TT 408 numbers
On The Tree
Joined: Apr 2010
Posts: 156
Likes: 0
From: LI, New York
Max Brake torque. It is essentially the point where a degree of timing added to the tune results in less peak torque or a severely diminished return in torque. I.E. 12 to 13 degrees netted you 15lbs but 13 to 14 netted you 2lbft. Your MBT would be 13 and I would set it at 12 in this hypothetical situation.
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.
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.
TECH Fanatic
Joined: Feb 2015
Posts: 1,080
Likes: 178
Direct Quote from good ol' Tom Vaught...
Higher compression ratios with gasoline and a fair amount of boost (say over 16 psi) 9+ to 1 compression ratio and 16+ psi will, at times, cause head gasket issues.
I was helping two guys (Jimmy and Vic Keen) in 1998. They were Super Street World Champion that year. They were the 2013 ADRL Pro Mod World Champions a year or so ago. They had a lot of issues with head gaskets on their 347 cid Ford engine in 1998 with 20+ psi of boost. Dropping the compression ratio to 8.75-1 allowed them to finish/win more races and have much less maint on their boosted engine. So there IS a "sweet spot" on this deal. http://www.speedtech-nitrous.com/customers.html
I was helping two guys (Jimmy and Vic Keen) in 1998. They were Super Street World Champion that year. They were the 2013 ADRL Pro Mod World Champions a year or so ago. They had a lot of issues with head gaskets on their 347 cid Ford engine in 1998 with 20+ psi of boost. Dropping the compression ratio to 8.75-1 allowed them to finish/win more races and have much less maint on their boosted engine. So there IS a "sweet spot" on this deal. http://www.speedtech-nitrous.com/customers.html
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
I'm sure I've been saying the same the entire thread lol
All this new craze for high compression is all good and well. With good fuel and tuning it works, and works well, but still only leaves a very small margin for error, if even that
Drop the CR to more sensible levels and things get so much easier, with so little effect on power or performance.
All this new craze for high compression is all good and well. With good fuel and tuning it works, and works well, but still only leaves a very small margin for error, if even that
Drop the CR to more sensible levels and things get so much easier, with so little effect on power or performance.
I'm sure I've been saying the same the entire thread lol
All this new craze for high compression is all good and well. With good fuel and tuning it works, and works well, but still only leaves a very small margin for error, if even that
Drop the CR to more sensible levels and things get so much easier, with so little effect on power or performance.
All this new craze for high compression is all good and well. With good fuel and tuning it works, and works well, but still only leaves a very small margin for error, if even that
Drop the CR to more sensible levels and things get so much easier, with so little effect on power or performance.
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
I'm certainly not saying to go as low as say 8.0:1, but if you're scared of HG issues, whether they have any foundation or not ( I've never had any problems with mine on mile runs etc ), then it makes perfect sense to not try and push the edge with high CR's
And I would say little power, nothing that couldnt be recouped with another couple of psi boost, and it would still be far safer at the higher boost with less CR.
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Verdad Gallardo And it also gives you more chance of hitting MBT before the onset of knock or dangerous conditions.
I'm certainly not saying to go as low as say 8.0:1, but if you're scared of HG issues, whether they have any foundation or not ( I've never had any problems with mine on mile runs etc ), then it makes perfect sense to not try and push the edge with high CR's
And I would say little power, nothing that couldnt be recouped with another couple of psi boost, and it would still be far safer at the higher boost with less CR.
I'm certainly not saying to go as low as say 8.0:1, but if you're scared of HG issues, whether they have any foundation or not ( I've never had any problems with mine on mile runs etc ), then it makes perfect sense to not try and push the edge with high CR's
And I would say little power, nothing that couldnt be recouped with another couple of psi boost, and it would still be far safer at the higher boost with less CR.
That's true for peak HP but not area under the curve. I agree with most everything you posted though.
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
You could just as easily say it's essential to run a 403 vs 376 because of area under the curve. Or that a 5.3 or 4.8 would be crap because it will never achieve the same area under the curve as the bigger motors.
