't help, I just don't have any desire for him to build me a motor at this time.
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
And comparing to Honda motors that have a pretty much open deck...the LS platforms arent that bad, as they have well supported bores at the top of the deck.
IMO if people want easy stronger gasket clamp, bigger/better studs are the easiest or cheapest
Subarus and I presume other 4cyl and maybe other engines too often go to 14mm or 9/16 studs. I can only speak for Subarus as I've worked on them, but 14mm studs with good quality gaskets can easily hold 40psi boost with a good turbo ( with a decent block too )
I wonder though that almost all incidents of colouration indicating some HG loss of sealing are always on the exhaust side. Could the smaller casting bulk on this side be part of the cause. I wonder if perhaps a little more torque on these studs vs the other 5 might be worth considering ?