Crappy day at the dyno

[dhardison]

I recently performed a light rebuild on my 454. Installed a new HYDRAULIC cam (flat tappet - Duration 284/ 292, Lift .572/ .590), new matching lifters, new matching springs/retainers/locks & new pushrods. I had the heads milled 0.030" and other than new main/rod bearings and having the crank journals polished I didn't touch the short block (11.25:1 factory popups).

We got the 454 hooked up to the dyno and she fires right up. We let it run for ~25 minutes to let the cam break-in. So far, no runs, no leaks, no knocking, etc. We let the engine cool down for a bit and changed the oil. Everything looked great and I was excited for that first pull.

On the first dyno pull, she pulled hard until 4500rpm when it fell on it's face and started shooting fire out of the headers (both sides). We did some jetting changes since the dyno showed a rich condition, but on the 2nd pull it did the same. We then checked the valves and determined that they were adjusted too tight. We readjusted them to zero lash plus a bit of a turn. On the next pull she pulled good 'til 5500rpm then fell on its face again.

We need a motor that'll turn 6000 and were hoping for 450hp/400lbft torque. Instead in the pulls we got the best we saw was 340hp and 450/lbft torque. We tried a few other things like swapping in a new distributor, running the valves again, but in the end we were basically stumped. We'd been there 7 hours and decided to give up for the day.

Thinking that it's just not enough cam, we've ordered a new higher lift SOLID flat tappet cam/lifters/springs plus a new MSD 6AL distributor/coil setup. If anyone has any thoughts on what the problem might be with the hydraulic cam, I'm open to any suggestions. We gained 1000rpm by readjusting the rockers to zero lash, but there's no way we we're going to make the additional 60-110hp we need in the remaining 500rpm, before we hit 6000rpm.

Dan

[MarkM66]

What heads on on it?

I had a mild 468 with a hyd cam and it made more hp then that at the wheels. Pulled to 6000 rpm with ease.

Did you play with the timing curve at all?

[Madspeed]

What were the cam's suggested srpring seat pressure and open pressure?

and where these recomendations met on the heads?

Allmost sounds like springs are to light

[critter]

Did you check your oil again for any signs of a cam lobe going away?

Sorry, but I'm gun shy with all the problems since they pulled the zinc from the oil.

[dhardison]

What heads on on it?

I had a mild 468 with a hyd cam and it made more hp then that at the wheels. Pulled to 6000 rpm with ease.

Did you play with the timing curve at all?Heads are:
Open Chamber LS-6 & LS-7 Head, 425hp,
Casting # 6272990
intake / exh valves: 2.19" / 1.88"
Material Cast Iron
Combustion Chamber Open 118cc
Intake Runner 325cc
Intake Port Type Rectangular
Exhaust Port Type Square
Flow: valve lift /Intake /Exhaust
.05 32 24
.10 69 53
.20 125 103
.30 183 140
.40 233 176
.50 264 198
.60 292 204
.70 - 207

We played with the timing a bit. The distributor is locked so no curve. We started at 32 and took it up to 36. It made more hp/torque at 32.

[dhardison]

What were the cam's suggested srpring seat pressure and open pressure?

and where these recomendations met on the heads?

Allmost sounds like springs are to lightThe recommended spring pressures are 120 Lbs Seat @ 1.820 Installed Height, 340 Lbs Open Pressure. We checked a handful of springs are most were around 115lbs seat. Maybe we had some coil bind issues.

[dhardison]

Did you check your oil again for any signs of a cam lobe going away?

Sorry, but I'm gun shy with all the problems since they pulled the zinc from the oil.Yeah, the cam and oil looked fine. We took lots of precautions by using Shell Rotella D oil along with GM EOS additive plus lots of cam lube.

[Skip Fix]

Dan my flat tappet hydraulic 239/247 @ 0.050 in my pump gas 455 Pontiac pulled well over 6200 with no issues with similar springs and 1.8 rockers. A DUI HEI also dynoed the same as an MSD distributor and 7AL box. 525 hp on the dyno more like 550 using the Moroso slide and mph/wt.

