BBC iron oval intake

General engine tech -- Drag Racing to Circle Track

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F-BIRD'88
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Re: BBC iron oval intake

Post by F-BIRD'88 » Fri Oct 06, 2017 1:09 pm

Further, on a Qjet carb the AIR CLEANER matters A LOT. Get a GM air cleaner ( prefered ducted type) with proper base shape contour. it MATTERS A LOT. many of the pretty aftermarket air cleaners STINK in a functional sense.
All jetting evaluation most be done with the air cleaner installed. It matters more than most think.

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Re: BBC iron oval intake

Post by LaVelle » Sat Oct 07, 2017 8:21 am

F-BIRD'88 wrote:
Fri Oct 06, 2017 12:45 pm
For what is the best carb spacer height I cannot tell you exactly. You are going to have to try a few and see.

I suggest 1" minimum up to 2 1/2" or so. A stack up of 3/4" spacers is easier to carve out by hand with a die grinder. The typical cast alumunim Qjet carb adapter spacer that you see is 3/4" thick.

If you have access to a mill or at least a big drill press it makes carving the holes a lot faster.

You can make up low cost carb spacers out of wood (good plywood) to test with without braking the bank
or spending more money that nessessary. You are going to need to do some drive testing with the spacers
to find the best combo of spacer(s) height and type(s). Be prepared to rejet the QJet carb too.
Even a simple low cost narrow band O2 sensor on the exhaust can really help you dial in the carb.

Qjets are great carbs when properly jetted for the specific engine and bad carbs when not properly jetted.
That is why GM had so many different setups for the Qjet.
I wish I had kept my old 1968 396 325HP 4MV Qjet carb. it was a good one on many of my BBC and SBC motors, way back.

Here is the thing...You have the RPM intake on hand to test against as a bench mark to compare.
I think with that, you can make the factory hi rise cast iron intake with this mod and spacers
do the job very well.
if I was going to do large valves at all I would not go up to a 2.19". I would go 2.12" 2.14" at max.

Calculate the road speed and the resulting engine running rpm at that speed and keep that in mind
* the rpm will be lower than you think) so you don't get all crazy on camshaft duration.

On the heads avoid the thought of hogging out the bowls too much removing that funnel venturi under the
valves. on a mild cam the valve stays close to the seat (relative) and that funnel venturi shape helps the air go around the valve ( at low and mid lift) and go into the chamber. This venturi shape just under the valve matters. When you port the valve bowls think velocity and air flow quality around the valve and pressure recovery at low and mid lifts...( because that is where the valves spend most of the time with a mild cam VS a larger duration/overlap high lift racing cam for a higher rpm race motor.

On a (Mild low rpm) motor where the valves stay relatively close to the seat most of the time there is more to it than just getting more raw flow. And the motor spends most of the towing trip time running at part throttle, not WOT. I believe the BBC vortec L-29 heads are good for this.

One of the smart guys here that does BBC's will tell you which valves ( part numbers) {2.12" to 2.14") to get .
* GOFAST or Joe Sherman or.... VortecPro or
I have a piece of 1/2" big enough for one plate, so I'll get a 1" piece that I can make two at that thickness.
That should make for nice increments.
And yes I have a drill press and access to a mill, that's why I figured it would be easier to make them in the long run.

Wouldn't comparing to the Air Gap RPM that I have to it, kind of be apples to oranges, being it's a square bore?

Figuring on caming for around 1000 to 5000 rpm, 5500 rpm tops, being cruising RPM at 60 mph will be around 2800 rpm with the gear and tire size.
An old gear head told me, (build for torque and horsepower will take care of it's self) as a general rule.

The heads will get smoothed out and the big lumps removed, (not going to reinvent the wheel) with a 30 degree back cut on the valves.
With torque being the primary concern staying with the 2.06/1.72's has an appeal to it.

Built a 350 sbc for a truck decades back and used the old power pak 283 heads w/1.72/1.50's, Comp 262 and the thing pulled like a mule.
It was all said and done and would start to nose over by 4500 rpm or so, but well suited it's purpose.
I'm thinking along those lines for this build, just simple and basic, nothing fancy or exotic.

