Blown head gasket
 

Hey guys, Its been awhile. Hope everyone is having a great summer and going fast! So I have been running my blown 489 chevy bb all summer every weekend and its been running like a champ. 83 mph at 5400 with a 27 3 blade. I had changed the top pulley and now up to 8.5 to 9 lbs of boost for the past 2 months. Was running 77 to 78 mph @ 5000 with 6.5 lbs of boost with the other pulley and same prop. Saturday noticed a miss and idled in for about 15min or so. Pulled some plug wires and found 3 dead holes 1,5,7. Had water in all three.
Pulled the head this afternoon and the top right of the head gasket of # 7 was burned through to the water jacket but the spark plug showed NO sign of detonation? It looked great. Pistons all looked good. I pulled the plugs on the right bank and the #8 plug had lost 1/4 of the tip and splatter was obvious . All the others looked perfect. Not sure why the rear 2 cylinders got beat up and how the plugs can be in such good shape on the bad side?:poopoo:

I think I mentioned to you, a couple times this year, that you were pushing your luck spinning a 174 B&M blower, to make 6-7lbs of boost on that engine. So you went and turned it up to 9lbs of boost, and hurt the engine now.

Not only do those little blowers superheat the intake air temps, they also have poor fuel distribution with a single carb. Your rear cylinders were more than likely, starving for fuel.

When you have lean mixture, lots of ignition timing, smoking head gaskets or beating the piston, is pretty common when the engine is at its peak torque range. Also you had mentioned in your thread back in may, that you did a compression check and you had 150 psi in the cylinders. That is a bit high for your normal supercharged marine pump gas roots blower setup. It can work, as that is what my cranking psi is, but for it to work, you need a proper setup. Like right size blower, cool water temps, limit the boost amount ( I run 6psi with no intercooler), and a good amount of fuel to keep things cool.

Copy that MT. What make head gasket are you using? I know I have reached the end of the line with my set up.

I have MLS gaskets. Problem with mls is that they are so tough, many times you will melt a piston before burning the gasket thru.

If your going to keep that blower, use fel pro gaskets and cheap bolts so you have a relief valve before it melts a piston ;)

Sorry to high jack the thread but have a question about the 174 on a 454. With that blower on a 454 can you run it for extended periods of time like 30 or so miles on a leg of a poker run or is that to long and would build up to much heat?

You can run it, I just wouldn't do it at WFO.

Are you talking wide open the whole time? That is a complicated question that needs a lot more detail. Even the 174 can be ran for extended periods, but at low boost and chilled for ultimate safety. Bigger blowers make less heat and carry more CFM at lower PSI. Compressing air causes heat, plus that little blower spinning at 20k rpms causes heat. Heat causes detonation, excessive compression without the proper octane causes detonation.

Honestly, the OP at 9 lbs with no chiller I am surprised it was just the HG

To funny lil red. 4bus, I have a chiller ! I'm crazy but not nuts!

Got everything back together and fired her up. Second lesson learned. Should have had the head checked. Low compression on 1 ,5 and 7. 1 and 5 being the worst. Did a leak down test and looks like the intake valve's got beat up a bit. Did a quick tear down and off to the machine shop with the head this morning.

Besides backing the boost down, I'd be very sure you have enough fuel to keep things cool

I'm curious as to what kinda jetting your running?

Im going to say 89 frt and 90 or 92 rear. I was going to stager rear jetting this time to help compensate for the blower

What size carb is it again and do you have power valves ?

Its a 850 done up to a 920. Nickerson did it. Still have pv's. I have a theory on the boost. I was thinking back when I changed the pulley and I kind of remember it being about 7 to 7.5 lbs. We have had some cooler temps with low humidly. I attributed that towards the boost being up a bit towards 9lbs. Found out today that the intake valves were heading south in the bad cylinders that were beat up from heat. Because of the blower being constant positive pressure, I would never hear the tell tale sound of popping out of the carb from a bad intake valve. Lesson I learned, If the boost increases on it's own by any amount, start looking for a reason.
Ah the joys of a blower motor, having fun and still learning.

Sometimes folks idea of fun is pretty amazing but that's what makes the world go around I guess. Best of luck with those fun blower motors of yours!

I'm doing a 177 on a very mild 502 right now with a 1050 dominator at 98 squared. We shall see come next week when I fire it up. Only looking to make 4.5-5.5psi. Hopefully things workout. It's a brand new build at 8.75/1 compression

off to the machine shop
 

Hi, I was curious what the machine shop charged you to do your head and what was actually done? Thanks in advance.

