oldeskewltoy

The whole purpose of this head is to experiment with porting ideas, and then putting those ideas to the test - using a flowbench. With that said, a few things besides the head had to be arraigned - for one setting up and re-calibrating the flowbench. Up to now I've either had 82mm, or 84mm cylinder sleeves, this was the first time with the 86mm sleeve. Besides the new sleeve, the bench surface had to be prepared to "take" an SR20 head. I need a jig to keep a hand drill square so I can drill the appropriate holes........ said jig speaking about drilling the appropriate holes....... |blink| .... you'd think Nissan would have stuck with metric.... have you ever tried to find a 15/32" dowel??? Good luck!!! I eventually found a company who would make me 1000... at the cost of $195.00 :no: So... its time to see if I can make something that will work... 1/2" thick wall aluminum tubing... add an inline cut.... and viola... 15/32" dowel.... now that I have the dowel solved... lets go to the bench..... **IF** I were to try and use a "conventional" layout, the holes from the Toyota heads would interfere with the new holes needed for the 15/32" dowels... so a slight rotation of the layout provides me an unmolested area to drill to receive the dowels. So with the new adapter, and a new mounting solution set up, I re-calibrate the bench for the 86mm adapter, and so now that the bench is ready....... More to come...... :D

Yes..... BUT I can't measure inside the flowbench sampling cylinder. The head is sealed down against the bench. I can measure inside the port. (I guess I could make a jig so I could either blow through the intake port, or draw through the exhaust port and then have the cylinder affixed to the head and THEN measure around the valve head.....) BUT if you are asking if the intake valves are too close "A" (shrouded) to the cylinder wall for a good draw.... they might be(I doubt it), but there are far more flaws to address that are far easier to quantify/fix before I worry about valve shrouding. I needed to make another tool....... very simple caliper A stock intake port is approximately 27mm (+ or - 1mm) and 100mm long @ that diameter A stock intake splitter is approximately 24.5(+ or - .50mm) wide.... So... how much "extra" material is around the HLA? Maybe the first question should be What is an HLA? HLA = Hydralic Lash Adjuster - for simplicity think of this as your shims for adjusting valves. An HLA fills with oil and acts as a fulcrum for a "Y" shaped rocker. The HLA fills and removes the excess gap between the rocker and the cam. middle example is stock set up The HLA is 17 mm in diameter, making the HLA hole 17.0something in diameter, but surely under 17.1mm... so subtracting 17.1 from 24.5, that leaves us about 7.3mm of unnecessary splitter width. What we don't know is how evenly set the HLA bore is in relation to the two bow-legged intake ports. Exact HLA placement inside the splitter is as yet not fully determined by me, or a photo or some other evidence I've been able to find. The cut away shown a number of posts above doesn't include the HLA :( The view below kind of shows it, and yet it isn't specific. What you can tell in the view below is the HLA does interfere on the intake side, while it appears to not be an issue on the exhaust side. So, by simple mathematics there is SOME room along the splitter for removing some material to help "straighten" the port, and remove some of the bow-leg the ports follow. This will help, but my little home made calipers found another problem.... no guessing on this one.... we know the valve is 34mm, the bowl/seat @ 29mm, and now.... Think about that for a moment... the port = the throat for nearly 4" of length. The "throat" in an intake port is the narrowest point inside the port' date=' it is designed to help speed up airflow a short distance from the valve. This narrowing also limits reversion(the air/fuel charge "bouncing" off the closing valve and moving back up the manifold). Often times, especially in performance engines, the throat is preceded by a gradually tapering section that goes out to the flange, and it either connects to an intake plenum, or an ITB. The tapering section is similar in principle to a velocity stack. The SR20, having a "throat" 4" long only chokes down the air volume by having a set diameter through this part instead of a tapered diameter. So if, along with straightening out the air passage we can add a taper to each port, in theory, we should be able to see noticeable gains in volume, with minimal loss in velocity. So lets move on to what all this means.... Intake port - 4 panel as it transitions from stock to "within the lines" = inside "stock" openings - note I have not increased the opening size, I've worked within the original casting, and at no time have worked beyond that. The outermost green dotted crescent highlights that the area just inside the ports edge got the majority of the work, and not the edge itself [img']http://ost.ebeans.ch/albums/userpics/10005/sr20__1_intake_port_4_panel_1k_pixel_tall.jpg[/img] Look carefully... in the 2nd view down I diagram what I'm doing. Note the orange dotted line, it shows where I worked the splitter at its widest point. It shows I changed the shape, that I removed a bit more material from the roof and floor of the splitter while taken only a minimal amount from the splitter wall. Remember our measurement of 24,4mm, that is at the narrowest point at the center of the splitter, but do to the extreme arc of the port, the splitter at the roof and floor are closer to 40mm, and with care offer up a LOT of material that can be removed if done carefully... as shown by the time you get to the bottom view. The other green dotted line/arc show additional areas of material removal. They also begin to highlight the narrowing, and shaping of the splitters leading edge. So... why did I leave a large section of the port walls untouched? A unique view... 3 slightly different angles on my SR20 port work. Cylinder #2, my control, on the left, cylinder #1(within the lines) on the right... ... these views help to show how I've worked the top and bottom of the splitter, it also shows how I've shaped the bowls to blend into the seats. The top view shows the splitter roof, the center view shows the center work, and the bottom has more of a focus on the splitter floor. Also the short radius blending is plainly visible. This photo also shows I left a large portion of the port walls untouched... so I ask again... Why did I leave sections of the port wall untouched? more to come..... :D

