308 2V head porting - Ferrari Life
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post #1 of 144 Old 03-09-2011, 05:28 AM Thread Starter
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308 2V head porting


Because I’m just not busy enough with the V12 and house projects I went ahead and promised a couple guys I’d have a look at what can be done with 308 2V heads flow wise. My engine simulator says there are a lot of problems with what ferrari was doing engine set-up wise up though about the 348 vintage engines, with one of the items being the port/valves are just way too big for the flow the heads are making causing all kinds of bizarre pressure plusses in the intake and exhaust systems.

I have 2 different requests to answer at the moment.

The first question is what is the right head set-up for a carb 308. Contrary to what many seems to believe, weber carbs don’t actually flow ever well and severally limit how much hp can be extracted for the engine so on a carb engine the goal needs to be making the most of the carbs. The word on the street is that the Michelotto 308s used 208 heads which have much smaller valve/ports and I suspect that is exactly the right answer….and I have a loaner 208 head to play with. This is where I’ll start tonight and post plenty of pics.

The second request is what exactly can be done to get hp out of a 2V 308 with no other restriction place on the project. My software says that once the engine is fitted with cylinders ad crank form 360, the cams I picked for my V12, a custom intake and header it should just tough 450hp at 8500-9000 rpm…..if the flow number can be achieved. Even for this build the math says the stock valve seat ID is too big and will need to be reduced but the valve may need to be bigger because the Ferrari cam design limits what can be done cam wise. A big valve on a small seat will make the 2V head act more like a 4V head and work better with the possible cam options….if that combination can be made to flow. I’ll have a scrap 308 head in my hands in a week or 2 so I’ll see what can be done wiht it once I’m done with the 208 head.
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post #2 of 144 Old 03-09-2011, 05:53 AM
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Because I’m just not busy enough with the V12 and house projects.....
Mark, you poor fellow. It sounds like you're feeling bored, neglected and unloved. I'm sure all your buddies here can help you out if you need a few more projects?

Speaking of which...... I could use some help/advise on an air distribution issue I'm having with a twinscrew supercharger on a DOHC V8. The supercharger's discharge is right above the front 4 cylinders, so they're getting all the air and run lean until the manifold pressures up. We compensate for this by tweaking the individual injector trims, then take out the tweaks when it's on boost, but this is a bandaid approach because it's obvious the front 4 are carrying the load of the motor down low.

It would be much better if we could balance out the air flow and encourage some of it to go to the rear holes, not just the front 4. The manifold design is just a simple, single plane type plenum.

I'm leaning toward putting some slide throttles inside this puppy with a pneumatic actuator to restrict the front 4 a bit while it's under vacuum conditions, then letting them open up under boost. Not the simplest solution to be sure, but then why do something simple when the complicated solutions are so much more interesting?

'99 550, Rosso Corsa / Nero, S/N:114654, Assy: 31836, Engine: 52084

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post #3 of 144 Old 03-09-2011, 05:57 AM
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Because I’m just not busy enough with the V12 and house projects I went ahead and promised a couple guys I’d have a look at what can be done with 308 2V heads flow wise. My engine simulator says there are a lot of problems with what ferrari was doing engine set-up wise up though about the 348 vintage engines, with one of the items being the port/valves are just way too big for the flow the heads are making causing all kinds of bizarre pressure plusses in the intake and exhaust systems.

I have 2 different requests to answer at the moment.

The first question is what is the right head set-up for a carb 308. Contrary to what many seems to believe, weber carbs don’t actually flow ever well and severally limit how much hp can be extracted for the engine so on a carb engine the goal needs to be making the most of the carbs. The word on the street is that the Michelotto 308s used 208 heads which have much smaller valve/ports and I suspect that is exactly the right answer….and I have a loaner 208 head to play with. This is where I’ll start tonight and post plenty of pics.

