2TG-3T Hybrid Discussion

[af300e]

Just thought of something else.
There doesn't seem to be any sign of light detonation on the crown of your piston, just bang, and it blew the ring land out. Maybe you just leaned out for a short period in the front carby? Anyone else have a theory?

[jeffro ra28]

Since this has happened twice on a said good setup.

Please answer one question for me.

Was the engine dummy assembled by you or your machinist prior to machining/flycutting the pistons? both builds?


MAN, those valve reliefs are WAY to deep!

Cutting that deep and wide on the valve relief kills any ring land stability that piston ever had. Combustion stresses would deform that ring land area like an inbred retard, causing it to flex then break then it all turns to shit and the whole lot breaks away.

I think that really is a piss poor effort. It looks like he was intending you to use a 80mm intake valve or something. No offense.


I actually got away with taking SFA away from the valve reliefs when i built mine, I dialed in my cams with slightly wider lobe centers however.

This is stock piston

[jeffro ra28]

Mixture looks ok no 4 point scuffing on the skirt so it's not getting hot from a weak mixture.

Cheers Dave.

Actually, lean mixtures may cause a decrease in temperature.

How can you judge a mixture purely from a piston crown color or scuffing?

[Celica_73]

Ok the dummy fit and machining was done by the engine conditioner.

Second the reason for the decompression not that you can't run an engine at that compression ratio but the cast piston can't handle the force (what the engine guy told me anyway) to run high CR you need forged pistons. I know what you need my CBR600RR runs 12.5:1 and runs on 91 fuel with knock sensor but think they have forged piston different head design.

Another point the refills actually needed to me machined deeper as to get correct valve timing isn't possible with those cut and the valves are over size couldn't tell you how much Rod (The Toyman75) can tell you that as it was his head.

[af300e]

I know what you need my CBR600RR runs 12.5:1 and runs on 91 fuel with knock sensor but think they have forged piston different head design.

Knock sensor is a bit different as it will just retard the timing (within parameters) until the knocking stops. That's why I cite the dirt bike as an example of running high comp on shit fuel. No knock sensor, no fuel injection etc. (Sorry if i'm stating the obvious).

Head design makes a significant difference, 12.5:1 on pump fuel would probably strain the design of the old style head but wouldn't expect 12:1 to be outside the realms of practicality and 11.5:1 would be fine. You may be able to achieve 11.5:1 with a thicker head gasket and that could save you some bucks.

Which head are you running?

I'd research the forged piston thing, I've heard that above 80hp/L you should use forged items. That gives you about 100fwkw if you are 1.7L. You have one RS piston now, so that offsets the cost of forgies

[Celica_73]

Not buying new piston or rings! Current rings are still fine and the and I have 2 good piston left from the first rebuild which are being used.

Your 80Hp/L I have heard that but using that formula Toyota should have had forged in new as the 2TG was around 75Hp/L so really all hybrid should be running forged piston. You'll find many don't. As the formula is only a guide.

The new engine guy does build race engine and has been for 30 odd years so I trust his judgement and yes that include 2TG and 18RG engine from what I've heard Include a hand full of 2TG/3T hybrids

[af300e]

Your 80Hp/L I have heard that but using that formula Toyota should have had forged in new as the 2TG was around 75Hp/L

2tg's are 120hp from factory? Is that what you are saying?

[Celica_73]

yes the 2tg is factory stated as 120hp

[af300e]

Not bad at all. Still, another reason for forgies is revs, eg cbr600 redline at what, 15,500rpm? What did the standard 2tg rev to? 7000? A toyota casting is pretty good too.

[Celica_73]

Did a bit of google search on piston and found this article

http://www.enginebuildermag.com/Arti...e_pistons.aspx

States late under the instalation section about compression ratio limits of pistons

"For most naturally aspirated street engines, 9 or 10:1 is about the recommended static compression limit for 93 octane pump gasoline. An engine with aluminum heads and/or forged pistons tends to run cooler and may be able to handle a little more compression, but not too much."

Granted that is for 93 octane and will be running 98 but I am also aim at 10.5 which i know is low to most people standards but should be drivable and still perform reasonable.

"Piston-to-valve clearance is also a very important consideration especially with long duration cams and oversized valves. The standard rule of thumb is to allow at least .080" of clearance for the intake valves and .100" for the exhaust valves. The valve pockets that are machined into the piston must also be the right one for the type of heads that are used. Consequently, aftermarket heads that have a different valve angle than the OEM heads will typically require different pistons"

Engine guy told be I had 0.060" clearance currently and cam time still not correct.

Jason

[allencr]

MAN, those valve reliefs are WAY to deep!

+1

What happend to pic #3?
That piston looked like it was an attempt at high-compression, high-lift AND non-interference!

[jeffro ra28]

Engine guy told be I had 0.060" clearance currently and cam time still not correct.

Jason

Gee! i wonder what sort of cams you have? Well maybe what makes it look so deep is the fact he cut the valve releifs suit a 80mm valve or something ridiculously large!.....

I cant remember exactly what i took from mine but it wasnt a great deal and i used waggot 256 duration @ .050" lift cams AND decked the block 1mm to gain some positive deck height.

Anyhow.........

[Celica_73]

Ok Good news Engine is running and producing pretty good power.

So quick update
Cams used are Camtech Profile 401A
Current CR is 10:1.

Piston from last destroyed engine pictures included as you might be able to see the valves were just touching the piston. There are also photo of the the new piston machining used in current build beside the old cracked piston.

Current results from the engine on the dyno
Max power was 151bhp @ 6500
Max torque was 140ftlb @ 5000

rpm bhp tor
2500 52.1 109.4
3000 66.4 116.2
3500 82.2 123.8
4000 101.5 133.5
4500 119.1 139.4
5000 133.4 140.2
5500 139.6 133.4
6000 149.7 131.6
6500 150.9 121.9

Those interested final carby jets were MA 170 M 135 P 60

Cheers again for all those who gave advise
Jason

[w810sc]

well done 151 BHP! those are good figures.
You say those are the results form the engine on the dyno -
so 151 x 0.7457 = 112.6 kw at flywheel.
I wonder what figures you get when you dyno it in the car? eg: drive train losses.
keep us posted.

fonz

[Celica_73]

From what I understand and researched.

"Horsepower loss through drive train is a constant percentage based on the type of transmission you have. A manual transmission loses around 15%-17% of engine horsepower and an automatic transmission loses between 20%-25%."

For those interested
151 = 112.6 kW
140 = 189.8 Nm
128.85 = 96.05 kW
125.3 = 93.44 kW

So going off that 151bhp at the fly minus the 15-17% would be 125.3 - 128.85 bhp or 93.44 - 96.05 kW at the wheels but that sounds way to high compared to other engine in the forum. I would have guessed 114 bhp or around 85 kW at the wheels at the most. No plans for to do a power run on the Chassis Dyno due to the cost.