|
why not used turbo/super WITH high comp pistons?
#1696213
11/08/14 06:57 PM
11/08/14 06:57 PM
|
Joined: Jul 2014
Posts: 68
USA MO
cdoublejj
OP
member
|
OP
member
Joined: Jul 2014
Posts: 68
USA MO
|
as far as i know forced air doesn't work as well with high compression domed pistons versus flat top, dish or reverse dome. ON TOP of re dentition and octane and heat. I'm got in to debate with some one and as far as i know of all the engine builders i have talked to say dished and reverse dome is usually best setup for forced air, it sort of "cups" the explosion, harnessing the energy. if i'm not mistaken some of the force from the explosion gets trapped in the dish instead heading straight for the rings. any ways i don't have day to spending googling this stuff so i made this thread to link to he/she to see OR form me to learn why i'm wrong. EDIT: link: http://www.reddit.com/r/cars/comments/2lm2sz/1894hp_twin_turbo_ford_gt/clwtz57?context=3
Last edited by cdoublejj; 11/08/14 07:01 PM.
|
|
|
Re: why not used turbo/super WITH high comp pistons?
[Re: cdoublejj]
#1696214
11/08/14 11:01 PM
11/08/14 11:01 PM
|
Joined: Nov 2010
Posts: 3,696
jersey
Spaceman Spiff
master
|
master
Joined: Nov 2010
Posts: 3,696
jersey
|
I call bullspit on that article. 2,000+ hp from a stock block lt1?? NO WAY. also, aftermarket LT1 heads didn't exist in '99, not gonna happen with stock LT1 heads. What intake did they use? certainly not the stock one at that power level. what ignition system? Not the optispark!!
526 cubes of angry wedge, pushbutton shifted, 9 passenger killer!
|
|
|
Re: why not used turbo/super WITH high comp pistons?
[Re: Cab_Burge]
#1696216
11/09/14 01:51 AM
11/09/14 01:51 AM
|
Joined: Jun 2007
Posts: 2,646
Plymouth Meeting, PA
bigtimeauto
Trophy Winner
|
Trophy Winner
Joined: Jun 2007
Posts: 2,646
Plymouth Meeting, PA
|
I don't own a dished piston so I must be doing something wrong
BB, TT5,Procharged 3300lb Street Car 4.79/154
|
|
|
Re: why not used turbo/super WITH high comp pistons?
[Re: dogdays]
#1696219
11/10/14 04:45 AM
11/10/14 04:45 AM
|
Joined: May 2011
Posts: 625
Oakville, Wa
HOTMOPR
mopar
|
mopar
Joined: May 2011
Posts: 625
Oakville, Wa
|
I believe it just depends on the type of motor you want to build. Take 2 identical motors, one with flat top and one with dished pistons. The dished piston will have the ability to run more boost than the flat top combo. So from BDS boost chart a 8-1 motor at 14 psi of boost has a final compression ratio of 15.6-1. If your flat top combo is 10-1. At 14 psi the final compression ratio is 19.5-1. On the 8-1 motor you could run 22 psi to reach 19.5-1.. I was told that a boosted motor is easier on parts than any other combo. So why not build a lower compression motor and give it more boost to make the hp? Wouldn't it be easier on parts and wallet? Am I wrong?
Last edited by HOTMOPR; 11/10/14 04:47 AM.
67 Barracuda, 470" B, Glide, FuelTech FT600, Precision, Ptc, QA1, Calvert, Smith racecraft, Afco, Dana 60. 275 radials
|
|
|
Re: why not used turbo/super WITH high comp pistons?
[Re: HOTMOPR]
#1696220
11/10/14 04:54 AM
11/10/14 04:54 AM
|
Joined: May 2011
Posts: 625
Oakville, Wa
HOTMOPR
mopar
|
mopar
Joined: May 2011
Posts: 625
Oakville, Wa
|
67 Barracuda, 470" B, Glide, FuelTech FT600, Precision, Ptc, QA1, Calvert, Smith racecraft, Afco, Dana 60. 275 radials
|
|
|
Re: why not used turbo/super WITH high comp pistons?
