Compression ratio question for 12lbs of boost

[bulldog5.0]

I am in the process of building a Teksid shortblock to go with my Vortech setup. My question is, I a, about to buy my pistons, and want to know which CR to go with. My setup will be as follows:
Teskid block
forged cobra cranks
Forged pistons(dish still in question)
MMR stage 2 cnc ported heads
Comp xe270ah cams
Eddy intake w/6061 elbow
75mm tb
42 lb injectors
90 mm maf
Vortech V1 T Trim w/ power pipe, Treadstone intercooler and 3.5" piping.

I need to know if 10:1 CR is too high for 10-12lbs of boost... I want to stay as high as I can to retain low end torque...

 

[manolith]

how much power do you want and what fuel will you use. remember that boost is not what will limit your horse power. fuel is going to be the limit of a built motor. higher compression less boost or lower compression and lots of boost will have pretty much the same peak combustion pressure. seeing that your blower will max out at around 700rwhp i would keep it at 10.1 compression.

 

[03Steve]

What are the cam specs?

 

[bulldog5.0]

how much power do you want and what fuel will you use. remember that boost is not what will limit your horse power. fuel is going to be the limit of a built motor. higher compression less boost or lower compression and lots of boost will have pretty much the same peak combustion pressure. seeing that your blower will max out at around 700rwhp i would keep it at 10.1 compression.

I will use 93 oct. on the street, and 93/116 cam2 mix on the track......I am hoping to make between 550-650HP estimating with my combo

 

[bulldog5.0]

What are the cam specs?

106200 - Xtreme RPM Series

 

[Brutal Metal]

use a low single digit cc dished piston..

 

[Adiabatik]

I would recommend E85 but hat isn't going to fly with your fuel system. I'd say your max CR would be 9.5

I run a 9.5 CR on 16psi and 91.

 

[manolith]

I will use 93 oct. on the street, and 93/116 cam2 mix on the track......I am hoping to make between 550-650HP estimating with my combo

i would keep the 10.1. call your tuner and see what he recommends you to do.

 

[MOTOWN M]

10.1, 93 octane, and Methonal injection and you are more than safe @12psi , but loose the 42lb injectors, and get a 60lb set.

 

[stroked mach]

10.1 and some 93 should do great and if you want togo for broke hit it with some e85 and spray lol

 

[itSSlow98]

12psi is about the max on 93 at 10:1. I would go with that personally. I did 10:1 on my turbo setup and it is night and day low end over stock 8.8 compression

 

[bulldog5.0]

OK, so if by chance I did want o go ith 13-14lbs of boost, then 9.5:1 would be my max then right? Just really a hypothetical question. Just wanting to know if I ma on the right path with my thought porcess...lol

 

[IUP99snake]

Is this a street car? Do you plan on running any more boost in the future?

If this is purely a street car and you don't plan on running any more boost, I recommend going with a higher compression ratio.

If you plan on adding more boost in the future, it might be wise to go with a slightly lower CR around 9.5:1 or so.

Since you have a centri blower, it's only going to make 12 LBS of boost at redline. The other 99% of the time, it's going to be making less than 12 LBS. And when you're driving around town, you're probably not going to get into the boost at all. It's almost as if you're driving a car without a blower when you're cruising around in traffic. With that being said, you want it to make good bottom end off boost power.

You can pull timing right at the top to eliminate the chance of detonation, while still maintaining good power at lower boost levels throughout the rest of the RPM range.

Worst case scenario, you can always get meth injection to help manage detonation.

Compression is just one way to manage detonation. There are lots of other ways to manage detonation, such as ignition timing, fuel delivery, fuel type, etc. etc. Unlike all the other ways of managing detonation, compression is the one thing that can't be changed once it's set in stone.

Prior to my existing combination, I had a forged 8.5:1 motor with 99/01 heads & cams. I got it because I wanted plenty of room to expand without the rotating assembly being the limiting factor. It was an absolute dog on the street.

Because a centri only makes peak boost at peak RPM, you had to work hard and rev it to the moon to get it up and going. For example, If I floored it in second gear, the tires would stick until it got above 5K RPM and then the tires would break loose.

My existing combination is much more fun to drive on the street. The throttle response is a lot quicker and you don't need to rely as much on the boost to get up and go.

On the dyno, the low compression motor made more "peak" HP, it was the high compression motor that made more power throughout most of the RPM range.

 

[bulldog5.0]

Is this a street car? Do you plan on running any more boost in the future?

If this is purely a street car and you don't plan on running any more boost, I recommend going with a higher compression ratio.

If you plan on adding more boost in the future, it might be wise to go with a slightly lower CR around 9.5:1 or so.

Since you have a centri blower, it's only going to make 12 LBS of boost at redline. The other 99% of the time, it's going to be making less than 12 LBS. And when you're driving around town, you're probably not going to get into the boost at all. It's almost as if you're driving a car without a blower when you're cruising around in traffic. With that being said, you want it to make good bottom end off boost power.

You can pull timing right at the top to eliminate the chance of detonation, while still maintaining good power at lower boost levels throughout the rest of the RPM range.

Worst case scenario, you can always get meth injection to help manage detonation.

Compression is just one way to manage detonation. There are lots of other ways to manage detonation, such as ignition timing, fuel delivery, fuel type, etc. etc. Unlike all the other ways of managing detonation, compression is the one thing that can't be changed once it's set in stone.

Prior to my existing combination, I had a forged 8.5:1 motor with 99/01 heads & cams. I got it because I wanted plenty of room to expand without the rotating assembly being the limiting factor. It was an absolute dog on the street.

Because a centri only makes peak boost at peak RPM, you had to work hard and rev it to the moon to get it up and going. For example, If I floored it in second gear, the tires would stick until it got above 5K RPM and then the tires would break loose.

My existing combination is much more fun to drive on the street. The throttle response is a lot quicker and you don't need to rely as much on the boost to get up and go.

On the dyno, the low compression motor made more "peak" HP, it was the high compression motor that made more power throughout most of the RPM range.

It is more of an occasional street car/occasional track car.... I am considering going with 13-14lbs of boost at some point, but I don't plan on going much higher tha nthat is any...my wallet dictates that for me...lol

I am considering meth....just concerned on how often i need to re-fill it, and how much it costs each time, etc....

I still might stay at least at 9.8:1 if I don't go 10:1...then if needed, I will go with meth....just about to order my pistons now...what I decide for them will be a determining factor as well.

 

[2001SilvrGT]

I'm in the process of building my teskid block also on my 99 cobra. I went with a 5.2 dish piston from diamond. I was going to do a flat top and bring my compression around 10:1-10:5 maybe more, but I decided to play it safe and give me enough room to grow if I want to throw more at it. My compression is going to be around or close to the stock 99/01 cobra compression. I'm going to be running my procharger P1SC with 10-12lbs of boost depending if my fuel system lets me, at it for now. Eventually will after I save up some money and after I do my fuel system I'll be upgrading my head unit to a D1SC head unit

 

[Helomech74]

I had a 10.2:1 motor running 16-18psi on 93 octane, worked perfectly fine and no issues. Make sure the tune is spot on and you get your fuel from good source (Avoid stations that don't get high volume of traffic.) At 10:1 and 12psi you are perfectly fine with 93 octane. No need to add methanol injection, but you need to dump the 42lb injectors for some 60's at least and I would ditch the Lightning maf in favor or a slot type for ease of tuning.