posted on November 25, 2009 20:59
Extreme Engine Tech: Technosquare's Monster Naturally Aspirated Toyota 4AG - Part 2
By Mike Kojima
In our last edition of the building of Technosquare's monster Toyota 4AG, we mainly looked at the details of the bottom end. Now we will finish our tour of the bottom end and delve into the engines cylinder head which is the heart of any high performance engine.
The 83mm x 83 mm stroker motor gives 1800cc. The 200 extra cc's makes a huge difference, fortifying the 4AG's notoriously narrow power band. The engine cranks out over 250 crank hp, more than the most highly developed Formula Atlantic engines of yore and 30 more hp than the previous 1600 cc version of this motor. On a Dynopack chassis dyno the 4AG ripped out 216 whp, a hell of a lot for a naturally aspirated 4AG. You have to remember that a RWD set up typically robs 20% from the crank power levels vs the 15% more efficient FWD transaxles typically steal.
|Wiseco forged pistons are used. To maintain the best possible stroke to rod length ratio, the pin is moved as high in the rod as possible. It even intrudes into the oil ring groove slightly. Strut type construction is used for light weight. The skirts are moly coated for less friction and better wear of the skirts and cylinder walls. The dome volume is set to give a 13:1 compression ratio. Technosquare deburrs and cleans the dome of all sharp edges which could result in hot spot causing detonation. The pistons feature double pin oilers and use a tapered wall lightweight 20mm tool steel piston pin for minimal weight. This is the post 1988 4AG pin diameter, up 2mm from the older, weaker, flexy 18mm pins. The pin is retained with Cosworth style round wire retainers.
|This close up shot shows the radical pin placement, intruding into the oil ring groove. This sort of design usually has higher oil consumption but allows the longest possible connecting rod for an improved rod ratio and lower piston speed. The piston has anti detonation grooves between the top of the piston and the top ring. These grooves buffer the detonation shock waves and protect the top ring. The also reduce the contact area high on the piston for less friction. The grooves also reduce expansion at the top of the piston to reduce the likelihood of scuffing under extreme heat. A pressure equalization groove between the compression rings improve ring seal at high rpm by acting like a reservoir for leaking combustion gasses, improving the seal of the second ring.
|The rings are fairly conventional. The upper compression ring is a narrow 1mm chrome face design. The second compression ring is a 1.2 mm iron ring. Both rings are low tension for reduced friction and less likelihood of flutter at high rpm. The oil ring is a conventional 2 rail design.
|The stock 4AG valvetrain uses shim on bucket valve adjustment. This system has trouble at over 8000 rpm and 8.5mm of lift. The cam lobes tend to flip the valve shim off of the top of the cam follower. When this happens the cam lobe beats on the retainer and causes the keepers to fall out and the valve to drop, destroying the engine. To prevent this from happening the valve train is converted to TRD Formula Atlantic stuff. Double valve springs are used with titanium retainers that are designed to accept a small adjusting shim. The cam follower goes over the shim preventing it from getting flicked out by the cam lobe. You can see one of the small adjusting shims next to the cam followers. This is called a shim under bucket system and is used in motorcycle and other high RPM engines. TRD big valves are used, they are 2mm bigger than stock. TRD Formula Atlantic cams are also used, 320 degrees intake duration and 304 degrees exhaust duration. Both cams have 11mm of valve lift. The cams are set on a 102 degree lobe center.
Wednesday, November 11, 2009 10:52 AM
Great article as usual Mike.
I have a few questions:
Doesn't the TRD logo stamped onto the valve create hot spots?
Would a flat head valve increase the compression ratio? Why TRD did not use it/ or consider that?
Also, when big cams are used (like in this case). The shims have to be replaced to accomodate the bigger lobes. How do you know which shims thickness to use?
Thanks in advance for your time, and keep up the great work!
Wednesday, November 11, 2009 11:13 AM
You all have covered some impressive builds so far... Any chance of a turbo Rotary build-up in the future?
Wednesday, November 11, 2009 4:32 PM
with a build like this being NA. Why didn't they opt to have gas ports incorporated into the pistons to help with gases. Also what type of rings are they using? Nitride steel top with napier second? I'd like to see them use a hell fire ring their next go around.
Thursday, November 12, 2009 7:31 AM
Great to see this overachievement. I'd like to see the flow bench results from the head work. (For us mere mortals looking to only improve what we have)
Hopefully you'll show what this goes in and what you do with the fuel injection. I'm recommending MegaSquirt as it concurs with my budget.