The second request is what exactly can be done to get hp out of a 2V 308 with no other restriction place on the project. My software says that once the engine is fitted with cylinders ad crank form 360, the cams I picked for my V12, a custom intake and header it should just tough 450hp at 8500-9000 rpm…..if the flow number can be achieved. Even for this build the math says the stock valve seat ID is too big and will need to be reduced but the valve may need to be bigger because the Ferrari cam design limits what can be done cam wise. A big valve on a small seat will make the 2V head act more like a 4V head and work better with the possible cam options….if that combination can be made to flow. I’ll have a scrap 308 head in my hands in a week or 2 so I’ll see what can be done wiht it once I’m done with the 208 head.
What sort of ratios do you look for with intake valves vs exhausts?

It looks like the newer 4V heads have huge intake valves in comparison to their exhausts. On the 308QV, they're much closer in size.

I've been reading quite a bit about C6 Z06's lately (2V heads) and the exhaust valves are approx. 73% the size of the intakes in diameter - 55.9mm vs. 40.9mm. - which would make the surface of the exhausts something like 54% if my math isn't too far off.
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post #4 of 144 Old 03-09-2011, 09:46 AM
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I got to stay away from threads like this.
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post #5 of 144 Old 03-09-2011, 09:57 AM
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I got to stay away from threads like this.
Oh come on, a 350-400hp naturally aspirated 308 would be an aweful lot of fun and make all the right sounds...
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post #6 of 144 Old 03-09-2011, 11:51 AM Thread Starter
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Mark, you poor fellow. It sounds like you're feeling bored, neglected and unloved. I'm sure all your buddies here can help you out if you need a few more projects?

Speaking of which...... I could use some help/advise on an air distribution issue I'm having with a twinscrew supercharger on a DOHC V8. The supercharger's discharge is right above the front 4 cylinders, so they're getting all the air and run lean until the manifold pressures up. We compensate for this by tweaking the individual injector trims, then take out the tweaks when it's on boost, but this is a bandaid approach because it's obvious the front 4 are carrying the load of the motor down low.

It would be much better if we could balance out the air flow and encourage some of it to go to the rear holes, not just the front 4. The manifold design is just a simple, single plane type plenum.

I'm leaning toward putting some slide throttles inside this puppy with a pneumatic actuator to restrict the front 4 a bit while it's under vacuum conditions, then letting them open up under boost. Not the simplest solution to be sure, but then why do something simple when the complicated solutions are so much more interesting?
I had the same problem with my 308 when I switched from a roots to a screw blower. I was able to fix the low end issue by installing a diverting vane but that screwed up the top end. The final solution was to relocate the blower to the back of the intake with a longer drive. The easy solution is exactly what you did and honestly it’s not that bad really.
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post #7 of 144 Old 03-09-2011, 12:11 PM Thread Starter
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What sort of ratios do you look for with intake valves vs exhausts?

It looks like the newer 4V heads have huge intake valves in comparison to their exhausts. On the 308QV, they're much closer in size.

I've been reading quite a bit about C6 Z06's lately (2V heads) and the exhaust valves are approx. 73% the size of the intakes in diameter - 55.9mm vs. 40.9mm. - which would make the surface of the exhausts something like 54% if my math isn't too far off.
There is no simple answer there and a lot of reasons to do different things.

Modern engine have pretty small exhaust valves and flow to prevent unburned fuel from going out the exhaust….so it’s a pollution/mileage thing.

80s and earlier Ferraris have WAY to much exhaust flow for either hp or economy. The general rule is the exhaust flow should be 70% to maybe 85% of the intake flow and generally an exhaust valve wants to be closer to the seat ID size than an intake valve but it’s very much a case by case thing. My TR heads have 34mm intakes and 28mm exhausts, I think the exhausts could have been a touch smaller I think, but 28 was a common off the shelf size so 28 it was.
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post #8 of 144 Old 03-09-2011, 04:08 PM
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In the early days of water cooled VW's guys used the 2v diesel heads which had MASSIVE ports, notched the heads to fit giant camshafts and ran as much compression as possible. They were also stroking the hell out of them as opposed to spinning big RPM. The engines were making surprising power.

