Compression vs head gasket type

[knighty]

trikes - scrapping the block is obviously going to be painfull - so you might be able to rescue the situation if you have say M12 threads - drill them out and tap to something like M14 or slightly bigger - which will also give greater thread engagement.......also if you are running head bolts - now is probably time to start thinking abour converting to studs and nuts.........whereby the stud is screwed into the block before the head is fitted, and bottoms out in the block and is therefore solid, then the nut clamps down the fitted head......the reason people do this is that bolts are notorious for giving un-even clamping loads on head gaskets in high performance engines - the nuts and studs will more evenly distribute the clamping load on the head gasket - catch my drift

if you go to M14 studs and nuts.....you will need to either drill the head out for M14 clearance.......or......get some studs made with M14 thread one end and M12 the other, with a M12 shank to pass through the standard head - the latter sounds a better option to get rid of the yielded threads in your shagged block

just to warn you - the stud threads MUST be of the rolled variety.......not screw cut on a lathe or with a die.......rolled threads are a must for extra fatigue/cracking resistance........I would suggest you phone ARP and pick their brains regarding whats available off the shelf before you comission expensive custom jobbies

cheers

knighty

.

[trikesrule]

knighty this 12:1 engine is belongs to one of the other competitors (B grader). My regular team has fitted ARP Studs to one of their race engines but the engine man and team owner didn't read the instructions - guess they thought they knew better. 12:1 head has to go back on this weekend and the dyno man has to squeeze it into his schedule. Found a lot of things not quite right (or worse). I sourced another set of head bolts for this engine. Am making a good set up out of two. All you guys have been great - thanks. NotsoSwift - I'm a 2-stroke man. Your right these things are dinosaurs. I have another ?. Should I drop compresssion to a lower number. Remember this 12:1 is on BP Ultimate with octane booster and the deck is under the thickness it could be......trikes

[trikesrule]

Hey guys reckon I have found what was causing this 12:1 engine to blow head gaskets. Read on. I was testing the fuel pump flow and the best I could do was a slow trickle. Curious I looked further. Tried two more second hand pumps and nothing changed. Inspected the fuel line thoroughly going right back to the tank. Found nothing astray so I installed a new mechanical pump. Still nothing more than a trickle. Went to the tank, pulled out of the car and pressurised it. Seemed ok. Uuum. Went inside the tank and checked to see if the pickup was too close to the floor. It was almost right on the floor. Thought I'll lift that up and away from the floor about 20mm. Ummmm I wonder, got a long bar and lightly flexed the pick up tube. To my surprise as soon as I touched it it fell into the bottom of the tank. Extracted broken tube and upon inspection the metal had a rusty gray crack nearly all the way round. It was hanging on by 1.5mm of steel. Another problem solved I hope.........trikes

[johnny yuma]

repetitive leaning of the mixture by intermittent fuel starvation would also burn the piston crowns,valves and seats, and make it difficult to drive on a dirt track speedway with the tail out I would imagine.You would notice a bad miss too.

[johnny yuma]

From reading knightys post I'd say Ian Tate was talking the same thing ie studs and nuts instead of head bolts. Mind you the XU1s had to go flat out for 1000km not a 10 km screamer-but they only ran 10.5 to 1 ratio.

[trikesrule]

Hey guys Great News. The regular speedway team I'm with (13.7:1 engine) ran successfully last night. Heat 1 Finished last with a flat left for most of the race (D'oh!). Heat 2 started off the rear and our driver blasted off the start to be in the lead on Lap 2. Steadied and won by half a lap (8 lap race). Feature - 12 laps In the lead by end of lap 1 and lapped the entire field. Two cars were lapped five times! Commentator said David Hart (our driver) had a weapon! Yep our driver and I had our eyes on! I nailed the track set-up and Dave circulated a few tenths outside the track record. Only slowing slightly when a faint misfire crept in. I suspect those Top Gun lead(s). When the car was on the dyno Thursday one of the leads had to be replaced even though it had only done a few racing laps. To say a dominant showing was performed is an understatement and a lot of people were stunned at our speed. On another subject the 12:1 engine car is not back together yet as their is no rush at the moment as most of the competitors banded together and have ordered four 200 lt drums of Sunoco 101. We ran Sunoco 104 last night and the engine sounded nasty good. Thanks guys - awsome help and it's good to be back in victory lane......regards trikes PS just a couple of little things to sort.

[Notso Swift]

So you went the dedicated race fuel... see post number 2!
It would be interesting to whip the head off to do a visual when every thing is running well.

[trikesrule]

That Sunoco fuel just transformed that engine. Totally amazing. We've ordered a 44. Not going to touch the engine while it's going this well. Going to order a set of Magnacor leads and have some one make a slightly bigger N/S so as we can make an effective jet change if (and it will) it gets colder. Just got to catch up on the other maintenance issues. Stuffed two tyres, developed a leak from the master cylinder. Temp guage died, broke some welds and the trailer got a flat. Thats racing. Nice to be up the front again and not sitting down watching the racing........trikes

[trikesrule]

