you should see the feelings I have for your mother when i stick it in her a$$ without vasoline :rockon: :banana: ....DA snake boy!!!cobraracer46 said:
ordered a built shortblock
- Thread starter UCBeau
- Start date
My current setup in my 96 Cobra has 8.5:1 compression pistons and 20psi of boost and when I freshen it up if the pistons have any wear I will be going with 9.5:1 compression, you wouldn't believe how much more low end torque a centrifugal supercharged mod motor will make with higher compression. There is a great thread about this on the Corral in the SVT/DOHC forum, just search for compression.
Actually I'll save you the effort, here is the thread:
http://www.corral.net/forums/showthread.php?t=601010&highlight=compression
The only time I'd ever go 8.5:1 is if I were going with a positive displacement blower or twin turbo.
http://www.corral.net/forums/showthread.php?t=601010&highlight=compression
The only time I'd ever go 8.5:1 is if I were going with a positive displacement blower or twin turbo.
cobraracer46
Banned
Thank you :beer: Finally an intelligent post! Yes, with out a doubt high compression is the way to go with a centrifical. Why lower the compression and compromise the car in the one area it gets used the most, low speed street driving? :shrug: It just does not make any sense.viperbluelx said:
SanDiego01Snake said:
I wouldn't advise going larger than the T-trim for a street car, the JT-trim sucks on the street. I talking to a guy that put JT-trim his Mark8 and it made 420rwhp at peak through the 4R70W. Needless to say he was disappointed cause he couldn't spin the motor the RPM he needed to on the street to take advantage of the very peaky JT. He swapped to an S-trim and made 445ish rwhp with a MUCH better curve and it was a completely different car on the street.
I just don't see the point in going with 8.5 compression when 9.0 or 9.5 can be just as safe and make more lowend torque.
Paul
Paul
On my built engine I went with 8.79 to 1 compression (daily driver), and I believe it is way to low for a centrifugal blower. If I would have done it all over again I would have gone 9.1 to 1 at the bare minum or higher. I believe you will regret taking the compression out of a 4 valve motor..especially with a Vortech Blower these supercharger's do not like low compression that's for sure..
SanDiego01Snake said:I know a guy who had a 04 cobra shortblock put into his 97 cobra, 8.5:1 compression..still made over 500 rwhp
Yes, but I bet he had a lot less power below 5k than if he went with 9.5 to 1. 8.5 is okay for a positive displacement blower and a centri race car but not a street driven centri'd car.
SanDiego01Snake said:I know a guy who had a 04 cobra shortblock put into his 97 cobra, 8.5:1 compression..still made over 500 rwhp
I thought we were talking about torque not HP? :shrug:
Good stuff. You will love the not having to worry about that the short block under loads!SanDiego01Snake said:
what a bunch of horseshit.
I guarantee you that you will not feel a hint of difference between a 9.0 motor and an 8.5 motor below 3000rpm. The difference is maybe 10rwhp, MAYBE.
If you want to run a bunch of boost on pump gas, low compression is the way to go.
My car is not a dog out of boost. Most cars aren't that quick at part throttle, NA 9.85 cobras included. However, when I want to go fast, I floor it, and bam, im in boost.
On the street, 8.5 compression is the way to go. 85% of the time, its under less stress than a stock motor. Only at high boost will you be at a higher dynamic compression ratio. Id much rather lose 25lb ft of torque then have to worry about blowing my forged motor every two seconds with 10 to 1 cr.
in terms of safety
when not in boost
8.5>9.5 or above
when in boost
8.5>9.5 or above
You will make a little less torque, but you can make up for low speed part throttle power with some added timing, and additionally, added timing up top will add power that you can't use with higher compression.
for a track only race car, Id use compression as high as possible.
I guarantee you that you will not feel a hint of difference between a 9.0 motor and an 8.5 motor below 3000rpm. The difference is maybe 10rwhp, MAYBE.
If you want to run a bunch of boost on pump gas, low compression is the way to go.
My car is not a dog out of boost. Most cars aren't that quick at part throttle, NA 9.85 cobras included. However, when I want to go fast, I floor it, and bam, im in boost.
On the street, 8.5 compression is the way to go. 85% of the time, its under less stress than a stock motor. Only at high boost will you be at a higher dynamic compression ratio. Id much rather lose 25lb ft of torque then have to worry about blowing my forged motor every two seconds with 10 to 1 cr.
in terms of safety
when not in boost
8.5>9.5 or above
when in boost
8.5>9.5 or above
You will make a little less torque, but you can make up for low speed part throttle power with some added timing, and additionally, added timing up top will add power that you can't use with higher compression.
for a track only race car, Id use compression as high as possible.
