Re-mod of Ironhead Crossflow intake runners & quote .

[Anonymous]

Yesterday I moded my 250 cast iron head crossflow to take smaller intake runners.
I went to a number of exhaust fitters and tracked down some 1 3/8 O/D mini exhaust pipe (32mm internal diameter). I then got them to crush and bend it slightly in a number of places (down to 30mm internal). I then cut it into about 80mm lengths with the the smaller crushed end inserted into the runner nearly all the way to the bowl and the bigger end up to the entry point. I then had them welded all the way around the pipe and then cut off and ground flat with face and reemed out a bit at end to match manifold.
30mm may sound small at exit but I found that standard the runners exit into the bowls at about 31.5mm and one at nearly exactly 30mm the entry point to the runners was closer to 38mm than 40mm
From previous post I think some of the Alloy crossflows have 33mm inlet runners and others have 35mm so I might be a bit on the smaller side of things (32mm) and am hoping it doesnt restrict power too much under 5000rpm but should have better throttle responce.
Just curious does anyone know what size the alloyhead crossflow intake runner is when it exits into bowls?

Performance buildup mag vol 13 no 3 page 46
says on LS1 engine after filling bottom of intake on head and manifold "The filled heads/manifolds lifted figures into the 276-280kw (370-375HP) range straight away. But instead of getting just 150 KW at 2500 rpm, there was 180KW avialable."

 

[xctasy]

The 1972 2V 250 was about 42 mm.

Yella Terra sold 40 mm port XC heads on exchange, so I suspect it was 40 mm as well.

My 1977 head certainly is 40mm .

Early 1979 XD iron x-flows had 35 mm intake ports.

The Alloy heads were only 32 to 33 mm.

See the pattern? Ford made the ports smaller and better in shape with each change. Kenneth Duckworth from Cosworth commented that the ports were so big on Fords canted valve US engines that the foundry should cast in arrows to tell the fuel air mix which way to flow!

The 30 mm ports will work fine. I'm aware that Chevrolet has the most advanced mass produced head flow engineers in the business. This is no put down on Fords US Dearborn or Aussie Broadmedows guys. The early 1979 X-car 2.8 V6's were the first cars to use cast in flow modifiers in the base of the intake ports. It helped build very good BSFC figures, and helped low end torque.

The 1996 LS1 is a very restricted combination in terms of cam and BMEP results. It has poor low end torque and only makes power with large amounts of revs. The real key is its benchmark ignition system and superb flow management of the ports which creates mixture mtotion.

The 1988 GM 3800 is similar, revs more highly tha the XR6 yet has no extra power. A very basic design with superb execution. Just like the first Holden Commodore VB suspension, the whole thing looks very simple but it has been sorted by engineers who work till late, sorting the basics out.

If you fill the base of the port with Devcon JB Weld, and create what David Vizard called a biased Apple Port, you may gain much better fuel economy, and keep the high end power.

From memory, Ford Cortinas gave about 150 hp at 7000 rpm with 30 mm intake ports. 30mm should be plenty of port area for the 200 hp mark at 4500 rpm or so.

 

[Anonymous]

4500rpm and 200HP is ok but I was hoping to go a little more. If the horse power is governed by the smallest piont of restriction which in my case is 30mm exit into bowl down from 38mm at entry (my standard runner size) what is alloy crossflow 32mm down to 24mm (I doupt it). Why make a runner so large at entry and so small at exit if the exit point would squeeze all the power out of it?

My mate down from Queensland the other day tells me that over there they fill the intakes with molten bronze or brass and then drill them out.

Thanks xtaxi
I might change what i wanted to get out of it and go for lower rpm power.
Cheers Tim

 

[xctasy]

I've check some on-line references rather than muck you about with actual calcs. I personally think that the reduction in port area is wise, and I don't fully aggree with the actual recomendations.

I must admit that the on-line stuff is more traditional, and they point blank suggest that the stock 38 mm port is ideal for power at 4600 rpm and torque at 3700 rpm. I am convinced there is 225 hp and 250 lb-ft to be made with the right cam, but can't prove it.