[Re: HOTMOPR]
#1696221
11/10/14 05:37 AM
11/10/14 05:37 AM
|
Joined: Aug 2003
Posts: 43,251
Bend,OR USA
Cab_Burge
I Win
|
I Win
Joined: Aug 2003
Posts: 43,251
Bend,OR USA
|
My personel experience with Craig Railbeck(SP?, He owns BDS  ) is that he does not under stand many things he sells, I assembled and built and dyno tested two very similar blown gasoline 426 Hemi street motors, one with his combination of a all out high dollar BDS 10:71 blower(3 of them actually before switching to another brand ) with his recommended engine package, his recommended EFI system and tuned EFI. The other motor was built with a little more compression, his was 8.5 to 1, the other one was 9.25 to 1 using a street Littlefield 10:71 with a set of Carb. Shop blower Dominator carbs. His motor made around 960 HP at 6500 RPM using C16 race gas at 17.0 lbs of boost, we sped the blower up and it ended up making right at 1060 HP at 22 lbs of boost but it would not repeat, it would start breaking up around 5400 RPM with him tuning it  The other motor with CA pump gas made 927 HP at 7300 RPM with 7 lbs of boost at 33 degrees total timing, it would repeat with no problems. We sped the blower up (reverse the pulleys from 12% underdrive to 13% overdrive) on it and that motor using race gas made 1027 HP at 12 lbs of boost at 6500 RPM, it had to much timing with 25 degrees total we learned later  The owner was happy and it was getting late in the afternoon so we stop testing and took that motor home. My message is it is better to up the static compression ratio on a roots blown street motor and run less boost than it is to run the compression lower and add boost  I hope this helps someone avoid making the mistake of assuming BDS parts are all good, not so  Go somewhere else for Roots blower parts and advice
Last edited by Cab_Burge; 11/10/14 03:53 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
|
|
|
Re: why not used turbo/super WITH high comp pistons?
[Re: Cab_Burge]
#1696222
11/10/14 03:02 PM
11/10/14 03:02 PM
|
Joined: Jan 2003
Posts: 684
St. Charles, MO.
Slingshot383
mopar
|
mopar
Joined: Jan 2003
Posts: 684
St. Charles, MO.
|
The more compression you have, the smaller your tuning window.
1994 Undercover Chassis 125" altered
stack injected big block, soon blown and injected
Member of The Torque and Recoil Club
|
|
|
Re: why not used turbo/super WITH high comp pistons?
[Re: Slingshot383]
#1696223
11/10/14 03:20 PM
11/10/14 03:20 PM
|
Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
HotRodDave
I Live Here
|
I Live Here
Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
|
Basically the more boost you have the more room you need in the chamber before igniting it to keep it from detonating. Detonation with that much A/F mix in the chamber is very bad news. That is why the more boost generally likes less timing and dynamic compression, just gives you more room to stuff the mixture into. Boost is not always easier or cheaper to build power with, you have a lot smaller tuning window to get it right and you have a ton more plumbing, brackets, fabrication... cluttering up under the hood that in my opinion is not worth it till you start needing near 1000 hp as there is plenty of NA stuff out there to get close to that BB or SB without the added crap under the hood. I prefer keeping it simple as far as possible but I do understand the allure of swapping pulleys to get more power, there is just a lot more behind the scenes you don't hear about till you start trying to install air coolers, blow off valves, figure out packaging, funky exhaust routing fuel systems including more expensive boost referenced carbs or EFI pressure regulators... that is why I like to bore and stroke for more power... got to have some kind of crank rods pistons any how so
I am not causing global warming, I am just trying to hold off a impending Ice Age!
|
|
|
Re: why not used turbo/super WITH high comp pistons?
[Re: HotRodDave]
#1696225
11/10/14 03:47 PM
11/10/14 03:47 PM
|
Joined: Feb 2003
Posts: 4,953
Houston, Texas
TheOtherDodge
master
|
master
Joined: Feb 2003
Posts: 4,953
Houston, Texas
|
Quote:
Boost is not always easier or cheaper to build power with, you have a lot smaller tuning window to get it right and you have a ton more plumbing, brackets, fabrication... cluttering up under the hood that in my opinion is not worth it till you start needing near 1000 hp as there is plenty of NA stuff out there to get close to that BB or SB without the added crap under the hood. I prefer keeping it simple as far as possible but I do understand the allure of swapping pulleys to get more power, there is just a lot more behind the scenes you don't hear about till you start trying to install air coolers, blow off valves, figure out packaging, funky exhaust routing fuel systems including more expensive boost referenced carbs or EFI pressure regulators... that is why I like to bore and stroke for more power... got to have some kind of crank rods pistons any how so
What you aren't taking into consideration is the driveability and maintenance for the power you get.
For example, currently, I make about 700 hp. I called my buddy to come over last weekend to prep the truck for the track this Friday and we stood around looking at each other and said, well, we are done! I haven't even had to change plugs in 2 years or adjust the valves. 
Although there are some fab skills you must have or you will have to pay someone, it isn't all that bad. I don't have much cluttering under the hood with funky exhaust routing. I just flipped some shorties around and boom! Underneath is even cleaner with 1 3" pipe and 1 muffler and much more quiet than an N/A motor of the same power level.
Cost-wise, it is probably about 25% higher than N/A of the same power level because you don't have to get high $ heads, expensive full length headers, high pressure valve springs and good rocker, high dollar pushrods, 2 mufflers, high stall converter, etc. And if you go FI, the data logging is priceless.
I know this isn't a discussion on that, but I wanted to clarify the benefits of a turbo setup.
|
|
|
Re: why not used turbo/super WITH high comp pistons?
