TT 408 numbers
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
Good head studs, good head gaskets and generally a good build.
And dont get greedy with timing and never run anywhere near detonation and it will live a fairly happy life.
A slightly lower CR will be more forgiving for sure.
Lower CR, safe timing and more boost will survive longer than a high CR, aggressive timing and less boost.
Boost itself is not the engine killer, it's pushing timing/CR/fuel limits where the risks lie.
And dont get greedy with timing and never run anywhere near detonation and it will live a fairly happy life.
A slightly lower CR will be more forgiving for sure.
Lower CR, safe timing and more boost will survive longer than a high CR, aggressive timing and less boost.
Boost itself is not the engine killer, it's pushing timing/CR/fuel limits where the risks lie.
Good head studs, good head gaskets and generally a good build.
And dont get greedy with timing and never run anywhere near detonation and it will live a fairly happy life.
A slightly lower CR will be more forgiving for sure.
Lower CR, safe timing and more boost will survive longer than a high CR, aggressive timing and less boost.
Boost itself is not the engine killer, it's pushing timing/CR/fuel limits where the risks lie.
And dont get greedy with timing and never run anywhere near detonation and it will live a fairly happy life.
A slightly lower CR will be more forgiving for sure.
Lower CR, safe timing and more boost will survive longer than a high CR, aggressive timing and less boost.
Boost itself is not the engine killer, it's pushing timing/CR/fuel limits where the risks lie.
Yeah but there is only so much a 370ci with 66/65's can make "reliably" and it isn't 1300whp
[QUOTE=asubennett;18757583] I subscribe to this 100%. I'm not even sure the 150 mph 1/8th guys stuff would last to the 1/4.
Not sure. I know there are quite a few though. Unfortunatley the type of racing (halfmile/mile/roll) I intend on doing is more of a numbers game.[/QUOTEp]
I believe skinnier went 174 in 1/4 but is also using the ARP625 studs for extra clamp.
In 1/8 mile people have gone 150plus with 4 bolt heads but no chance of that living in 1/2 mile and beyond. Your going to face issues with what you want to do and 4 bolt heads. The duration of abuse is so much longer.
I believe skinnier went 174 in 1/4 but is also using the ARP625 studs for extra clamp.
In 1/8 mile people have gone 150plus with 4 bolt heads but no chance of that living in 1/2 mile and beyond. Your going to face issues with what you want to do and 4 bolt heads. The duration of abuse is so much longer.
I’d think the low compression stuff would really shine if head clamping force is an issue, esp. in a 1/2 mile event. With low compression, you could make the same power with less overall cylinder pressure. IE less clamping force would be needed.
For example, let's say 28:1 is the highest level safely achievable before detonation creeps in on 2 identical engines where compression ratio is the only difference.
12:1 engine being boosted 20psi gives 28:1 effective compression.
7:1 engine being boosted 45psi gives 28:1 effective compression.
The lower compression engine would have roughly 70% greater power potential at the same effective compression.
Info and math behind the theory here...
http://www.modularfords.com/threads/...boost-pressure
For example, let's say 28:1 is the highest level safely achievable before detonation creeps in on 2 identical engines where compression ratio is the only difference.
12:1 engine being boosted 20psi gives 28:1 effective compression.
7:1 engine being boosted 45psi gives 28:1 effective compression.
The lower compression engine would have roughly 70% greater power potential at the same effective compression.
Info and math behind the theory here...
http://www.modularfords.com/threads/...boost-pressure
Show me two motors of the same size that make the same power, but one with significantly less cylinder pressure. This is part of the reason these 370-408 threads get so divided. This thread however is not a discussion of "trying to stay in the efficiency island".
The bottom line is that a larger engine will make more power reliably (when not limited by a turbos efficiency) than a smaller motor. Why?????? Because it takes less cylinder pressure in the bigger motor to make the same power as the smaller motor.
Unless I'm just completely missing something here.....it's basic physics.
In a longer run you are generating more heat in the system. You need to greatly increase cooling systems and watch the tune. As chamber gets hotter it becomes more detonation prone. A more conservative tune is required imo.