A few different views of the SR20DE port passages.... Now compare those views with a few others..... Same similarities... while there are other differences.... Two of the views above seems to show the SR20 intake ports to have a similar shape to a Formula One design :thumbup but hold on... the F1 design doesn't have an HLA to avoid :mad:, the top view showing the port layout is our issue here. The port opening is marginally 50mm (do to costs, the port opening varies at the seam from 49 to 50), the intake valves are less than 9mm apart from each other, and the HLA makes the port splitter somewhere close to 23-24mm at its widest point.... and so you get a bow legged intake port..... More can be done here ... mostly because this is a production automobile head, and as such typically there is enough casting material available to better shape, not only the intake port... but often the entire head. The SR20DE has a 34.25mm intake valve Our valve seat ID measures... doing the math... the seat bore is almost 86% of the valves diameter. This percentage is very good for a stock set up, typically I try to get the bowl to 85%-90% of the valves diameter to equal the seats bore. So since the seat is in the range, only minimal work will be performed on the seat. As I begin to work cyl #1(staying within the lines). The very first things I look at is the seat and bowl alignment. This SR20 is far better than a few of the 4AG heads I've worked, SOOOO the focus on the SR20 intake seat/bowl is the short radius.... #1 cylinder - Note the protrusion on the bowl on the right(#1 valve), it doesn't have to be a lot, that protrusion you see makes the low lift airflow stagnant because at the valve the air/fuel charge has to navigate a sharp angle. The #2 seat/bowl shows the initial reshaping of the short radius. A bit more work in this view, the #2 bowl is showing mild re-shaping to allow more volume. I'm careful to port areas that will "straighten" the angles, or in this case do my best to minimize the bow legged effect. With that in mind note I worked the outside of #2 bowl(far left of bowl on left). This minimizes the angle, that the air/fuel charge has to navigate. A similar, yet not quite as significant amount of material was removed from the inside(right) of the bowl on the left. A slightly different perspective... showing the overall shape of the bowl and seat transition - the key areas to note in this view are the 3 and 9 positions inside each bowl Lets get back to our control... #2 intake bowls, and seats So what I've done is increased the area around the bowl for the opening valve to draw upon. More to come........ :D

