Stroker: Titan Engine: My Story

Hi All,

Have a 1992 XJ 4.0 with auto tranny. I've a lot of weight on this vehicle and wanted more HP to move it all.

Purchased a stroked 4.0 from http://www.titanengines.com/. Engine is bored 0.030 over and has a different crank bring it up to 4.6 liter according to Titan. Paid about $2100 for the engine plus shipping, core. Titan assured me that engine would not run extra hot and would run on mid-grade fuel, 89 octane here in CA. I was told the only mod I would need is to purchase 24 pound injectors, which I did. They built engine almostly immediately and in a week or so I had it. Installed without major problems.

Started engine. No big clunks! But it seemed to heat up really quickly and run much hotter than expected. Temperature indicator showing near the red while traveling 45 MPH on level ground at about 60 deg F air temperature. Ok, I guessed the engine was just really tight.

Drove 800 miles out to Tucson from San Diego and back. Engine ran really hot but by driving carefully I managed not to loose any coolant. Drove 800 miles to Mammoth. Very cold weather and didn't notice any heat problems except at one point where the Jeep was pulling really hard into a head wind.

On the above trips there were a couple of points where the engine started missing due to heat, but no coolant loss. Stopping for a moment allowed engine to cool and return to normal operation. Noticed significant ping on 89 and also 91 octane gas ate 2500 rpm. Mostly drive at 2000 rpm - 65 MPH.



Idle now rough. Compression test shows

#1 - 195 PSI
#2 - 205 PSI
#3 - 200 PSI
#4 - 195 PSI
#5 - 105 PSI
#6 - 155 PSI

Air pressure into cylinders causes loud hissing at intake manifold on #5 and very noticable hissing at intake from #6.

Head removed. Detonation balls of aluminum within cyl #6. Piston not too badly eroded. Intake valve on #5 cyl stem bent. Crack in head below #4 exhaust valve on #3 cylinder side.

Ok, engine has run hot and been damaged. The way I see it there are two problems: compression and heat.

Compression: 200 PSI cranking pressure seems really high for an engine supposed to run on 89 octane. This is a possible explanation for pinging. Don't know about heat. Does anyone know what compression pressures to expect from a stroked 4.0?

Heat, pinging: Possible explanations: lean air/fuel, advanced timing. To my knowledge the ignition timing is not adjustable, being set by the CPS at rear of motor. Correct?

If so this leaves lean air/fuel. The 24 pound injectors should allow computer to provide sufficient fuel. Oxygen sensor is not terribly old. Installed new factory fuel pump some months prior to engine swap and observed correct fuel pressure at that time. Anyone know anything about air/fuel adjustments for stroked 4.0? I've purchased a Auto Meter air/fuel sensor + gauge and intend to install this so I'll have an idea of mixture. But that's another thread....

So the head of my new stroker is wrecked and, because of the high compression numbers, perhaps the engine is not correctly built. I'll keep posting to this thread but I'm kinda discouraged right now.

Re: Stoker: Titan Engine: My Story

ship that bad boy right back to titan, Id say it was their problem

Re: Stoker: Titan Engine: My Story

Yes, it is certainly inviting to simply return the motor. But if it's been damaged by bad air/fuel or advanced timing it's not their fault. However if they've sent an engine with too high a compression ratio to run on 89 octane then they are responsible.

So the questions still need answering:

Does anyone know what compression pressures to expect from a stroked 4.0?

Is ignition timing adjustable by ordinary means (not including special CPS bracketing)?


Thanks!

Re: Stoker: Titan Engine: My Story

I have nothing to add specifically to your thread, nor answers to your specific questions.

I can, however say, that I compression tested my 200,000 mile XJ engine and came up with about 170 PSI in three of 6 cylinders. So, I don't think that your 200 is all that far away considering. That is a stock 98 4.0 with 170psi in 3, 165 in one, and no less than 157 in the other two.

Re: Stoker: Titan Engine: My Story

You need to find out the compression ratio 9.0-1 or 10.5-1, or any other ratio. That is what determines your octane level and when you may hear some ping or detonation. The correct specs for a compression test for a stock 4.0 is 120-150 psi. If I had to guess I would say that your 200 psi may be right for a stroked 4.6. The engine may also have been damaged by the running hot during your initial driving after installation. Heat is the biggest killer of a new engine. Did Titan send the engine with a thermostat installed?