Hey X1, Not sure on the charge is yet as the shop/friend hasn't put the bill together yet. Why are you asking? Are you in the middle of something similar. I also had him drill out an old head so I could use it as a guide to drill out one of the head bolt threads in the block that was sloppy and install a timesert. (cool product). I'll let you know when I get the bill. He took 4000 off the head, touched the seats up and installed 4 new intake valves. Had it running today and sounds good. 150ish on the compression test cold.

Whats the new plan of attack now that its back running?

Hey MT, Tried to call you a few days ago, went to your vm. I upped the primary to 91/92 and 95 on the rear and I still have pv's. Ran in on the water this morning running my 3 blade 27, bumped the timing back to 26 total, ran 72 at 5000 at 5 1/2 lbs of boost on FLAT water. I am wondering if it would live with the smaller pulley and the larger jets/timing. If I put on my 24 on that is double cupped I can get 6000 out of her and get 80/82mph depending on chop..
With the smaller pulley I was getting 7 1/2 lbs and spinning the 27 5300/5400 and that was about 80/82 depending on chop.
The motor sounds happy so I might just leave it alone at this point. Like you have said about 10 TIMES, I'm at the end of the rope with this set up. My best was 83 gps with the smaller pulley in good chop.

Man buddy that timming is low, you are putting lots of heat in exhaust side......

I was running 28 total. My motor has 9:1 maybe a bit more. I was told by Dean Nickerson {builder/carb guy} lwith an 8:5 to1 @ 5lbs that would push comp to 13:5/14:1. On premium fuel I'm past the limit. I was running 7.5lbs at 28 and took out intake valves. Granted that was with 92 with pv's on secondary and I now have 95's with pv's. Would that jet change been enough to cool the cylinders? I don't know......

Timing and jet will only crutch you so much. The hot air will eventually lead to detonation no matter how rich or how lazy the timing. Unless you want to up the octane of your fuel of course, but you will still be leaving power on the table. Engines don't make power off of boost, they make it off of airflow, and hot air brings your airflow down and your combustion temps up no matter how you cut it.

Seems like a few guys that have by-pass tube for the water pump have put dumps on the rear intake water jackets to help water flow in the back on the block and cool 7 and 8. One guy I spoke to told me his buddy had a BIG problem with 7/8 on four builds. Installed the dumps and problem solved. Something to think about ........

+1

Sorry I missed your call, its been a crazy week here.

Ok, theres a few things we need to look at here, for the big picture of what you have there.

Boost pressure in the manifold, is NOT the end all answer. I say this, because many tend to look at things like 8.5:1, with 5lbs of boost max. Its not that simple.

Not all blowers are created equal. A small blower, like you have, is going to generate a TON more hot air, than if you had, say an 8-71 on it. So, a 174 spinning like crazy, is gonna cause detonation much sooner than a 8-71 that may be underdriven at that point. The larger blower, may be able to run 8lbs of boost on your setup, on pump gas, and not hurt the engine, where as the 174 blower, may cause issues at 6lbs of boost. This is why with modern whipples, centrifugals, you can run more boost. The air is simply cooler.

Aside from the fact the 174 is struggling to make boost on a 489ci engine, (especially anything over 5psi), the fuel distribution is horrible, and even more with a superchiller. Retarding the timing to 26*, is a pretty good way to start tuliping exhaust valves. Retarded timing, is not the answer.

As far as the rear water dumps go. I agree they do not hurt, and I think they are a great help on a siamese cylinder block, like a 502. A 454 based block, doesnt have siamese cylinder walls, and cool a little better around the cylinder. Main thing they do is help prevent steam pockets from forming.As far as mercury's supercharged engines, like the 525sc, 600sc, 800sc, 575sci, those did not have rear water dumps, and also didnt melt #7/#8 pistons.

My advice would be this. IF you must keep that blower/carb combo, simply back the boost down to 5lbs, timing at 30*, and throw some big jets in there. Especially in the secondary side. Alot of people get scared of running it too rich on the big end, as for washing the rings out of it, and diluting the oil. My theory is though, at 5500RPM, you're not washing anything down past the rings. The extra fuel is being blown out the tail pipes. Now, you dont want a super rich idle, or low speed AFR, but a bit extra fuel on the big end, may prevent you from ripping this thing apart every season.

Now, if you are serious about keeping the engine healthy, being able to make some good honest power, I'd ditch the blower combo you have. I understand everyone is on a budget, as am I. But a great bang for the buck blower, is a 420 B&M. You can find them very reasonable. Sometimes complete with carbs and intakes for 2500 bucks. By going to that blower, which is close in size to a 8-71, you not only will dramatically lower your intake temps, but you're fuel distribution will be MUCH better. Your engine will pick up a bunch of power, pound for pound of boost. 6lbs with what you have, will not make as much power as the 420 at 6lbs.