I read through all the formulae, Here's what I found.
Smallest valve is 1.62"

See http://www.rbracing-rsr.com/machcalc.html

Inlet Valve Speed of Sound (MACH) Index
Your bore size is 3.68 inches with a stroke of 3.91 inches and has 1 inlet valves with a diameter of 1.62 inches. Running a valve lift of .471 inches at 5400 RPM, the inlet valve mach index is 0.598 . The mach index for maximum volumetric efficiency is .6 . Beyond .6 the volumetric efficiency falls off. As the mach index rises beyond .6 the volumetric efficiency can be increased by later inlet valve closings (60 to 90 degrees ABDC).

See http://www.rbracing-rsr.com/machcalc.html Inlet Valve Speed of Sound (MACH) Index
Your bore size is 3.71 inches with a stroke of 3.91 inches and has 1 inlet valves with a diameter of 1.95 inches. Running a valve lift of .471 inches at 5400 RPM, the inlet valve mach index is 0.505 . The mach index for maximum volumetric efficiency is .6 . Beyond .6 the volumetric efficiency falls off. As the mach index rises beyond .6 the volumetric efficiency can be increased by later inlet valve closings (60 to 90 degrees ABDC).

Using on 38 mm port, this is 1.76sq in"

See http://www.rbracing-rsr.com/runnertorquecalc.html

Calculate Peak Torque RPM

To find the rpm at which peak torque occurs for a given inlet runner / engine.
Engine Displacement (cubic inches only) 250 cubic inches
Number of Cylinders 6
Intake runner area 1.76 square inches
Peak Torque RPM 3725 RPM (calculated)

Considering maximum XC and TE power was 92 kw at 3700 rpm, the port could have been taken down to 29 mm (1.02 sq in) to get the 288 Nm at 2200 rpm torque peak. The fuel consumption would have been much better!



If you input the stocj XC/TE cam figures and CR into the following formula, you can calculate the bare minimum amount of compression rise needed for your new cam. Despite what I've calculated in the past, this formula doesn't agree that longer rod engines have less effective compression. It does calculate static cranking compression.

See http://www.rbracing-rsr.com/comprAdvHD.htm

It has the effective compressioin calculation listed in Practical Gas flow

Air flow is not related solely to port area. The maximum flow of air is a function of the total cfm from one cylinder and velocity and area.

Some people talk about ideal 'flow net' port length to port area profiles. The late Phil Irving had suggested profiles. GM has been using the Cathedral Port with superb success, where the sectional area changes a heep in the 4 inches before the valve. In practice, following someone elses 'grind it out to the water jackets' approach is always the wrong one. Especially when each runner on the Iron X-flow is biased and angled at a different vertical and horizontal plane, and at differnt planes from front.

The reduction of port area needs to be followed by a 2 mm reduction in the alloy intakes port. Port mismatching is the single most important thing to do. Brad Girdwood used to do this. Port mathcing and polishing heads is the biggest waste of money and time to the aftermarket ever devised. Form must follow function.

Look at the EB XR6. Tickford said the crank was too fragile, the ports too big and the valve springs were too soft for 180 kw (250 hp). They turned a 139 kw (186 hp) engine into a 161 kw (219 hp) at 4600 rpm screamer just by optimising. The ports on an ohc are too large for 220 hp, and the 35 to 40 mm X-flow ports are certainly too big for the 250 as a stock engine.

Trust your instincts.

Your four barrel 2V intake shows your brilliance as a modifier, and the x-flow beckons. Throttle the ports and get the ideal flow! You have nothing to loose except your fuel bill!

 

[Anonymous]

quote "The reduction of port area needs to be followed by a 2 mm reduction in the alloy intakes port. Port mismatching is the single most important thing to do. Brad Girdwood used to do this. Port mathcing and polishing heads is the biggest waste of money and time to the aftermarket ever devised. Form must follow function."

xtaxi
Just from looking at it my hunch is it will work very well and i was prepared even to lose a little peak power at around 4800 rpm which is where I was looking to max out. I have yet to track down a second hand four barrel inlet manifold which i assume will have about 40mm ports .
Are you saying in the above that if it is 40mm on the manifold down to 32mm on the head that to allow a (2mm mismatch over total diameter) when steping down to the 32mm entry into the runners is a good idea and that I should not bevel the runners back too much so the they match the manifold exactly? I will follow your recommendations!
Thanks Tim

 

[Anonymous]

Does my question make no sense is it confusing?

