Going the opposite way on compression.

Joesixpack said:
I see no reason to go above 17:1. You will be money ahead working out a secondary that will boost early, rather than try to gain a bit off boost.

What seems like a small change in compression ratio, can make a huge difference in pressure ratio......
Click to expand...

I agree on small changes, the stock ratio is 17.2, and if you check it its closer to 17.35 to one, so an increase to 18 5 to 19 to one is not out of the question. NA diesels are in the range of 22 to 1.

This compression is for a 600 hp street truck, where someone wants a truck with instant throttle response, little to no smoke, and fuel economy. You must address airflow in this equation. And improved Intercool is critical, a camshaft designed for this application, and cylinder head work. Not everyone wants all the hp they can make, its fun to have a truck that runs good and exhibits zero to little lag. I talk to many people every week, when helping them pick out a cam for their truck. I ask the same question “what is you honest and realistic intended use of this truck” , “ do you have to drive this truck every day , and do you have to depend on it “ . I then give them a realistic guidelines for achieving those goals .
If they are not asking for a all out build, and this vehicle is one they will have to depend on. Then the 1000 hp parts are not necessary. Out are big twin pumps, big injectors, and loose AR turbo’s.
So where does raised compression become applicable on racing programs.
First on limited turbo engines such as 2.6 . You can only get so much air in to the engine, the more compression you use, the looser AR you can use, and this allows gain in power by reduced turbine inlet pressure ( drive pressure ) .
Next this allows you to keep the intake valve open much longer, moving dramatically more air, this ability to move more air on these restricted turbo engines, drops boost down. If at the same turbine speed you have a reduction in boost, you move more CFM of air at a lower temp. This lower temp means denser air charge.
It all goes hand in hand , with compression.
 
How do these increased compression ratios affect longevity, especially since it is a higher hp build? What are the factory compression ratios on marine engines that have higher hp ratings?
 
markt said:
How do these increased compression ratios affect longevity, especially since it is a higher hp build? What are the factory compression ratios on marine engines that have higher hp ratings?
Click to expand...

Marine engines run at a constant rpm, at rated power for many hours, therefore the compression is lower. Using a marine piston is not always the best, if you going to have to cut pistons for valve clearance, the resultant compression is too low.
Again in performance application where you have the ability to tune around the low RPM , high cylinder pressure destruction , the compression should be no lower than 16.5 to one .
This compression strategy goes against what most people perceive as the accepted norm. The old methods were necessary when a mechanical injection system was used. Acceleration and throttle response was sacrificed for the ability to get around this low end destructive band. Once the power was up then good power was made, but if you slipped below a given point the motor was said to “fall off the charger”.
The benefits of having the proper engineered compression is be able to drive a looser, turbocharger, and not fall off of the power band. With this decrease in drive pressure, the power needed to overcome that high drive pressure decreased, and went to the rear wheels. The drop in drive pressure also resulted in reduced retained heat , and less intake charge dilution .
All of these aspects have to go together .
 
nwpadmax said:
GM 6.2s were high CR, and smallish turbo kits were made for those, but the bottom end parts couldn't take much.

Don't see why it wouldn't work if you had stout parts.

It's kind of the other end of the spectrum...cylinder pressure torque vs. high rpm HP.
Click to expand...


the NA 6.2/6.5 werent know for hP... they did heve very good throttle repsone and tq down low
iirc the NA 175hp version had close 400tq
 
COMP461 said:

So here is a good formula for a 600 hp street truck build, which will have unbelievable throttle response.
Take your CR engine , uses small injectors no more the 90 hp . mill the block .030. mill the pistons .025 . Having a quench ( head to piston distant ) of around .035 . next port the head , and use a good came designed for this type of engine . next use a small turbocharger ( 64) with a tight AR , and a E.D. wastegate . The compression will be around 18.75 to 19 to one. This combination will bark when the throttle is hit, almost zero lag.

Click to expand...

sounds like my setup
Smokem said:
You must not understand English, so let's try something else.

Ron volonta esser applicato qualche P7100.
Click to expand...
hahahaha. ron will be using a p7100.
 
Actually I agree with Greg on this one. High compression is a good thing for a daily driven vehicle. It makes it more usable in the areas you need everyday.

And I don't see why your wee bit stronger engines wouldn't withstand something like 18:1 when MB OM606 can make 500-600hp reliably with 22:1 compression and rev to 6000+. And have half of the displacement than you have.
 
Interesting read. Definitely curious to see the results if you go this route ron.
 
You must log in or register to reply here.
Back
Top