How compression + quench affects power - dyno.

[mendelmax]

Ok guys, some time ago I have modified my stroker. So i just wanted to share with the results. The numbers are pretty poor because of stock exhaust and really restrictive snorkel, but it shows the difference. Keep in mind, that the units are Newton-meters, not Ft-lbs!
Since it's described in polish, I explain:
moc = power
moment obrotowy = torque

The stroker main specs:
- 0.040 overbore
- 4.2 rods
- pistons dished to 16.5 ccm
- 7120 head with WJ intake
- stock renix camshaft (75* IVC)

Stroker is mated with AW4 transmission, 3.73 gears and 32" tires.

Now, the first version was made with over 0.090" quench, giving the SCR 9.36:1 and DCR of 6.93:1 according to our forum DCR calculator.
The results were amazingly poor:


So we decided to remake it a bit. Everything remained the same except for shaving the block to achieve quench of 0.060", which gave us approx 10:1 SCR, and cam advance of 5*, making DCR 7.7


Then we installed sequential propane injection, with custom injection mapping, that gave us a bit better torque curve:


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I find it pretty amazing to see the differences on the same engine. Now we retarded cam to stock specs, expecting a bit of gains in the upper RPM's. We'll dyno it as soon as possible, and I'll post the results

[Cheromaniac]

It looks like the wheel HP was measured first (blue line), then a coastdown test was done to measure "drivetrain loss" (green line), and then the two were added together to produce "flywheel HP" which is the red line.

The results look like:
Wheel HP before: 163.7PS (161.0HP) @ 3465rpm
Wheel HP after: 166.0PS (163.2HP) @ 3475rpm

"Flywheel" HP before: 197.1PS (193.8HP) @ 3475rpm
"Flywheel" HP after: 201.3PS (198.0HP) @ 3484rpm

"Flywheel" TQ before: 425.7Nm (314.0lbft) @ 3090rpm
"Flywheel" TQ after: 438.0Nm (323.0lbft) @ 3045rpm

The result is that the higher compression and cam advance produced a 4.2hp/9.0lbft gain.

[mendelmax]

Dino, you're comparing wrong dyno sheets You're comparing propane run (166RWHP) to petrol run (164RWHP), both with high compression. I posted propane run only to show how it can help even more gains.

The low-compression is the first one. There you can see only 109 RWHP.

Since we must compare apples to apples, it's essential to compare petrol to petrol run, so:
164 HP - 109HP = Extra 55 RWHP.
It's virtually 50% gain from the compression and quench itself. Oh, and the WJ intake that was swapped after the first dyno run, not before as I thought at first. To me it's a HUGE difference.

[Flash]

I have alway felt that more quench was stronger then less compression to fight Ping! at least on our 4.0/strokers

What fuel are you using on these theses ...91?

[Cheromaniac]

Dino, you're comparing wrong dyno sheets You're comparing propane run (166RWHP) to petrol run (164RWHP), both with high compression. I posted propane run only to show how it can help even more gains.

Oops, my bad.

The low-compression is the first one. There you can see only 109 RWHP.

Yeah, that definitely sucked.

Since we must compare apples to apples, it's essential to compare petrol to petrol run, so:
164 HP - 109HP = Extra 55 RWHP.
It's virtually 50% gain from the compression and quench itself. Oh, and the WJ intake that was swapped after the first dyno run, not before as I thought at first. To me it's a HUGE difference.

Indeed it is but I can't see the new intake, higher compression, and lower quench producing a 50% HP gain by themselves. Did you also change injectors or anything else that might have helped the engine so much better? The engine was massively down on power on the first run.

[BADASYJ]

From my experience higher compression will yeild gobs of power. Just going from 9: 1 to about 11: 1 on my 4.7 stroker was a major seat of the pants power increase. Its just not talked about enough because most of the strokers here are in street rides. Most people have to lower the comp. in order to make a streetable motor. Which is signifintly reducing power potential of the motor.

[mendelmax]

I think that totally ineffective quench and very low CR simply lead to improper fuel burn, this probably delivered more oxygen to O2 sensor, and this made the engine flooded, reducing power even further. At least that's the only way how I can explain this HUGE difference, because I have to agree, that by mathematic calculation itself it's impossible to get 50% gain this way.

But you're right, I checked the engine build dates and it appeared, that after this dyno run we also added a K&N filter (still on snorkel though), and we removed the 1.75" restriction on the exhaust (right after the header). I thought we did it all before this dyno run, but it seems I was wrong. It was simply very long ago.
Injectors and pressure regulator remained the same. So were the spark plugs.
But anyways, these changes affect top end power mostly, while the biggest difference here for me is the torque curve. And it has improved amazingly well after the CR and quench change.

We were considering getting even higher CR since the propane has about 110 octane rating (RON), but we didn't wanted to get into knock problems, because this is a budget build, so we couldn't afford any mistake.