2T-G/3T Hybrid Compression Problems

[sillycar chick]

Okay, so I've seen a lot of threads on this topic, but no-one seems to be having the problems I am having....

I am building a 2T-G/3T hybrid on the cheap for my daily driver (TA22), so I want to be able to run standard unleaded on it (since fuel costs a fortune these days). I have put the engine together and done a compresion test at got 200 to 210 psi per cylinder (manual says 165psi). This is with an 88261 head, 3T-C standard pistons (flycut of course) and even with a 0.55mm thick head shim! I am thinking this is about 11:1 compression ratio from my rough calculations.

I am aiming to get around 9.5:1 so I dont have detonation or pinging problems. I am about to trial a 1mm shim.

If anyone has done this conversion using the standard pistons, I would really appreciate some advice, so I hope someone can help!

[kayzee]

If you're going to take the head off, why don't you "cc" the combustion chamber while you're at it

[3T-GTE]

Going by my rough calculations (& fading memory) you should have a compression ratio of around 10.8:1.

Adding 1mm to your head gasket will drop it down to 9.7:1, as will cc-ing an extra 5-6ccs out of your combustion chamber.

While you've got the head off, just to make sure you don't have to worry about pinging... I'd also make sure that it is free from carbon buildup - that tends to cause "hot spots".

Good luck.
3T-GTE

[sillycar chick]

I cc'd the head chamber and top of piston using burette and some acrylic plate on top, and when I calculated out the comp ratio, I got somewhere around 8.9:1. So the 210 psi doesnt seem to make sense, if its 8.9:1 it should be around 170 psi? May be I stuffed up somewhere...

And the heads be cleaned up and valves re-lapped in a shop, I always like to at least get the head reco'd when its off, so I should be safe in that respect.

Head is going back on tomorrow provided I dont have any interruptions, so hopefully it all works out. Thanks for the advice!

[SeptemberSquall]

HJ Gaskets in Melbourne do custom head gaskets in two thicknesses (i think approx 2.8mm and 3.5mm) to suit 2T-G, give them a call if it would help with your problem.

[river]

Hi,

Sounds like a lot of effort and not very cost effective (as well as detuning a nice engine) to save a few cents a day.

Assuming you do 10,000km driving a year, and you get 300k per tank then you'll need to fill the tank (10000/300) 33.3, let's make is 34 times per annum.

Let's assume you put in 40litres per fill @ 1.20 per litre for standard unleaded. This will cost you (40 x 34 x 1.20) $1632 per annum.

If you used a 98RON unleaded @ 1.35 per litre, this would cost you (40 x 34 x 1.35) $1836 per annum.

By using regular unleaded over 98RON you will save $204 per annum, which is $3.92 per week (56 cents a day). Crikey, it will cost you more to buy a cup of coffe per day then it would to put 98RON into your car.

I'd hang the cost for better engine performance. Maybe if the price difference was getting up to $500-$700 per annum then I'd think about it. Also, if you're spending more than $400 in getting your engine detuned to run unleaded, then that's 2 years of 98RON petrol you could be running without having to do any detuning on the engine. In 2 years time you might have a better job and be getting more money and able to cope with the extra few bucks a week to put petrol in your car.

If, financially, you're sailing so close to the wind that a cost of $4 per week is going to break you, then I question the reasons why you're spending money on all this engine work, which surely isn't cheap.

The figures I used in the above example were indicative prices, and as petrol prices seem to constantly fluctuate, it's hard to put a definitive cost on the sums. Also the kms travelled per annum, kms per tank and litres per fill are indicative. You'll need to put in your own figures to get a more precise value.

seeyuzz
river

[SeptemberSquall]

Hi,

Sounds like a lot of effort and not very cost effective (as well as detuning a nice engine) to save a few cents a day.

Assuming you do 10,000km driving a year, and you get 300k per tank then you'll need to fill the tank (10000/300) 33.3, let's make is 34 times per annum.

