I have been reading up on advice regarding intake manifold port matching. With the numerous head options and various port volume and cross section areas it seems that almost all manifolds need some port matching. I am also looking at some old school manifolds, old style standard SBC intake port dimensions, to fit on modern larger port heads (23 degree heads designed for 1205 & 1206 intake gaskets) so I plan to break out the carbide cutters that I have not used for years. What is the current "best method"?

For a while the advice was to port the head & intake to the next larger size gasket (something I never liked)?

The old school advice was to find a close undersized gasket, match it to the head ports, and then match the intake ports to the resulting gasket (what I was advised twenty five years ago).

Now I read advice to only port match the sides & roof of the intake manifold runners, in the high velocity area, and to leave a reversion step at the port floor junction.

Others advise the opposite, match the floor and leave a reversion step in the port roof?

The more recent tech sheets from Edelbrock (the Super Vic, for example) advise a 0.025 reversion step on all four sides of each intake manifold port.

I was also taught to sand to a 60 or 80 grit finish (at best), and now I see CNC ports that leave what looks like concentric 0.010 steps in the intake ports, so has the finish spec changed as well?

Considering wet flow (using a carburetor), what is the current thinking?

Thanks!

 

A few months ago either HR or CHP had an article on this.
What they forgot were some before and after dyno results?
I also want to see some before/after w/carb spacers.
Is it the extra plenum volume that makes power, the cooler charge from an insulated carb or a little of both?
I've been interested in modding intakes for better flow. It would be nice to see some honest testing.
I read where an old 2L Ford was given the complete "Extrude Hone" treatment on heads, stk ex man and intake. The gains were impressive and the whole power curve was improved at all rpms. JMHO

Ricisan

 

Only source i know is D. Vizard "How to ... intakes and carburetors". $10-$15 still in print. I think this would be proprietory information if a head/intake porter learned and earned it by his trade - meaning posting it on the net would only take from his business. Porting, then flowbenching, then dyno'ing is a truck load of work just for one intake, head combo.

Brzenzinshi racing does this as service 866-236-6300.

Good luck,
cardo0

 

Thanks Guy's

This is a silent forum (and with the search scrambled, it's not much value without participation). I tried to find a thread about drilling and pinning to align the manifold to the heads (mock-up assembly pre-port match advice), but the search is FUBAR.

I had the Vizard book years ago, and lost it. What I did have was my book notes from my Pontiac racing days and the recent advice of two porting Technicians. When I mentioned I was working on old manifolds the Tech's opened up a little.

The advice summary was: focus on the roof and common wall (Gen 1 SBC) to gain a flush transition without a sharp corner, never make the head port larger than necessary (no oversize gasket match porting on the heads), and if in doubt a slight reversion step is OK (actually good, from the Edelbrock Tech).

They also said modern manifolds are very good (need minimal work), and old ones range from POS to good (need some work, lots of work, or it's easier to buy a new manifold).

The best unexpected advice was to use a inside caliper and make sure the old manifold ports were blended back into the runners to evenly remove pinch points. The advice was that old dual plane manifolds left much of the port roof pinched on the upper plane due to the cores they used (it is/was). It was not much of a problem with 283-327 displacements and stock heads. The pinch leaves a considerable speed bump when opened to a head matched 1205 gasket (worse with a 1206). With the port pinch corrected they said the old manifolds can work very well, but will lose low rpm torque compared to a modern computer refined long runner manifold. This is due to the old manifold's large plenum and tapering runner cross section and the relatively short runners (good for high rpm, bad for low rpm, compared to a modern design).

 

correct intake ports start big and consistently get smaller all the way to the valve head. Small port hogged out to big head port is a big no no.

correct ports give a ram effect to over fill the cylinder.

Buy the intake manifold with the correct matching size to the head . Only minor matching.

At the shop we use a bore scope with the intakes bolted to the heads

 

Maybe I can help here, we have a "bullseye" method we've been using for decades now! This is the post "from the past"!!

