Engine design and effects on timing..

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blow-thru
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Engine design and effects on timing..

Post by blow-thru » Mon Apr 21, 2008 7:27 am

In a recent thread it was mentioned that an efficient exhaust system and therefore all exhaust related parts{ ports/ lengths etc}, would enable the use of less total timing....
Could anyone expand on this idea???
Is this due to a cleaner chamber fill requireing less timing to burn the A/F mix ????

On a similar topic is it of any disadvantage to running a low total timing figure { other than missing out on power potential } if the engine is happy ????????

Cheers Carl...

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timing issues

Post by bigjoe1 » Mon Apr 21, 2008 10:59 am

I built a pretty good 408 Ford for bracket racing. I had 10.75 to one, so he could run pump gas and save money on race fuel. I did all my dyno testing at 32-33 degrees. THe engine made 667 HP at 6700 RPM. In the car, he found when it set the timing at 35-36, the car drove around better, and actually ran a little cooler, but the quarter mile times did NOT improve. Most engines sound better with more timing, but they might not make any more power.

JOE SHERMAN RACING ENGINES

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Post by Horndog » Mon Apr 21, 2008 11:01 pm

In a N/A only combo. timing requirements are directly related to how efficient the chamber design is. The more efficient it is, the less timing usually is required.

In any N/A engine, effective and efficient exhaust scavenging will always produce power as long as the cylinder can be filled correctly and in a timely manner. Lobe timing is the key, not spark timing.
Jim Horner

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timing

Post by bigjoe1 » Mon Apr 21, 2008 11:33 pm

I dont agree completely, I have seen BB Chevys that want a bunch of timing, and some small blocks too. I think that the closer the sparkplug is to the center of the cylinder, the less timing it will need for max HP, You might leave a bunch of HP on the table if you did not try more advance when your tuning. I had an engine sent to me to try and find more HP. The timing was set at 35 degrees because thats what the engine builder told him to run. when I got the carb dialedin, and advanced the timing up to 40 degrees, the engine picked up 50 HP, He did not know why the builder wanted to run at 35 degrees.

JOE SHERMAN RACING ENGINES

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Re: timing

Post by Horndog » Mon Apr 21, 2008 11:44 pm

bigjoe1 wrote:I dont agree completely, I have seen BB Chevys that want a bunch of timing, and some small blocks too. I think that the closer the sparkplug is to the center of the cylinder, the less timing it will need for max HP, You might leave a bunch of HP on the table if you did not try more advance when your tuning. I had an engine sent to me to try and find more HP. The timing was set at 35 degrees because thats what the engine builder told him to run. when I got the carb dialedin, and advanced the timing up to 40 degrees, the engine picked up 50 HP, He did not know why the builder wanted to run at 35 degrees.

JOE SHERMAN RACING ENGINES
I do agree with you if these engine combinations used hi-dome pistons and large chambers Vs smaller chambers and shorter domes.
Jim Horner

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Post by Ron Golden » Tue Apr 22, 2008 12:35 am

I dyno a lot of different engines and very few want timing less than 35 degrees. Most require timing between 37-40 degrees for best Tq and HP.

Ron

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Post by Lucky13 » Tue Apr 22, 2008 1:32 am

We run a engine that has a very small bore & a very long stroke that likes between 24 & 28 in N/A form with any kinda of decent CR (10.5 and up). WIth lower compression they like on up around 32*. The combustion chamber is old and not very good but with the real small bore I guess it doesnt need much timing. I have often wandered what it would want if we updated the combustion chamber.



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Re: Engine design and effects on timing..

Post by automotive breath » Tue Apr 22, 2008 10:09 am

blow-thru wrote: In a recent thread it was mentioned that an efficient exhaust system and
therefore all exhaust related parts{ ports/ lengths etc}, would enable the
use of less total timing.... Could anyone expand on this idea??? Is this
due to a cleaner chamber fill requiring less timing to burn the A/F mix ????
I agree, a poorly scavenged cylinder can require more ignition advance.
Another factor that can contribute to high exhaust gas concentration is
reversion, when exhaust gases are forced into the intake, fresh charge
contamination results. This produces extremely lean areas in the
chamber that can burn very slowly.

These regions containing high concentrations of hot exhaust gases can
develop into highly reactive “hot spots” in the chamber. Late in the
burning phase these hot spots become a source of detonation.

Here's a link to some reading on cylinder mixing of the fresh charge
with residual gas:

http://me.engin.umich.edu/autolab/Publi ... 002_05.PDF


"...this means that generally in the cylinder there will be fuel richer regions
with lower temperature and leaner regions with higher temperature. This
could be very significant, since high temperature leads to advanced
ignition timing and faster burn rates, while a lower equivalence ratio has
the opposite effect.
.."