Fire shooting out the exhaust is from fuel ignition when an exhaust valve is open, or WAY too much fuel out in the exhaust and the hot exhaust is lighting it. The only time I had that in a motor was when I THOUGHT I had the timing gears lined up. They were 1 tooth off.

Check distributor wires and timing first off. Then look at the plugs. Then start chasing down ignition issues on the top. Coil/MSD box. MSD boxes can have some strange symptoms when they go out,why the circle trackers have TWO boxes they can switch from in a race.

Then you need to double check tiing chain and dgeree specs on cam, particularly the cylinder it was popping on.

I've found coil bind usually breaks stuff like rockers or bends pushrods.

[dhardison]

Fire shooting out the exhaust is from fuel ignition when an exhaust valve is open, or WAY too much fuel out in the exhaust and the hot exhaust is lighting it. The only time I had that in a motor was when I THOUGHT I had the timing gears lined up. They were 1 tooth off.Yeah, for some reason the valves are out of control at high rpms. We double-checked the timing gears and re-degreed the cam (it was less than 2 degrees retarded). I think the springs weren't set up correctly or for some reason the lifters aren't staying pumped up at high rpm. A solid cam will take care of that.

[MonzaRacer]

Another thing is why in heck would you run a locked distributor. NO NO NO.
I have had so much trouble from MSD in my lifetime I cant relate all of the problems.
I have ran prupose built HEIs go 8k and never miss a beat.
For that engine I would have initial setting of 12 to 18 (your starter will tell you if its over advanced.
Get your centrifical advance in as fast as it can handle without spark knock.
Too many people skimp on timing for any engine. I try to get my centrifical in before cruise rpm.
My 402 has a smaller cam and it would pull to 7500 with a hydralic cam.
I would also find an on car spring preasure tester and double check the springs as they way have been mis boxed and make sure your seat preasure is good as they may need a reshim.
Good Luck

[dhardison]

The reason for the locked distributor is this motor will be in my Father's Nova bracket car, not a street car. I would never run a locked distributor on a street car. The seat pressures tested good with the hydraulic, so I don't know what's going on there.

We've pulled the hydraulic cam and associated lifters/springs in favor of a solid cam. I have dyno time scheduled for this Thursday afternoon/evening so hopefully there will be a better result this time around.

[dhardison]

We got the new cam/lifters installed (Crane mechanical flat tappet - Duration 292/ 300, Lift .618/ .638) and broke in the cam with the lighter hydraulic springs (engine still on the dyno from last week). No problems, so we swapped in the new springs. We made 4 pulls last night and our best was 544hp and 496lbft @ 6500. To say the least I was pleased. On the first couple pulls we were using the dyno facilities 2.5" primary, 5" collector equal length headers, but when we switched to my 2" primary, 3" collector NON-equal length Hooker headers we gained 10-15hp across the board and the throttle response was MUCH better. I guess the 454 likes a little back pressure.

We didn't have time to do all the changes/tuning I wanted so I'm going back Saturday morning to try different carbs, carb spacers, timing changes, etc. We should be able to tune it to 550hp/500lbft pretty easily, which in Dad's 3100lb '71 Nova should easily put us in the mid-high 6s (1/8 mile).

[EFI69Cam]

I guess the 454 likes a little back pressure.

It does not like back pressure, the 2" primaries are better matched to the cam.

[4MuscleMachines]

Congratulations, that is a substantial improvement over the old numbers.

[Skip Fix]

The smaller headers scavenge out the tube and chamber better than the larger ones, same way a smaller head port can have better velocity. My RAIV 400 Pontiac picked up .2 seconds and 2 mph going to a 1.75 from a 2".Before that it had bad reversion issues from poor scavenging.

[dhardison]

Went for the final dyno session this morning. Tweaked timing, played with jets and added a 1" carb spacer. Final peak numbers were 560hp and 508lbft of torque. These numbers were more than I expected, so I'm pleased. Thanks to everyone for all the input.

[Mike Holleman]

You should be happy with those numbers. Should make that Nova hum.
Mike