The ONLY effective way to a true "Port-Match".

1-Have heads pre-mounted on block to be used, with both head gaskets in place.

2-Use 2 pieces of masking tape or 2 spots of silicone and position intake gaskets in place.

3-At this point make sure the intake gaskets (marked R/L) fit the head ports the way you want them.

4-Lay the intake in place with 4 corner bolts, at this time you'll know if bolt location is OK.

5-Snug the bolts down, and using a 1/8" drill, drill 4 holes (1 at each corner) through the intake making sure where you drill you will hit the gasket (don't drill where there is no gasket below).

6-Let the drill tip go right through the gasket and stop on the head. Remove the intake and lay the gaskets on the respective sides as templates, (we use 1/8" "cleco" buttons to mount the gaskets back on the intake sides) and you can use (2) 1/8" drill bits for alignment. With the gaskets mounted on the intake, simply scribe out the ports on the intake and "grind away". By using this method we can literally leave a perfect "overhang" (reversion-wall) on the intake runner of .020"/.030" or we can make it "straight-wall" deal, no "overhang"!!

In simpler terms, the head port is slightly larger than the intake port.

It's your choice to line up the port perfectly or leave the "overhang". The entire procedure takes about 20/30 minutes to achieve and guarantees a "perfect" fit on the final ***'y. This procedure can be done on assembled long blocks that have been running and getting an intake change. We run the intake port "inside" the head port for anti-reversion only on street engines and not on the “track only" units due to the higher VE of race prepared engines.

Thanks, Gary in N.Y.

P.S. There is no other accurate way (that I'm aware of after 38+ years of engine building) to get "perfect" port alignment, period!

 

A big thanks Gary (and all), as this was the info I was searching for.

It looks like I may be drilling an intake to set the alignment pins. I have already sacrificed a set of 0.039 Felpro head gaskets to mock up the intake fit on the engine, and it looks like a sacrificial 1206 intake set will be the test case for the old design Bowtie Vic Jr intake I have. The heads are a mildly ported and unshrouded 67cc chamber version of the 1049 Phase 6 Bowtie castings with intakes slightly smaller than the 1206 gasket port.

I tried something like the pin alignment with the C3BX and the 1205 gaskets by notching the exposed portion of the gasket to the edge of the manifold. Then I lined it back up for the scribe marks. This transferred the port's floor-height OK, but it was hard to accurately align the fore/aft port width. I was going to try a second pair of scribe lines for the width alignment but the accuracy did not look that good.

The ported C3BX also leaves less than ~3/16" in the port roof at the head flange, with the 1205 gasket port roof height, so I was hesitant to go any taller. I can just see the edge of the blue port sealing line in the 1206 gaskets outside the edge of the ports when this manifold is roughly test fitted to the heads, and do not know if it will seal with just a thin 3/32 flange straddling two-thirds of the blue port sealer outline? Any advice on how thin is too thin?

If I run the C3BX manifold I may just have to live with the steep reversion step and trimming the gaskets. As it is, I took a good 0.200" from the manifold port roofs and removed some major pinch points about an inch into the ports, so It's got to perform better than the old rough casting. The free C3BX was my initial test case, the learning platform with my twenty year old tools (and 20-year stretch since I last did any port grinding work), before I start matching up the VicJr.

My goal is to have both manifolds port matched to the heads (now), so I can swap them out for some variety. The EA simulations reflect the manifold choice will result in a 20+ ft.lb. trade off in torque" with the C3BX better off idle to 4300 rpm and the VicJr better from 4700-7000 rpm.

I was told any port matching I do will help either manifold, and not to sweat getting a perfect flush wall. I was told a 0.060" reversion step is better than a 0.030" dam in the port wall (or a 0.200" step) and to be conservative (be easy with the die grinder).

My biggest immediate problem now is removing a steel hose nipple from the C3BX manifold that is in the hole closest to the factory temp sensor location. A PO of the manifold did not use thread sealer or tape on any of the plugs or bungs, and I have two that remain stuck solid (the manifold was free, what should I expect). The steel hose nipple is the worst and needs to be removed. Any suggestions to assist breaking the nipple loose without damaging the manifold will be appreciated.

