PreCup temp .. (1 Viewer)

[Tapage]

Hello there .. well let's talk about pre cups and IDI ..

My head temp ( usually fresh ) runs about 176 rolling with easy around the town .. if I push it, will go 180 plus .. if I nail it .. i can go over 200 with easy .. ( I have lots of fuel and 14 PSI of boost on my 2H ) while my EGT's still low or at least lower than my head temp ..

 

[gerg]

Your egts can't be lower than your head temp. What's your question exactly.

 

[Tapage]

There is not real question more a debate .. I know the nature of the beast .. one of the first things I did back in the day when I just got Tencha ( back in 1996 ) was install a VDO Pyro ..

Few months later I start playing with fuel and so on ..

 

[gerg]

If its a debate, what is your position?

 

[GTSSportCoupe]

This has potential to become an interesting coversation....some food for thought:

Toyota made ceramic pre-cups for a special edition 2LTHE. Can still buy the heads new...expensive though. Although a cool idea, it was a short run and DI won over anyhow.

I run a waterless coolant which prevents localized boiling around the pre-cups. I imagine this helps more efficiently carry heat away from them and helps keep them from overheating and cracking.

I run water/meth injection...when the water turns to steam during the compression stroke it absorbs heat. Might help cool the pre-cups.

Intercooler helps too...cooler air coming in helps.

Lower AFR is probably good for pre-cups. More boost, less fuel.

At the end of the day DI wins...no precups to worry about.

 

[Tapage]

If its a debate, what is your position?

IDI sucks !

Pre Cups sucks cracks and are problem to happen down the road ..

Guess IDI Toyota engines are not meant to be tweaked for more power ..

 

[Neil826]

I was looking at tapping the coolant gallery behind each precup with a small line to bleed out any steam before damage is done

 

[ZombieResponseUnit]

IDI is awesome. I found all 6 of my precups cracked on the H, but that was after a lot of over heating. I'd recommend not twiking these motors. If you're in a hurry to be somewhere, just buy a modern vehicle.

 

[gerg]

Heat up a piece of steel red hot and watch for cracks. You will wait for a very long time. Heat does not cause metal to crack. Cooling it tempers the metal. Cooling it rapidly tempers it more so. Tempering metal makes it harder and more brittle. This eventually leads to cracking, especially around sharp angles at the opening of the precup. I radize my precups when I port them to decrease stress there. Common metal working technique as crack want to propigate off of sharp angles. Cool the metal more slowly and from lower peak temps will decrease tempering. Idle your truck before shutdown and let the precups cool a bit along with your turbo.

If you "tweak" an engine for more power does the fuel inside have to burn hotter? Think about that for a second. More power means more heat, but not necessarily higher in cylinder temperatures. You can also achieve very high in cylinder temps without a turbo and very low power tunes, just have a very dirty air filter and a 1 1/2 inch exhaust pipe. That's a pretty common combo actually for older trucks. Tweak an engine for more power and run cooler egts is totally possible, just add more air.

IDI engines create high cylinder pressures due to high compression ratios which limit power potentials. That has absolutely nothing to do with precup design. Lots of assumptions going on here with little understanding of the problems.

 

[Tapage]

If you're in a hurry to be somewhere, just buy a modern vehicle.

Never in a rush myself .. but since I like pushing the limits there is Tencha doing it best with 40" chained and locked .. you, gearing along, turbo, fuel 2.5" straight pipe etc etc etc .. still get's hot ..

It's not an EGT problem .. it's a hi comp, with 14 PSI, load issue ( never a problem ) .. to correct ( better said handle it ) down shift, reduce throttle and all will be good.

As I said I got the nature of the beast ..

Precups are just the first point of failure ..

 

[gerg]

Precups break because of neglect. It is not a performance issue.

 

[Tapage]

Precups break because of neglect. It is not a performance issue.

neglect coz we ( I ) push it ( 2H ) beyond the Mr. T established limit ..

 

[GTSSportCoupe]

In theory, IDI engines can make more power than their DI cousins. Reason being they can achieve higher rpms. HP = Torque*RPM/5250.

Problem with all IDI engines is the heat absorbed into the head via the pre-cups. Makes for wasted energy (less economy), and stress to the head components through hot/cold cycling. Not much of a problem for low power to displacement ratio normally aspirated engines. Add a turbo and things get challenging.

I've pushed my little 2.4 to a power to displacement ratio of 60hp/litre (~145hp). This is like a 2H making 240hp or a 1HZ making 250hp. Certainly pushing things. I've done a lot to improve the motor, but probably the best damage prevention measure is the waterless coolant I put in. No water, no boiling, no steam, no hot spots. IMHO all turbo diesel IDI motors should run the stuff.

 

[gerg]

So when you say push it beyond estabilished limits, what do you mean? You assert its bad yet dont explain your logic.

 

[gerg]

I agree you've pushed your 2h beyond its design limits in regards to cylinder pressure and ringland strength, but your piston will die long before your precup will, all things considered equal. How does increased cylinder pressure or even increased incylinder temps cause precups to crack?

Nick they also make more power because they can run richer air fuel ratios and still keep egts in check.

 

[Tapage]

Nick they also make more power because they can run richer air fuel ratios and still keep egts in check.

coz the pre cups and heads it's taking it and then warping heads .?

They meant to take X amount of fuel at X cylinder pressure I'm certainly over that X number in both .. so I guess I over established limit of it or what it was designed for ..

 

[gerg]

No the prechamber is more effective at mixing the air and fuel than DI injectors. The swirl chamber is quite a cool gadget. It's why IDI engines can run much higher rpms vs DI engines. Unfortunately you loose lots of heat energy into the head.

Combustion temps don't warp heads. Overheating your coolant and boiling it in the head warps them. Never heard of anyone warping a head due to egts. I think if your egts were so crazy high you would melt a piston first.

 

[Tapage]

Well that's exactly my point ... looking to make more power ( beyond the Mr. T designed limits ) put more pressure on the cooling system that it can handle .. and then despite still having EGT room to go further .. water temps / head temps are the limiting factor ..

So at the end you can run an DI engine in the same cooling system and make it to put more power on the ground since it can handle better the temps despite EGT going crazy faster ..

 

[gerg]

If water temps are a problem for you clean your radiator or get a larger one. It's not the limiting factor for power on IDI engines. And I do believe IDI engines handle higher in cylinder temps better than DI because IDI pistons absorb less heat vs DI due to its piston bowl.

 

[gerg]

Here is what I did with my last set of precups since this is a precup thread and not an IDI sucks thread. Since heat loss into the head through the precup is a negative, I decided to decrease the loss by decreasing the contact surface area in which the precup uses to seat into the head. I scalloped the surface areas with a die grinder and decreased it by about 1/3 by my estimates. All precups already use machining processes to cut its contact area to a minimum, I just went a little further. I wanted to decrease contact area but maintain the cup securely in the head and not create room for movement.

I figure this will allow the cup to shed less heat into the head and thus the precup itself will run hotter than normal. This might decrease ignition delay and speed flame front propagation a bit.

It will also slow precup cooling upon shutdown as there is less area to transfer heat. I personally believe this is partly why precups crack. I also radized the outer edges of the openings to spread the stress out a bit as almost all precups I've seen that are cracked do so at the beginning of the outer run just after a long straight section. The machining is actually at a fairly sharp angle and also happens where the metal is the thinnest. I radized the corners but didn't want to change the opening shape much as it directs the air fuel mix in a specific way onto the piston. I also did some blending inside the precup to increase swirl velocity as there are many sharp steps and edges inside. I also wanted to decrease pumping losses exiting it.