This has been discussed in theory by Mk_e in Ferrari life...
This has been discussed in theory by Mk_e in Ferrari life http://www.***********.com/forums/projects-rebuilds-modifications/13731-308-2v-head-porting.html and are well supported by all the computer simulations and calculations I could make. I have 208 cylinder heads for this project but doubt and curiosity led me to put my 308 heads back on with the following changes while I build up the 208 heads and choose final chamber shape and CR. I used JB bond epoxy on a roughened and cleaned port floor as described below Homework. I kept the 1mm over size intake valve and settled for a minimum CSA of 1.16 sqinch = 31mm diameter port equivalent, just before the apex of the SSR. This CSA was measured with a 32mm valve with a 2cm long flat edge so as to form a D port. From the valve seat I was able to maintain 2mm radius seat below the 45 before cutting a 2mm 90 degree ( totally missing in the previous valve job ) I then set the floor height, SSR radius and straightened the walls out into the bowl etc. The effect is to raise the port centre line enabling a larger radius SSR like a waterfall into a 90 throat cut of the SSR and valve seat, before the 75 60 45 30 valve job. I used the 208 camshafts with intake 120 thou tdc ( 102 CL 24/48 ) and Ex 88 thou tdc ( 96 CL 30/42 ). First drive was a revelation, nearly driving through the car in front of me as I pulled out on to the road. I have made many incremental changes to this engine with ignition / camshaft timing and carburation etc, and thought I had gone from entertaining to competent but this change has been the most stunning from a driving stand point. The car used to make the right noises and increase in speed when asked. Now it has an intensity from 3K to 5K that makes the the front of the car bob upwards with acceleration like I have never seen before. Pulls really strongly from 1.5 k which nearly got me into trouble when merging into the traffic. I haven't pulled through 6.5 K yet and the way it delivers in spades I cant see the need would be there very often. For a road car this super responsive,forgiving and suprisingly quick. Will the shorter duration exhaust cam will strangle the higher rpm ability of the engine? How much of the performance is from the port size vs SSR shape vs the cam changes? When will the epoxy fail and destroy the engine? I need to check the 5K ignition timing ( now using mechanical distributors ) and the perform some rolling 3rd gear acceleration runs when the weather clears up to obtain some objectivity over the performance gain. Top end horsepower is unlikely to be changed without more rpm which was not the goal of the exercise. I wouldn't expect any one would do this, but it does add weight in my mind to the smaller port / longer duration cam michelotto 2v engine builds. Cheers Rob Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
3rd gear rolling 60-120km GPS time was a repeatable 5.4 sec. This is better than the best 5.5 that I could achieve with the previous configurations of cam and carb tuning. It feels quicker in normal use because of the sub 3K responsiveness which is not tested this way. Pulls hardest from 4.5 to 6.5 then falls away to 7K (its all over) The theory: The inlet port size & exhaust cam selection was based around the flow capacity of the 40DCNF and the inlet cams which flat line over the 6.5k mark on most 308 dyno charts. I sized the intake port to the 208 head. A 31 mm port is about the largest I could easily fit in the 208 intake port and should flow to 7K. The intake taper is 40mm at base of the carburettors to 35 at the entrance to the head then down to 31 above the SSR. Port volume is still large but hasn't hurt the throttle response which is the best I have experienced in this car. This includes the 34 chokes on the carburettors which are working flawlessly in this configuration ( ET 4x 1.2 mm upper holes and 3x1.2 mm submerged holes 2mm below fuel level) Exhaust blowdown has a significant effect on the character of this engine. The blowdown needs to be controlled to allow a pull on the intake charge to occur. Too much exhaust lift or early exhaust opening blows down too fast and reduces the pull on the intake charge and allows reversion of exhaust back into the cylinder when the piston descends. The large exhaust valves and ports encourage this rapid blow down which is fine at higher rpm but robs from the cars drivability under 4K rpm. With standard euro exh cams I found an exhaust lift at tdc of greater than 50 thou gave the cammy feel of the exhaust pull on cylinder filling over 3.5K . Over 70 thou tdc and the sub 3K rpm began to suffer from the increasing reversion. Stationary engines built for economy and torque often have large exhaust ports with short duration cams. Fine for that application, but they have a limited rpm window. This is true with these 208 Exh cams which really stops the car at 7K. It is on cam every where below this but strikingly so at or below 2K. I believe, and hope that the 208 exhaust port with 30mm valve head and exit size will control this blow down whilst providing greater exhaust momentum. This should provide a torquey motor with a wider rev range when using the euro exhaust cams ( or the P6 in the Michelotto cars). The question which begs to be answered is how the epoxy D port engine would behave with the standard / euro 308 exhaust cams? Are the low lift 208 exh cams holding back the intake port potential? I will do this before I pull the engine to install the 208 heads but that might be a year or two from now unless I find a reason or the energy to reconsider it earlier ( that 4l 500Hp engine build doesn't help) cheers