"...the effect of mixing in the cylinder is very important since it controls
the local temperature and composition in the cylinder. There is a
correlation between local equivalence ratio and residual gas fraction with
temperature. The assumption of homogeneous composition could be quite
inaccurate even under premixed conditions in the intake port..."

Image[/url]

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Post by rustang » Tue Apr 22, 2008 1:22 pm

I have a 347 ford with Dart Pro 1 170cc cylinder heads (unported) and flattop pistons. Compression ratio is 12.24:1.
On race gas (C12, and I've also tried C16) this thing only likes 29degrees of timing, 30 tops. When I first put it together the engine builder told me to run it around 34degrees. This lasted about 4 passes and I blew a headgasket between cylinders 6 and 7. There was aluminum on the exhaust valves, and I had to have the seats retouched too.

I've checked and rechecked the timing marks.

This head has excellent exhaust flow numbers. (in combo with 3" exhaust and x-pipe) I'm wondering if what's discussed in this thread (a good exhaust requiring less timing) may be contributing to my motor not wanting much advance also? Or since this motor has relatively restrictive intake and carb could that be making it intolerant to timing?

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Post by axegrinder » Tue Apr 22, 2008 1:48 pm

The intake manifold plays a part in this timing picture. Fuel distribution.

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Post by automotive breath » Wed Apr 23, 2008 12:58 am

rustang,

When you identify and eliminate the reasons why your engine is detonation
prone, I expect it to make more power with additional ignition advance. The
problem is likely not one specific thing but rather several little causes that
add up to a big problem. Also consider excessive or uneven cylinder head
temperature.

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Post by maxracesoftware » Wed Apr 23, 2008 5:34 am

rustang wrote:I have a 347 ford with Dart Pro 1 170cc cylinder heads (unported) and flattop pistons. Compression ratio is 12.24:1.
On race gas (C12, and I've also tried C16) this thing only likes 29degrees of timing, 30 tops. When I first put it together the engine builder told me to run it around 34degrees. This lasted about 4 passes and I blew a headgasket between cylinders 6 and 7. There was aluminum on the exhaust valves, and I had to have the seats retouched too.

I've checked and rechecked the timing marks.

This head has excellent exhaust flow numbers. (in combo with 3" exhaust and x-pipe) I'm wondering if what's discussed in this thread (a good exhaust requiring less timing) may be contributing to my motor not wanting much advance also? Or since this motor has relatively restrictive intake and carb could that be making it intolerant to timing?

likewise have seen between 27 to 29 deg BTDC on your type Engine
on my Dyno...and yes we tried as much as 34deg btdc and it hurt
power everywhere like yours . Pretty impressed with the Low-Timing
requirements of that type Head,
especially -VS- a similar small block Chevy combo wants more timing,
yet when playing around with various type Heads/Chambers,
and their varying amounts of BTDC Timing, i have'nt noticed
any major HP or TQ gains because of the faster burn chamber
yet...it just seems to make basically the same amount of HP for
the FlowBench CFM number..in other words, its not a lot
of difference in HP or TQ as you would expect,
it just seems to be like this =>

1-it will make 500 HP with 29 BTDC on the Ford
for given CFM

2-it will make 500 HP with 36 BTDC on the Chevy
for "same" given CFM

it does not seem to be a major Power gain,
but instead only very minor effect,
maybe its worth more Cruising down the HiWay at lower RPMs
under throttled conditions ?
Meaux Racing Heads
MaxRace Software
PipeMax and ET_Analyst for DragRacers
http://www.maxracesoftware.com
http://www.maxracesoftwares.com/forum/index.php
PipeMax v3.98   http://www.maxracesoftwares.com/forum/v ... f=14&t=249

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Post by blow-thru » Wed Apr 23, 2008 8:41 am

Thanks to all who have posted some very interesting points especially AB { I was hopeing you would join in } and there is more to my second part of my question ..
I have a stroker SBC in a heavy 4WD for towing and weekend fun, basic specs are 10.7 comp/measured 212/218 at .050" on a 110 lobe sep at 104 installed { card asks for 106} late 80's 193 swirl port heads ported with a dual plane and 750 vac .
Engine was built for gas {propane to you guys} so hence the slightly higher static comp but is being run in on premium pump until sorted .
My point to all this ramble is the engine can handle no more than 22deg total under full load in the higher gears without detonating ......
I have no problem with the way the engine runs { its faultless} and if wasnt for the verified timing { pointer and tdc mark} I would be seriously searching for answers.
The engine has no lack of power and low down torque but I'm wondering is there any power left considering conventional SBC timing figures are generally in the mid 30's .
Ive considered trying 20lt of race gas to see if it can handle more timing or is this possibly a combo issue ie small cam/advanced/high dynamic comp senario ????
Or have I magically stumbled onto a super efficient engine that does not need alot of timing ???? I somehow doubt this but its nice to wish !!!!!!!
Anyone have any ideas on why such a low total timing figure in my engine ?????
Thanks and Cheers to all ... Carl........

ps AB there appears to be a definate bias of mixture motion towards one side of the cylinder until very late in the cycle,even then its not very uniform...Is this the development of the "hot spots" or incomplete areas of combustion due to unhomogonous mixtures ????

