Inlet Port geometry - ZR-1 Net Registry Forums

tpepmeie · 01-10-2015

I have a first gen Indy racing league Aurora cylinder head laying around, and took the opportunity to make some intake port molds. It's an interesting comparison between these ports, which made circa 700 bhp with methanol (4.0 liters), and the LT5 ports.

first, look at the port angles. LT5 has significantly worse port to valve angle. The Aurora is very straight and tall. Look at the difference in valve stem length!

Aurora

LT5

Also notice the LT5 has a big dead space on the long side of the turn, or bowl area. This ideally should be filled, either welded or with epoxy, to keep the velocity high through that area. Not sure why we have that bulge.

Here is a good shot of the LT5's port to valve offset. I can only speculate that this was done intentionally to generate swirl motion in the charge. You can see the port makes a turn before the valve.

Another of the LT5, this time with both valves. You can see both ports make the turn toward the center of the chamber.

The Aurora port is totally straight.

tpepmeie · 01-10-2015

As for size... the Aurora ports support more than 120 percent volumetric efficiency, on methanol, at 10,500 rpm. And the intake port diameter is 34.5mm throughout. That's right. Smaller than a stock LT5. Mind you, the straight shot of the ports allow extremely high charge velocity. They flow more than 95 cfm per square inch of valve area--that's more than 360 cfm @ .500 lift. 34.5mm ports.

Notice how much of the valve seat area you can see when looking down into the port. Probably 80% of the valve area is visible from the entrance of the port.

The combustion chamber. 22cc's for a 93mm bore. Very typical for the 4-valve modern racing design. Notice the cones around the valve seats to help the air recover pressure as it enter the cylinder. And the significant squish area between the two intake and two exhaust valves.

LGAFF · 01-10-2015

What is the intake to exhaust ratio? You are correct, the dogleg is for port swirl.

FU · 01-11-2015

There is some interesting information between this post and Frankenplenum . There is some HP & TQ on the table here

A26B · 01-11-2015

here's a way to straighten the runners to the heads
https://www.youtube.com/watch?v=b5yKouUhiSQ

LGAFF · 01-11-2015

[QUOTE=A26B;218337]here's a way to straighten the runners to the heads
https://www.youtube.com/watch?v=b5yKouUhiS

I did a short writeup on this build in the last HOB....some good pics of intake....car is now undergoing more mods.

Pete · 01-11-2015

Todd,there are reasons for the port size in the LT5 head besides CFM #'s.
The LT5 head is 35.5 down the port.

I will explain/talk to you about it at BG.

Everybody throws CFM #'s out to make it look better then the other guys they are like Dyno #'s this is how they get customers in the door.

Pete

tpepmeie · 01-25-2015

Just a couple more fun facts about these heads.

The Aurora inlet ports are inclined from vertical by 45 degrees, and the valve is inclined by 10 degrees. Therefore 35 degrees is the net port to valve angle. Pretty tall, straight.

The LT5, on the other hand, is approximately 58 degrees from vertical. The inlet valve is also 10 degrees. ~48 degrees port to valve angle.

The air has to turn through ~13 degrees more as it approaches the cylinder. For this reason, we have to do things like flatten out the floor of the short turn to get the air to turn better. Tradeoff is that the area gets bigger than we'd like.

Contrast that with the Aurora port which is absolutely constant area throughout. This is a totally round port all the way. It bulges just slightly at the valve guide area to keep the area constant.

01-10-2015	#1
tpepmeie Join Date: Aug 2005 Location: Fishers, IN Posts: 814	Inlet Port geometry I have a first gen Indy racing league Aurora cylinder head laying around, and took the opportunity to make some intake port molds. It's an interesting comparison between these ports, which made circa 700 bhp with methanol (4.0 liters), and the LT5 ports. first, look at the port angles. LT5 has significantly worse port to valve angle. The Aurora is very straight and tall. Look at the difference in valve stem length! Aurora LT5 Also notice the LT5 has a big dead space on the long side of the turn, or bowl area. This ideally should be filled, either welded or with epoxy, to keep the velocity high through that area. Not sure why we have that bulge. Here is a good shot of the LT5's port to valve offset. I can only speculate that this was done intentionally to generate swirl motion in the charge. You can see the port makes a turn before the valve. Another of the LT5, this time with both valves. You can see both ports make the turn toward the center of the chamber. The Aurora port is totally straight. Last edited by tpepmeie; 01-10-2015 at 08:55 PM.