Curiosity overcame me. Original 228 @ 50 330 lift euro exhaust cams (vs 216 @ 50 and 305 lift) timed at the same LCA 96 which lined up exactly on the cam timing marks of the engine. This gave 110 thou lift inc lash at tdc. Impression lost some of the sharpness below 3K but gained over 1K rpm at the top end. The hit from 4.5 to 6K rpm remains but is augmented and runs through to 7.5k before fading. The carburettors that were EFI perfect with the short cams are not as well behaved now when below 3.5K. Results :- 5.2 seconds made up from the much stronger 5-7K power band. It now has more ferrari mojo than a toyota. Has the intake port/valve job helped? I can't objectively tell because I don't have real base line numbers other than exhaust tdc lifts around 80 thou with accel times of 5.5. The Forza adjustable cam pulleys are fantastic and I wouldn't have bothered with this job with out them. Deeper belt engagement, no jumping teeth on the pulleys and less belt tension required etc. Cheers Rob Image Unavailable, Please Login Image Unavailable, Please Login
Well yes. I increased the Intake lift to 140 thou at tdc (ICL 96). Acceleration time remains 5.2 sec but doesn't tell the whole story. What is lost below 5k is gained back above 5k. The car is happier to rev higher through 7.5k and feels even more enthusiastic. The hit from 5-7K is even more Ferrari like. Over 4.5k the trade off in lower rpm power seems worth it for the increased upper power band. The sweet smell of unburnt fuel from the cam overlap is more obvious now.
I did an AMC 304 engine with a lot of epoxy in the ports and intake manifold once. Tremendous low rpm power, and it made a big increase in the MPG I was getting. Ran it that way for about 4 years. I used A+B epoxy, which is a putty and much easier to place than JB Weld. When I tore the engine down, 6 of the 8 intake ports no longer had epoxy in them, and the two that did, the epoxy was loose. None of the ports in the manifold had the epoxy come loose. I attributed the epoxy coming loose in the heads due to the mismatch in the thermal expansion rate of the epoxy versus the cast iron head. I was not able to find any damage to the head or valves due to the ingestion of the epoxy. However this engine does have very stout valves with 3/8 inch stems, so the results may be different with he smaller stems on the 308. Have you done any flow bench work on the heads? The changes you made on the SSR can easily reduce the high lift flow of the port if you are not careful. If the shape is not right the air will separate off the SSR and go straight out the LSR side of the valve. When it does that it causes a vacuum on the SSR and actually sucks air out of the cylinder, recirculating it with the LSR flow. When this happens the flow actually goes down the more you lift the valve. Personally I size the intake valve, cam duration and lift, and carb choke size to give me the operating range needed. Then I size the inlet port area to maximize cylinder filling. I prefer high lift, large valves and a shorter cam duration (if possible). Large duration cams increase overlap which reduces bottom end performance (ie just off idle). Cheers Jim
Thanks for your comments. They mirror what I have observed, although I am continually supprised by the large effect the exhaust cam/port can make. I have some JB bond epoxy heads running for 7 yrs now on alloy heads but not as daily drivers and not with ethanol in the fuel. The title to the thread is somewhat misleading . It was more a scoping exercise for port size, volume, and exhaust flow in preparation for my 208 head install. I have always liked the big port short high lift cam. Under promises but often over delivers.The 308 head flow is controlled in the most part by the intake valve obstruction. It would need lift over 12.5mm to make full use of the port/throat area. This isn't going to easily happen so we are left with a valve size which might be ? Ok for torque but more open to the problems of reversion but not the lift to make power. So which parts to you optimise or match to each other? The carbs are probably the first choke point to which every thing else needs to be scaled. Flow testing the ports would have been good but I was to impatient. I spent some time wondering about how much to lay back the SSR but focussed on more obstruction than less. This means that I can lay back the port SSR as the next step of testing, before head removal. I look forward to that! Rob
I am reading this as a rhetorical question "So which parts to you optimise or match to each other?" so I will let you explain your findings. In regard to the choke size, I do not have enough data to say for sure, but I also believe you are at the point of needing 36mm chokes or larger. For your cross sectional area (CSA) calculations, are you using the actual area or the Hydralic area? Cheers Jim