first..... thank you for at least playing along.... :party: The plate is not for overboring the valve guides. "from another forum" bingo... it is the tool I'll be using to set the valve openings.... Here is a sample of it in use... the use is to show you the viewers that I can set this tool at any height... note the tool on the bottom of the photo... and note the valves @ the top of the photo. note one side is set much further then the other. That shows that I can adjust, and set each valve anywhere I want during flowbench testing Now being able to set the valves is important... just as important is knowing exactly how much... so I plan for the plate to accept a dial guage to read the amount of lift and the finished tool...... The dial gauge will "read" from the edge of the spring retainer and a view mounted to the head.... This tool is imperative in correctly reading the flow through the head. It allows me a VERY reliable - REPEATABLE method of measuring the valve lifts so that I don't "cheat". How can you cheat? Simple really, just be off by .001" or more and the reliability goes out the window... a PERFECT, ACCURATE valve setting tool is required to provide reliable figures Now that the valve setting tool is finished, its time to re-configure my flowbench to measure the SR20 head. Last Summer(2014) I had a new bore adapter "machined" to 86mm so I could begin to check cylinder heads that use that bore... (3SG, 1/2JZ, SR20, FA20/4U-GSE, and a few others....) I will then place an SR20 headgasket on the bench to determine where the alignment dowels will be drilled into the flowbench table to properly align the head over the 86mm bore adapter. Here is the "view" the flowbench will see... More to come....... :D

Let me drop a few more hints.... halve 29.... Does that make it easier... or harder??? What am I making??? :ninja:

No guesses... really? Not even a shot in the dark? :eatlead: How about a few hints....... The lexan sheet you see is just a template....' date=' the final version will be in steel [img']http://ost.ebeans.ch/albums/userpics/10005/normal_SR20_valve_setting_plate_lexan_and_steel.jpg[/img] Does that make it easier??? How about if I add that the "14 1/2" you see written on the steel plate refers to degrees, does that help at all???

Initial impressions.... the casting itself is a bit rough, more deburring could be done to the castings, especially the top of the head which holds the cams and valvetrain. The chambers on the other hand appear to be well placed, with very little evidence of edges that would promote detonation (ping). The intake paths are bow legged shaped to allow for the HLA, the intake seat/bowl could use blending to better take advantage of the angled port, and mild short radius. The exhaust bowl/seat is far worse, significantly too small, the port provides little or no room for an adequate short radius, while the splitter, port roof, and narrowing walls are far too intrusive, and appear to truly restrict airflow. Too begin with... as this head is one for discovery.... and as such I'll be performing different porting on 2 of the 4 cylinders, leaving 1 cylinder to use as a control. What do I mean when I say "control", I'll be using my flowbench to monitor any gains, or losses do to my porting work. I'll be leaving #2 cylinder and its ports completely untouched. I'm leaving #4 untouched for the time being, but may use it to "assemble" the knowledge I learn from porting #1 - within the lines, and #3 - outside the lines.

I've seen quite a few threads in Rollaclub showing SR20 swaps. As I've done some porting on the SR20, and I have a new client whose SR20VE I'll begin porting next week (if all goes well on delivery to me). Between now and then I'll drop a few photos, and some flowbench results from my "play" with a highport SR20DE Not a lot of fwd heads around so "beggars"(me) couldn't be choosey. For those who know something about SR20s... this is a 2.0 liter dohc 4 cylinder - fwd "highport" 1st gen SR20DE. It uses HLAs (hydraulic lash adjusters) as part of the valvetrain Obviously the first thing to be done - was cleaning up the mess And for easier imagination the paths through the head have been marked out in Sharpie The intake and exhaust bowls have been measured - nothing fancy so far... Intake: Exhaust: Observations Intake: the bowl and seat work allow the valve to breath to its maximum, the intake valve head is 34mm. Typically the best compromise is somewhere between 85% and 90% of the valves diameter should equal the bowl/seat. The SR20 is pretty good straight away at 86%(29.2mm). Short Radius - the short radius is the only place to easily increase the overall valves draw on the port. A un corrected short radius that interferes can have little or no air flow at lower lift points. This will hurt overall filling of the cylinder, and lower power Exhaust: The exhaust valve is 30mm, using the same formula (85%-90%) the seat/bowl should be at least 25.5mm(85%), but stock exhaust seat/bowls are only 24.7mm on average(82%). The short radius was garbage interfering far worse in the exhaust port then it does in the intake. more to come..... :D

thank you.... JDM AE86 is not likely to happen, but 1st, and 2nd gen Camry shouldn't be a problem..... would you happen to know now MUCH longer they are???