01-10-2015	#2
tpepmeie Join Date: Aug 2005 Location: Fishers, IN Posts: 814	Re: Inlet Port geometry As for size... the Aurora ports support more than 120 percent volumetric efficiency, on methanol, at 10,500 rpm. And the intake port diameter is 34.5mm throughout. That's right. Smaller than a stock LT5. Mind you, the straight shot of the ports allow extremely high charge velocity. They flow more than 95 cfm per square inch of valve area--that's more than 360 cfm @ .500 lift. 34.5mm ports. Notice how much of the valve seat area you can see when looking down into the port. Probably 80% of the valve area is visible from the entrance of the port. The combustion chamber. 22cc's for a 93mm bore. Very typical for the 4-valve modern racing design. Notice the cones around the valve seats to help the air recover pressure as it enter the cylinder. And the significant squish area between the two intake and two exhaust valves.

01-10-2015	#3
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,193	Re: Inlet Port geometry What is the intake to exhaust ratio? You are correct, the dogleg is for port swirl. __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359

01-11-2015	#4
FU Join Date: Mar 2004 Location: Found Member Posts: 4,346	Re: Inlet Port geometry There is some interesting information between this post and Frankenplenum . There is some HP & TQ on the table here __________________ Frank Urbo. NCM Lifetime member # 982 Registry Founding # 237

01-11-2015	#5
A26B Join Date: Dec 2003 Location: Arcadia,OK Posts: 3,393	Re: Inlet Port geometry here's a way to straighten the runners to the heads https://www.youtube.com/watch?v=b5yKouUhiSQ __________________ Jerry Downey JERRYS LT5 GASKETS & PARTS http://www.jerrysgaskets.com 1994 *ZR-1*, Black/Black, Lingenfelter Aerobody, 416cu in, 3.91 gears, coil-over susp, Brembo brakes, etc. 2016 Black-Red, 3LT-Z51 Auto 8-speed.

01-11-2015	#6
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,193	Re: Inlet Port geometry [QUOTE=A26B;218337]here's a way to straighten the runners to the heads https://www.youtube.com/watch?v=b5yKouUhiS I did a short writeup on this build in the last HOB....some good pics of intake....car is now undergoing more mods. __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359

01-11-2015	#7
Pete Join Date: Dec 2003 Location: Chicagoland,IL Posts: 2,679	Re: Inlet Port geometry Todd,there are reasons for the port size in the LT5 head besides CFM #'s. The LT5 head is 35.5 down the port. I will explain/talk to you about it at BG. Everybody throws CFM #'s out to make it look better then the other guys they are like Dyno #'s this is how they get customers in the door. Pete __________________ '91 #1635 PoloGreen 350 LT5 11.09 @ 129.27 11.04 @ 128.86 474RWHP 400RWTQ http://www.youtube.com/watch?v=SFNFOhGGlR4 http://www.youtube.com/watch?v=ZlRIOMwaDYY https://sites.google.com/site/peteszr1garage Last edited by Pete; 01-11-2015 at 04:25 PM.

01-25-2015	#8
tpepmeie Join Date: Aug 2005 Location: Fishers, IN Posts: 814	Re: Inlet Port geometry Just a couple more fun facts about these heads. The Aurora inlet ports are inclined from vertical by 45 degrees, and the valve is inclined by 10 degrees. Therefore 35 degrees is the net port to valve angle. Pretty tall, straight. The LT5, on the other hand, is approximately 58 degrees from vertical. The inlet valve is also 10 degrees. ~48 degrees port to valve angle. The air has to turn through ~13 degrees more as it approaches the cylinder. For this reason, we have to do things like flatten out the floor of the short turn to get the air to turn better. Tradeoff is that the area gets bigger than we'd like. Contrast that with the Aurora port which is absolutely constant area throughout. This is a totally round port all the way. It bulges just slightly at the valve guide area to keep the area constant.