Raced (speedway) 13.7:1 last night on sunoco 101. The car was a tad slower than 104 but it was still quick (just) enough to win three from three. Darn driver kept hitting the same hole in the track and every race he came in with the left side steering arm banana'd. Lucky to finish the Feature letm alone win it. With five to go I noticed the alternator light on as the car went past. Yep it flung the belt off and the temp was on 240 when he came in (geez). When I asked why didn't he pull in he said ' wanted to win that one and needed the points)'. But what damage to the engine I wonder? 12:1 car also ran. He took the car to a mechanic(?) who installed another set of points and a new GT40 coil. In the first heat his car was popping and banging but he finished. I whipped his plugs out - all was good here. Went to the dizzy removed the cap and there it was - the points were set to about 50 thou. Reset to 17 thou. (chicken man we call him) and while he was sitting on the dumby grid an Official walking past noticed some liquid leaking out under the engine area. Someone ran up to me said help help Chicken mans cars leaking fuel everywhere. Anyway I fixed that for him on the Dummy Grid (not supposed to work on the cars on the dummy grid but the Officials allowed it this time). Anyway he ran fourth and in the Feature he finished a creditable third. Over the moon he was. It's the first Feature he's started this season (this is our eighth meet). So thanks guys for your assistance I had many a beer for you that chicken man bought. (Hic!!!!)...trikes

[trikesrule]

13.4 :1 engine won our State Title last night in circle track (Speedway). Was a tough night at the 'office' but we place third in two Heats and won three other Heats. That put us on Pole. In the Feature we led from Start to Finish. That makes two in a row. Now to get the Championship lead back Thanks for all your help guys!!...........trikes

[trikesrule]

Thought u guys might like to know what I found during our last speedway meeting. The stromberg carby (down draught single) base had a crack running 2/3 of way round and thru the butterfly area. Wonder how long thats been there and how come it didn't start whistling till the last round? Do cracks just leak without whistling? If they do it might explain our head gasket failures. Maybe it wasn't the fuel. Time will tell.....trikes

[pheyden]

I believe you have been chasing all of the wrong dragons. Yes, good maintenance is a must. You cannot expect to win with bad fuel pickups, cracked carbies etc.

[pheyden]

Just a few more comments.

The computed compression ratio really means absolutely NOTHING. In order to get an idea of whether an engine will run on a particular octane fuel you need the following information.

Cam duration (seat to seat)
Intake valve closing
Computed Compression Ratio

From this you will be able to compute the Dynamic Compression Ratio (DCR)and this will give you a much better indication. I say indication, because there are other factors at play.

I will use a 1000cc motor running 12:1 as an example. In one case using 290 degree camshaft, on 108 degree lobe centers, installed 4 degrees advanced, with a intake closing of 69 ABDC, with a 65.75mm bore and 117mm long rods we computed a DCR or around 9.5:1. This meant that the effective displacement of the motor was around 800cc. The exact same engine with a 318 degree camshaft, same other specs had an intake valve closing of 83 degrees ABDC. This computed to an effective displacement of 680cc, or some 120cc less. This resulted in a DCR of 8.3:1. or a full point less.

Now the 8.3:1 motor would happily run on 101-102 octane fuel. The 9.5:1 motor was a totally different story, it would definitely DETONATE with the same fuel. There would be only two solutions, a) lower DCR b) use higher octane fuel.

At the moment we are running motors successfully with solid copper head gaskets at DCR ratings of 10.3:1 (13.8:1 computed compression). This requires 110-112 octane fuel.

If you list the cam details for me, I will do a computation of DCR for you and give you an indication of where you might stand.

Of course if the carburetion system leans out at high RPM (broken carburetor) then this would not help. The little pick signs in the top of the piston are tell-tale signs of detonation.

A good squish area between the piston and the head will also help. Try to aim for 0.027-0.040 inch. This will give good fuel mixture turbulence and help prevent detonation.

A good rule of thumb is "if you push on the gas pedal and the car does not speed up, or worse yet slows down, shut it off." You have experienced detonation.

Paul

[GORDON STREETER]

Originally Posted by pheyden

Cam duration (seat to seat)
Intake valve closing
Computed Compression Ratio

From this you will be able to compute the Dynamic Compression Ratio (DCR)and this will give you a much better indication.

What's all this then. Its complete news to us !

[dtype38]

As Eminem's mum used to say: "If you can't say something nice....

[icemachine]

...you can only run as a conservative politician?

[ian_w]

Uhmm... Not sure that Dynamic Compression Ratio is correct.

What you are doing is calculating the volume of the cylinder when the inlet valve closes and comparing it to the clearance volume. This calculation makes the assumption that as the piston starts to rise from BDC with the inlet valve still open that the charge in the cylinder is pushed back out through the inlet valve. This is a valid assumption at low speed - which is why a long duration cam gives poor low speed torque.

However, at higher speed inlet tuning pulses and induction ram start to take over. Even when the piston is starting to rise air is still entering the cylinder due to the inlet tuning. This results in the volumetric efficiency ( the volume of air inducted compared to the geometric volume ) being upto 120-125% for a well set-up 4 valve race engine.

So more appropriately, your Dynamic Compression Ratio should be:

DCR = Geometric CR * Vol Eff / 100

The value for DCR will obviously vary with engine speed.

[GORDON STREETER]

Before anybody gets bogged down with technicalities I have built a fair few race engines over the years. Having tried all sorts of compression ratios (some with dire consequence's) the conclusion that I came to is that most engines producing good reliable power run a compression ratio between 8.5 and 9.1 .
This is from the inlet valve closed and varies on the type of engine / cam/ and combustion chamber shape, running on roadside pump (5 star) fuel.
Obviously this can change using very high octane fuels but not by an enormous amount.

[GORDON STREETER]

http://www.flickr.com/photos/1634503...73159/sizes/l/
Just to show I know a little bit about what I am talking about.

[dtype38]

Mmm, 3.4 secs faster than Richard's XJS... that's one damned quick Anglia you've got there Gordon!