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?

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.

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.

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….

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

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

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

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

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.

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.

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

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

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

Real simple stock ported heads, vs aftermarket and small headers... Toss some MAST 305 Black Labels on the LS7 against it or Brodix BR7 273STS... And up the header to 2" Also test hi ram vs trinity with each THAT would he awesome... But stock to aftermarket come on, it's shape, CSA, entry all of it hell back cut on valves...I assume it was a Johnson short travel on both both same seat and open pressures? I assume something was a choke factor they ended up same peaks.... I'd really love to see this test maybe u don't know call my crazy but trick flow 260 LS7 head apples apples same cc? Everyone remember that's not remotely a stock LS3 head at all modified port design, chamber and valve angles to be more like an LS7... I do appreciate the content since I run that cam and cubes...( BR7/ram) I was thinking of going to a dual 4500 efi tb top just to eliminate restrictions with ported runners... I'll say looking at fueling I'd guess mine makes peak power at 7300ish and flattens out it like a 7500 shift for recovery...SO that is spot on... Thanks pretty damn close testing for me if you tossed on a Hi Ram haha

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

Ls7 myths! Ported LS3 kicks ass!

Factory Ls7 ported heads vs Aftermarket Ls3 heads with Ls7 valve angle.... Lmao. Test would have been better with TFS ls3 vs TFS ls7 heads

Properly matched combinations...

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

I am hoping that eventually Brian will build my dream motor for testing. A Re-Sleeved LT1 @ 4.185" x 4.125" 454cu to see just how much N/A Power a set of LT4 Direct Injectors can support.

Awesome 👏 👏👏👏

Love the no lid

Keep testing

I’d be curious to see the Mast black label Ls3 heads used in this kind of test. Mast uses the LS7 rocker for their ls3 port heads. So I’d wonder if in that particular case would the mast black label fellas make more power everywhere because they offer the same cam specs with more air speed and similar volume? Or if it would just end up the same since the head/cam isn’t the limiting factor.

Because 1 7/8 headers , too small 2'' or 2 1/8'' will change the done

You should do the plenum thing on a live feed

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.

I think that this test proves that back in the day when guys with a doggish toilet bowl headed 350 wanted to wake it up a bit, would simply grab a pair of the smaller chambered 305 HO/Iroc (L69 ?) Heads and bolt them on, even though the valve sizes were smaller and be more than happy with their results. The upgrade was mainly Compression ratio, but the additional port velocity even with the small valves didn't seem to hurt.

Common plenum is always a restriction . Is there a cnc ported trinity center body?

So you need an IR intake, that uses motorcycle like slide throttles in order to have zero restrictions, but still manageable.

Hey rich you can get about 1 inch of cam lift out of a smog cad 472 500 Bv

Comparing stock ls7 heads to aftermarket heads. Yes I'm aware the heads were ported but aftermarket isn't held to factory standards

Curious if y’all got any BSFC numbers?

I just wanted to be one of the first to comment

Stock ported heads vs Aftermarket heads. The LS7 heads would have done better if the LS3 heads was ported stock.

What are the valve angles on each? Does valve angle matter necessarily, or just the fact it allows a better port design? Ive always thought angle on a LS vs a Gen 1 SBC being the main driving point why an LS was so much more efficient and powerful.

Wow!!!

When are you going to build the L78 again

Hey Richard. What about a comparison to OEM LS3 heads, with the 15* valve angles. Wouldn't there be a difference in flow in comparison to the 12* LS7?

The intake hurt a ton on the Ls7 heads. I'd say 20hp and the same tq going to a 4.5 CID

I have a mental image of that no-plenum pull. "Alright, here, hold the engine at 4000" *Walks into dyno cell with ear-muffs on* *Pulls plenum off with grunty facial expression* * Looks at you through glass and points up* *does dyno pull* *Looks at you and gives cut-motion signal* *plops plenum back on engine* *walks back into dyno room* "Alright, what did it do?"

Need a set of old school mechanical injection manifolds made to test, bet its the fastest

Dodge 4.7 testing?

if it had been a larger ci engine would the ls7 heads made more power . Or more camshaft and run to a higher RPM or both

Sounds like you need to test a modded trinity with a 112mm tb on the ls7 next! (Ironmask Airflow does that mod)

Hey richard what would be also cool would be a nitrometh mix vs race gas is it worth it ?

Ahoy boys! Hit the Like Button!

Ngl im shocked the ls7 head’s didn’t do as well. On paper they should be much better so someone please try to explain. Also would these results change with forced induction? Bigger could be better with boost..

Did the 1 7/8th headers choke it a little? Maybe 2 inch would have made a difference?

Love it 😂😂😂

Do you think you would even notice a 26 hp increase with a 722hp engine with the individual runner manifold when driving a car on the street or even at the race track? I don’t know if I would notice an 8 hp increase on a 240 hp stock 5.3.

Which LS3 heads came with 12 degree heads?

Given all the advantages present with the LS7 head and how it was marginally outperformed by the LS3, I would assume that those particular LS3 heads are "perfect" for that combination. IMO There doesn't seem to be any airflow demand for the .040 greater lift because annecdotally I can tell you 1.7-1.8 rockers make a difference when there is demand. Theres also no separation between the curves at the VERY top of the curves to suggest a higher RPM or larger cube engine would benefit from the lightweight valvetrain and greater lift. All of this is assuming the intake manifold is IDENTICAL though.

Or an ls in a foxbody

Want to please the ford and chevy guys. Put a ford 460 in a squarebody chevy. Lol

Wow very surprised by the results... i thuaght ls7 heads were a decent size leap in performance.. i guess not when both worked over

Itb intake!!

Wow that's crazy everything was bigger like lift and valve and it should it of made more power for the ls7 head so crazy oh well

OK... now we need LS3 with titanium exhaust valves and 1.8 rockers...

LS7 exhaust valve slightly shrouded compared to the LS3

Brian tooley is getting a rep for lying about his cam specs and for not knowing his cam lsa principles Bloodviking

Wrong cam shaft lol.. not enough cam for hp potential

Well. That wasn't exactly an apples to apples test.

LS3 FTW.. ditch the notorious valve dropping ls7 heads.. something wrong with its geometry even in the aftermarket heads they suffer from abnormal valve guide wear heard it from an engine builder.. he installs 6 bolts LS3 heads on big bucks 427 builds with confidence

Headers too small

Valve shrouding hurt the LS7