ForcedFirebird's m20 dyno thread.

[ForcedFirebird]

How much of a difference do you think it is with and without that 2mm off the deck? Im guessing that bumps the CR from ~8.5:1 to ~9.5:1

The added stroke is what bumps the compression - swept volume. The 2mm off the deck is because the crank is 6mm more (3mm up, 3mm down strokes), but the rods are 5mm shorter than b25. Taking the 2mm puts the pistons back up close to the head. If you didn't shave them, you would have an extremely large quench/squish (distance between the head and pistons at TDC).

[2mAn]

How much of a difference do you think it is with and without that 2mm off the deck? Im guessing that bumps the CR from ~8.5:1 to ~9.5:1

[ForcedFirebird]

How is an "extrude hone" done in a curving intake runner like that? I'm trying to picture the hardware that does this. Is it just smoothing, or removing metal to enlarge the diameter?

Thanks -

https://www.youtube.com/watch?v=2QBc59YZYxA

[LateFan]

How is an "extrude hone" done in a curving intake runner like that? I'm trying to picture the hardware that does this. Is it just smoothing, or removing metal to enlarge the diameter?

Thanks -

[ForcedFirebird]

my guess is the differences are mostly breathing mods

looks like that cam isn't doing shit

I just pushed the car into a spot to pull the diff, and something is dragging pretty hard. It's very easy to push backwards, but going forward is 2x the effort.



As far as the 2 engines and the cam, one added lift/duration for more flow with nothing upstream, and the stock cam car increased flow before/after combustion. I have dyno tested headers similar to these and they are worth 5-8whp/tq - but we are missing closer to 10.

[LowR3V'in]

looks like that cam isn't doing shit

[digger]

my guess is the differences are mostly breathing mods

[ForcedFirebird]

Could the extruded intake have made that much difference and if I may ask what that costs ?

I have a feeling the diff is causing parasitic loss. Going to pull it out tomorrow anc check it out.

It's amazing that both graphs are basically identical upto 5000rpm.

So the first has
- standalone ecu
- header
- exrtrude hone
- bbtb and fine style inlet
- tighter squish clearance

But the second has a IE 272, is it regrind or Schrick knock off ?

New cam.





Two other differences are the first one has 3.73 final drive, second has 4.10 with oil pressure relief blocked (~80ish psi oil pressure max), and first had 10w40 conventional, second had 10w60 (~65 max oil pressure) - but don't believe the oil made the difference as they both were hot enough.

[digger]

It's amazing that both graphs are basically identical upto 5000rpm.

So the first has
- standalone ecu
- header
- exrtrude hone
- bbtb and fine style inlet
- tighter squish clearance

But the second has a IE 272, is it regrind or Schrick knock off ?

[jeffnhiscars]

Could the extruded intake have made that much difference and if I may ask what that costs ?

[ForcedFirebird]

Did these both have stock cams and non-adjustable cam gears?

have you seen any power from retarding the cam seeing as allot of people resurfaced/shaved heads but with no adjustable gear.

Honestly I have not done much with the adjustable gears on the dyno.


Here's the graphs from Sat.



81mm crank, 130mm rods, b25 pistons, .080" (2.03mm) off the deck, stock cam (and cam gear), in house rebuilt head, .035 quench, bored throttle body, extrude manifold, eBay headers, single 2.5" exhaust through 2 mufflers. MS1 with a smooth elbow pipe, cone filter.





81mm crank, 130mm rods, b25 pistons, .080" (2.03mm) off the deck, IE 272 cam (stock cam gear), in house rebuilt head, .050" quench, stock intake/TB, stock exhaust manifolds, single 2.5" exhaust with a single resonator. Stock ECU re-mapped at the dyno.


I believe this car "should" have made more power, was actually a little disappointed. Later after watching a video sent by a friend, I can hear a lot of diff noise that was impossible for me to hear in the car while tuning (one car bay with a dyno in it). Doubt we will bring it back to the dyno, just rebuild the diff and send it racing.

[LowR3V'in]

have you seen any power from retarding the cam seeing as allot of people resurfaced/shaved heads but with no adjustable gear.

[Reichart12]

Ahh thanks for the clarification. I must have missed that if you mentioned it before. Still good power output.

[redlightpete]

Did these both have stock cams and non-adjustable cam gears?

[ForcedFirebird]

Wow those numbers are fantastic for a 2.7 stroker. That's promising data for anyone thinking about going that route.

These are NOT 2.7 short blocks with a 885 heads. They are 81mm cranks, 130mm rods, stock b25 pistons and machine the block deck to get compression height back. We took .080" off these blocks, but beware of squish. Both engines got shaved heads, one was too close at .035" piston to head clearance. To be safe without measuring, I would suggest taking .070-.075" if you want to use an off the shelf head gasket.