let's talk compression : UgH!

[theKbStockpiler]

I did try to do a search on this by the way.

What compression ratio will work with premium pump gas with a turbo without special coatings and just a intercooler?
Thanks for your expertise!

[buguy]

That's a tough question and I think pretty hard to answer. Every combo is different. There is no real way to know how efficient it will be with the intercooler. Here is a start.
http://www.wallaceracing.com/boost-comp ... o-calc.php
Check out this chart too: http://www.goodvibesracing.com/Compression_Ratio.htm

[theKbStockpiler]

Thank you for the links. Looks like I will have to cut my boost level by %50.

There isn't a spool up calculator some where is there?

Also will an aggressive cam allow higher ratios or is overlap a bad thing with boost?

Thanks for your expertise!

[buguy]

I've looked before with no luck to see if there was a calculator that told you what octane you would need at what CR and boost. I'm not real sure what you mean by a spool up calculator?
Sorry I don't know crap about the cam kind of stuff.
I would have to think running a water/meth injection would solve all your problems. You could run a decent CR and high boost. Maybe in the 9:1 range and 15-20 psi of boost. I think I've seen water/meth is like 116 octane. $450 for a pre packaged 2 stage kit doesn't seem so bad when it really would let you almost double your hp. Since your going to use FI you will have more possibilities than most of us. It allows you to be spot on with your tune and that makes a huge difference.

[buguy]

Also I've read that for every 25 degrees you can drop temps with an intercooler would be like being able to use one octane less on fuel. Or boosting for one octane more fuel. All you can really do is guess how much yours will help. Or look around here and see what others have found on dyno's and such and plan accordingly.

[theKbStockpiler]

Thanks for all the help!

I want sort of a convertible engine that will be good with N/A and be able to be a mild boost engine. The option for more boost would also be nice. I guess I'll plan around 7.5-8.5 compression ratio for cheap gas non-boosted or be able to run maybe 10lb of boost on high grade. My homemade fuel injection system is not going to work the first try so I want to swap the 914 computer in and out. I have not decided on how exactly I'm going to do this. Maybe a 'Power Box' to fool the speed density system at first and then try to design something better. My project car has multiple aspects like being a daily summer driver along with being able to test my own electronics on it.

[buguy]

Sounds reasonable to me.

[Chip Birks]

7.5:1 would be super lame off boost, blah. What cam are you thinking?

[buguy]

Ha! Try 7.3 on a stock engine Chip!

[Chip Birks]

Now you know why I don't have a stock one!

[theKbStockpiler]

Basically I want a slightly aggressive cam that will work N/A or with boost.
If I'm not using the turbo set up I want an engine that just moves the RPM range in the advertised duration of 266-268 in muscle car numbers. I realize turbo engines do not work well with overlap so that will be considered soon. I guess I will be looking for a cam with the fastest ramps that does not damage the lifter bores or otherwise cause excessive wear.

I have been researching available turbos on the net and was wondering what ball bearing or otherwise close matches there is with a New T3? There are a lot of T3/4's available but not just the T3.

[buguy]

Man I don't know much about cam selection but really you should probably make a decision on if your going to turbo or not. I can't imagine trying to pick something that would work both ways. I think I would have a hard enough time picking knowing exactly what I wanted to do.
Are you looking for a new turbo? Maybe here? http://www.turboneticsinc.com/performan ... s/t3-turbo

[theKbStockpiler]

I think some cams are marketed as being compatible with a turbo.

[panel]

Found some good info here from the sticky:

http://www.shoptalkforums.com/viewtopic ... 3&t=118493

[Clonebug]

Compression is determined by your cam overlap. The more overlap the more static compression you can run.......but you will have a softer bottom end too. It will take time for the cam to come on and then the turbo will come on and you get a short rush of power just before you shift.

I think for a street car you want a cam that gives you decent low end and then combine it with a turbo that compliments that.

Take my setup for an example.....

7.8:1 compression and .420 lift......I built it at the time to be cheap........therefore it has stock heads and stock rockers. I added the solid shafts later once I had some money.
It has great low end and the turbo comes on at 2400 rpm. The other turbos I ran would peak the boost slightly earlier but would not maintain it.
I could get 17 lbs. boost at 3500 rpm but it would taper to 13 at 5000 rpm.
This new turbo will max at 3600-3800 and 22 plus lbs. boost but will hold that level til I shift.

With my transmission at 4.12 and 28" diameter tires it loads the turbo really well. There is really no weak spot unless you are in fourth gear and 1500 rpm's and then floor it. It takes a bit for the engine to get into the sweet zone which is about 2400- 2800 rpm. After that it just pulls like a train.
If you keep the rpm's at or around 3000 rpm you have instant response.
The bigger the turbo the more you have to drive it like a race car. You have to keep it in the area that the turbo responds.

Now........ you can offset that with a bigger engine but you start over in all your cam and turbo calculations......It always comes down to how much hp you want at what rpm and what cost.

You still have to pick a turbo that will flow the amount of air for the hp target you want.....How close to that target the turbo is will determine how much lag you will have.

Using my engine as an example again........the turbo will flow enough air for 270 crank hp. I am at about 225 crank hp so I have a turbo pretty closely matched to what I need for excellent response.



For a mild cam 8.0:1 compression is a good place to

If you put a bigger cam in it you might be able to go to 9.0 or 9.5:1 compression.

Keep your IAT's low and pull timing to keep from detonation and you too can run 22 plus lbs. of boost.

It's not actually very easy but it can be done. Attention to detail is what is needed.