(snipped all the calcs etc etc etc)

That's all very nice, but I think the point is that 11:1 compression is going to be pushing into detonation territory on the old hemi chamber design, even on magic premium pump fuel. After that, Martini or Elf fuel is much more than $4 per week more expensive. But it's not just about the fuel cost, it's about long term reliabilty.

[o_man_ra23]

I was running 10.5:1 compression with 98 ron fuel and heavy timing with no pinging. Also, if your worried about detonation, retard your timing a few degrees, or better still disconnect the vacuum advance off your dizzy and set the max timing to about 28 degrees instead of the optimal 33.

Cheers, Owen

[river]

Hi,

But it's not just about the fuel cost, it's about long term reliabilty.

I didn't address any reliability issues in my post 'cos these concerns were not mentioned by the originator. Yes, if your engine is pinging then it will cause damage and this is not a good thing.

What oman23 said can help with the pinging. Also you don't need to drop it all the way to 9.5 comp ratio - you can get away with 10 or a little over.

The fact that this is a hybrid 2TG/3T engine implies the owner wants a bit more performance than over a standard 2TG and therefore (it appears to me) defeating the purpose of having such an engine if you aren't going to put the best fuel into it. In terms of reliability, initial & running costs, leaving the standard 2TG engine would of been the best solution.

In any event, when it's all done I'd be interested to hear how the engine performs running on standard unleaded.

seeyuzz
river

[sillycar chick]

Wow river, you really put a lot of thought into my question!

Just to keep you all updated, I have just done a compression test with the 1mm shim and got 175psi per cyl, which I think equates to 9:1, just over the standard 2T-G setup. The 2T-G I started with came from the wreckers and I had no idea of the condition of the engine, so I pulled the head off to find it could have done with a rebuild (lots of carbon and sludge build-up).

And septembersqull is right about the reliablility factor, as it is a daily driver. I needed the right compression ratio so I dont have to strip the engine down for a rebuild every 18 months.

The main reason I tackled this project was because my dad tried this conversion years ago and ran out of time and money, and I really wanted a challenge to build up my experience. So I had every part I needed at no cost, except the head reco at $400 and VRS gasket kit (cant remeber the price). My dad even had a 1mm shim he was going to try, but never got that far.

My ride will be up in the members rides forum soon, so you can see what I got for $1100. I think when you add it all up, Im still under $2000 for what I think is an awesome reliable daily driver in terms of value for money, with a little bit of poke just for fun!

[river]

Hi,

Wow river, you really put a lot of thought into my question!

To do anything less would be a disservice to your question and search for knowledge, myself and the Technical Forums.

I wait with eager anticipation to see pics of your ride and the successful conclusion, with write ups, of your project.

seeyuzz
river

[Celica RA45]

you should be able to run 11to 1 comp ok on mobil syn 8000 the fuels these days are better than when the old 2tg was running on 96 super .
just a note my 2tg had a comp ratio of 10,8 to 1 so 11is not far off .
my new engine is 12 to 1but that is a 4valve a cyl motor
as river says and me get it dyno tuned so they can fix timing and jetting done

[sillycar chick]

I have always thought if you are going to run things to higher compression ratio, the engine wont last as long unless its designed for it ie. stronger components, balancing, higher quality bearings, rings etc to withstand to extra forces exerted inside the engine......???

I would love to build an engine with higher compression ratio, but I would go all out with forgies, shot-peened rods, complete balancing etc. which costs money :-(

As I mentioned, I was given all the parts for my 2T-G/3T and had minimal to spend on the project, so I am aiming to have a reliable run-around while I get started on my major project, my RA28 sitting in the shed waiting for some paint and a decent donk! Just gotta save some dosh for now!

[o_man_ra23]

The 3T and 2T setups were quite good, even in the -C models. They will all handle the extra forces of higher compression, and the decent RPM (balancing isnt expensive on a 4 cyl) Id say go for the high compression, itll help with low down torque.

Cheers, Owen

[pro_k]

2TG with 11:1 Compression runs fine on mobil synergy.

Like River said it will be a shame to get less performance out of an already built engine. No point going backwards to save a few $!