Reality is, they are all quite capable regardless.
You could also say the same about say factory castings vs good aftermarket heads. There will be gains to be had from many different routes.
I just dont see pushing CR to the extremes as being in any way necessary, or any real benefit.
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 ?
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 ?
Edelbrock 245cc heads with a little work. Compression is 9.3:1.
Based on the VE table, mine makes max torque around 7000 rpm. On my best pass, I was at 22 lbs of boost at max torque and 20* if timing.........hence the trashed head gaskets.
I think why most leak on the exhaust side is a result of two factors. One, as you mentioned, is the cylinder head has a little less rigidity on that side. Tightening the bolts even further on that side would do little to nothing to help this. It's in the casting. The second is from the exhaust heat. You'll see in a another post in this thread where I am now going to a reversed cooling set up. Water enters the engine via 8 ports, each aimed at the backside/exhaust side of the combustion chamber. I have also completely filled the engine with hardblok and welded the decks shut on the heads. There is no more water between the head and the block. Water will be pulled out via 4 -8 fittings where the steam ports used to be. At the same time I also upgraded to 1/2" head studs.
No motor mounts.
Edelbrock 245cc heads with a little work. Compression is 9.3:1.
Based on the VE table, mine makes max torque around 7000 rpm. On my best pass, I was at 22 lbs of boost at max torque and 20* if timing.........hence the trashed head gaskets.
No motor mounts.
Edelbrock 245cc heads with a little work. Compression is 9.3:1.
Based on the VE table, mine makes max torque around 7000 rpm. On my best pass, I was at 22 lbs of boost at max torque and 20* if timing.........hence the trashed head gaskets.
Who ended up doing your machine work? Also excuse my ignorance but if you completely filled the block where does the water circulate? Just in the heads? And I still can't believe your having all this trouble at only 22psi and 20* I'm assuming this is on E85? My timing was about the same but I was around 26lbs. Have you ever actually verified your timing?
Who ended up doing your machine work? Also excuse my ignorance but if you completely filled the block where does the water circulate? Just in the heads? And I still can't believe your having all this trouble at only 22psi and 20* I'm assuming this is on E85? My timing was about the same but I was around 26lbs. Have you ever actually verified your timing?
Not really. I've seen a lot of guys push 20* or more with 100 octane or above on these motors. My plugs look new.
I have too and strong parts will take that abuse for a while - Are you certain that every single degree of timing was increasing torque dramatically before adding it?
No but all signs point in the right direction. To be fair I haven't actually verified my timing. When this motor is out back together I will be spending A LOT more time on the dyno.
That would be smart. I predict, you will be shocked on the dyno where adding timing brings about diminishing returns.
Who ended up doing your machine work? Also excuse my ignorance but if you completely filled the block where does the water circulate? Just in the heads? And I still can't believe your having all this trouble at only 22psi and 20* I'm assuming this is on E85? My timing was about the same but I was around 26lbs. Have you ever actually verified your timing?
Water only circulates in the heads.
Fuel is C-16
A timing pointer was built when the motor was put together. I verify it with a light. So yes, my timing is exactly where the holley says it is.
You also have to remember, my power adder robs a ton more power than yours. Lets say the motor was making 1200 horsepower to run that 154 mph at 4110 lbs. My blower at that speed eats about 250 horsepower (been verified). So my crank/rods/pistons/heads are seeing the equivalent of about 1450 horsepower. This is number is inline with my fuel flow numbers as well.
My engine at 1200 horsepower sees a ton more stress than your does at 1200 horsepower because of the type of power adder. Factor in the insane weight difference and you can begin to see why you are able to get away with much more boost/timing than I can.
http://www.yellowbullet.com/forum/sh....php?t=1332810
Some hope for us 4 bolt head guys - Note - Great crankshaft - alleviating some stress on the caps & Fire Ring Head Gaskets - No water pushed. Block is not filled.
Some hope for us 4 bolt head guys - Note - Great crankshaft - alleviating some stress on the caps & Fire Ring Head Gaskets - No water pushed. Block is not filled.