Case for the turd head?

The log. Yes it is the worst naturally aspirated intake ever "designed", and I've hacked a few off in the name of abstract knowledge.
My question:
How much difference does it really make using a 2v Oz or Argie head vs a late 70s big valve log head when supercharging (or turbocharging)?
Seems to me that aside from the differences in flow rate of the actual intake ports there shouldn't be much difference, since regardless of volume, both intake plenums are pressurized, to say 6 - 8 psi (m90 guy here). In fact in the case of a turbocharger, wouldn't the smaller volume of the log plenum pressurize faster? All the heads can be ported, although with the log head it's a challenge to do the whole runner, most porting hp gains are made by work on the bowl, valve seat transition, and shrinking the valve guide boss anyway. I will conveniently disregard the exhaust advantage of the stock Argie individual port head.
Just random idle thoughts on the train this morning.
Rick(wrench)

Three stock engines, one log head, one Aussie 2v and one Argie 2V, all get turbo/supercharged with same parts. The log head would produce much less HP than the other two, because of the restriction in the log head, the reason is that all engines are not the same and even though you put the same turbo one each engine, they all flow at different rates. Your Turbo my be designed to produce 8 psi on a 3 liter engine in our example the log head may show 10 psi, the Aussie 8 psi and the Argie 6 psi but the Argie and Aussie would still produce more hp than the log head because of the restriction in flow. Just because it indecates 10 psi doesn't mean it is making more HP.

Now if I was on a limited buget and could only afford the Turbo vrs the Aussie/Argie head, then yes the turbo on the log head will boost the HP more than changing to better flowing heads by itself.

Look at the fabricated intake manifolds of Jason Ghiller (the very quick red Falcon at Fullboost) or Mike (MTS-250). They're certainly homage to the "log" idea and short runnered, but with a larger reservoir.

Jason Ghiller

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Alex

Anybody got some pics of 'custom' manifolds to replace the 'crappy' log manifold??

Mustangaroo":bqwovdzp said:

Just because it indecates 10 psi doesn't mean it is making more HP.

Click to expand...

Ok, so if I understand correctly the issue is that the chamber filling will not be equal due to the restrictions in the manifold. What if we crank up the boost until the chamber filling is equal to the other heads? Granted, I understand that the better heads have more potential, but is there really anything wrong with more boost on a poor flowing head? Seems to me that with equal chamber filling the power output and detonation risks are also equal regardless of how much boost it takes to get there.
Joe

Hmmmph. Can't even start a good argument over here.
Joe

I'll bite, JW. I'll start a fire with the F350 dualie truckload of hay you've placed by a 10 psi blast furnace...me!!!! :splat: :fume:


I'm kind of missing the disiplined english to make a go of the description, so I've held off all these posts on log verses 2V.

The most important point is

1) a turbo engine is detonation limited

2) a log engine is breathing limited

3) the log head is thermally compromised. When the intake heats up, it stays very hot, raising the octane requirement. If the 2v to log are like the old Mini A-series, the following relationship accrues. With the heat stove, about 8 octane points more are needed to get performance in a 10:1 engine than in a 2V. In a10 psi turbo, a 2v may get away with 89 octane with an 8:1 compression. In a log, it would need 7:1 before detonation sets in.

4) at 10 psi, the air flow is varied between the cylinders more than in a 2v, so the total 10 psi pressure will bank up, reducing out put from the exhast to the impellor. The engine speed at which the idealy sized turbo gives 10 psi on a log will be much lower on the 2V. Log head turbo changed to a 2v turb responds no differently to the normal 2v head transplant. Smoother, more detonation free, racers, better response, and more power for eavy pound of boost.


5) What is loosened on the log is loosened on the turbo. If there is a 40% increase in just the 2v, there will be a close to 40 % improvement in the 2v turbo over the log. There may be a law of diminishing returns, but it is very slight.
Remember, a turbo is just a gas turbine sharing its intake with a recipricating piston engine. If the base engine does 150 hp before a 10 psi turbo as a 2-bbl 2v, and 105 hp as a 2-bbl log, then the 10 psi turbo will likewise give a 43% power boost when turboed. 225 hp verses 160 or so psi. As said, there may be a diminshing return, but that is the way thing are played out. The turbo doesn't have much change on things, it just makes efficent head work even better than a log head. Yes, restricted heads love turbos, but great cylinder heads love them just as much!

Taken together, a 10 psi log engine runs into detonation quicker than a 2v.

Explaination:
Both detonation, mixed with poor breathing, results in more detonation. If you did Morse tests, (dynometer tests on groups of cylinders that are alternatively turned off), you'll find number 5 and 2 detonate more than any other cylinders under load. On a log or 2V, no 1 is always detonation free, number six is often cookes just after 5 and 2 detonate. It's all to do with lean backfires at high velocities due to poor intke runner distribution. It's nothing to have a 12:1 air fuel ratio at Number 3 and 4, but 14.5:1 at no 1, 2 5 and 6. Under straight acceleration on a quarter mile of dyno run, the mixture travels 4" to the valve at cyl 3 and 4, and up to 12 feet to cylinders 6 and 1. There is a loss of efficency in total air flow at each end of the engine, and the good balance that exists in the 2v engines great intake is missing in the log heads, especially the early ones.



