Unless he meant to put an 8 instead of a 10 
View Poll Results: Whats the best CR to have for 15-22 pounds of boost?
11:1
8
2.87%
10.5:1
4
1.43%
10:1
20
7.17%
9.5:1
59
21.15%
9:1
67
24.01%
8.5:1
95
34.05%
8:1
26
9.32%
Voters: 279. You may not vote on this poll
CR for big boost...
OK, so I've got the motor apart for freshening and have a few options I could go with for heads. I was at 8.5:1 with dished/relieved pistons on a 402. I'm running a D1SC pretty much max pullied for what the motor turns and I'm not really wanting to drop the $ to step up to an F1. So, instead of looking to boost for power, anyone see a major problem with going with a smaller chamber and getting into the 9.5 or 10:1 area? Forged Lunati bottom end and iron block. I guess I'm not grasping the difference between increasing cylinder pressure through additional boost and doing so by bumping compression. The car was at 600rwhp through an auto at 8.5:1, 13.5 psi, a mild cam and heads with unported pockets. I'd like to get into the 750 range with an additional CR point to 1.5 points, AFRs, a cam change and the same blower set up. Any feedback would be appreciated.
Last edited by crashinaz; Feb 2, 2008 at 07:39 PM.
If you are maxing out the D1SC, and plan to stay with pump gas, even with all the forged internals I would reccomend staying with a 9:1, maybe 9.5:1 with the help of meth injection or race gas. Anything higher than that and you will be getting into the "not so safe" range on pump gas.
There are alot of enginering controls one can employ to control detination under full boost. Controling the engine jacket water temp, keeping it under 165 degrees will help for example. Controling engine oil temps, air intake temps, camshaft profiles, piston crown shape, head chamber shape, just to name a few.
It will not be as "Safe" or as easy to do as lowering the compresion. But there are alot of good reasons for me to do it this way instead of the other. You guys are right in that it is not something that I or we would want to sugest to a newcomer to do. But it is not a big deal at all to have 10:1 or even 11 or 12:1 with 15+ psi, if you are building an engine that is only a max effort, and will only run the best fuels (race gasoline) out there. This I think was the thread question. Not CR on pump gas fuel.
My vote for this thread is for 9:1 or under for pump fuel.
My vote for this thread is for 9.5:1 up to 11:1 for racing fuel.
Disclaimer for next statement:
(Be warned, this is not the "safest" idea, nor is it for the novice, it is only for the pro's
)And if you have the will to defy the odds then I would build for 10:1 to 11:1 on pump gas.
OK, so I've got the motor apart for freshening and have a few options I could go with for heads. I was at 8.5:1 with dished/relieved pistons on a 402. I'm running a D1SC pretty much max pullied for what the motor turns and I'm not really wanting to drop the $ to step up to an F1. So, instead of looking to boost for power, anyone see a major problem with going with a smaller chamber and getting into the 9.5 or 10:1 area? Forged Lunati bottom end and iron block. I guess I'm not grasping the difference between increasing cylinder pressure through additional boost and doing so by bumping compression. The car was at 600rwhp through an auto at 8.5:1, 13.5 psi, a mild cam and heads with unported pockets. I'd like to get into the 750 range with an additional CR point to 1.5 points, AFRs, a cam change and the same blower set up. Any feedback would be appreciated.
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Verdad Gallardo The higher the altitude, the less effitiant the engine becomes. It will lower the dynamic compression some, so people compensate for it by raising the static compression. Have you ever noticed when you buy fuel at the pump when you are at sea level, super unleaded is something like 93 octane, and then as you travel higher in altitude, the super unleaded octane rating drops. By the time you get into the mountains in Colorado I think I have seen super unleaded that was 89 octane. The reason for this is the altitude change. Maybe someone else would like to explain it deeper.
The higher the altitude, the less effitiant the engine becomes. It will lower the dynamic compression some, so people compensate for it by raising the static compression. Have you ever noticed when you buy fuel at the pump when you are at sea level, super unleaded is something like 93 octane, and then as you travel higher in altitude, the super unleaded octane rating drops. By the time you get into the mountains in Colorado I think I have seen super unleaded that was 89 octane. The reason for this is the altitude change. Maybe someone else would like to explain it deeper.
OMG!!!!
I can't believe the poll results! We've gone so far with the design of this amazing motor and your going to send it back to the dark ages with 8.5:1?
Well when you don't go as fast as the next guy-then you know where to turn.
last combo was a 347, 10.1, stock ported heads, 20 psi, pump and meth and ran 9.6 with a 1.8 short lifting, curb weight 3480-full AC and all options.
line me up with the 8.5 car anyday.
fwiw-no intercooler, 9.5:1, 30 psi, 310 cubes, 3300lbs, 8.5's all day long in the summer.