Thursday, November 12, 2009 10:12 AM
Some answers to the questions. The hot parts of the valves are the edges, not the face, this is typically the coolest part of the valve. If the valve face was flat the valve would weigh a lot more. Its easier and less detrimental to performance to reduce the chamber volume by other means. As far as shim thickness, these are Yamaha FZR motorcycle shims and its impossible to tell you how thick they would be because there are many variables to that, remember that valve clearance is set with these so the valve depth, wear, etc really affect this.
As for turbo rotary stuff, Eric Hsu is a rotary expert and I am good friends with the Berganholtz brothers so its a possibility, I just have to be in the right place at the right time.
The article has a whole thing on the rings, look up and read. I am noticing that gas porting seems to be falling out of favor for some reason that I am not sure about. It was envouge about 5 years ago. My piston engineer friends say that gas porting greatly reduces ring life and they are eliminating it or greatly reducing the number of ports from previous designs.
Dunno about the flow results but Hasselgen was the premier formula Atlantic Toyota engine builder and they had impressive results. However I was less than impressed with the quality of the porting and headwork on this head. Howard Watanabe of Technosquare was also not impressed and he touched the head up to improve things in the valve pocket a little and unshrouded the chambers more.
We will be featuring the AE86 time attack car this engine goes into sometime in the future.
The engine will probably use 48mm webers although a more modern fuel injection system may be used.
Thursday, November 12, 2009 10:34 AM
i read the portion on the rings but it doesnt distinguish whether or not he is running a napier or not. Ring failure I've seen on boosted applications with gas ports to be more prevalent however on a NA build we have not seen any adverse affects if the proper precautions are dealt with. I look forward to the rest of the build.
Thursday, November 12, 2009 10:49 AM
Like it says the rings are conventional. I don't think Napier rings are all that common. I think they have issues with oil control and long term life as the second compression ring has some oil control functions. I don't know of any engine builders that use them outside NASCAR, but perhaps Eric might chime in here.
I don't think gas porting causes ring failure, just faster wear. What precautions besides the obvious cylinder wall finish and end gap do you do to prevent problems?
I defer this sort of stuff to my piston engineer friends and don't try to second guess them.
Thursday, November 12, 2009 12:37 PM
Webers? Go with what you know, I guess.
Individual throttle bodies are available from the 20V 4AGEs, although I am not an expert on the manifold interchangeability. Club4AG.com would be a good reference.
Aside from that, all the other sensors for a good EFI system came with variations of that engine.
Thursday, November 12, 2009 4:32 PM
Napier rings have the most oil control out of any of the rings used. I only use these rings for both street and race applications. The standard rings used with Wiseco are napier second scraper rings. CP uses a second compression ring for the oil ring with little to no oil control to them. They state they like to run a larger than normal gap to help with oiling issues vs. having a dynamic ring act as the work horse. I personally don't like that. I want a functional ring to work all the time. Believe me I know the engine being built will run extremely well I was just curious as to why they didnt opt to go napier and so forth.
Thursday, November 12, 2009 5:17 PM
Its kinda odd because it was my understanding that Napier rings are for engines with dry sumps or other apps with sorta dry cylinder walls. I also thought they were for short duty cycle engines as well.
Are you talking about using another compression ring as a scraper instead of the normal 3 piece oil ring???
Thursday, November 12, 2009 5:17 PM
The engine uses TWM throttle bodies and Autech ECU.
Saturday, November 14, 2009 3:53 PM
Nope we used them from Nascar/Pro Mod/Outlaw/Drag/Motorsports. CP piston uses what appears to be a second (thicker) compression ring for the second ring. They still utilize a 3 piece oil ring.
Saturday, November 21, 2009 10:58 AM
I have a 5A motor going together also but using a HKS Crank turns out the stroke is 3.265 instead of 3.267. I have Carrilo rods with 18mm wrist pin. The crank has 40mm mains. good to see all your hard work paid off. I am already planning a 4.5AG long rod motor ha ha
Tuesday, December 15, 2009 10:16 PM
A couple points:
1. Cool. So rare to see 4age builds.
2. I think it would be neat to see a tech analysis of the mythical 9age (7afe block, 1zzge 95mm crank, 83mm bore for ~1950cc).
3. As to a possible turbo rotary build, I would look up Mark Warner, as he is a bit of a rotary nut, and turbo book author to boot. And a real P.E.
Wednesday, July 04, 2012 10:26 PM
I see in the cylinder head porting that the bosses for the valve guides are shaped but not removed. Are they necessary from an airflow or valve guide support perspective? Or can they be removed without penalty?
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