Best SBC Aluminum Intake for Street/Strip Qjet 355?

[AHotRod]

Cliff and all,
    I currently have a GM aluminum intake that I smoothed, blended, radiused and port matched to the heads,with my self built Q-Jet with Cliffs parts and book. It's a 9-1 compression, 355 , old World Sportsman II heads and a small hydraulic roller 210/215 @ .050 - .462 Int lift/.470 Exh lift on 110* C/L.
    The engine runs fine, but is a bit of a pooch for a Hot Rod, runs out of steam by 4000 rpm, so I'm considering a camshaft change and asking if another intake would be in order, and if so, which one would you recommend?
     The RPM range will be idle to 5500-ish, the rear gears are 3.55 and the Coupe weighs in at 2100 lbs.

Your thoughts?
Glenn


 

[Mudsport96]

I don't believe the heads are the reason you lose steam at 4000 rpms. That camshaft is fairly tiny. Is your block a factory roller block or do you run retrofit rollers? Also, what is the max lift your heads can handle? The GM LT4 hot cam is a good choice but, if you're heads can't handle over .500 lift you have to stay with the 1.5 ratio rockers.
Do you have a manual trans or auto? Going with too much cam will be annoying with an auto and stock converter.
Heck I bet you could find a decent stock lt1 or lt4 cam on eBay, in a coupe weighing 2100 lbs it would hustle.

[Cliff Ruggles]

In that RPM range you'll find it difficult to outran a factory intake.  They are excellent parts and the iron ones help with thermal efficiency allowing for a leaner mixture to be used.

I know EVERYONE tosses them aside and runs right out and buys an Edelbrock Performer or RPM intake, but they don't do any better if as good as a stock one when teamed up with engines that are used from idle to 5500rpm's or so.

If you ever get the chance attend an NHRA sanctioned event and watch some of the SA cars run with those intakes.

The factory really did know what they were doing with these things.  I took a Pontiac iron intake and modified it a bit under the carb to look like a Performer or RPM.  Then dyno'd it on a 434cid engine making close to 500hp.

I also took a Pontiac HO intake (reproduction) and did the same thing.

The HO intake made 487hp

The RPM made 491hp

The factory iron intake made 497hp!

When I think back to how many intakes are sold each year for much smaller engines making much less power it still amazes me folks don't give the factory parts a chance and spend their money in other areas.

Anyhow, a very good cam for sure is the GM LT4 roller.  It has a decent amount of seat timing and wide LSA.  Pretty easy to make 400hp or so with it using the Sportsman heads.  I like to see a bit more compression even with that cam, we build our 355's here with the Sportsman heads (64cc) and shoot for .025-.035" squish distance and mid 10's for compression.  They will easily manage pump fuel as well.  We also like the CS-179R camshaft if not going to a roller cam.  It's basically a modern version of the 327/350hp cam, and will make great power in those engines with excellent street manners......Cliff

[AHotRod]

I've had 2 NHRA Stock Eliminator cars, a L/SA '70 Buick Skylark GS  350 automatic and a I/SA '74 Corvette 350 and yes, with a stock-legal intake a guy could squeeze 375 HP out of it with those mountain motor 'stocker-camshafts'. A acid ported intake was worth 10-20 HP depending on who did it and how well you could find a way to get it all.

I'm not afraid to get after my intake and open it up some more.

Question:  On the fuel delivery side, is it going to be necessary to run 1/2" fuel line (with a return) and an electric fuel pump to feed this street engine?

I've been driving it for many years on 3/8" fuel line and a factory stock Carter mechanical fuel pump.

[Cliff Ruggles]

For most "street" engines under about 500hp very little need for a "race" type fuel system unless you will find perfect traction and run 1.6 or quicker 60' times.  At least that's what I've seen here with this sort of thing......Cliff

[AHotRod]

Have you done any testing with carb spacers on a factory intake Cliff ?

[77cruiser]

Is the GM intake similar to an Edelbrock performer or RPM?

[Cliff Ruggles]

I've done extensive testing with spacers on various intakes.

ALL of the single plane intakes I've tested require one to get the most out of them, especially if you are using a spread bore carb on them.

The huge secondary throttle plates hang pretty far into the plenum area and can cause MAJOR distribution issues and considerable power loss.

One dual plane intakes I have tested a variety of 1" spacers in various materials, aluminum, wood, etc.

The only spacers that worked better than no spacer at all was a semi-open spacer, or basically one that divided the front barrels and was partially open in the back. 

Fully open spacers were HORRIBLE on every dual plane intake I tested one on and 4 hole spacers weren't much better.

A fully divided spacer worked pretty well but the semi-open is the only one that ran quicker in MPH at the track vs just one 1/4" thick stock Q-jet open gasket.  It still ran a little slower in ET as it gave up some 60' time but ran more MPH showing for sure it made more top end power.

I'd add here that I tested spacers on a 455 CID engine making around 514hp and 587tq, and didn't really see any benefits anyplace using one.  Not if you consider the problems they bring in associated with having to "cobble" things up some with the carb sitting that high.

I also found that having to use a shorter air filter which moved the air cleaner lid closer to the carb KILLED off a bunch of power, and flawed the testing so I had to make a customer filter for the opening of my Shaker assembly (1974 GTO) just to get good test results with the carb sitting up that much higher.