 

63 340 HP, I w as reading your last post about comparing the C3B to the Victor. Prior to doing the dyno test with AFR and Car Craft on our stroked 62 327, I did an A to B intake swap. I baselined the car with a #8120 Weiand dual plane at Famoso. I swapped the intake, then went back to Famos with the Team G the following weekend. The Team G was ported by AFR and opened up to a 1206 Felpro gasket. My camel humps were matched to a 1205 Felpro.

One thing AFR insisted on was to use the double thick intake gasket with the Team G. P/N 1266, with a 1206 opening size, for port alignment.

Our car was a better match for the dual plane on paper: 3.36 gear, 1800 converter, 9.6:1 compression, mild solid F/T with 18" vacuum @ 800 RPM. Left in Drive, the trans shifts between 5000 and 5100 RPM.

With the 8120 intake, the Vette went 12.79 seconds at 107.XX. The following weekend, it went 12.77 @ 108.XX with the Team G. I honestly expected the car to slow down, but it didn't. In fact, it picked up nearly 1/2 MPH with the Team G. Both the Team G and #8120 were selected for their hood clearance on a stock solid axle Vette. I liked the drivability much better with the Weiand, but to be honest the Team G isn't terrible. I think if the trans shifted higher and the car had more converter, there would have been a bigger MPH difference between the two intakes.

FWIW, while I was waiting for the dyno test, I put a dished piston 383 from my old truck into the 62. It was fresh, had only about 10 miles before I drove 105 miles to Famoso to race it. It had a mild Engle HR Cam with 224/232 @ .050", on a 112* LS cam, unported 180 CC (actually poured 191 CC runners) Dart Pro 1 Platinum Heads, and a C3B intake. The Car went 12.64 @ 107.97 MPH it's first pass. I hot lapped the car and went 12.68, then was booted from the track for the lack of a roll bar. The engine idled with a hair under 16" vacuum, and drivability was excellent.

I would think the C3B would benefit from some plenum work, such as a larger notch in the divider, similar to an Edelbrock RPM intake. I used a 4 hole 3/8" insulating gasket with the C3B. If I were to do it over, I would use an open hole gasket.

I have not been to the track since the AFR head and HR cam swap on the 62. We did drive to Scottsdale AZ with Car Craft for a drag test, but was rained out. I am looking forward to getting a dual plane back on the 62, which I can't do until I get some 1/4 mile numbers for the magazine.

Wes

 

Good reporting on the viability of the C3BX, thanks.

My distilled down question is, "will leaving only 0.150" of port roof at the manifold to head flange be good enough to achieve good gasket sealing?"

Somewhere about 150 thousandths will be the thickness of the manifold port roof casting that remains on the C3BX above the 1206 port, if I open it to an ~0.030" reversion step.

The thought of the milled plenum divider will have to wait until I get the engine together and do some testing. Some of the 3-barrel C3BX's have a small notch, my model has the intact divider. I was told the RPM's smaller plenums (compared to the old C3BX plenums) benefit from the ability to draw from both sides of the carb (the advice was it may not improve the upper rpm performance as much).

Thanks!

 

I would be worried about having a leak with that little of a sealing surface. You might end up chasing your tail trying to tune do to vacuum leaks, or sucking oil. A 1205 is a pretty good sized port opening, unless you're really wanting to rev.

Not exactly related, but I have a pair of rare 1959 #550 heads off my 59's 283/270 HP engine. One of the chambers and ports were opened up to a 1205, and a fair amount of grinding done. With a 1.88 intake valve, the porter got 232 CFM @ .500". Against my better judgement, I let him go further, and he broke through the bowl. The 1205 is a bit larger than I would feel comfortable using with a #653 2X4 intake. Unless I have some welding done, I have nothing more than a rather expensive door stop...

Wes