Re: Stoker: Titan Engine: My Story

I run 10.3 CR here in Colorado at 5000 ft. The key to running low grade fuel is in getting the quench right. My stroker has only overheated once in 25k miles and that was when the clutch fan puked.

What cam does the engine have? Hopefully not stock.

Re: Stoker: Titan Engine: My Story

newXJ said:

You need to find out the compression ratio 9.0-1 or 10.5-1, or any other ratio. That is what determines your octane level and when you may hear some ping or detonation. The correct specs for a compression test for a stock 4.0 is 120-150 psi. If I had to guess I would say that your 200 psi may be right for a stroked 4.6. The engine may also have been damaged by the running hot during your initial driving after installation. Heat is the biggest killer of a new engine. Did Titan send the engine with a thermostat installed?

Click to expand...

Yes, 9.0:1 or 10.5:1 is the question. But I don't know how to measure the compression ratio directly. I can just measure the cranking pressure and try to work backwards.

Agree that heat kills engines, especially new ones! No, I installed my own thermostat and am confident it works correctly. I measured thermostat housing temperature after start and it came right up and leveled off at proper temperature. Think I'll do a boil test on the thermostat now that it's out. Might as well.

Heat is almost certainly the cause of the damage to my engine. But what caused it to run so hot? Timing might and of course running lean will absolutely do it. I'm trying to eliminate timing by asking if timing on a XJ is adjustable - maybe I didn't adjust it right. But if not timing then what's left is air/fuel. I strongly suspect bad air/fuel has damaged this motor.

Thanks for the 170 PSI observation. The Titan is supposed to be somewhat higher compression ratio so maybe 200 PSI is resonable. I'd really like to directly measure the compression ratio (9:1 or 10.5:1?) but I just don't know how do do this.

The cam is stock, or so I requested of Titan. Other posts here at claimed problems with 'hotter' cams.

So I still need to know: Timing adjustable? Cranking pressure for a 4.6 stroker?

Thanks!

Re: Stoker: Titan Engine: My Story

Take a pix of the plugs and post them up.

Re: Stoker: Titan Engine: My Story

Those compression test results sound right (well, except for the bad holes) for a stock cammed engine at lower altitude. A larger cam will cause lower psi numbers in the test, I have a 12.6:1 motor that shows 180 psi because of the altitude and cam. As for why it got hot- are you absolutely certain all the air was bled out of the cooling system during installation? I've done a poor job of that before and not had it show up on the gauge until I got to Moab, 500 some miles from here.

Re: Stoker: Titan Engine: My Story

scratch that...i didnt realize you had an actual wideband...for a second there I thought you were talking about one of those dumb autometer light shows.

I suggest running the sensor pre-cat, right around where the stock sensor is.

Re: Stoker: Titan Engine: My Story

Autometer now makes wide band air/fuel meters.

I like the ones that can data record.

I might add a DTEC wideband piggyback system so I can tune the fuel curves and data record. It also reads exhaust temps.

Re: Stoker: Titan Engine: My Story

Compression pressures should be directly proportional to the compression ratio given the same ambient air temperature and pressure and the same engine temperature if the cylinder volume and head volume is the same. Assuming this, your cylinder pressures on the good cylinders indicate a C.R. of 11.7. I don't think the good old 4.0 would run well at that ratio.

Fred

Re: Stoker: Titan Engine: My Story

Fred said:

Compression pressures should be directly proportional to the compression ratio given the same ambient air temperature and pressure and the same engine temperature if the cylinder volume and head volume is the same. Assuming this, your cylinder pressures on the good cylinders indicate a C.R. of 11.7. I don't think the good old 4.0 would run well at that ratio.

Fred

Click to expand...

Ok, here is a picture of the plugs

http://i25.photobucket.com/albums/c91/kristinhead/IMG_3771.jpg

Plugs #1, and #2, although they look dark in the photo, are actually closer to #3, and #4. #5 and #6 are dark. All plugs are discolored on one side only.

My Titan is supposed to have the factory stock cam, nothing out of the ordinary.

As for bleading the water jacket.. No not absolutely certain but I did the best job I could. Other posts here at say that the '92 cooling system doesn't require bleeding, not like the older pressurized overflow systems. At any rate I ran the engine for several heating/cooling cycles and noticed only perhaps a quart of intake of coolant. Don't know how to blead my system...