Anyhow, on one test outing I swapped 4 spacers back to back and made 2 runs with each one.  When the smoke cleared and dust settled the car ran the quickest ET with no spacer at all and just one 1/4" thick gasket.  The fully divided spacer was close but still a few hundreths slower in ET.  The semi-open spacer was just a tad slower in ET and just over 1.5 mph faster.

From what I saw on my big CID engine using one on a dual plane intake isn't worth the effort, and I'll bet the results wouldn't have been as close on a much smaller engine and slower car.

So bottom line, really not worth the effort on a dual plane intake at least to 500hp or so, and for sure you need to use one on a single plane intake.  On the dyno and at the track my engine lost a BUTT LOAD of power not using a fully open/well blended 1" spacer on both single plane intakes I tested.......Cliff

[AHotRod]

Is the GM intake similar to an Edelbrock performer or RPM?

Jim,
  My factory intake is similar to a Performer.
Glenn

[AHotRod]

Cliff,
  Most excellent information and results regarding the spacer testing.

I wonder what the real life comparison of intake flow on your Factory iron intake is to a Chevy SB Factory intake.  I'm certain you know what I'm referring to.

I'll share this with you.  On our SBC "Stocker" engines, as you know we are required to use stock intakes and carbs.... as well as almost everything.
We are allowed to use 2 carburetor gaskets.

On numerous engine combinations from 305 - 350 CID, extensive testing was done on the Dynos as well at the strip. Four hole gaskets and open gaskets were tested in all thicknesses and all combinations.
To fast forward to the best results .... installing a FelPro 1908 ( 1/4" thick open gasket) on the intake manifold, then adding a FelPro 1905 (1/4" thick 4 hole gasket) on top of the other, then the Qjet. This combination yielded a increase in torque and horsepower of 6-10 HP depending on the specific engine, and quicker E.T.s.

In addition to this, every air cleaner base under the sun was tested, and nothing came close to the GM factory bases, all the aftermarket stuff hurt airflow, fuel curves and HP. 

We also tested the engines and cars with and without air cleaners. Some ran best with nothing but a base on the carb, some ran best with a K&N 4" filter installed. My belief is that different cars produced different under hood environments which produced different results.



Question: Have you ever experimented with a 2" - 2-1/4" or 2-1/2" header collector? 


Glenn

[AHotRod]

I don't believe the heads are the reason you lose steam at 4000 rpms. That camshaft is fairly tiny. Is your block a factory roller block or do you run retrofit rollers? Also, what is the max lift your heads can handle? The GM LT4 hot cam is a good choice but, if you're heads can't handle over .500 lift you have to stay with the 1.5 ratio rockers.
Do you have a manual trans or auto? Going with too much cam will be annoying with an auto and stock converter.
Heck I bet you could find a decent stock lt1 or lt4 cam on eBay, in a coupe weighing 2100 lbs it would hustle.

I have a retro-fit hyd roller (old block design), TCI turbo 400 ...  my goal is to get this puppy to hunt ... I'd like to be around 400+ HP with my factory aluminum intake and Qjet.
I agree on camshaft selection, to big is a bear to deal with and one has to rpm the snot out of your combination to make good power.

Can you post that David Vizard port intake information? 

[Cliff Ruggles]

400hp is easily obtainable with the Sportsman II heads on a 350 engine build.

I build ours here with flat top pistons and shoot for .035" squish distance.  This put the static compression ratio in the mid 10 to 1 range, but they will EASILY manage pump fuel w/o issues if the right camshaft is selected.

Very tight squish is a major player with those engines and rewards the end user with excellent performance, improved combustion efficiency, and less timing and fuel required to make the best power numbers.

I have tried quite a few different camshafts in them, and it's difficult if not near impossible to outrun the plan old 327/350hp grind, or something very close to it in a HR profile.  NONE of the "modern" profile cams have ever been overly impressive to me, and for sure the really tight LSA stuff is NOT the best direction to go from what I've seen here.

Single pattern is fine with Sportman heads as they have excellent exhaust flow and intake to exhaust flow ratios.  Unless you cap one up with stock log type manifolds no need or benefit from the dual pattern cam anyplace with those heads.

I still wished Crane made their excellent "Blazer" series of camshafts, there were long seat timing, wide LSA and not a lot of lift.  This made them excellent in long term use and very easy on the valve train.

We used to use the smaller one, pretty sure it was the 280H for truck engine builds and the larger 300H for street car engines.  They were both single pattern camshafts.  After the crappy "smog" heads started showing up in the early 1970's dual pattern camshafts became the trick of the week, and even today most offerings we see will be a dual pattern design......Cliff

[Mudsport96]

I have a retro-fit hyd roller (old block design), TCI turbo 400 ...  my goal is to get this puppy to hunt ... I'd like to be around 400+ HP with my factory aluminum intake and Qjet.
I agree on camshaft selection, to big is a bear to deal with and one has to rpm the snot out of your combination to make good power.

Can you post that David Vizard port intake information?

I found it and reposted it, may have to click on the pics and make them larger not sure why the showed up smaller.