[Re: HotRodDave]
#1696227
11/10/14 04:04 PM
11/10/14 04:04 PM
|
Joined: Jan 2005
Posts: 3,635
Oakland, MI
dizuster
master
|
master
Joined: Jan 2005
Posts: 3,635
Oakland, MI
|
Quote:
Basically the more boost you have the more room you need in the chamber before igniting it to keep it from detonating. Detonation with that much A/F mix in the chamber is very bad news. That is why the more boost generally likes less timing and dynamic compression, just gives you more room to stuff the mixture into.
It's not about having more "room", it's about keeping the temperatures below the octane detonation threshold limit. As you compress air, it heats up. If you start with hot air (boost), it will get even hotter. Get the air hot enough, and it will self-ignite part of the air/fuel mixture without the aid of the spark plug... that's what detonation is.
There are LOTS of high compression turbo motors, especially on the turbo limited classes. But it requires good fuel and/or good intercoolers.
Timing is all about creating the most pressure you can, with the biggest crank/rod angle you can. If you make peak pressure at TDC, the pressure tries to push the crank out the bottom of the block. If you make peak pressure at 90 degree's of crank angle, then you would create the maximum torque possible.
The reality is that if you wait until the piston is 1/2 way down the cylinder to optimized the crank angle, the pressure has dropped from expansion so much that it won't make any power. Timing is all about getting the "sweet spot" of pressure vs. crank angle. The reason that boosted motors require less timing is because the burn is "quicker" then N/A motors. Quicker burn means that you need to start the burn LATER in crank rotation to optimize the crank angle and the pressure. As a matter of fact, on similar power motors, the boosted motor will actually have LESS peak cylinder pressure then the equivalent N/A powered motor. Sacrificing lower pressure on the boosted motor is made up for with the more optimized crank angle. This is because the turbo motor doesn’t loose as much pressure when the piston travels down the bore a little further then the N/A does (because there is more Air/Fuel to maintain the pressure).
As and example at 10psi non-IC on E85, I can put enough timing in my motor to slow the car down (loses power) without detonating anything. I am not limited by detonation. I am simply past the point of optimization of pressure vs. crank angle. (no different then having too much timing in a N/A motor with good fuel). However that being said, I only need about 25 degree’s of timing at 10psi vs. 32~34 degree’s of timing N/A. But like I said… it’s not because of detonation, it’s because of burn speed.
Quote:
Boost is not always easier or cheaper to build power with, you have a lot smaller tuning window to get it right and you have a ton more plumbing, brackets, fabrication... cluttering up under the hood that in my opinion is not worth it till you start needing near 1000 hp as there is plenty of NA stuff out there to get close to that BB or SB without the added crap under the hood. I prefer keeping it simple as far as possible but I do understand the allure of swapping pulleys to get more power, there is just a lot more behind the scenes you don't hear about till you start trying to install air coolers, blow off valves, figure out packaging, funky exhaust routing fuel systems including more expensive boost referenced carbs or EFI pressure regulators... that is why I like to bore and stroke for more power... got to have some kind of crank rods pistons any how so
I beg to differ… not all combo’s have to be complicated if they are well thought out before you start. Nor do you need to be at the 1000hp level to break even. Nor do they need to be as expensive as a N/A motor.
Here is a pic of mine. No intercooler, ONE bracket, and two exhaust pipes. Hardly what I would call complicated, or a bunch of “added crap” under the hood. Every street car needs exhaust work. Having the tail pipes go over the axle, through the shocks, and out to the bumper on a N/A car is no more complicated fab work then what I have. A pair of $40 exhaust manifolds, feeding into two simple tubes out of them. My “expensive boost reference carb” was $720 for a 750HP Holley already converted for E85. That’s what $160 more than a stock 750HP? The turbo was $650, and was the biggest single expense of the build. I guarantee you can’t compete Dollar per HP with what I have, and at only 15~16psi this motor already makes in the 775~800hp range.
And the beauty is… turbos are SOOOO easy on parts. This still has a un-touched cast crank in it…
There is nothing to be scared of with a turbo build… don’t let the N/A and Supercharger guys scare you.
|
|
|
Re: why not used turbo/super WITH high comp pistons?
[Re: TrxR]
#1696228
11/10/14 04:11 PM
11/10/14 04:11 PM
|
Joined: Feb 2003
Posts: 4,953
Houston, Texas
TheOtherDodge
master
|
master
Joined: Feb 2003
Posts: 4,953
Houston, Texas
|
Quote:
what compression ratio and fuel are you running in the Dakota?
9.2:1 and pump 93.
Diz: 
|
|
|
Re: why not used turbo/super WITH high comp pistons?
[Re: TheOtherDodge]
#1696229
11/11/14 03:21 AM
11/11/14 03:21 AM
|
Joined: Jun 2007
Posts: 2,646
Plymouth Meeting, PA
bigtimeauto
Trophy Winner
|
Trophy Winner
Joined: Jun 2007
Posts: 2,646
Plymouth Meeting, PA
|
how can you have a discussion about static cr and boost yet never bring up camshaft design?
BB, TT5,Procharged 3300lb Street Car 4.79/154
|
|
|
|
|
To many variables for one size fits all application 