I agree that 11:1 is not where I want to go and run on 89 octane. But seems like I'm getting conflicting opinions as to how to translate 200 PSI into compression. I'm measuring the engine with a factory stock cam at sea level and at about 65 deg F ambient air temperature with the engine warmed up.







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Re: Stoker: Titan Engine: My Story

Fred said:

Compression pressures should be directly proportional to the compression ratio given the same ambient air temperature and pressure and the same engine temperature if the cylinder volume and head volume is the same. Assuming this, your cylinder pressures on the good cylinders indicate a C.R. of 11.7. I don't think the good old 4.0 would run well at that ratio.

Fred

Click to expand...

Fred, walk me through the math on that if you wouldn't mind. I need to learn something today.

Re: Stoker: Titan Engine: My Story

200/150 * 8.8 = 11.7

It's Friday night and I've had a few, but I can't for the life of me think of any reason why the above is wrong.

Fred

Re: Stoker: Titan Engine: My Story

Or:
Modified compression pressure/Stock compression pressure = Modified compression ratio/Stock compression ratio

Re: Stoker: Titan Engine: My Story

JJacobs said:

Fred, walk me through the math on that if you wouldn't mind. I need to learn something today.

Click to expand...

Well... if you want the math try


http://en.wikipedia.org/wiki/Compression_ratio

Unfortunately this math brings up unknowns such as the valve timing and the actual value of the exponent. About all that makes much sense is the statement towards the bottom which is


if the static compression ratio is 10:1, and the dynamic compression ratio is 7.5:1, a useful value for cylinder pressure would be (7.5)^1.3 × atmospheric pressure, or 13.7 bar. (× 14.7 psi at sea level = 201.8 psi. The pressure shown on a gauge would be the absolute pressure less atmospheric pressure, or 187.1 psi.)

There are some 'if' in this statement but the 187 PSI for a 10:1 motor seems to say to me that my 4.6 stroker has compression greater than 10:1. But this depends on the valve timing. 10:1 is just the static compression which is calculated by determining the total volume and the volume swept by the piston, not taking into account how much air is reversed thru the intake valve prior to its closing. But there's the math anyway...

Mike

Re: Stoker: Titan Engine: My Story

Fred said:

Or:
Modified compression pressure/Stock compression pressure = Modified compression ratio/Stock compression ratio

Click to expand...

Thanks Fred. Using over2land's 170 PSI on a stock motor, and guessing the stock motor to be 9:1 (anyone know the actual ratio for a stock 4.0?) I calc

(200/170) * 9:1 = 10.6:1

I don't know what ratio my Titan is supposed to have, I'll ask Titan Monday.

Mike

Re: Stoker: Titan Engine: My Story

I think 170 is way off. The factory calls for 150 max which corresponds to:

8.8(stock compression) * 14.7 lb/in^2(sea level atm pressure)= 130 psia, which is in the neighborhood of the factory specs.

Fre

Re: Stoker: Titan Engine: My Story

Fred said:

I think 170 is way off. The factory calls for 150 max which corresponds to:

8.8(stock compression) * 14.7 lb/in^2(sea level atm pressure)= 130 psia, which is in the neighborhood of the factory specs.

Fre

Click to expand...

Ok... according to the wikipedia article you've made a slight mistake in using 8.8 directly. Their formula gives

final pressure = initial pressure * (compression ratio)^exponent.

They give exponent as 1.4 but later say 1.2 or 1.3 is what is used. The exponent allows for the effect of compression upon air temperature (the air gets hotter when compressed and thus produces even more than expected pressure). If I use 1.2 exponent with 8.8 compression ratio, and 14.7 PSI atmospheric

final pressure = 14.7 * (8.8)^1.2 = 200 PSIA or 185 PSIG.

Well I don't know what they are smoking at wikipedia since 185 PSI seems really high to me for a 8.8 compression. And I used the lowest value of exponent, 1.2, although they give 1.4 at the start and later say 1.2 to 1.3. Oh well... so much for math!

But I agree that the same cam timing with different compressions should be related by the ratio. So

(200/150) * 8.8:1 = 11.7:1, still bad news for my motor since the wikipedia article says 10:1 is a normal top limit for gasoline engines.

Thanks!