Wow Jim, I don't know how you knew it but the next post was going to be "The answer to the question no one asked". And you guessed it! 36 chokes are in the carburettors already, I am just debating 140/170 AC or 150/200 AC. I suspect the fuel presentation may be lousy below 5k but I need to find out for my self. The bore/ throttle plate diameter is the limitation at this choke size. The CSA is measured area and sits the optimal air flow speed at about 7K rpm (wallace racing calculators). I just wanted to check I wouldn't be strangling this engine with smaller ports or exhaust flow. "which parts to optimise..." if I knew it would already be done, so I will just pass on findings if they confirm or deny current practice. Cheers Rob
I have my own engine model. A few years ago I did a mild port job and a little bit of modeling of a 308GTSi. Based on one model I ran I expect you are looking at something in the ballpark of 250 hp with this engine. But I do not have enough info to properly model your engine. I am not sure what you mean 150/200 AC, I assume 150 mains with 200 air correctors. For 250 hp at 7000 RPM I am estimating 150 mains. My model does not have an estimate for air correctors. Most cars I have tuned with this size main like 180 air correctors. The throttle shaft can be modified. I cut off the side that has the screw head and install a button head screw. I also file any protruding threads off so they are flush with the shaft. I am not sure what the top of the carb looks like but a good radius on the inlet will also improve the carb flow. So it is possible to get a little more out of the carb even if you are maxed out with the choke size. The wallace calculator does not give enough information, but my guess is they are using the wrong area. I also prefer a slightly lower Mach number for my calculations. The difference in areas may explain how they are able to get away with the higher Mach number with their area calculation. You should be using the hydraulic area. For a round pipe the hydraulic area and the actual area are the same. But when you deviate from that the hydraulic area is smaller than the actual area. The error in these two areas resulted in the RPM band in my AMC being 500 to 1000 RPM lower than expected (I don't remember the exact number anymore). Here's an example of the results from my model. Engine # Ferrari 308 GTSi # Cylinders 8 Rod Length Inches 5.311 Stroke Inches 2.795 Bore Inches 3.189 RPM Peak Hp RPM 7000 Airflow w Man Carb etc @ 25" CFM 124 Deck Height Inches 0 Recip Weight grams 712.0 Gasket dia Inches 3.189 Gasket Ht. Inches 0.04 Comb Ch Vol CC's 33.8 Piston Vol CC's 0 Int. Opens deg BTDC @ ~0.006" 23 Int. Closes deg ABDC @ ~0.006" 59 Ex Valve Opens deg BBDC @ ~0.006" 67 Ex Valve Close deg ATDC @ ~0.006" 15 VStem Dia Inches 0.314 Valve Dia Inches 1.668 Lift (in) Inches 0.369 Duration degrees 262 LCA degrees 112 Advance degrees 4 Results Displacement Cubic Inches 178.61 Comp Ratio 10.38 Displacement CC's 2927.43 Critical Port Area Inches^2 1.13 Acceleration at TDC g's 2818 Effective Compression Ratio 8.50 Carb size mm 36.0 2 Valve Predict BMEP psi 173.09 Peak Torque ft-lbs 204.93 Peak Torque RPM RPM 5300 Peak Hp Hp 254.1 Peak Hp RPM RPM 7000 Primary ID Recommended Inches 1.47 Idle Vacuum in Hg 18.00 Race exhuast yes, ie close to 0 backpressure Cheers Jim
Wow, Thanks for sharing for your time and knowledge Jim. I will try the 150 main / 175 AC combination on the weekend with possibly some more exhaust lift at overlap. The modeling is pretty much the optimum of what I have seen, with Hp 245 & CR 9.6. I will struggle to have a CR under 10.5 with the modified 208 chamber and my current pistons. Thanks Rob
I have been here before. 36 choke F24 with elevated air holes & 140 main/170 AC AFR 12.2@3k 12.4@7K just a bit too rich up high and still feels a little flat up 6k+. Accel time 5.3 sec. Full midrange and a great bellow when flooring the accelerator. Must be a combination of the exhaust and now increased induction volume. Put in the 130 main/170 AC for interest and had flat AFR 14s almost every where! Too lean. The goldilocks solution will be the 135 main jet, but I put in a 130 main @155 AC. = Accel time 5.3 and much cleaner AFR trace 13.2-12.4. A bit of lost time below 5K with the 36 Choke. Now for the top end weakness. The computer simulations for these camshafts indicate In105/Ex105 ICL would best preserve torque over 6.5K with the least loss below that number. So I moved my cams from In95/Ex95 ICL (140/110 thou tdc) to 105/105 (100/80 thou lift at tdc ). A big change in overlap! With the 36 chokes the accel time is now 5.4. The real story is the better low speed behavior < 3K when pottering about and better brake vacuum. This time is a little better than a previous 5.5 (34Choke) when using exhaust 80 thou tdc lift but Intake lift 130 thou. But the real revelation is the top end. It continues to make power to 7.5K+. The engine always fell over above 6.5K ( felt flat) and more recently I could carry some momentum through 7K. It now continues to accelerate and makes the corners seem much sharper than they used to be. Not so much 5.5K mid range exuberance but some real high speed pace. The top end may just be mostly cam rather than port flow related. Hope to work that out with the A-B-A test of the epoxy removal. Cheers Rob
