LS3 VS LS7 HEAD TEST-WHICH PORTED HEADS MAKE THE MOST POWER? 720+ HP 427 TEST MOTOR (FULL RESULTS)

I appreciate that Richard dedicates so much time to continuously proving an internal combustion engine is just an air pump. It doesn't matter if you cylinder head flows a million CFM if your rotating assembly doesn't support that flow in it's operating RPM. Who knew?

On one of our desert race LS7 engines we tested a set of WCCH CNC LS3 heads with Fast LSXR W/102 throttle body VS WCCH CNC LS7 heads with Fast LSXR w/102 throttle body. The LS7 had 13.5 CR. All I’ll say about the cam is it was 257 on intake. The test fuel was VP late model. The LS3 heads were down on power everywhere on their respective curves. Peaks were over 20 down with LS3 heads. But every combination has different outcomes. I wasn’t that surprised that your LS3 heads did that well. As a matter of fact I think I’ll use one our old LS7 blocks and build it with a set TFS 255 heads we took off another engine.

The intake manifold is the limiting factor, the cfm demand of that 427 at 7100rpm is 370cfm, the reason the LS3 heads picked up torque was because of the higher airspeed past the valve. You can see with the test without the plenum that it can now peak further out at 7500rpm which is a cfm demand of 390cfm. Lastly it’s not the throttle body itself that is the restriction, it’s because the runners primarily have airflow entering from the side closest to the throttle body, as air is being drawn in, it is being replaced from only one direction, from the throttle body end so airspeed at the runner bellmouth is uneven around the bellmouth, effectively reducing the cross sectional area efficiency of the entry. When you removed the plenum the runner entry can now use the entire cross sectional area of the entry efficiently, the airspeeds even out instead of being much higher on one side.

Ive been waiting for this for a long time. Love it

Love your videos, I wana see you do some n/a LS videos showing how you can make more/less power from really “small” things. Like oil, piston rings, or engine machining.

I’m guessing the smaller port on the ls3 helped velocity and thats why it made more midrange. And maybe the tb was a little restrictive on the ls7 at the top once demand was there….

I always wondered what the hp difference would be between these heads. Thanks Richard

Awesome 👏 👏👏👏

Good to see this test, not giving up any with my aftermarket LS3 Texas Speed Heads.

Wow.. Pulling the plenum from a running engine in the dyno room has got to be the most bold thing ever attempted in a dyno cell.

One old trick we used to do on the old sbc engines was to use 305 heads on a 350 bored block. But you need to majorly port them otherwise the compression gain of about 2 points will only equal out as the 305 head passages are more restricted then the 350 heads. Bloodviking

Excellent test. Isn't there an aftermarket ls3 head with ls7 port height?

,,, like the WOT, ,,, wide open throttle, ,,, ! ,,, you can catch it off a variable rev limiter also, but kind of hard on parts .

Properly matched combinations...

Fantastic. Thank you so much @richardholdener1727 I think in terms of ITBs all the time from working on bikes. Never though of open IRs. Now my head is spinning on this for the LSR car.

Keep testing

Really neat seeing the BTR intake ran as an IR one!

Great comparison if I had to have bet before watching I’d picked the LS7

Oof! Lighting off a 427 with no throttles whatsoever is a ballsy move!

Love the no lid