Toymods Car Club Inc: Tech & Conversions => 2TG verses 4AGE Facts !

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Bill Sherwood
Forums Junkie

Location:
Brisbane / Gold Coast
Registered:
May 2002

Re: 2TG verses 4AGE Facts !	Sat, 01 June 2002 09:10

I'm not going to do the pages and pages of diatribe that I used to do, I'll try to keep it short. For road use, the shim-over bucket is fine. The reason is that with a 4AG you don't need to run as much cam as you do on the 2TG to make the same power. The reason for that is the extra breathing of the four valves that the 4AG has. Some numbers. The area of the 2TG valve at 10mm lift is 15.07²cm, (48mm diameter inlet valve) the area of the 4AG is 19.16²cm at the same lift. I'm not sure what the stock lift is on the 2TG (been a few years) but at the stock 4AG lift of 7.5mm (the area is now 14.37mm) the 2TG would need to lift the inlet valve 9.5mm and I don't think they've got anything like that lift stock. You can also run the 32mm (or even 33.5mm) diameter inlets in the 4AG's, so the flow can be proportionally more. Putting bigger valves in a 2TG is hard to do, as you run into clearance problems with the valves on overlap. The 4AG with its smaller cams & valves & included valve angle doesn't have anywhere near as much problem. Speaking of this in the combustion chamber, the 2TG is pretty ugly indeed. The 4AG has a pretty good chamber, and to get good compression you don't need a big dome on the piston like the 2TG does. The squish areas on the 4AG are also much better. Yes, I used to muck around with the 2TG's, with the 88220, 88222, and 8261 heads so I know a little about them. The shim-over buckets will run a 0.360" (9.1mm) lift cam, I've done it for a while but it's not a good idea long-term. I'd say more like 0.330" would be much safer. The shim-unders will take a 0.380" lift no probs - that's what I run right now - though I've seen 0.440" lift used. (too much IMHO) Anyway, this is the main part of the reason why you don't need such a big cam in a 4AG to make them go well, they don't need it. I won't repeat it all here, but a very good comparison is made on my 'Two valve Vs four valve' page, where I talk about the old 1300cc 3K race engine Vs the 1300cc Suzuki twin cam. The 3K ended up being pretty much a cranky full race engine that made less power than the Suzuki. The Suzuki uses ~275° 0.355" cam, which are really just big road cams. The 3K used 12.8:1 compression (we had to cheat and use 20% toluene in the fuel to stop it pinging) while the Suzuki runs regular 98 unleaded with 10.25:1, as per the rules. The 3K had valve gear trouble past about 8800rpm, whereas the Suzuki is rev-limited by the rules to the stock 8000rpm. That's the difference that a decent multi-valve engine can make over a well-worked two valve. If you're going to compare stock engines then the power figures are there to see, as added above for the 2TG & 4AG and they speak for themselves. If you're going to talk modded engines, let's make it street ones. Mine's a street engine and it makes a genuine 140ft-lbs odd and 190hp odd. I also get a genuine 42mpg and it drives much like a normal car. I'd like to see a 1600cc 2TG do all that. My next 4AG will have more like 230hp in street trim, and it'll also drive like a normal car. How much would you have to spend on a 2TG to get that amount of power, and how driveable will it be? If you doubt about the power of my car, then just ask Shano2 and/or MR2-V, Haydn, as they're both been for a ride in the car. I mention 1600cc again - like I did earlier - to be able to compare apples with apples. IF you're going to talk 1900cc odd, then that's not a reasonable comparison, and so by those 'rules' I'll use a 3SGE which is much closer to 1950cc that the 2TG can be taken out to. The best 3SGE I know of is in the British Touring Car series, and they make up around 310 - 320hp at reasonable revs (8500) and I'd guess about 185ft-lbs. Again there's no way a big bore/stroke 2TG is going to make anything like that. Rod mentioned 200hp odd, and that's more like it. Rod also wrote, "Formulla Atlantic run a Shim Over* set up". No they don't, they all use shim-under. I assume that this was a mistake. "Lets face it Shim under really does suck"* As was that. "As for the Cosworth comparison your point is ???" The point is that it's a copy of a well-proven and highly successful competition engine. The BDA is known to work very well indeed, and so a good copy of it can only be a good thing. FWIW, the head on the small port 4AG has much the same porting as the BDA, but the design of the head on the 4AG is much neater indeed. "RPM Limits - Bill you say a "Stock" 4AGE bottom end will handle 9000rpm. Was that with truely stock rods or were they shot peened and linished ?" I assume that they're stock rods, as when I got the engine in 1990 I never touched the bottom end, never even took off the sump. I would not recommend using more than 8500rpm much though. "Statements on personal preference are not what I want." You didn't get one. "Statements like your initial post do noone any favours least of all the lesser informed." I stand behind what I say. If given the choice, there is absolutely no reason why you'd use a 2TG over a 4AG. If you want something with more capacity, then there's always a 7AG and then a 3SGE, both of which will obviously make more power than the equivelant T engine. The only advantage that a 2TG has is that it can be bored quite a lot and it has a shorter stroke, that's it in practical terms. Classique71 - That 240hp is straight from a guy that builds them, Jamie Aislabie in Rotorua. He said that the best he ever got was 242hp, and that's at the flywheel. [Report message to a moderator]

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