Compression Ratio for TT

[miamispd]

I recently ordered the CPE side mount TT set up.

What is the ideal CR to run? I want to make as much power as possible on pump gas. I am thinking 8.5:1 may be the way to go. This way I should be able to run more boost and make more power compared to 9.0:1 or 9.5:1. However, running a higher CR may make the car more responsive (despite less hp/tq) on the initial hit.

BTW, I am building the car for the street not the track.

What Compression are the TT guys running?

 

[Joseph Dell]

I've run everything from 8.5:1 up to 11.5:1 in TT cars. figure this: 3% power loss for every point of compression (so the books say). in a viper, 8.5 is a bit lethargic. 9.0:1 or 9.1:1 is a good number. If you aren't running water/**** and this is 100% street, go with the 8.5:1 and **** it up b/c you will make more power on the top end (more boost) but the viper has lots of low-end grunt as-is so you aren't losing _that_ much.

With the right heads, plugs, pistons, etc... 10.0:1 is possible with 10-12lb of boost... and that is a happy car. But the perceived 'high' CR isn't really... the combination is all in the tune.

JD

 

[Greg Good Cylinder Heads]

miamispd...."it depends" on your combination. Will it have ported heads and a larger camshaft?

You need to figure the volumetric efficiency into the equation. The higher the V.E., the more air will be trapped in the cylinder when the intake valve shuts and the higher the *dynamic* cylinder pressure will be.

Stock heads and stock cam can handle more boost than ported heads and a larger cam that is 10-12 degrees bigger than stock. The ported heads and big cam raise the cylinder pressure a lot. You can have a safe combination for stock heads/cam, but put ported heads/larger cam on the engine and then have a detonation problem.

 

[Kevin D]

I recently ordered the CPE side mount TT set up.

What is the ideal CR to run? I want to make as much power as possible on pump gas. I am thinking 8.5:1 may be the way to go. This way I should be able to run more boost and make more power compared to 9.0:1 or 9.5:1. However, running a higher CR may make the car more responsive (despite less hp/tq) on the initial hit.

BTW, I am building the car for the street not the track.

What Compression are the TT guys running?

If your looking to go with the twin T66 side mount set-up from CPE go with 9.0CR...you'll safely run 15psi and make ~1000RWHP on pump gas...

If you went with a more radical turbo set-up and were looking for record boost numbers (i.e. 20PSI on pump and 30+PSI on race...then 8.5CR)

If you're running a 'relatively mild' side mount T66 set-up don't sacrific any response/drivability and just go with 9.0CR...

 

[miamispd]

Thanks to all.

 

[GTSjbud]

This is awesome information!

 

[plumcrazy]

from what i've been told, the higher the compression the smaller margin of error for tuning. you can have a high CR but you gotta be closer to dead nuts on with the tune. the less CR you run, the more room for error.

and i also went with 9:1 for that reason. (SC'd though)

 

[V10TT]

Keep in mind this car will ahve Heads, and cam, and it lives in the So. Fla. HEAT.
I say 8.5 CR.,and don't sacrifice power on Pump gas.

 

[dansauto]

from what i've been told, the higher the compression the smaller margin of error for tuning. you can have a high CR but you gotta be closer to dead nuts on with the tune. the less CR you run, the more room for error.

and i also went with 9:1 for that reason. (SC'd though)

yes and no, it may be safer and give more margin for error with a lower compression motor, but off boost its much harder to trim the A/F and keep the car from running too rich and going thru plugs.

 

[Disturbed]

I'm willing to bet 8.0:1 is too low and 11.5:1 is too high.


Really, 9.0:1 is great for a street car running small boost on pump gas.