Look at some of the landspeed racing stuff. Cooling is important but sustaining wot for so long is way different than an 8 sec drag race.
But i have seen two personal friends use 6.0 block based builds with 4 bolt oem heads run 8.3-8.6 at 165-167 mph in 3400-3500 ish lb setups
One is a Ly6 dyno'd 1052 thru th400. Other is a 408 dyno 1091 on 20 lbs but 8.3 run was on 23 so its closer to 1150 whp.
Ly6 hasnt had issues. The 408 is lifting heads. Used arp studs and still pushed alittle. Had o ring block and heads but machine shop screwed it up i guess and it didnt work. Still pushed.
Some have luck some dont. Tune is important too. Too rapid of a cylinder pressure rise could upset things. Controlled rise over entire stroke can extract power without necessarily a high peak pressure
My sbc is a lower comp type setup, 9:1 but decent cam it cranks low pressure. Guess its why i can run 25+ psi on just 93 oct and not have issues. Interesting to see a test of two identical setups but one 8:1 and one 10:1 and see what happens, as long as fuel isnt a detonation concern.
Look at stock ls7 with boost. 11:1 run 5-6 psi somewhat safe and make 650 whp lets say. Any higher boost on pump gas things become a concern. Throw in low comp pistons you can run higher boost now and make more power.
Look at some of the landspeed racing stuff. Cooling is important but sustaining wot for so long is way different than an 8 sec drag race.
But i have seen two personal friends use 6.0 block based builds with 4 bolt oem heads run 8.3-8.6 at 165-167 mph in 3400-3500 ish lb setups
One is a Ly6 dyno'd 1052 thru th400. Other is a 408 dyno 1091 on 20 lbs but 8.3 run was on 23 so its closer to 1150 whp.
Ly6 hasnt had issues. The 408 is lifting heads. Used arp studs and still pushed alittle. Had o ring block and heads but machine shop screwed it up i guess and it didnt work. Still pushed.
Some have luck some dont. Tune is important too. Too rapid of a cylinder pressure rise could upset things. Controlled rise over entire stroke can extract power without necessarily a high peak pressure
My sbc is a lower comp type setup, 9:1 but decent cam it cranks low pressure. Guess its why i can run 25+ psi on just 93 oct and not have issues. Interesting to see a test of two identical setups but one 8:1 and one 10:1 and see what happens, as long as fuel isnt a detonation concern.
Look at stock ls7 with boost. 11:1 run 5-6 psi somewhat safe and make 650 whp lets say. Any higher boost on pump gas things become a concern. Throw in low comp pistons you can run higher boost now and make more power.
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
If anyone needs a lesson on how to push water on a 4-bolt 408 I'll be open for questioning for the next 2 days only. lol
Got "pushing water"? - YouTube
Got "pushing water"? - YouTube
.
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
The bottom line is that a larger engine will make more power reliably (when not limited by a turbos efficiency) than a smaller motor. Why?????? Because it takes less cylinder pressure in the bigger motor to make the same power as the smaller motor.
Unless I'm just completely missing something here.....it's basic physics.
Unless I'm just completely missing something here.....it's basic physics.
Look how hard people are pushing 4.8's and 5.3's, likewise small 4cyl motors.
Block/head structural integrity mean a lot too
Those smaller bore motors have much stronger blocks due to the smaller bore.
And then with boost it also depends on compressor efficiency. Pushing tiny turbos beyond their limits on a large motor will never be as reliable as pushing much larger turbos within their limits and efficiency island...and the latter will make more power, and both engine and turbos will be happier.
That applies to any compressor ( ignoring mechanical drive loads applied to crank etc from a blower which is a different topic )
TECH Apprentice
Joined: Dec 2004
Posts: 358
Likes: 1
good point. look at what duttwieler and george poteet do for their turbo bonneville beasts and you get a great platform
displacement is plenty at 370 they build little short strokers with big @$$ turbos and huge cooling and injection to get over 2 or 3k hp and hold it together
I think a small bore 4.8 with studs and e85 with the right short stroke forged crank would work pretty well with oliver rods and pistons made out of unobtanium
I'd like to think the billet caps would be a good idea too.
the right tune is critical as stevie mentions and huge fuel flow
I'd love to try a LS next build, but I'm going to have to scrounge for the good 6 bolt heads and block which are pricey.
