Dyno comparison: 9:1 comp vs 10:1

[boosted hybrid]

I had an opportunity to measure the difference between 10:1 compression set-up, and than dropped to 9:1 compression. The previous engine was a stock OEM gsr bottom end. The bottom end was swapped out with a 9:1 CP pistons/Eagle rod 0.020" gsr bottom end.

The set-up was as follows:

Inline pro manifold
Gt28rs
2.5" downpipe, 2.5" exhaust with an itr muffler (def. a restriction)
Tial 38mm wastegate (9psi wastegate spring)
Spearco intercooler
Drag IC piping
RC 550cc injectors
Walboro 255lph HP pump
3bar map sensor
Neptune Tuned

What was changed:

Bottom end
9:1 CP pistons, eagle rods, ACL bearings

No boost controller, the pulls were done on a 9psi Tial wastegate spring.

Here are the results:



To show that there was no difference in boost pressures, here is the boost pressure plot:



This is probably the most accurate test that you can perform. NO other changes were made to the system. What was interesting between the two tunes is that it took 6-7 degrees more timing than the previous 10:1 compression tune everywhere in boost to get to MBTT (maximum brake torque timing).

[et Phil]

Sorry I had to keep that graph that big so you could see the lines.

Great comparison!

[Cyphear]

Good work! So 15whp loss for a 1 "drop" in CR.

Whats interesting is the low end power is almost the exact same. So maybe another 1.5psi would have made the 9:1 and 10:1 curves the exact same.

[LostSolVTEC]

Good work! So 15whp loss for a 1 "drop" in CR.

Whats interesting is the low end power is almost the exact same. So maybe another 1.5psi would have made the 9:1 and 10:1 curves the exact same.

so much for saying you lose your low end with dropped compression huh?

[Alstare]

Sweet...

Am I reading the pressure plot wrong though or is one run at 9psi and the other at 11psi? If so isn't the old 10whp for evry 1psi general rules taking place here?

Either way pretty sweet test... I wonder what the results would be like on all motor alone.

[boosted hybrid]

One pressure plot is like 0.25~0.5psi higher than the other. They are at approximately 8.5~9psi. With wastegates running off of just a spring, and no boost controller i ofter see 0.5~1psi fluctuations in the boost pressure from the wastegate getting hot.

[armed ferret]

still, all we have here is proof that raised compression doesn't necessarily have a big impact on the lower end as previously though. now, i could see where a setup running 11:1 would have more lower end than 9:1. but still......not too chabby.

[bigwig]

Does this kill all the "compression helps the turbo spool" garbage?

[boosted hybrid]

One thing to remember is that the turbo that is being used is a gt28rs, and its a log manifold. The log manifold will have a higher exhaust pressure in the manifold, as well as needing less exhaust energy to spin the smaller turbine wheel in the gt28rs.

[Toda Party]

6-7 degrees, wow

[Isratyper]

lol why he still have a itr muffler, lol sorry if i laugh its just because even when i was stock itr b18c5 i have just changed my muffler for a straight one i feel the difference imagine on this turbo i deff loss a lots of whp

[boosted hybrid]

About 20-25whp worth of power loss pretty much everywhere, with slower spool. We dropped the muffler and found out how restrictive. I can say that its the quiestest turbo car i have ever driven in and tuned.

[Toda Party]

word man, i'd rather take 20 less hp vs 20 more tickets every month for loud exhaust by ze coppers

[STHPERFORMANCE]

Nice test

[RyanCivic2000]

Nice comparison. Wouldn't it be true though that if more boost was run and more peak power made, the power difference between 9:1 and 10:1 compression ratios would increase?

Also I thought that MBT was mean brake torque, not maximum brake torque.

[boosted hybrid]

Wouldn't it be true though that if more boost was run and more peak power made, the power difference between 9:1 and 10:1 compression ratios would increase?

Also I thought that MBT was mean brake torque, not maximum brake torque.

It will be more of a difference, but it wont rise linearly or expotentially. Unfortunately i wont be able to measure that difference on this particular set-up.

Mean indicates average. The MBTT is the point at which there is maximum or peak torque occurs.

[alpha]

Bringing this back from the dead.

Jeff, were both of these fully tuned/retuned?

[boosted hybrid]

In both comparisions its tuned vs tuned.

[Safe Haven]

Will this allow you to run more boost on pump gas, than it will at a higher cr for instance?

[Scholzey]

with the tuning for this, were you able to tune for best power or did you have to retard timing on the higher compression engine? or was best power achieved with less timing due to a quicker burning combustion chamber?