Over a 2 year period from 2012-2014 I had driven Surreptitious less than 1500 miles... a lot of this was because a certain tuning shop (in Hillsboro Oregon) had no idea how to properly set and program the FJO system. :down: Shortly after I swapped in the 6 speed she went back for a "final" adjustment. LONG STORY short.... once I got it back the last time.... I had to "fix" cam timing, (they had adjusted it to make their tune work...???) and swap in the earlier tune :bash: Move ahead 2 years(Spring 2014)... Surreptitious goes to Loynings, and is tuned on their steady state dyno. She is "tuned" in each rpm band for power. Off to DEQ(emissions testing) and fails.... 1100 HC, 5.0 CO. I bring her back in, they make a few adjustments, I go back to DEQ... 214 HC, 0.447 CO - She passes :party: and no new cat required this time.... :thumbsup: Now as far as performance.... She idles...(between 1000 and 1100) she idles and doesn't stall when coming to a stop... she idles with all the installed electrical draws on (lights, wipers, heater fan, 100 watt fog lamps) she even idled with the cooling fan on @ the inspection station without stalling or stumbling while the test was being performed... This tune is only a few days old... but so far it has inspired some new confidence... what was never a problem... she always (with one exception) planted great power... What is odd... I'm only running 2 BTDC degrees of ignition timing... OPINION: They did the reverse of what I thought to be needed..... I figured more timing (not less) would make it want to idle up.... What they did was feed in the less timing and they opened up the throttle plate a touch. With the throttle plate open' date=' this lowers the pressure in the manifold... and so when there is a change like vacuum being drawn to run the brakes... or a alternator puts a load on the system there is less pressure change in the manifold... less pressure change, less unstable idle.... and so it idles pretty well under loads now. The above is the change after the failed inspection.... [u']BEFORE[/u] the failed inspection... They did a lot of changes in the map... the fuel map especially. If you remember the 2nd tuning shop had set the original fuel map as best they could... but with a 6mm hole in the manifold he did the best he could. Once I found the hole, and fixed it I DEPENDED on the self learning feature to "fix" the fuel map. Well... now she has a dedicated fuel map built on a steady state dyno to keep AFRs(between 12.5 and 13) in the peak range to make power, and protect the "fragile" OEM cast pistons from detonation. So, back to the car.... with my new found trust in her overall character... and to signify her change from temperamental toy :( ... into reliable, dependable toy :) She gets her first new set of wipers in over 5 years a set of Anco Aero Advantage..... Why?? Now that she runs well besides wipers working, I felt it is time to finish up the parking brake. I should have kept the lengthening to 3/4"' date=' I did about 1 1/4"(length of threads) and although it now works, I have little room left for further adjustment... If/when that time occurs that it is out of adjustment, I'll cut off the bindings and place the two sections a bit tighter together... but for now... we have a working parking brake..... [img']http://i79.photobucket.com/albums/j143/oldeskewltoy/ae71/handbrakefitted_zps5310a07e.jpg[/img] more to come..... :yes:

"Tall" can be relative.... when I had my AE86, I used a Richmond 4.10, but that was still rowing the T50. Part of the reason I went with the 3.9, was the J160's 1st gear of 3.874. The T50 uses a 3.587 1st gear. So with the J160 first, I effectively have a very similar 1st gear/final drive ratio as someone running a 4.30 with their T50 1st. In essence the 3.8 first, and the 3.9 final are like keeping the 4.30, and adding an extra tall O/D. As to highway speeds, I'm turning about 3400 @ 70 mph, which delivers about 33mpg. At 3400, I'm already in the torque band where it is at, or over 100#/ft at the wheels(this begins at about 3300), and I can smoothly accelerate from there in top gear. so yeah... it all fits together nicely a short ride in my car - apologies for picture quality, but audio is rather nice :) -