A simulation based on 2V head flow data with Ferrera exhaust valves and +1mm oversized Ferrera intake valves. I haven't corrected for the overly optimistic VE but the trends are what you can feel when driving with the different cam settings. 10 Hp more between 3.5 to 4.5K and a fuller top end, or 10 Hp 4.5 - 5.5K hit ( 65 vs 75 Hp change from 4 to 5K) Bring on VVT. Cheers Rob Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
The top end may just be mostly cam rather than port flow related. Hope to work that out with the A-B-A test of the epoxy removal. The epoxy is now gone! What a b@s$#&d of a job. Before the epoxy I had hand cut the SSR to achieve a 2mm 90 degree throat cut before forming the turn to the port floor. Removed the epoxy with tungsten carbide tools and chisels down the intake ports, no sanding rolls or grit contamination. Widened the outer cheek at the SSR down to the port floor continuing the port bias off the centre line. All checked with the inspection scope. Port shape 40mm to 35mm at port entrance to 32mm at start of the SSR. Retimed the cams to roughly 97 CL Intake/100 CL Exhaust, after way too much studying of computer simulations for these euro cams. Thinned the DCNF throttle shafts to improve the fuel signal for the larger chokes. First run with the 36 chokes and narrow band AFR. Lots of noise and revs but anaemic 5.8 & 6 sec and lean < 500 mv. Second run 34 chokes with old jetting. 5.0 sec accel 60-120kph and still lean at 650 mv ! But the real action is above 120kph ~ 7K. I never believed these cams could support up to 8K, but with the choke point opened to 32mm+ and a decent SSR it's there for the taking. I can't detect any loss in torque or throttle response having removed the epoxy. Through the gears is even more impressive with the accel pumps covering up some of the leanness in the current jetting. More fuel and some dyno numbers will be interesting. Take home message is to have your SSR shaped by someone who knows about these heads if you fit larger intake valves. Cheers Rob
Hi John, I am using the F24 with elevated 1.5mm lower air holes. These tubes are really quite rich when stomping on the accelerator due to the large fuel well volume around them but the higher low holes tend to damp that behavior. There is less fuel for them to elevate. The smaller air holes also seem to reach saturation (choke) at high flow and stop diluting the fuel delivery and enable a flatter fuel delivery curve. I will get road and/or dyno AFR confirmation in the next month or so. Just accelerating through the gears, even with the stoichiometric fuel delivery I can't get over how much power I have been missing over all these years! I feel quite stupid about it, assuming the shop that did the valve seat work had sorted the SSR to suit the larger valves.
Could someone please summarize, in plain simple terms with no acronyms, what this is all about? OP dove right into a lot of technical stuff without any preamble.
This thread was spawned from here: http://www.ferrarichat.com/forum/308-328-sponsored-yellow-compass-group/423336-dcnf-progression-tuning.html and led to : http://www.ferrarichat.com/forum/308-328-sponsored-yellow-compass-group/445918-cam-lca.html The acronyms are discussed within. Hope that helps Cheers Rob
Hi Rob, If it's not too much too ask could you give me your thoughts on using the CAT cams 1700402 cams on a carb 308 with a 348 crank (81,25 bore x 75mm stroke.) Static compression will be about 10.5:1 and I am not going to do any welding of the ports (just planned to match carbs-manifolds-ports and clean up around the seats.) I don't want a screamer but a traffic driveable car that can pull nicely to 7k and sounds like a Ferrari should http://www.catcams.com/products/camshafts/datasheet.aspx?ENGINE_id=137&CAMSETUP_id=413
Okaaay .. well I am an engineer albeit an ancient one and still a bit confused. I get that your 308 has lackluster power and flat spots in certain situations. Owned enough of them to sympathize on that point. So you are fiddling with the carburettors and the valve timing ... some improvement. Now you have figured that if you narrow the inlet ports in the head you will get some more improvement, but this requires relooping through the whole valve timing exercise .. how about cutting to the chase and telling us what kind of incremental BHP you can get out of these motors via all of these adjustments and what the new torque curve looks like? And does any of this translate to injected motors? It seems that the narrow port thing just borrows performance from WOT to improve partial throttle performance. (Yes I can use acronyms!). There's another guy on here that claims significant improvement in BHP by using a bigger plenum and some other stuff to improve inlet flow that seems to contradict your findings, can't find the posting right now. And what's next ... more aggressive cams? Exhaust manifold and piping? And finally what about emissions? Some of these cars are still subject to emissions testing in many states. I suspect there is a reason Ferrari set the cars up the way they did. The carb'd cars are hard enough to smog at the factory settings.
