Intake manifolds make no diffrence to losses in torque or HP below a set CFM ! in fact the less the better in fact until a set CFM in fact. it's only when the intake become restricted that such becomes an issue in fact !

Going to big an intake is total rubbish in fact ! same with too big a CFM Carby is just BS !

How come my HX intake on my 5.0L could feed it fine at 5300RPM at 213KM/H with a Waggot 20/60 Cam and stage 3 heads.

Not to mention before that with a stock Cam, that i could blow away my mate who had the same car same diff ratio same M21 4sp and a TQ20 Cam and same carby but he had a Perfomer intake on his. 3rd gear runs side by side say and just walk past him easy. Oh mine was jetted rich tho.

I was set on going to put the Performer intake on mine but i got it welded up at the water jacket face's as they were corroded badly, all good so i left the stock intake on. the dude that welded it said it may warp and be buggered ? so the Perfomer was number one on the list, but she worked out just fine and sat on it for another 15 years.

A mate put on a Torquer intake that was total crap for a street car. he has a 30/70 Cam in it and should of gone for the Perfomer intake, but i diots convinced him the bigger the better load of BS !

Another thing i wonder about the EGR Heads and the exhauset going under the intake may be too much heat and that dropes power ? I think water heated is better, but had no problems with my HX intake not having intake heating at all as it had Pre EGR Heads. ran rich and did not need a choke in QLD.

I have to question that issue of Street Machine, not in the flow figures but in reality on the road reality ? I am not against the Perfomer intake at all. and i would be the firest to think also that a HX intake is total crap, i would of believed such for sure ! but i know the reality for a fact.

I remember test driving driving a Ex yellow QLD HWY Patrol car VK 5.0L auto dual exhause what a slug ! and a VB SL/E 5.0L with dual exhaust what a slug ! a HZ 4 sp GTS that a mate had dual exhause what a slug ! A mate with a WB Caprice what a slug but it handeled well.
That stock original HG GTS 308 auto with just dual exhaust i test drove would just totaly kill all of them cars, totaly eat them ! I loved driving that car ! i had to have it ! but a dude bought it when i was test driving it !

Well the HT-G GTS 350 4sp -VS- HT-G GTS 350 auto is compression. but sadly it's not rated in DIN ! to get a true picture.

The HQ GTS 350 is just low compression, but the 1973-4 is the ribs in the intake that are the problem loss of perfomance ? it would be good to see such in DIN.

The HJ and later LH 5.0L engine has 9.7:1 and no ribs in the intake ? and the HX 5.0L has 9.4:1 and ribs in the intake. so with dual exhaust on all it would be good to see such in DIN !

Then we have the VB 5.0L Dual exhaust with DIN figures and the Single exhaust DIN figures i suspect they are the same as the HX-Z would be ?

Then we have the Blue 5.0L and it's the same engine as red really bar spark plugs are set and Electronic ignition but same power say bar a bit more RPM and look at all of that increase in Torque just with ignition ?

I would say that flow is in regards not only full throttle, but as RPM's become higher ! Why i think that is so, is because if a intake flows X at Y lets say 3000 rpm and 4000 and 5000 ? the true raiting has to be restricted at the higher end of the rpm limit that creats the issue of lack of power because it's restricted at that flow and not to mention if the flow is too much then you will loose low down torque for sure.
So i see the issue is with restriction coming in at a set rpm limit badly effecting perfomance.

If a Intake can flow X then it can never make anymore Power, as that's the set limit.

That's why when mods to cyl heads one may go bigger Valves or then start with porting work to increase the flow, but then again fools believe that the better flowing numbers are the better ? but you can go to big and loose perfomance as well.
Like you do not want to put a L34 size exhause valve in a stock like red 253 because they loose perfomance. the stock Red v8 in and ex valves heads are near like the size of an XU-1 say.
So the 253 has good size valves to breath well.

