I was looking at options for enlarging the intake manifolds and came across a US company that can do it with hydraulic abrasive gel (for lack of a better term) they quoted $1500 for a set. Looking at videos from the company and other outfits it seems like a far more precise way to enlarge everything uniformly and match flowrates via computer. For some of you who know alot more about this then I do...

am I correct in specifying that the max diameter of the runners is to be 38mm and not a hair more?

and would this increase in airflow overwhelm the engine without specific ecu modifications or would the various sensors (o2 etc) allow for everything to run normally until such modifications can be implemented?

Thanks

 

I would not go 38mm, this is way too big for a stock engine. I had a head Norm loaned me from a hydroplane which made 610hp from 6.0L and the intake ports were 38mm at the opening. I have flowed my intake manifolds and opened them slightly to match the port and removed the injector bump, I have not touched the plenum end and the manifolds flow WAY more than my modified head.

You need to look at the intake system as a whole. If I have a fire hose and feed it through a garden hose I will not increase the volume of water out of the garden hose, (without increasing the pressure turbocharging).

 

Thnx, do you happen to know what the max cfm is for stock throttlebodies? I've read somewhere that the stock size was actually fine for moderate gains, nothing extreme of course. I've already got high-flow aftermarket filters and the entire front face of the filter housing (where the trumpets would be) cut out and replaced with mesh, I think AJ6 engineering still does enlarged throttlebodies but if it isn't necessary then why bother at this stage.

This is a video of some work from one of the companies I think it would be worth trying, I have a spare set of manifolds I can sacrifice.

 

Extrude honing is a surface finishing operation. It does not enlarge or remove a significant amount of material. I've never seen any proven dyno results but I suspect it's a good process to ring out every last HP from a race type engine where 3 or 4 HP might matter. The largest encumbrance to head flow is the valve, valve angle, and inlet port shape and design. When it comes to engines most of my vast experience is with Chevrolet....and I know there are many 240 HP TPI engines still running around, there are many 350 HP TPI engines using the exact same intake but performance heads and camshafts. When it come to performance and meaningful gains, you have to work backwards... first, the valve size, seat angle, inlet shape, port design, manifold matching and so on.

Also important to remember port velocity, if a port or runner is too large, the mass of air becomes heavy and stalls at low/medium RPM killing torque and power.
Case in point is the Chevy L92 head, it has a large port and flows in excess of 300 CFM right out of the box, but most amateur racers use the L76 head which has a smaller port and just flows 240 CFM. Cleaned up these are the go to heads becasue they make far more power under 6000 RPM where it can be used in most road and short track situations. The L92 heads are for the mega buck 7000 to 9000 RPM dry sumpers.

Los of differences for a road car vs racing application, I suspect that 600 HP v12 engine uses a camshaft with aggressive ramps that slams the valves open, and would wipe it self flat in a road car at low RPM after a short while..

 

i guess i was ahead of the curve back in 1994, my 1978 V12 inlet manifolds were Extrude honed by a company in NJ,USA, cant remember who tho!

i carefully measured them in and out also Plenums before sending them,, i can roughly say they opened them up all the way thru about an 1/8" inch, also took out the injector humps and bumps, and some of the bolt boss intrusions, much smoother surfaces, they were pretty rough inside,casting flash etc., best part was the runner turn in mouth, nice smooth contour!

NOW if they helped power i donno, never run the car before many small engine mods??

 

 

Thats a really cool video to watch and an awesome technology. I remember back in the 90s when either Jim Wolf or Stillen were selling extrude honed intake manifolds for 300ZXs.

 

Stock throttle bodies flow 600fcm good for over 500hp from a single TB. I know a friend of mine has built a LOT of high performance Jaguar V12 engines maxing out at 800hp naturally aspirated. I have had these conversations with him. He built a V12 with custom manifolds and a single stock TB that made 500hp @ 7800rpm.

Power gains will be made from enlarging the plenum and increasing the distance from the plenum wall to the entrance of the runner. Cleaning up the exhaust manifolds and free flow exhaust after the manifolds.

 

warrjon , thinking about it , yes it just maybe cheaper to make custom manifolds than Extrude them?

cant quite remember 1994, but it was not much back then ,and seems its out of style nowadays!

also back then very little information was around about larger plenums for for Jag V12! in USA.

i thought the plenums were much to small anyway, so oppted for extrude!

ron

 

From the conversations I have had with Norman the plenum is too small, BUT also the distance between the runner entry and the plenum wall is too tight, it should be at least 3 x runner diameter. Runners 1A/B and 6A/B are the worst where the plenum wall is about 40mm from the runner entry.

Norm's advise was to cut the plenum off and weld on a 100x100mm box section and move TB to the front.

The cam was 0.440" lift, 95mm bore, valves we from an LS1 and custom chamber in the head (pre-HE) This engine was in a hydroplane.

 

Sounds like the bmw v12, I have a set of those manifolds to. Some other interesting designs have the v12 throttlebodies (rolls royce I think) in the middle but facing inward almost where the distributor would sit.

If aiming for a road legal faster Jag, is $1500 to enlarge and smooth a bad deal or cost effective compared to fabricating all new things.

 

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i'm quite sure Extrude would be more than be enough for a serious road car V12.

ron

 

Not to mention the Ferrari V12 from the 612, 575 making over 500

Have a look at the manifolds of the F140 engine this is what to do with the plenum. The F140 made nearly 800hp in its hipo form.

 

this is what i think is best for inline engines, V12 would need two, this one was also Extruded inside, beautiful piece!
V12 would need two TBs connected by adjustable cables(0r DRIVE-BY-WIRE). EEK.

the square box type(been there done that)is OK but these types long tapered seem to be preferd lately. this engine came from factory with 6 TBs, but changes in concept used large TB.

inline 6, 3.2L,car made close to 1000HP at 10,000 rpm,terrible thing to drive , triple plate clutch jerk your head off, almost impossible in road traffic! But to each his own!

 

F140 engine from a Ferrari 599 making 661hp