The books which cover this are there in the bucket load.

Rick(wrench) xtaxi said it best just then! But now having said that, if your on a buget or just don't want to go the Aussie 2v or Argie route, then just do it! yes it will make less HP for the same boost, but who cares just turn the boost up and go for it. look what Does10's has done with his 250 log headed inline six. Besides being cheaper you will have more room for the j-pipe and turbo on a log head vrs the Aussie 2v head and intake.

If the log ends up bein bad at holding in heat, would that mean the longer you drive it (in one trip) the worse things will get detonation wise? Im gonna have to go with the log head for now, but I want to daily drive my car, so am I lookin for trouble or will it be alright?
Matt

From FullBoost.com.au



I'm sure this fellow could've afforded a regular manifold if he believed it was the best approach.

I worked on this case with Engine Analyzer quite a bit. The results were heavily in favor of the Aussie and Argie heads. With the same shortblock (200 cid), same carburetion, same turbo, same boost (12psi with a 65% efficient intercooler). Results:

Log Head: 307HP @ 4800
Aussie 2V: 382HP @ 6000
Argie SP head: 390HP @ 6100 rpms


Now those calculations were done from flowbench data of a big log head versus an Argie head. I gave the Aussie head a slightly poorer exhaust flow rating than the Argentine head.

The log head was much more limited to timing advance than the other 2 heads.

xtaxi":2lwp9dic said:

3) the log head is thermally compromised. When the intake heats up, it stays very hot, raising the octane requirement. If the 2v to log are like the old Mini A-series, the following relationship accrues. With the heat stove, about 8 octane points more are needed to get performance in a 10:1 engine than in a 2V. In a10 psi turbo, a 2v may get away with 89 octane with an 8:1 compression. In a log, it would need 7:1 before detonation sets in.

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might be a few misconceptions in this, so bear with me please

what if you could take a log head like this


and coat the intake track with jethot, or something similar? (does jethot even resist gasoline?) would that negate some (if any) of the heat problem inherent in the log head? or would you need to expand it to a ceramic coating on the valves and combustion chamber?

i only used that head as an example because it should be easier for them to reach all the areas

John,

What happens when you crank up the rpm's on the log head??

Log Head: 307HP @ 4800
Aussie 2V: 382HP @ 6000
Argie SP head: 390HP @ 6100 rpms

Click to expand...

Later,

Doug

All right! Sometimes it just takes a load of hay dumped on the bonfire to warm things up a bit I hadn't even considered the thermal affect of the log head. Makes sense to me.
Joe

Evan - The problem is that that the resistance to flow in the intake is what´s building that heat in a forced induction application. Coating would just insure that the heat stays in, making things worse. Porting helps things quite a bit - more so on a turbo´d log than a N/A version. The only good solutions are radical intake modifications.

Doug - those are the peak HP numbers. HP begins to fall at higher rpms.

Rick(wrench) xtaxi said it best just then! But now having said that, if your on a buget or just don't want to go the Aussie 2v or Argie route

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Nothing like that (the budget part), after I'm done experimenting on a few more log heads, I'll buy an argie head when they become available.
I hacked up another log head last week to check out a theory. This one was a late "big" log head. The runners are shaped completely different in cross section from the earlier heads. The big log runners are sort of a round cornered square, whereas the old C2 head had perfectly round runners (that were smaller). I was trying to shave the log off bit by bit until there was just bunch of open runners with the bottom part of the log between them. Unfortunately the runners trumpet out in funny shapes before they get to the log. This would probably work better with an early log head. I may try the triple carbs and a split big log. A plate between 2-3 and 4-5 should do the trick. Tap each mini plenum and run a balance tube between them I think. Three Wolf Enterprises Corvair Rochesters would work great. EASY to tune, all jet sizes still available, etc. The improved carbs flow about 90-95 cfm each.
Hey now, how about SIX individual mini plenums and SIX bone stock Corvair rochesters (80 cfm). That would be stupid over the top! I wonder if they would all fit on top of the log? I'm going to go measure.
When do those argie heads start shipping?
Rick(wrench)

edit

woops temporary insanity.

Inliner,
I like your numbers! Kelly's TurboFalcon is making a calculated 312hp based on ET and weight. So your numbers are pretty close. We run her car at 12lbs. of boost with a log head and she's going through the traps at 5100rpm.
Ummmm! 390hp with a head swap? According to a hp calculator, that would mean that Kelly's car would be able to run an 11.9 sec. ET!
Mike....where's our Argie head!
Will

I agree with does10s, I didnt really think about anything like that, for the price but now I'm making alot, and I think a different head could be in my budget! I'm going to start looking at them now!