85 C4 Dyno results
06-22-2017, 07:15 PM
#1
85 C4 Dyno results
I am so excited! Just got back from the dyno. I spent 2016 rebuilding my 1985 Z51 4+3, and I have been tuning it for 2017. Thanks everyone here, you have been great offering me advice. I never could have done a project like this without all the online help I have been offered.
Here is a list of my engine mods:
Hedman longtube headers
Pypes 2.5” stainless dual exhaust
Valve job with slightly stronger crane springs
Melling roller timing chain
I went with the thinnest OEM spec head gasket I could find to keep compression up.
Crane gold race 1.6 roller rockers
Pocket ported the iron heads, along with light porting and blending of the heads, upper/lower intake and runners.
De-screened the MAF
Coolant bypass on the throttle
Removed all EGR and AIR parts, and reprogrammed the ECU to keep EGR modes from being active
TPIS air pump replacement pulley.
Moates APU1 for chip tuning
Bosch heated O2 sensor
Bosch wideband O2 sensor with AEM AFR gauge
It looks like I’m getting 300+ hp at the crank.
The guy was stopping at 5250 RPM as the power started falling off. From the graph, the engine was still breathing well, and not choking like a stock L98 TPI would.
I put in an overlay for a stock 1985 C4 Hp/Torque at the crank for comparison.
Here is a list of my engine mods:
Hedman longtube headers
Pypes 2.5” stainless dual exhaust
Valve job with slightly stronger crane springs
Melling roller timing chain
I went with the thinnest OEM spec head gasket I could find to keep compression up.
Crane gold race 1.6 roller rockers
Pocket ported the iron heads, along with light porting and blending of the heads, upper/lower intake and runners.
De-screened the MAF
Coolant bypass on the throttle
Removed all EGR and AIR parts, and reprogrammed the ECU to keep EGR modes from being active
TPIS air pump replacement pulley.
Moates APU1 for chip tuning
Bosch heated O2 sensor
Bosch wideband O2 sensor with AEM AFR gauge
It looks like I’m getting 300+ hp at the crank.
The guy was stopping at 5250 RPM as the power started falling off. From the graph, the engine was still breathing well, and not choking like a stock L98 TPI would.
I put in an overlay for a stock 1985 C4 Hp/Torque at the crank for comparison.
The following 4 users liked this post by BlueTwoToneCorvette:
06-23-2017, 12:34 AM
#4
Love that Torque Curve...that's what really sets you back in the seat !!
06-23-2017, 01:38 PM
#7
The dyno is a AWD Dyno Dynamics Dynamometer.
The cam is stock.
It’s a dual exhaust, with x-pipe, no cats. The mufflers are just a perforated S-curve.
Does the standard ~15% MT drivetrain loss apply to the torque value? That would make the torque scale up to around 425, which is impressive.
I just ordered a cheap open top plastic filter cover. I didn’t want to cut my stock one. Taking the cover off made a measurable difference in HP and torque.
I was thinking that the iron heads were limiting the flow enough that it wouldn’t have made a difference. Perhaps the TPI can suck air in faster than it can get past the cover in the midrange, and the flow through the heads isn’t maxed out yet. Up top it doesn’t seem to make as much of a difference as the TPI and heads are probably limiting flow.
The cam is stock.
It’s a dual exhaust, with x-pipe, no cats. The mufflers are just a perforated S-curve.
Does the standard ~15% MT drivetrain loss apply to the torque value? That would make the torque scale up to around 425, which is impressive.
I just ordered a cheap open top plastic filter cover. I didn’t want to cut my stock one. Taking the cover off made a measurable difference in HP and torque.
I was thinking that the iron heads were limiting the flow enough that it wouldn’t have made a difference. Perhaps the TPI can suck air in faster than it can get past the cover in the midrange, and the flow through the heads isn’t maxed out yet. Up top it doesn’t seem to make as much of a difference as the TPI and heads are probably limiting flow.
06-23-2017, 01:49 PM
#8
Safety Car
The 15% number is valid for both torque and HP, remember that is just a guideline but it helps you determine crankshaft power. The reduction in restriction did help, nice job.
06-23-2017, 06:52 PM
#9
Race Director
Good job. Next task it to take it to the track and get some real numbers!
06-24-2017, 08:48 AM
#11
Race Director
Surprising you made that much power without a cam change.
06-24-2017, 11:23 AM
#12
I spent a lot of time on the heads and intake with a die grinder. The stock iron heads were very bad right where it makes the biggest difference, around the valve areas.
The head exhausts had rough iron casting nodules around the valve guide boss on the long side. The sides had a casting ridge, and the short side had a lip, and carbon buildup. It was very rough looking compared to the intake side.
The head intake valve bowls had significant shallow depressions that would kick the mixture away from the edge disrupting flow on the long side right before it hit the valves. You want it to be perfectly uniform like the inside of a curved trumpet. Also the valve guide boss was huge and had a sharp, wide edge that sticks out into the flow. The short side had a small lip, and was more of an angle than a radius. There were numerous wide, flat casting bumps/symbols 1 to 2 mm in height at various places. Minor casting ridges in the iron along the intake length, and the surface had a sandy finish from the iron casting that was too rough for best flow.
Porting iron is easy because its hard, and it grinds slowly, which makes it less likely you will make a mistake. Although, you are working mm from the valve seats and if you touch those with the cutting head you just ruined your head. I was very very careful.
I think the head work and the 1.6 rockers worked well together to maximize the stock cam.
The head exhausts had rough iron casting nodules around the valve guide boss on the long side. The sides had a casting ridge, and the short side had a lip, and carbon buildup. It was very rough looking compared to the intake side.
The head intake valve bowls had significant shallow depressions that would kick the mixture away from the edge disrupting flow on the long side right before it hit the valves. You want it to be perfectly uniform like the inside of a curved trumpet. Also the valve guide boss was huge and had a sharp, wide edge that sticks out into the flow. The short side had a small lip, and was more of an angle than a radius. There were numerous wide, flat casting bumps/symbols 1 to 2 mm in height at various places. Minor casting ridges in the iron along the intake length, and the surface had a sandy finish from the iron casting that was too rough for best flow.
Porting iron is easy because its hard, and it grinds slowly, which makes it less likely you will make a mistake. Although, you are working mm from the valve seats and if you touch those with the cutting head you just ruined your head. I was very very careful.
I think the head work and the 1.6 rockers worked well together to maximize the stock cam.
Last edited by BlueTwoToneCorvette; 06-24-2017 at 11:25 AM.