But how do i explain that my HX Intake manifold on a stock reco 308 could blow away anything of the same ilk HQ and even a HJ with TQ20 Cam in a 3rd gear run ? you can not play games with that sort of thing as their is nothing to it !
Then when i put stage 3 heads on it and a 20/60 Waggot Cam, boy did it crack on then ! The Torque !

But then again morons claimed that if i went to a single 2 1/2 exhaust i would pick up a lot of power over my twin 2 1/4 free flowing and loud. They were totaly convinced i would get heaps more power ! like hell it did, it killed the power like huge loss of power. i believe that red 308's a touchy to exhaust, they have to flow as free as can be, so as to get the best perfomance out of them.

Here is that article. This clearly shows you why the HX intake is a dog and restricts flow hence performance. I wish I could find the magazine with the colour images, but to make it even more obvious the test is with stock red pollution heads (see the U shaped EGR port) and you can see the logs on the head faces of the ADR27A intake, so its HX.

Edited by user Monday, 23 September 2024 4:55:43 PM(UTC)  | Reason: Spelling

Yes, UP to 260hp in theory, but that is 260HP gross as well, maybe 175hp DIN maximum depending upon the exhaust, air cleaner, air temperature, fule quality, fan belt tension etc etc - all the crappy variables that you don't know when using DIN figures. It is badly restricting the heads, and everyone knows that the stock 308 intake valves are a performance inhibitor themselves - a decent return can be had by putting in larger intakes (aka L34 and V5H engines). The stock HT-HQ 308 intake (all the same engine bar the sump and a bit of plumbing) could make UP to 313hp. That is a huge performance inhibitor from the ADR27A intake to lose a potential 53hp. In reality it removed 34hp peak - remember there is nothing in there to disguise itself in those figures, it is a proper GM20 test with lab fuel and controlled ambient air pressure and temperature using the dyno exhaust. I bet that intake probably did as much to strangle performance as putting on a HT-HG 2BBL intake and carb would. I'm not saying the HX engine wasn't tractable, at lower rpm it probably performed well as it would have had lower air flow, but when you start looking at peak figures (be it SAE gross, net or even DIN) it will suffocate the engine. At WOT that intake would be like restricting the Quadrajet's secondaries to only open to 70%.

I think it's Net figures in fact !
VB 5.0L dual exh is 169HP DIN
HQ 5.0L dual exh is 196HP NET.

Quadrajet do not open the secondarys all the way unless it's needed ? I think it's the air type of cleaner that affects perfomance of the Secondarys from not opperating as they should ? Nothing to do with what goes on under the carby regards intake manifold would tamper with the opening.

I think it was to do with the HK 327GTS or was it the HT 350GTS That got a better breathing air filter some time after they came out ?

I know some USA cars would not open the secondarys as it should because the air filter was to restricted. I can not remember which one, a Pontiac big block V8 i think and lost 40hp.

It's the stock intake valve that can be a bit to small on the 308 red.
The stage 3 and YT heads are just a cheap way to go about adding power to a 308.
I have seen even stock exhaust valve size red and a L34 intake make real good power figures but pro ported ! not stupid ported mined you !

Look at the Torana L31 and the L34 Power figures ?

Bigger valves and huge port job do not work well, I have seen that done, to much porting of the exhaust can kill perfomance as the red V8 has good ports ? a old 302 Windsor V8 ports are crap and so is the Cleveland V8 on the 302 they are to big a port ? The 351 Cleveland 2V head can be made to perform better than the old 4V heads. look at Bathurst and the figures XY GT-HO and then the XD makes more power and the XE even more at Bathurst with 2V heads !

Edited by user Wednesday, 25 September 2024 9:51:55 AM(UTC)  | Reason: Screwed up quote, fixed and posted text in later reply.