The best 308 numbers I personally have seen are 320HP from an EFI 2v and 400HP from a CIS 4v, both were 3.6L bored/stroked. Both engines were built by a very reputable Ferrari engine builder.

My understanding is that Webers can't keep up on the 4v heads. The idea for the 2v 308 may be more torque oriented than HP oriented.


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post #9 of 144 Old 03-09-2011, 05:25 PM Thread Starter
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I got the flow bench cleared off but didn't have time to do any flow work. Here's a few shots of the 208 head. The ports are way smaller than 308 ports....it looks like a stock 308 exhasut valve is about right for the intake and the manifold is going to need quite a bit of fill it looks like.
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post #10 of 144 Old 03-10-2011, 03:45 AM Thread Starter
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In the early days of water cooled VW's guys used the 2v diesel heads which had MASSIVE ports, notched the heads to fit giant camshafts and ran as much compression as possible. They were also stroking the hell out of them as opposed to spinning big RPM. The engines were making surprising power.

The best 308 numbers I personally have seen are 320HP from an EFI 2v and 400HP from a CIS 4v, both were 3.6L bored/stroked. Both engines were built by a very reputable Ferrari engine builder.

My understanding is that Webers can't keep up on the 4v heads. The idea for the 2v 308 may be more torque oriented than HP oriented.
In the late 80s early 90s the guys still running English motorcycle (Triumph, Norton) realized the exhaust port was a lot bigger/better than the intake port and started putting the heads on backwards to make hp.

Webers are definitely not optimal for flow. The 40mm 308 carbs set the practical hp limit around 275 to maybe 300 with crazy cams. With the 44 mm version (I think OEM on ducatis) you can get to 320 or so which is a 4V with mild porting and stock cams and well below what’s possible once the carbs are replaced with EFI….but a lot of guys like carbs for the simplicity and nostalgia so I think it’s worth the effort of seeing what can be done to make them work.

Here’s a couple sim runs for various carb engines. Notice on all these engines the torque goes flat or is dropping at 5000 rpm. That is the carbs running out of flow so IMO the best carb engines would be setup with heads that kind of match the carb flow so you get a nice wide torque curve from near idle up the 5000-6000 where the cars just can’t fill the cylinders any more. Small ports with stock carb cams makes a pretty nice engine
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post #11 of 144 Old 03-10-2011, 06:29 AM Thread Starter
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The guy who 208 head I have has a set of P6 cams and I kind of sense he’d like me to say it’s ok to keep them so I’ll spend some time optimizing the set-up around those cams…which have GOBS of duration.

The first thing is to change the lobe centers. 103/114 seems about as good as it gets without killing the top end hp and are the dark green/red lines on the graph and show a pretty nice bump to the mid-range form my generic starting point of 110/110.

I’ll also play a bit with valve OD v seat ID….I’m guessing this will want the smallest possible valve that will cover the seat hole to try to reduce the very low lift flow to try to wipe out the effect of some of the duration.

Some of the software art comes in to. Normally the OEM headers need to be called small tube but that is kind of related to tube v valve size so installing much smaller valves make re-classes the headers as large tube. This only matters on 1 or the 2 methods the software uses, but I normally report the average of the 2 methods, so it does matter that.
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post #12 of 144 Old 03-10-2011, 06:52 AM Thread Starter
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Here’s a graph of the 2 ways the software is calculating HP/torque.

The simple method is based basic pumping math mixed with data from lots and lots of dyno runs.

The wave method is calculating pressure pulses in the intake and exhaust to figure out what is flowing in and out of the cylinder so the math is completely different form the simple method.

Unless I say otherwise, all the graphs I post are a “hybrid” method. This is kind of a weighted average that trusts the simple method math more at low rpm where the wave energy is low but trusts the wave method more at high rpm where the pressure waves are much more pronounced.