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Post by David Redszus » Wed Apr 23, 2008 11:28 am

Residual burned gases (RGB) that remain in the combustion chamber will dilute the incoming charge. Since RGBs are inert, the volumetric efficiency has been reduced and the engine will require more ignition timing.

A mixture that is either too lean or too rich will also require more timing.
A mixture that is very close to stoich (for that particular fuel) will require the minimum amount of timing (and spark energy).

A combustion chamber that is poorly designed with long flame paths will require more timing. A compact, fast burn, high squish velocity chamber will require less timing. Spark plug location and tip temperature will also determine ignition timing.

Surface hot spots that will increase the local rate of combustion will necessitate less timing to avoid pre-ignition or early peak pressure.

Fuel sensitivity (RON-MON) will determine the operating range at which the MBT must be retarded to avoid detonation.

Has anyone worked with ion sensing to determine timing and mixture?

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Post by Tuner » Wed Apr 23, 2008 2:00 pm

My point to all this ramble is the engine can handle no more than 22deg total under full load in the higher gears without detonating ......
You deserve to be commended because you recognized your engine’s timing requirement and acted appropriately. Many people have timed that spiral port cylinder head at 36° and ruined several engines doing nothing about the detonation but bitching about it. People’s preconceived notions about timing have damaged a lot of engines because the “more is better” syndrome is almost a religion. It certainly has a cult following.

In the early 90’s, I watched some otherwise reasonably intelligent guys burn down Chevy 90º V-6’s, one a week all summer long at the local 1/4mi. oval. Fuel used was Unical 110. In Chevrolet’s “Power Manual” the instructions for modifying that engine clearly specify to use no more than 24º with its “swirl port” cylinder head. That’s the casting with the intake port only on one side of the valve guide and a spiral in the pocket under the valve. They also used the design on 350’s and Mopar made a similar head for the 318. The first couple of times I quoted what the Chevrolet book said about the timing they scoffed and ridiculed Chevrolet for such nonsense. Third week, I brought the book to the track and showed them the italics where Uncle GM tried to help. Two months later they were down lotsa $$$$’s, still at 36º and still looking for bigger radiators and oil coolers.

About a year ago I set up a QJet and an old single-point distributor for a Goodwrench crate motor that went into a `57 Chevy. The engine is the 350 truck version with the swirl-port head (like the V-6) and the hyd. roller cam. Once again, the guy in the shop (worker-bee) who installed the goods couldn’t believe the small numbers in the timing instructions and tried it his way. When it pinged and idled rough the “Quadra-toilet” was “too lean” in spite of 6%CO (at idle) on the 4-gas. The shop owner put one of the other guys who wasn’t as over-qualified on it and everything turned out fine when the timing was set correctly except for having to put up with the worker-bee muttering under his breath for a few days. For some reason the same guy has no problem setting the timing at TDC on the same engine when it’s in the Chevy truck with a computer and the TBI on it. For what it’s worth, that `57 Chevy has been averaging 18+ MPG around town and 22+ on the highway. Edelbrock intake and C.I. ram-horn exhaust manifolds.

That characteristic of (what misinformed people consider) ‘intolerance to spark advance’ is normal for that cylinder head design. When I set up a distributor for the spiral port head I treat it like a cross between the Poly-Spherical 318 Mopar and the 216-235 Chevy 6. They don’t need as much initial as similar valve timing with a regular head until the cam gets over about 230 at .050”, they want what timing they do want early (2000RPM), they don’t want much, and they like a teeny bit more timing to creep in at very high RPM. They seem to like a ‘normal’ vacuum advance, 15° between 8”hg & 15”hg.

Here’s a link http://www.innovatemotorsports.com/foru ... php?t=5125 to a discussion about detonation, timing, octane, etc. and the effect of detonation on exhaust gas and how that affects WBO2 readings. The dyno victim is a 632 Ford that made best power at 28° even with C16 that didn’t knock at 32°. With C16 it made 120 more HP at 28° than it did at 36°. Guess where the owner wanted to run it?

If you have Innovate’s LogWorks software you can look at the data. There’s WBO2 for each cylinder.
A mixture that is very close to stoich (for that particular fuel) will require the minimum amount of timing (and spark energy).
Unless something’s changed since Taylor’s MIT research prior to and during WWII the A/F (with gasoline) that has the highest combustion velocity hence requires the least spark advance is very near .87λ (12.8/1). The A/F that requires the least voltage to ignite is very rich, on the order of 10/1. The voltage measurements are reported in 30’s era research so I doubt if there was CD ignition involved.

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