 

[xctasy]

I'm out of my depth. I like the idea on a short rod, long stroke engine with small ports and six independent runner ports giving over 1.4 lb-ft per cube, but I haven't got my ideal package worked out.

A port missmatch works when the intake manifold is smaller than the intake port. It works by re-introducing the poorly atomised fuel,
(raw fuel which is greater than 60 microns in 'ball' size) back into the airstream. Every one seams to think aerodynamic, smooth ports create power. They don't, they may gain peak power but they always loose power and raise specific fuel consumption throughout the rev range. Peak power is never used on the street.


I have this three pronged dilema.
1. I guess I was too inclusive in saying 'your okay throttling the ports down to 30mm'. To port mis-match, you'll have to go down to 28 mm in the intake manifold diameter to make it flow well. You'll gain low end torque, but will find the high-end power is down.

2. Fact is, the stock XC/XD ports size 35-40 mm is perfect for a more than 240 hp engine, but it does have poor biased port shape and entry. It may help mixture motiin on a high lift cam engine, but on a stocker, it screws up fuel mileage.

3. 30mm is okay for the 130 to 180 hp area in the better shaped XD 1/2 to XF head. Plenty of 33 mm ports can go to 180 hp. Dick Johnston re-shaped the intake manifold and ports for 196 hp. I'd say 30 mm is as small as you can go in the 200 hp area.

That's all I can say.

Flowbenches can lie if mixture motion is lost. Great CFM flow doesn't always create good power and economy throughout the rev range, because the mixture has to ignite evenly . If you go to a smaller port, but one which is still fairly rough in microtexture it should be better than the grind out jobs. If it has a port miss-match, all the better.

We can play with the cam, lift, carbs and ignition, but few people ever go down in port size becasue they are only chasing power.

I think you are chasing ideal torque and good economy, with enough power for it not to be strangled. I favour this approach, becasue I think it works.

Be brave, you can always return the spec to factory again. Meatime. take a punt on tig welding the intake runner down in diameter, or wraping some guitar wire around the inlet manifold port, peg it down with some small 1.5 mm drills, and then slop some JB Weld on the intake manifold port is a semi rough state to create the port mismatch. Everything can be reversed if needs be.

Sorry, this is 'out there', but you should gain better low end torque and maintain reasonable power.

 

[Anonymous]

Thankyou
Thing that really made me go with 30mm is that i got a socket on the end of an extension (the socket was 29.9 something mm) and pushed it down inside of the 38mm runners until it stopped i then got a torch and shone it in through the valve end. The result, no light coming through into runner near perfect fit. I figured if stock head was good for 240 hp then my mods would be ok for same if I didnt go smaller that this size.
Im thinking I was wrong? Other thing is Ive got that new 465 4bbl which is probably not suitable for a low torque cam.

I found this on the web from Puma race engines for Ford 1600 GT Crossflow with 27mm ports out to nearly 31mm for 135-140HP its easy to do the calcs for an estimate of about 200 Hp for a six. I dont know how successful I will be in using this as a kind of benchmark.

"The inlets have a big chamfer at the manifold end which can deceive the inexperienced eye until you actually measure properly. The exhausts are round and about 27mm in diameter but look small. The inlets are slightly oval and a tad deeper than they are wide and look big - but they are only about 27mm wide and 28mm deep - almost the same size as the exhausts. you'll see that if an inlet port is not to restrict its valve it needs to be up to 75% of the valve diameter for road engines and 80% for race engines. It depends on port efficiency, intended cam lift and other factors but it's a good guide. The crossflow inlet port is therefore small even for its standard 38mm or 39mm valves and to supply a big valve properly like the 41.3mm one it looks like we might potentially need to open up the ports to nearly 31mm (75%) for road tune and 33mm (80%) for race tune.
AFTER MODS POWER OUTPUT
You hear about plenty of 200 bhp crossflow engines but you never see any tested. There was an all steel full race one in CCC magazine recently with that much claimed power (recently being spring 2001) which ended up making 162 "flywheel" bhp on the rolling road if I remember correctly - and it might not really have had that much but only an accurate engine dyno would have told. I trust the supposed flywheel figures from most rollers about as far as I can swing a cat that's hanging on to a grand piano for grim death but that's another story.
An average engine in the above spec makes about 110/120 bhp if you're lucky but on a really good 41.3/33.7 valve head that's been modified by an expert you can see close to the 140 sure enough - mid to high 130s anyway. Maybe another 8 bhp or so with a 244 but you'll get fed up of the lack of low down power on the road. Any tractable road engine with more than 130 bhp is pretty good actually compared to most of what's out there."