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Re: BBC iron oval intake

Post by LaVelle » Sat Oct 07, 2017 8:24 am

LaVelle wrote:
Wed Oct 04, 2017 5:55 pm
ProPower engines wrote:
Wed Oct 04, 2017 1:10 pm
I would use the 2-0 intake. They are much better then the iron intake.
I just finished a 454 oval port build with 781 heads and the stock aluminum snow flake intake which looks the same as the Edelbrock performer was about 70 hp better then the tall iron intake with a Q-jet carb. Took a bit to tune but was worth the time and effort.
I just finished one like that, 781', a Performer, 230 @.050/ .550 lift cam.
Does 11.38 - 12.43 in my 3700 lbs. Pontiac
That should be 12.38- 12.43 in my 3700 lbs. Pontiac.
Ran 12.41 @ 107 mph with it last night.

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Re: BBC iron oval intake

Post by LaVelle » Sat Oct 07, 2017 11:33 am

F-BIRD'88

What do you think of this for a camshaft?

Lunati High Efficiency hft #06205

210/215 @ .050 ( 260/265 adv.) .500/.513

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Re: BBC iron oval intake

Post by F-BIRD'88 » Sat Oct 07, 2017 3:47 pm

LaVelle wrote:
Sat Oct 07, 2017 11:33 am
F-BIRD'88

What do you think of this for a camshaft?

Lunati High Efficiency hft #06205

210/215 @ .050 ( 260/265 adv.) .500/.513
it is a (very) good choice. That is the idea.

Comparing how it runs with the RPM intake will give you a bench mark to compare against.
You can stick a a carb adapter on the rpm intake and test the Qjet.
See just how the factory intake (with your mods and spacers 'stacks up"

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Re: BBC iron oval intake

Post by pdq67 » Sat Oct 07, 2017 3:56 pm

I am also going to mention the L-29 heads!

They are true large oval, although smallish, Like 230 or so cc's vs the larger like 255 to 260 cc regular large oval heads, PP's are down around 200 cc's or so if not mistaken.

L-29's also have a 100 cc, fast burn heart-shaped chamber that will probably need the, "beak", trimmed some to keep piston interf. to a min. Good heads imho for a mild build.

pdq67

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Re: BBC iron oval intake

Post by LaVelle » Mon Oct 09, 2017 1:42 am

pdq67 wrote:
Sat Oct 07, 2017 3:56 pm
I am also going to mention the L-29 heads!

They are true large oval, although smallish, Like 230 or so cc's vs the larger like 255 to 260 cc regular large oval heads, PP's are down around 200 cc's or so if not mistaken.

L-29's also have a 100 cc, fast burn heart-shaped chamber that will probably need the, "beak", trimmed some to keep piston interf. to a min. Good heads imho for a mild build.

pdq67
The 100 cc chamber would be nice.
But aren't the L-29's a Gen V head with the funny water jackets?
I'm running a Mark IV.

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Re: BBC iron oval intake

Post by F-BIRD'88 » Mon Oct 09, 2017 2:06 am

I believe the L-29 Vortec 7400 (7.4L) BBC heads are a "Gen VI" BBC head.
They do work on a Mark IV 454 BBC and there is a head gasket that allows this.
Someone smart will know the head gasket part number for this.
Gen 6 BBC head on a Mark IV bbc block.

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Re: BBC iron oval intake

Post by LaVelle » Mon Oct 09, 2017 2:20 am

Things look pretty good.
Took a tape measure to the 3931067 and the RPM and they are basically twins other than the RPM has about a 1/2" taller overall height.
With the discussed modifications and 1" spacer it should perform well.

Intended combination:

2 bolt 454 Mark IV block (.030 )
Cast crankshaft turned and balanced.
Truck 3/8" rods w/ARP bolts. ( resized, floating pins )
TRW L2399F pistons .030 ( 8.7 w/119 cc )
Lunati cam # 06205 210/215 @ .050 - .500/.513.
Heads; # 236 peanuts, ported, 2.06/1.72" valves w/30 degree back cut.
Intake; modified 3931067, 1" split spacer.
Holley spreadbore # 6210 ( 650 cfm )

Comments, suggestions?

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