Russ I can't speak for Rob, but I enjoy this sort of thing. It's the journey (the experimenting and learning) as much as it is about the destination (a better performing car and the satisfaction of achieving that.)
This: "Four separate and distinct areas require possible reworking to minimise the effects of pressure reversion, if not eliminate them completely. First, the exhaust system flange and primary pipe should be about 1/8-inch larger on all sides than the port opening in the cylinder head. Second, the intake port face in the cylinder head should be about 1/8-inch (1/4-inch on the diameter) larger than the intake manifold runner, then the port should be funneled down to more normal dimensions as it approaches the intake valve. Third, the intake manifold runner should be about ¼-inch larger in diameter than the carburetor throttle bores, and the runners funneled down to a smaller dimension at the manifold mounting face. The idea is to make deliberate mismatches at these three points. The reasoning behind this is that there is pretty conclusive evidence that the downstream pulses (the good guys) take the shortest distance to get where they're going, while the reversion pulses (the bad guys) stay close to the walls of the carburetor, intake manifold runner, intake port, exhaust port and exhaust pipe. The deliberate mismatches make abrupt changes in cross-sectional area, which are highly beneficial in damping the unwanted reversion pulses. In addition, the air/fuel mixture traveling downstream is pumped into areas of lower-than-normal pressure, which in itself, helps induce a larger volume of mixture into the cylinder, and the same is true on the exhaust side. Edelbrock Equipment Company has made a couple of prototype manifolds incorporating the mismatch concept for the L-16, L-18 engines with encouraging results for a first attempt in damping reversion pulses. The fourth are that may require a change is valve timing. By itself, valve timing can have rather dramatic effects upon the presence or absence of pressure reversion. If a reversion problem exists, the changes should be made one at a time and in the order shown until the problem disappears completely or is at least helped considerably. At the points of mismatches, leave the edges square and sharp. DO NOT ROUND OFF THE SHARP EDGES! Perhaps strangely, there are highly modified L-series engines with no reversion problems at all within the normal operating speed range."
I experienced the same with F24 tubes. I had best luck with F36 tubes but changed the float level 2mm so there was just a small amount more fuel in the float chamber. This helped with the transition that the F24s seem to help with, but at the cost of idle tip in. Might want to try 1 size larger main just but with around a 150 air corrector. A larger main jet typically brings the fuel on the main circuit a bit sooner.
I have searched for the Ferrari 308 Performance Handbook, or 101 Projects for Ferrari 308 etc but have failed. The information is not easily accessable and some of it is just steeped in myth and inaccuracy. Most of what I have done is more of a diary and a direction than instruction. Roughly right rather than precisely wrong. The summary of what I can say up to this point : The DCNF carburettor as supplied can be improved upon both in terms of drivability and emissions. Cam timing changes the whole character of the car with the euro cam sweet spot at 96-98Intake/98 -102Exhaust with the smaller numbers for the lower compression builds (less overlap and lower emissions). No dyno charts, only acceleration runs and my impressions.. Port shape does not benefit from reduction in volume leading up to or including the short side radius. I don't know if the loss of the hourglass waist at the head entrance made any difference. The short side radius is really important in a port where flow is limited by valve lift . This would be true in the plenum EFI setups as well. Most EFI plenums are too small in volume and many are restrictive in runner size for normally aspirated applications. I have no experience with the ferrari efi manifold and the last WUR CIS system I handled was put in a box when I replaced it with EFI. I will put up the images of the catcam HP/TQ vs euro in a std crank then in the 348 crank 10.5 combination in the next day or so. The intake valve to piston clearance will dictate how much advance may be possible compared to the catalogue 105/105. The larger the overlap, the more the exhaust system will influence the results particularly below 4.5K. I am still using the 1.88 Inch OD venturi inserts at my collector outlets, but once again can't prove their percentage worth in torque preservation. Cheers