Xtaxi
Should only have to mismatch a little from 30mm manifold to 32mm intake, as is 32mm internal at entry point all the way along approx 50-60mm of runner length and then graduates slowly to 30mm internal over last 25mm (appox) of intake runner before exiting into bowl?

 

[Anonymous]

Ill have to think over this for a few days. 200 hp more torque and mod a standard 4bbl intake. maybe?

Got some inlet manifold steel paste made by "car go"it is a two part with hardener. Requires mix equal parts and takes five minutes to set.
I tried some on a 40mm peice of pipe I had and narrowed it down to 30mm with paste at end then boiled it in water and soaked it in petrol with no apparent ill effects. Also hit it with hammer until pipe deformed paste cracked but still would not come out. I think Ill use this as Ive tested it and so long as surface is rough its sticks very well.
I intend to build it up to a metal collar inserted at exit from manifold. Should work a treat.

 

[xctasy]

To the crowd

"I 'm sure you all think we are nuts here!, but Tim is on to something!

Tim.

Nothing is gained unless you test an idea, and see how it goes. Since you are clearly reducing intake runner size, then it is okay to use a filler as long as your are double-ly, triple-ly certain it won't be injested.

As I've said, it is a dream of mine to optimise a pulse tuned small runner 4.1. You are close to something.

The 302 Boss guys used to Devcon down the huge intake ports. It's a sound idea.

The port mismatch is a sudden increase in port area, like a venturi in reverse. It works if it is sudden.

I've dropped you a PM.

 

[Anonymous]

Damn, I forgot to see if it was combustable. Ill have to do an explosive test as well. Wheres that old lawn mower?

 

[Anonymous]

I ended up taking out all the exhaust pipe out of the cast iron intake runners in the head because I was concerned that 30mm ID may be a tad to small for 200 plus HP and am confident that 32mm ID same as Alloy crossflow is more than ok for this level of HP.

After taking them all out I ended up re-inserting about a 34mm ID pipe for the end two runners which were curved. Bending it in a pipe bender reduced it down to about 32mm ID all other runners can use standard 32mm ID straight pipe.

Did similar to 4bbl intake manifold using a combination of both sizes to get a good result. Im also making up a 18mm aluminium spacer to go between the head and the intake manifold match ported to cover and stop any epoxy I used to hold the runner inserts from coming lose at manifold or head exit, entry points. Went for 18mm thick aluminium for benefit of making the runners a bit longer. Im taking picks along the way

Just in case anyone is wondering why I am bothering to do this the latter alloy heads got it right with size of intake runners for a streetable engine. Fords Iron head Crossflows were too big on the intake. Im wanting to make the torque curve as fat as it can be up to about 4800 rpm. I would have used an alloy crossflow but it would not fit into my TD Cortina engine bay without the manifold hitting the firewall.

Read below 30KW extra at only 2500 rpm for an LS1 up from 150KW is alot extra just through a filled intake!

From: Performance buildup mag vol 13 no 3 page 46
says on LS1 engine after filling bottom of intake on head and manifold.

Quoted as follows:
"In standard form the LS1 has a minimal cross-sectional area of about 2.93 in2 at the inlet manifold face theoretically enough air to make more than 700 HP get past."

"When the job is finished the cross sectional area in each port is reduced to about 2.3 in2 which multiplied by eight, will pass enough air for 500-550HP (373-410KW) "
"The standard heads were getting 260-270kw (348-362hp) at the wheels with the particular cam they were using. The filled heads/manifolds lifted figures into the 276-280kw (370-375HP) range straight away. But instead of getting just 150 KW at 2500 rpm, there was 180KW avialable."


Most cars wont make 180KW at 5000 RPM not 2500 RPM???
The Honda designed Alloy crossflow heads are much smaller in intake. I figure they knew what they were doing.