Roots blown stuff likes big carbs. Perfect example. Last weekend, I was running my boat. I noticed my starboard engine, was only hitting 5lbs. (always at 6lbs). I starting thinking the blower was tired or hurt. I got back to the dock, and started looking around. Turned out while I changed jets prior to the weekend, I had pinched the secondary accelerator pump linkage on one carb, and it was keeping the secondarys on one carb from opening (twin 850's). So, my one engine, was really working of 6 barrels instead of all 8, or lets say instead of 1700CFM, I had 1275cfm of airflow. That was enough to make my engine down on power from 3500-5500RPM. These are 468 engines, not 598's either. Theres also proven theories that on roots blowers, if you undercarb them, the air temp in the manifold will go up.

Back in the day, your typical 250 blower, single dominator carb, was pretty much maxed out at 700HP, regardless of what engine was under it. A 489, with the right cam, heads, blower, is fully capable of 750-800hp on pump fuel. But, in your case, you have a blower, and carb, probably capable of no more, than about 600-625hp on pump. A 420 blower with a pair of big carbs, can do 900-1000HP, but thats about it on pump fuel.

A+ post right there! :)

Thanks MT for the info and hope you had a good weekend! You are a BIG help! Will bump the timing back up to 30. Changed jets on Thursday to 92/91 on the frt and 95 on the rear. Ran all weekend and kept an eye on the plugs. a bit dark but way better then hurting something. Pulled hard and was low 70's @ 5000rpm. I'll keep you posted.

Also, be careful with plug readings. They can be deceiving, especially with the gas we get today.

http://www.dragstuff.com/techarticle...ead-plugs.html

Lets also not forget, when talking about " how much boost" what role the camshaft plays into the equation.

I wouldnt try running 7lbs of boost with a towing cam coupled with a moderate compression ratio.

Very true, which starts the discussion about dynamic compression ratio vs. static compression ratio and the role that plays in cam selection, especially when forced induction is involved.

Yes sir. Thats why I kinda have taken the general "compression chart guidelines" with a grain of salt. There are so many variables.

Supercharged engines, especially for marine, have such a bad wrap. Guys will always say "I dont want blowers, too many problems", based on a cousins buddy's, brother who melted a piston after installing a blower on his 454.

The entire package must be though out thoroughly.

I've always felt that camshaft selection does not get nearly enough attention in a roots blower application because of the lack of lag as opposed to something like a turbo motor where cam profile can make a huge difference in how an engine behaves. That certainly goes to your point of the entire package being considered.

The other misnomer is how people look at boost as the end all be all of power production. An engine could care less about how much of an inlet side restriction (AKA Boost) is going on, it is much more interested in mass airflow as it is nothing more than a giant air pump. This is where simply knowing what your intake air temperatures are in the manifold can give you major insight into what is going on with combustion temperatures.

Totally agree Matt. I've seen or heard guys look at me or my buddy's like we are CRAZY for not having an intercooler. Heard things at the bar like, "No intercooler, better keep the boost at 4lbs". Alot of us have been running without them for years with no issues.

Icdedppl is turning a 10-71 at 3% underdriven. Makings 6lbs of boost right now. At wot his intake temp is 130ish. Now, take that 10-71 off his engine, and bolt a 256 blower on there, and make 6lbs. Intake temps will likely exceed 200*. I'd rather run the 10-71 at 8lbs, than the 256 at 6lbs.

My buddy is building a similar build this year, with 10-71s. But he will have a blower shop intercooler. I am anxious to see the intake temps on his. All these years intercoolers been out for roots blowers, I have not seen 1 legit test, of measuring intake air temps before and after the install. For what some of these units cost, I need some data before I write a check, or trust adding more boost safely.

Brad (Smith Power) related a story to me about a dyno session where the power output just kept slowly dropping. He finally went outside and found the hose feeding cold water to the intercooler had been turned off. Turned it back on and the engine's power came right back. On race gas, so no engine damage was done due to the mild heat buildup. This was on an over-driven roots deal. Not really big pressure, big heads and cam though. 1000+HP

You really need an O2 sensor to get the af dialed in. If you have a bung in your exhaust you could use my Innovate af meter and sensor to get a read on whats happening fuel wise in your engine. We appear to be in the same area. Ive also been running 454s on 177s for a number of years and have some knowledge in that area.

Thanks for the offer Blue. I just may take you up on that. As MT said I'm at the end of my line with my set up but if I keep it, having it run at its best would be the way to go.