Yeah 8.5.
I can't believe the poll results! We've gone so far with the design of this amazing motor and your going to send it back to the dark ages with 8.5:1?
Well when you don't go as fast as the next guy-then you know where to turn.
last combo was a 347, 10.1, stock ported heads, 20 psi, pump and meth and ran 9.6 with a 1.8 short lifting, curb weight 3480-full AC and all options.
line me up with the 8.5 car anyday.
fwiw-no intercooler, 9.5:1, 30 psi, 310 cubes, 3300lbs, 8.5's all day long in the summer.
Yeah 8.5.
OMG!!!!
I can't believe the poll results! We've gone so far with the design of this amazing motor and your going to send it back to the dark ages with 8.5:1?
Well when you don't go as fast as the next guy-then you know where to turn.
last combo was a 347, 10.1, stock ported heads, 20 psi, pump and meth and ran 9.6 with a 1.8 short lifting, curb weight 3480-full AC and all options.
line me up with the 8.5 car anyday.
fwiw-no intercooler, 9.5:1, 30 psi, 310 cubes, 3300lbs, 8.5's all day long in the summer.
Yeah 8.5.
I can't believe the poll results! We've gone so far with the design of this amazing motor and your going to send it back to the dark ages with 8.5:1?
Well when you don't go as fast as the next guy-then you know where to turn.
last combo was a 347, 10.1, stock ported heads, 20 psi, pump and meth and ran 9.6 with a 1.8 short lifting, curb weight 3480-full AC and all options.
line me up with the 8.5 car anyday.
fwiw-no intercooler, 9.5:1, 30 psi, 310 cubes, 3300lbs, 8.5's all day long in the summer.
Yeah 8.5.
LOL-I'm still shaking my head. I was talking to certain cam designer about this the other day and we talked about CR too. He's and old fart and his brother builds some bad *** motors for alot class racers-he too couldn't beleive how many people are still in the dark ages!
Oh well build to 8.5, let those waste gates hold down that 25 plus psi when 12.5 psi and 11.1 CR will do it better while making more power and torque.
8.5? Save that for the warranty department!
Oh well build to 8.5, let those waste gates hold down that 25 plus psi when 12.5 psi and 11.1 CR will do it better while making more power and torque.
8.5? Save that for the warranty department!
Exactly, not everyone has a pure race setup. If thats what you are going for than sure go higher CR but on the street or both whatever may be there is allot more risks involved running high CR and boost. I for one don't wanna be running race gas 100% all the time. Have fun with that. I know you can't beat the highest CR possible with a certain ammount of boost. Its the efficiency factor obviously and will really wake it up down low. I sure the hell don't wanna be pushin water or pop a gasket. I am going lower CR which I'll be able to push more boost and my current combo further with a safe piece of mind wherever and whenever I want. If I was building a track car than yes it would be stock CR or higher. I will still make gobs of power regardless.
Exactly, not everyone has a pure race setup. If thats what you are going for than sure go higher CR but on the street or both whatever may be there is allot more risks involved running high CR and boost. I for one don't wanna be running race gas 100% all the time. Have fun with that. I know you can't beat the highest CR possible with a certain ammount of boost. Its the efficiency factor obviously and will really wake it up down low. I sure the hell don't wanna be pushin water or pop a gasket. I am going lower CR which I'll be able to push more boost and my current combo further with a safe piece of mind wherever and whenever I want. If I was building a track car than yes it would be stock CR or higher. I will still make gobs of power regardless.
This is where are the holes are. Do you really think it's that easy to dial up 20 psi? Sure if you stick banana's in your exhaust.
The more boost you try to dial up the more demanding you are on everything.
I ran 16-20 psi on PUMP GAS AND METH, and over 900 rwhp with a F1R, and drove the car everywhere-I live about 130 km from the track. Drove to cruises, to my engine builder which was another 150km away, the donut shop looking for action and still got 26-28mpg with my AOD-my car is far from race-all the accessories are still intact-and will remain that way.
I'll take the higher compression anyday-that's my choice but looking at my #'s I think it did alright for a little 347 and stock ported heads.
Oh well-I'm not gonna try to convince everyone-maybe my engine builders right-I should keep this to myself.
I am not saying that high CR and boost is not a good idea. Both of them will make a ton load right but you obviously have the added effects of the higher CR just that you give up some of that safety factor is all I am saying. Different people have different goals, some aren't comfotable with the higher CR, including the engine tuners themselves. If you can find a builder/tuner that reccommends you to go higher CR and give you his personal guarantee well than you are a lucky man I guess. For going max, all out performance and not so worried about duability/safety and have a big wallet than by all means do it up! With confidance in your tuner and builder of course 