I believe I can make 1k plus pretty ez and 1300 plus when pushed
On The Tree
Joined: Apr 2010
Posts: 156
Likes: 0
From: LI, New York
From my understanding, peak cylinder pressure happens around the same point as peak torque. Moving the point of peak cylinder pressure (torque) higher in the RPM band, generally helps keep the heads on. So if this theory is correct, a 4" stroke 408 would generally have a torque peak lower in the RPM band, leading to head sealing issues.
Just earlier in this thread Orr89rocz posted a good example. Two engines, both making similar power. The 3.62 stroke engine does not have sealing issues, while the 4" one does.
So long story short, Move the torque peak higher and you're more likely to keep the heads on. Doesnt mean you cant to it with a long stroke, just size the cam/turbo accordingly. At least that's my theory LOL...
Just earlier in this thread Orr89rocz posted a good example. Two engines, both making similar power. The 3.62 stroke engine does not have sealing issues, while the 4" one does.
So long story short, Move the torque peak higher and you're more likely to keep the heads on. Doesnt mean you cant to it with a long stroke, just size the cam/turbo accordingly. At least that's my theory LOL...
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
Using more rpm's will certainly help in some areas because of the torque aspects...of course then you need to consider what's needed to hold the engine together at the higher rpm's.
But if making a lot of power on what some might not consider a super strong platform, then I dont think a longer stroke is the way to go, especially when you know the pistons etc will be dropping well out of the bore at BDC.
If it was a tall deck and using a longer rod too, then probably no problem at all with the 4" and high rpm's
But if making a lot of power on what some might not consider a super strong platform, then I dont think a longer stroke is the way to go, especially when you know the pistons etc will be dropping well out of the bore at BDC.
If it was a tall deck and using a longer rod too, then probably no problem at all with the 4" and high rpm's
From my understanding, peak cylinder pressure happens around the same point as peak torque. Moving the point of peak cylinder pressure (torque) higher in the RPM band, generally helps keep the heads on. So if this theory is correct, a 4" stroke 408 would generally have a torque peak lower in the RPM band, leading to head sealing issues.
Just earlier in this thread Orr89rocz posted a good example. Two engines, both making similar power. The 3.62 stroke engine does not have sealing issues, while the 4" one does.
So long story short, Move the torque peak higher and you're more likely to keep the heads on. Doesnt mean you cant to it with a long stroke, just size the cam/turbo accordingly. At least that's my theory LOL...
Just earlier in this thread Orr89rocz posted a good example. Two engines, both making similar power. The 3.62 stroke engine does not have sealing issues, while the 4" one does.
So long story short, Move the torque peak higher and you're more likely to keep the heads on. Doesnt mean you cant to it with a long stroke, just size the cam/turbo accordingly. At least that's my theory LOL...
Sound logic if you ask me. The 4.8/5.3 engines making ridiculous amounts of HP that everyone is talking about shows this.
TECH Fanatic
Joined: Feb 2015
Posts: 1,080
Likes: 178
Lots going on in the land of physics than just cylinder pressure. Short stroke big bore/strong block is a reliable combo. The old Chev 302 opened some racing eyes back in the mid 60s.
Interesting article on bore vs. stroke. http://rehermorrison.com/tech-talk-5...ich-is-better/
Never thought about the ring friction/heat in a long stroke setup.
Interesting article on bore vs. stroke. http://rehermorrison.com/tech-talk-5...ich-is-better/
Never thought about the ring friction/heat in a long stroke setup.
Riddle me this. If the Aluminum heads lift in between the studs at not at the studs. Would an iron LS head securely mounted to an iron block not stay together?
I'm assuming the aluminum heads lift because they are soft..
I'm assuming the aluminum heads lift because they are soft..
Would be interesting test. But i know some small block chevy aluminum heads have similar deck thicknesses as lsx stuff but dont seem to lift due to 5 bolts per cyl. Think theres something there with bolts per cyl for sealing.