In a perfect world the 2 method would both give the same answer, but that is never the case. Normally the wave model will predict higher numbers than the simple model and when it doesn’t you know your set-up is probably not very near optimal…..and on a stock 308 (or any pre-90s ferrari) the wave model pretty much chokes and provides no useful information other than the set-up is bad.
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post #13 of 144 Old 03-10-2011, 07:15 AM
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I like the direction the modeling is going, I always like to modify the cam timing slightly to give the car a more "peaky" feel. They feel dull with such a broad curve.

The 103/114 lobe center should keep the carbs from acting up in the lower register as well.

I think the P6 cams, 208 heads and properly setup (not generic OEM) intake/exhaust manifolds should give a nice set up.


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post #14 of 144 Old 03-10-2011, 07:42 AM Thread Starter
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I like the direction the modeling is going, I always like to modify the cam timing slightly to give the car a more "peaky" feel. They feel dull with such a broad curve.

The 103/114 lobe center should keep the carbs from acting up in the lower register as well.

I think the P6 cams, 208 heads and properly setup (not generic OEM) intake/exhaust manifolds should give a nice set up.
Yeah…although modern cams area whole lot better.

Here it is with P6 vs the cams I had made for my engine….but the modern cams require shim under bucket so that adds to the expense of using them. All i did was drop the cams in with no other optimization.
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post #15 of 144 Old 03-10-2011, 07:50 AM
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Interesting stuff to say the least.
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post #16 of 144 Old 03-10-2011, 08:28 AM Thread Starter
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If I can figure out how to reduce the low lift flow intake flow a bit the low end gets quite a bit better without causing much harm up top….of course I don’t know how exactly to make flow worse as I’ve never tried…..sink the valve a bit maybe….or maybe do something to the seat…..????
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post #17 of 144 Old 03-10-2011, 01:52 PM
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Well, the valves are already a bit shrouded...perhaps using a larger OD Intake valve without opening up the seat much will add to the shrouding and slow low lift flow without killing high lift flow.

Your suggested cam change actually looks good. Nice torque gain without killing the top end. What is the increase in average power and torque?


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post #18 of 144 Old 03-10-2011, 01:55 PM
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What simulation software are you using? Wouldn't mind poking around on it myself.
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post #19 of 144 Old 03-11-2011, 01:43 AM Thread Starter
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I got a little time. I opened the seat ID to 31mm and cut the seat to accept the 308 36.5mm exhaust as the intake, though on a clay velocity stack and onto the flow bench......65cfm.

The goal is 95cfm (@10" water pres) so there's a bit of work to be done.....

It's not a surprise that the number is about 65. Ferrari had some kind of formula they followed so a 3 liter V8 got 92 cfm, a 2 liter would get 2/3s of that or 64cfm. It's also not a surprise that even though I opened the seat 1.5mm the number is still 65cfm....because for some reason I don't understand the ports are hourglass shape with the choke point right about where the intake bolts on, this is true on every engine I've seen up though the 348 which is a little better then the 355 is fixed.

On the 208 heads the min dia is about 28mm at the manifold mount...it should be more like 36mm or maybe a bit more. The 308 intake manifold is about 34mm where is meets the head, so tonight I'll open the 208 port to match the 308 intake and I'm guessing that will add 10-15 CFM. After that is done the rest of the work will probably be from the guide to the seat, but I like the get the basics right before I spend any time on details.

I think these heads will work out really well for a carb car once they are sorted....I like what I see so far any way
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post #20 of 144 Old 03-11-2011, 03:23 AM Thread Starter
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Well, the valves are already a bit shrouded...perhaps using a larger OD Intake valve without opening up the seat much will add to the shrouding and slow low lift flow without killing high lift flow.

Your suggested cam change actually looks good. Nice torque gain without killing the top end. What is the increase in average power and torque?
From 1k-9k, the P6 gives 192hp/187 ftlb average and the web cam gives 194/198.

If you look from 2k-6k where the engine will spend most of its life on the street the P6 is 159hp/198ftlb v 172/218 for the web cam, so a little better than 10% gain.
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