Wow... I kinda dropped the ball..... :wasted: Oh.... that timeslip... was with the 5 speed and my car was still equipped with the original highway gearing - 3.58 final drive!!! :no: Now... not only add in a 6 speed with oh so better ratios... but the final plan also incorporates running a 3.9 final drive as well! Back when I ran the 15.77, I didn't give much thought to it... but the 6 speed and shorter gear might even allow ME to get her into the 14s??? BUUUT... with the S series 3.58 final drive... in reality... I don't need any gears beyond the first 4 8| Sooooooo... its time to swap in a final drive more appropriate. Here is Richmond Racing's 3.9 T series diff...... (originally for Legends/Dwarf cars) fitted into a GT-S housing. The Richmond is assembled with zenki spider gears... so zenki axles are the call. The emergency brake cables need a fabricated bracket on the driverside(thank you Jesse), and a zip tie around the axle hop line mount to secure the passenger side cable. Now... along with the diff, I have to swap in a different brake proportioning valve, because instead of drum brakes... I'm now running rear discs. Doing some research All USA AE86 drum brake cars use valve 22040, while the GT-S uses valve 12040. I then look up my car, and low and behold, the valve is the same as a drum brake AE86 - 22040. So even though I have a different master cylinder, AND the proportioning valve is mounted slightly lower, the lines will not have to be customized to fit the GT-S valve! So I remove the drum brake valve, and swap in the GT-S valve. Then I go about bleeding the brakes. At this point brake bleeding can be a REAL pain... because there is no longer any fluid in the master OR the proportioning valve... so I go about palm bleeding. What is palm bleeding??? You fill the master most of the way, and you put your palm over the reservoir and work your hand like you would a toilet plunger.... This slowly pumps the fluid through the master, and the proportioning valve allowing me to circulate the fluid without having to pump the brake pedal, or use a power bleeder. All new TRD suspension bushings will tighten up the whole rear end keeping the axle properly placed under the back of the car. Many folks don't know but there is a right way... and a wrong way to install TRD suspension bushings....... Care was used to install the bushings correctly. More to come....... :D

and a bit closer of a view of the worked short radius compared to the unworked side At this point the head was shipped back to my client, so he could have the head re-surfaced and re-assembled.

#2 on left and #1 on the right On the intake side all I did was knock back the guides, and guide bosses, and made the bowls round to fit/follow the valve seats.... OH I also added a very gentle short side radius.... and opened up the bowls a bit as well. Here we are with 4 chambers, 4 exhaust ports, and 3 intakes finished... More to come.... :D

and now that the one unfinished port get finished..... a bit more to come....... :D

correct on the 172... best I can figure one, or possibly both of the valves were incorrectly adjusted..... for that reading a few views of working the exhaust side..... minimizing the guide boss, and tapering the guide - both to minimize their effect on the outgoing exhaust flow reshaping the exhaust port a bit of before and after.... slightly different perspective... more to come..... :D

Anyone??? How about some help..... the glaring error is the ported side @ .200" lift, 177.33 is incorrect.... anyone care to guess about how far off it is???? I had a talk with my client, he is hoping for an exhaust to intake flow ratio approaching 80%. This is going to be extraordinarily difficult because the stock Blacktop flows about 61%, and the first attempt at porting the exhaust side did improve things, now 67%, but a further gain of 13% seems a long goal at best. My first attempt at porting the exhaust was limited because I didn't have a gasket to know where my edges were, and I didn't want to port beyond the gasket, for doing that would cause serious flow issues. So the initial porting on #4 exhaust was from about 33.6 to about 33.7, because not knowing the exhaust gasket left me a bit in the dark. My client sent me the OEM gasket Port on far right is #4, even with the gasket in the "down" position, there is still some room available in the port roof, and room all the way around the port. So now that I had a gasket, work begins on #2 exhaust port. Redline in the 2nd panel is the gaskets edge. A bit more dramatic.... The stock Blacktop gasket outlet is 36mm. Port #2 is now out to 34.8mm(on right), the previously port #4(to 33.7mm) is on left Later this week I'll get this on the bench and see what if any improvement there is over the first numbers. as a reminder.... the numbers @ 28"....... Ported Exhaust (#4 - port on left) - .050 - 35.38 .100 - 65.88 .150 - 93.73 .200 - 113.50 .250 - 130.63 .300 - 139.92 .350 - 146.33 "New" exhaust port readings, #2 port - on right .050 - 34.98 .100 - 65.03 .150 - 93.67 .200 - 113.32 .250 - 131.88 .300 - 142.53 .350 - 150.92 The reason testing stopped @ .350 was my client is limited to 9mm of lift (.354") So now the intake @ .350" is @ 197.8cfm, while the exhaust is now @ 150.9, the exhaust to intake flow ratio is now a tick over 75% at peak lift, and over the lift range the exhaust to intake ratio is now about 71.5% (was 61%) More to come..... :D