Those figures don't add up. VB 5.0L with dual exhaust is quoted as 125kW@4200rpm DIN which is close enough to 169hp. HQ was never quoted in DIN or Net or with exhaust. It was advertised as 240hp@4800rpm but the real SAE Gross is 226hp. You could sort of work out an estimate for HQ with dual exhaust as a DIN figure by using the earlier HZ (9.7:1) engine which was 216hp SAE Gross and subtracting the later HZ/VB 5.0L (9.4:1) 169hp DIN figure giving you a 50hp difference. Take that 50hp off the HQ's 227hp and you get 177hp DIN with dual exhaust. Not exact but in that range. It's also mean the HJ engine would be close to 200hp DIN with dual exhaust.

One thing of interest, in the original GMH dyno tests for the 308, they did do both SAE Gross (GM20) and SAE net (GM1):

HT 308:
226hp @4800rpm, 310lbft@3400rpm GM20.
160hp@3800rpm, 250lbft@2200rpm GM1.

Note that GM1 isn't just added stuff, it also runs different ambient temp. GM20 is 60F, GM1 is 100F.


HK-HT air cleaner were modded by dealers cutting holes or slots into them. In the day all it took to wake up any HK onwards with a Quadrajet (308, 327 or 350) was to dyno it, adjusting the Quadrajet so it opened the butterflies 100% - most didn't, set the timing correct and turn the air cleaner lid upside down or cut holes in it. Plus of course add dual exhaust if it wasn't there already. A HT-HG GTS350 picked up heaps just by doing that, turned it into a 14.8s quarter mile car.

L34 quoted power figures are a mixture of fact and purpose. GMH didn't build race cars. They didn't have to for GroupC, they just had to homologate the base vehicle (the LH SL/R 6cyl) with 500 units produced. The SLR5000 and the the SLR5000 were framed as variants on the original car and for any variant (or evolution of type) just produce 500 sets of parts (in some cases 250). They didn't need to build the cars, but the way to get rid of the parts was to build cars, and that is what they did with the L34. The car was not designed to be a fast road car,its parts were simply made to homologate enhanced bits that could not be changed/modified under GroupC rules. Which is why it had bigger brakes, flares, modified heads and intake, "roller" rockers, flat top Chevy style slipper pistons, stronger rods, larger fule line, better distributor setup, short tubular headers etc. It kept the stock exhaust, cam, carby and air cleaner, ran 6" rims and D70 tyres. It was never going to be a super powerful engine with that little cam, tiny dual exhaust etc. It didn't need to be. GMH simply claimed the stock power output. All you'd need to do with a stock L34 is fit a 2" twin exhaust, better cam and air cleaner and it'd pick up massive power. In March 1973 Redco ran the engines on their engine dyno. These are engines with alternator etc, and will be regular pump fuel and ambient air, not lab controlled hence why the stock engines shows 190hp and lower rpm than the GM20 test figures. These will be without an air cleaner I believe and open pipes out of the exhaust manifolds.

Stock HQ/LH 308 - 190hp @4100rpm.
Standard L34 5.0L - 260hp @ 4800rpm.
L34 engine with HP pack - 310hp @ 5500rpm. I believe this was the 780cfm vac sec Holley, Wade 140 Cam, solid lifters, roller rockers and better plugs - in terms of engine improvements.

There is nothing to believe or not, it’s fact. Those figures are off GMH’s own engine test printouts. GM20 and GM1 are GM standard controlled engine dyno tests. Both on the same dyno, no single exhaust, both use the same engine dyno exhaust. GM20 (SAE Gross) is optimum power, that is why it’s at lower air temp. No accessories driven, uses dyno water cooling. GM1 is at elevated temp and has water pump driven, no alternator from memory.

That 260hp has to be taken in comparison with the 190hp Redco got with the stock 308, they set them up the same. The opened up intake manifold will help as much to peak power as the big valves and compression. Pissy little cam will have been a big hp thief though it was retarded which help peak power. The modified distributor they used would have helped it a bit too at higher rpm.