Chassis dyno and road test

[fizz]

Just got my car back from chassis tuning. It was one of those dynos that bolt up directly to the rear wheel hubs. TPIS in Chaska mn and I recommend him. Engine is a 493, 6 pack, 2" tti headers with 3" tti exhaust out the back, lunati hyd roller 294/302 cam, stealth ported heads, supposed 10.2 compression diamond pistons, l460 silver sport auto trans, 391 gears.  Engine did 575hp @ 5600 on engine dyno with different cam, switched to this cam to make it more streetable. Did 427 hp @ 5300 and 466 tq @ 4100 on chassis dyno. Has pinging problem with 91 octane nonoxygenated gas so had to run race gas additive to 98 octane, this was at 28 degrees timing with a rev-n-ator box, so probably similar to 32 or 34 degrees with an orange box.  Made 15 hp more without air cleaner, dyno operator thinks that dynomax super turbos are killing some power, so ordered a pair of dynomax ultra flows. So, looks like the shop who built the engine didn't match the pistons with the head chambers, and he went mia after he got paid. We are going to pull the oil pan this week to fix a leak, will try to see if there is a piston part number from the bottom, otherwise I will pull the heads and fix the problem next winter. Road test, drove nice, love transmission once tuned, good power, pretty gassy at idle. Dissapointed I have to rum $1/ ounce octane booster, and the gassy idle, but what do you guys think?

[HPP]

The switch to the smaller cam probably introduced the pinging. If the builder put everything together to work as a system, the cam duration was most likely matched to the dynamic compression ratio and altering the cam timing with the smaller duration put your compression over its limit. I've never seen a part number underneath a piston, but it never hurts to look.

Yes, restrictions such as air filters and full exhaust do tend to pinch horsepower. However, they are necessary for street use so the best you can do is try different types to see if you can minimize the loss.

You could always look at methanol injection as a means to avoid octane boost. They aren't cheap initially but are effective and can be run off windshield washer fluid to eliminate detonation.

[fizz]

I wouldn't think 10.2 compression would be that sensitive to cam choice, though.

[fizz]

And it did the same thing in the car with the bigger cam

[firefighter3931]

I'm questioning the 10.2:1 static compression. With the outlined combination to achieve that result you would need a dished piston in the 13-14cc range. If the builder used a flat top with simple valve reliefs the compression ratio is likely over 11:1 static.

How did the afr numbers look when they had it under load ? Was it lean by chance ?



Ron

[fizz]

That's what I suspect also. 12.48-12.61 air cleaner off. 11.86-12.58 air cleaner on.

[BSB67]

What is the cam size?

What air cleaner?  Got a picture?

[c00nhunterjoe]

 

[c00nhunterjoe]

Also, fwiw, this aircleaner (with flow thru lid also) cost 12hp on the engine dyno, but is worth not having a rock go through the motor in the staging lanes...

[fizz]

six pack air cleaner with kn filter. .560/.565 lift  243/251 duration  110/106 lsa.  I plan on running the air cleaner. Just info.

[BSB67]

Good info on the air cleaner.

I would think that with that compression ratio and cam timing you would be okay.

Do a cylinder cranking pressure test and report back the results.

[fizz]

cranking compression hot 172. Looks like piston-head ok then? Pistons are diamond 23663 which is 10.3 compression on a 72 cc head down to 10.5 on 80cc, and 10.1 0n 84 cc. Not sure what ported stealths are supposed to be or if anything was done to them to change volume

[c00nhunterjoe]

Just realized my prior post didnt take the picture. Its a 572, made 820 hp. Avg street mill probably wont lose as much, but it gives you an idea.

[fizz]

Cranking compression hot 172. Pistons are diamond 52421 which is less than 10 compression with an 80cc stealth head, so I would surmise pinging requiring octane booster with our local 91 octane gas is from another problem, like poorer gas than advertised. Went from black springs to purple today, that sure woke it up. It definitely likes the rev-n-nator box better than the orange mopar, at least at the current timing settings.

[BSB67]

Cranking compression hot 172. Pistons are diamond 52421 which is less than 10 compression with an 80cc stealth head, so I would surmise pinging requiring octane booster with our local 91 octane gas is from another problem,

I think so.  What plug/plug number are you using?  Has the timing mark (damper/tab) been checked?  What is the in car WOT fuel pressure?

[fizz]

plug is a ZFR6F- 11 ngk. The dampner was looked at (didn't show obvious signs it moved) but not checked for accuracy. I will get a guage and check fuel pressure (I have the mechanical hp carter pump from Mancini) Hey, I really appreciate your guys' time in helping me sort this out!

[firefighter3931]

Based on the 172 psi cranking compression you should be fine with pump gas. I would get a piston stop and check the indexing on your balancer. Either the timing is off or it's going lean on the top end. The AFR's on your dyno pulls look fine....if anything a bit fat so I'm leaning towards a timing issue. 


Ron

[fizz]

FWIW, it would ping on the upshift. Also, went from black spring to purple and engine seemed a lot happier. It doesn't ping with the octane booster. Could it be that the engine would go lean on the upshift, because the outboard carbs closed. I will check the timing mark on the dampner, but think I should try it now on pump 91 no octane booster. If that works start bumping the timing up a couple degrees at a time. Thanks for the patience, I am learning.

[BSB67]

FWIW, it would ping on the upshift. Also, went from black spring to purple and engine seemed a lot happier. It doesn't ping with the octane booster. Could it be that the engine would go lean on the upshift, because the outboard carbs closed. I will check the timing mark on the dampner, but think I should try it now on pump 91 no octane booster. If that works start bumping the timing up a couple degrees at a time. Thanks for the patience, I am learning.

You mean after the shift?  What is the jet size in the center carb?  Did you get an A/F measurement under constant cruise load (i.e. center carb only)  Does it only knocks under WOT at lower rpm, and then clears up as the rpm goes up?  If so, that means that you are close.

Can you post your A/F graphs?

Try the NGK R5671A-7 or 8

Increasing the center carb jet size by 2 might help.

[fizz]

Yes, when the engine speed decreases as it shifts to the next gear. I didn't get a graph, bur air/fuel by RPM, which I could have somebody post for me. Jet size center carb is 66. I will try those plugs, but could you explain what that does?

[fizz]

FWIW, takes 1000 rpm to idle somewhat clean cold