the intake side..... paper towel in exhaust port is acting as a "cork", remember these are used valves, in used seats, and stuffing the opposite port to the one being test allows for honest figures. The numbers @ 28"....... Unported Intake - .050 - 58.15 .100 - 110.87 .150 - 146.30 .200 - 168.30 .250 - 180.08 .300 - 186.65 .350 - 191.22 .400 - 194.10 Ported Intake - .050 - 60.02 .100 - 114.30 .150 - 149.20 .200 - 177.33 .250 - 185.47 .300 - 192.33 .350 - 197.78 .400 - 202.35 There is a glaring error on one reading, can anyone find it??? I likely over adjusted one valve, What should it read (about/approximate)?? setting up to do the exhaust side Unported Exhaust - .050 - 32.45 .100 - 65.52 .150 - 90.95 .200 - 110.12 .250 - 122.80 .300 - 130.25 .350 - 135.48 .400 - 140.43 Ported Exhaust - .050 - 35.38 .100 - 65.88 .150 - 93.73 .200 - 113.50 .250 - 130.63 .300 - 139.92 .350 - 146.33 .400 - 151.20 More to come...... :D

Alas... not the intake side.... A friend of mine has done some intake port molds.... My focus will be mostly on the exhaust side. I will be reworking the intake as well, but initial inspection reveals the newer 4AG heads are cast better then many of the older 16V heads.... at least this 20V head is. I begin on #4(left), since the bowls already merge pretty well with the seats, my biggest task is a to "build" a short radius, to minimize the intake guides, and guide bosses, and to gently straighten port/bowl mismatches. #4 is on the left... you can also see where I've done some mild blending in the chamber, of the factory machining marks. And to the exhaust on #4(left).... I seem to remember the info "out there" saying the Blacktop had 35mm exhaust port outlets.... I measured these, they come in around 33.6 ish mm. The ported one is about 33.75mm..... this was before I had an exhaust gasket to know the port limits. Besides the re-taper, I've also "rebuilt" the shape of the guide bosses to minimize their effect on flow past them. I've also added a minor radius to the exhaust guides to further minimize flow disturbances The view from the chambers... With #4 mostly finished(right)... #3 has been cleaned, and #2(left) is still a bit "carbon coated". As I did with the SR20 head, I'll be doing with this one. I'll be mounting this on the flowbench a bit later so that I can test the 3 ports all on the same day, and under the same conditions. This will allow me to quantify the port work. more to come..... :D