cobraracer46
Banned
First of all, a stock Cobra has 9.8.5 to compression and dropping it down to 8.5 to 1 will result a big torque deficit right where our cars need it the most: low speed street driving. When you loose torque, you definitely feel it.quadcammer said:
why would you want to do that when a 10.5 to 1 or 11 to 1 motor does not give up anything in performance and as an added benefit, an 11 to 1 compression motor gains torque instead of loosing it. On top of that, there is no need to spin the blower really high or gear the car aggressively like you have done to make up for a torque deficit because there isn't one. As an example, one daily driven street and open track cobra has an 11 to 1 short block with a Vortech SQ, an aftercooler and with just 10 psi of boost, the car is putting out over 660 Hp at the wheels. As an added benefit, since the blower is only putting out moderate boost levels, it is under less stress and belt slipping problems are not a problem.quadcammer said:
We all know that running a very low compression ratio with a centrifical blower will result in a major torque deficit and the fact you had to add a really low rear end gear to your car to regain low speed drivability conforms it. Motors blow from rods failing and from detonation so choosing a quality rod like a Carrillo billet steel piece and keeping engine temps under control and having a good fuel system to eliminate detonation will result in a reliable engine.quadcammer said:
Once again, You will make a lot less torque when you loose over a point of compression and you will have to go a lot further than adding more timing. Running 4:30+ gears is a band aid and not practical for a highway driven vehicle.quadcammer said:
i gotta go with quadcammer on this one
and the instant boost thing for the twin screws and roots blowers in regards to CR is retarded as well, like quad said your not gonna se elevated CRs until you are higher in the RPM range.
Honestly when i get my motor built i am looking to go with a 9.1.1 CR or so then crank up the boost so i can run it on pump gas. With higher CRs your not going to be able to run much timing on pump gas. 11.1 CR + boost = detonation on pump gas uless you pull so much timing you won't think your car is blown
Sandiego you made a good choice by going with a lower CR
and the instant boost thing for the twin screws and roots blowers in regards to CR is retarded as well, like quad said your not gonna se elevated CRs until you are higher in the RPM range.
Honestly when i get my motor built i am looking to go with a 9.1.1 CR or so then crank up the boost so i can run it on pump gas. With higher CRs your not going to be able to run much timing on pump gas. 11.1 CR + boost = detonation on pump gas uless you pull so much timing you won't think your car is blown
Sandiego you made a good choice by going with a lower CR
SanDiego01Snake said:
I forgot you have to run that "not-so-good" gas.
there is no point in arguing this.
cobraracer is blinded by Grigg's nuts. He knows everything about a car that he didn't build, he doesn't own, and he doesn't drive. He knows its daily driven (I doubt it), that it made 660rwhp on 91 octane (doubt it), etc etc. He read about it in MMFF and now he's an expert. He also knows a hell of a lot about blown cobra's, yet doesn't own one, drive one, or build any.
I've HAD both. I know what both feel like. I know how rich i had to run my 10.5 cr motor. I know that it felt sluggish because of the lack of timing. I know that sometimes gas is not great and with high compression, you are risking your pistons even further.
The fact is, most people who get blowers have already modded their car NA. That means that they most likely already have 4.10 or 4.30 gears. They can keep them. Who the hell under gears these cars anyway?
Who is lunching rods? I make max power at 7200, well short of the rods recommended 8000rpm limit. We don't need billet Carillo rods to make decent power. Oliver I beams are fine if you are overstressing H beams.
Not to mention, with 11:1 compression and 10 psi, your effective compression is 18.48. With 15 psi and 8.5 compression, its 17.17. The extra 5 psi will more than make up for any differences in compression, and it still ends up having lower effective compression.
Centrifugally blown cars will never be torque monsters. They are designed to run at the top end of the rev range. Hence, you use a proper gear, and a proper blower pulley and motor to make the thing work in its powerband.
This comes from about 4 years of experience with blown cobras, including 10.5 cr and 8.5 cr. I can tell you that for a daily driven street car, 8.5 is great.
cobraracer is blinded by Grigg's nuts. He knows everything about a car that he didn't build, he doesn't own, and he doesn't drive. He knows its daily driven (I doubt it), that it made 660rwhp on 91 octane (doubt it), etc etc. He read about it in MMFF and now he's an expert. He also knows a hell of a lot about blown cobra's, yet doesn't own one, drive one, or build any.
I've HAD both. I know what both feel like. I know how rich i had to run my 10.5 cr motor. I know that it felt sluggish because of the lack of timing. I know that sometimes gas is not great and with high compression, you are risking your pistons even further.
The fact is, most people who get blowers have already modded their car NA. That means that they most likely already have 4.10 or 4.30 gears. They can keep them. Who the hell under gears these cars anyway?
Who is lunching rods? I make max power at 7200, well short of the rods recommended 8000rpm limit. We don't need billet Carillo rods to make decent power. Oliver I beams are fine if you are overstressing H beams.
Not to mention, with 11:1 compression and 10 psi, your effective compression is 18.48. With 15 psi and 8.5 compression, its 17.17. The extra 5 psi will more than make up for any differences in compression, and it still ends up having lower effective compression.
Centrifugally blown cars will never be torque monsters. They are designed to run at the top end of the rev range. Hence, you use a proper gear, and a proper blower pulley and motor to make the thing work in its powerband.
This comes from about 4 years of experience with blown cobras, including 10.5 cr and 8.5 cr. I can tell you that for a daily driven street car, 8.5 is great.
Thanks for the supportDouble"O" said:
I realize 8.5:1 might not be ideal for a centrifugal car, but I had to balance my current power desires with my future plans, taking into account the gas out here, and that it is a street car. Cobraracer46 is a straight moron, he's using one example of a high compression boosted car owned by a BIG performance company to justify his position. Glad to see smarter folks have posted in this thread with some good info for me.
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