Its been a while back since I have done this engine type. Looking back at this experience, I have come to the conclusion that this is very much like the V8′s I have worked with all these years sans the other half, and I have a 4 cylinder!
This 2TG comes with a 2-valve full “Hemispherical Chamber”. This is the same as the Chrysler 392-426 Hemi Head V-8.
This particular Cylinder Head design was the scourge of Top Fuel Engines from the 1960′s to now with just a little change in the Hemi design.
Besides Top Fuel dominance of this design, it was also the scourge of the “Stock & Super Stock” NHRA racing. This gives this design considerable potential that if an individual decides to Supercharge or use High Compression ratios, this can Embarrass a lot of our new High Tech Engines…
From my conversation with Engine builders from here in the US to the Phillippines, one thing comes absolutely clear to me…
The 2TG’s that are being built to run on the streets do not have enough “COMPRESSION”. It is at a disadvantage if run with anything lower than 12.5:1.
When this is built for the streets, compression ratios of 9.5:1 or 10.5:1 is usually used. At this compression ratios it is at a distinct disadvantage as i explained in the previous articles about chambers.
This Hemi Chamber design is lacking a “Swirl” component in the ports flow characteristic, this design lacks response in the low-mid RPMs. However as soon as higher engine speeds is attained this is where it shines….
When a Hemi headed engine is boosted by a Supercharger or a Turbo, now it is at its Best! This is due to the “Straight Crossover design of the Intake Valves”, which is directly in front of the Exhaust valve. This design, at High RPMs, is a tremendous advantage as the gases don’t have to make a 90-degree turn from intake to exhaust port.
I also noticed that when individuals put a stroker crank, they run the same rods that are far too short to start with.
Now when you add this much more stroke, the Rod/Stroke ratio becomes really bad. Cylinder wall side loading and internal reciprocating drag goes up… Result = Engine failure if you’re making serious power. If you’re not, then you’re probably lucky, but not for long…
For any “High-revving 4-cylinder engine”, keep the stroke smaller than the bore size.
The net effect is an engine that has a lot more bottom-end torque than previously. However, top-end RPM will be lower than before if the same induction and camshaft is not improved or upgraded.
If the induction and camshaft is upgraded to the next level, your RPM capability will still be limited by the bad stroke and rod combination.
However I noticed that these engines exhibit a lot of RPM potential.
The engine does not respond very well to changes easily as it could have, if it had the proper compression ratio as it was designed to be run with.
That being the case, if High Compressions past 12.5 is attained, this will be much more responsive to changes in cam, carburetors, and ignition improvements.
What does it need to be a serious Engine? I would keep the stock stroke, run the longest connecting rod possible and move the piston pin as high as possible to get the rod length!
And give it a lot of compression and run race gas. The result – A killer 4-cylinder!