I recently was sent a 20V Blacktop (Noir Crowning) head...... so once unwrapped and set up on the bench.... inspection begins.... Over all the casting quality has gotten much better. Although there still is port-bowl-seat shift, the shift amount - at least in this head, is minimal. There is one REALLY, and I mean REALLY odd ball bit........ the 3 intake valve seats have NO semblance of an even 3 angle... Looking into the Blacktop service manual the 3 angles are suppose to be 30, 45, 60. Well the throat cut - 60 degree cut, in essence is the bowl angle and so the back of the port (highest pressure area) has no effective throat cut, while if you look carefully, the throat cut at the short radius is so small, it also becomes more or less insufficient... and the the throat cut between the two... is nothing short of an extreme change - from a width @ the back of the port of almost 5mm, to the width at the short radius of the port of less than 1mm. One thing is certain - the factory put a lot more effort in to making the bowls and seats as smooth a transition as the factory could do... the bowl machining marks you see are not by me... those are all factory machining Adding some more info.... The heads thickness measure..... My dial caliper is likely off by .001" and getting a chamber volume and it is very close to SamQ's 37.8cc measurement.... I'm closer to 38cc Further inspection...... shows a few issues on the exhaust side... look @ those casting marks.... as they travel from the bowl to the port. Also the small "step" in the machining/casting hurts flow, especially at lower lifts. More to come........ :D

seems simple enough to me... costly... yes, although $3000 gets(got) you a fully assembled J160 with theLEEN adapter AND the LEEN shifter relocation - it is bolt it with a T50 bell housing and unless I can raise $30k... the LEEN will no longer be available :((

just released....Elizabeth Tan - "Somewhere New" - E7 drifting @ 3/4 the way through...

from another forum You can also do the same with the shims...... I have about 100 3.0mm shims... thinking of using the shops shim grinder' date=' and then finish with 1000... make my own batch of thin shims - down to 2.3mm or so from another forum... Great question! Many people have earned their masters, or doctorate writing on this very subject. My education in the subject began when I built the engine for Surreptitious. Using the TRD Bible as a guide, I worked the combustion chambers to minimize all the sharp edges caused by the factory machining. I then brought the head to Loynings Engine Service... a well known Formula Atlantic builder. It was there I began to build a relationship with the shop. I was allowed in, and allowed to see the Atlantic heads upclose. I spoke to their lead head porter and he gave me some advice and offered some guidance. The rest I've gleaned from many other sources..... I'm a member of a number of forums where I'm the one doing most of the learning ;) The 2 theories... a) are nearly moot when discussing a 4AGE. This is because the fuel is only added directly above the valves in a 4AGE, in a carbureted application this might be more of a concern since the air and fuel are mixed and travelling through the ports together... BUT Most people who argue/discuss atomization, or laminar flow tend to minimize the effect of the dynamics of an engine. These dynamics are the airflow is NOT consistent... the airflow in an engine is dynamic it moves toward the valve, stops, moves a little away, and then moves toward/past the valve into the engine. This means the air stream is not flowing, but is more like the dance called the bunny hop... 3 steps forward, 2 steps back.... It is harder to say it helps atomizes, or laminar flow when the airflow is not smooth, but buffetted. b)removing too much material from the chamber is a bad thing... you lose something called port reversion but removal of some material is required so you can remove hot spots from the chamber that cause ping/pre-ignition. A simple explanation of port reversion is a valve opening inside a funnel, the valve opening is always a metered opening thus keeping velocity up as the valve opens. So it is a trade off, the fact that the 4AG head is cast as it is means there is more advantage to CAREFUL material removal so that compression can be raised increasing the engines ability to make power. Port reversion tends to lessen as the valve angle increases. Port reversion works great on GM LS series, or other engines were the valve angle is less then 15 degrees, the effects of port reversion lessen as the valve angle increases. The 4AGE has steep valve angles. Now as far as my bowl and seat work, I'm mostly fixing flaws that occur because the head is a mass produced part destined for corporate profit, so flaws creep into the equation. I remove the flaws. Now as an example of why flaw removal is important, someday watch a stream, or brook, watch how the water interacts with the stream bank, watch the eddy currents, now watch a water slide... no eddy currents.... So, I've discussed the bowls and seats, and chamber deshrouding... but I have not yet discussed my exhaust port re-taper.... ;)

In my 4AGE powered AE71, I'm using the blacktop flywheel, the late (smallport AE92) pressure plate, and disc. When I was using the T50, it all worked along with the T50 throwout bearing and clutchfork. Get the flywheel, and pressure plate balanced... Benefit:over a kilo lighter, yet it is all OEM