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cranking compression on alcohol motor, cam advance question

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Re: cranking compression on alcohol motor, cam advance quest

Postby xenginebuilder » Thu Jan 10, 2008 8:24 am

seefour wrote:I have a alcohol motor and the cam is in on 107 c/l , 108 sep 775-757 266-273 @.050. the cam is supose to be in at 104 int ex 112 now its 107 int 109 ex.


I agree with other posts here that the .050" numbers might be on the small side, but based on your cranking compression I'm guessing the cam also has a relatively loose lash spec? Maybe .028"-.030"? The actual seat timing might be 20 deg smaller than a different lobe design with the same .050" numbers and a .012"- .016" lash spec. You're intake valve is closing pretty early to get that much cranking compression.

i have a transbrake but never used it, I leave off idle


Why Not?

plugs gapped at .025


In my experience, that tight a plug gap does not get enough spark exposure to the mixture for reliable ignition, no matter what the box. If your ignition can't fire across a gap of .035" -.040" at w.o.t., you need to upgrade to whatever different ignition that will. When you start throwing around a lot of spark energy, your plug wires need to be really good, and completely free of dirt and oil, or you end up trying to ignite the outside of the engine...
If you lend someone $20.00 and never see that person again, it was probably worth it.
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Re: cranking compression on alcohol motor, cam advance quest

Postby Scott Smith » Thu Jan 10, 2008 9:27 am

seefour wrote:I have a alcohol motor and the cam is in on 107 c/l , 108 sep
775-757 266-273 @.050
the cam is supose to be in at 104 int ex 112
now its 107 int 109 ex
my cranking compression is 240- 245 lbs, I was wanting to put it back on 104 c/l like its supose to be. when does cranking compression become to much and the motor fights itself? being a alcohol motor would it like it better with more cylinder pressure?


Why is it supposed to be in at 104?
All that will do is kill P to V clearance on the intake side and make the cranking compression higher. (Might want to order one of those 24 volt starters) :lol:

You stated the numbers at 775-757 266-273 @.050
Well that doesn't help much without the .020 numbers but sounds like a good cam for a 10:1 motor.

:wink:
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here in texas

Postby seefour » Tue Jan 15, 2008 7:23 pm

I have a friend that I know who races 10.5 outlaw with a blown injected BBC motor car runs 4.50's in the 1/8 mile. He runs a 7AL2 and the HvII coil, tried a 7AL3 and then a MAG and the car slowed down.
Now Im not knocking experience but MSD says for a drag car the 7AL2 and HVII coil will work fine and they didnt try to sell me anything different???
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cam shaft

Postby seefour » Tue Jan 15, 2008 7:29 pm

the cam was specked for a 385 inch motor , I changed mid stream to a 4.0 stroke from 3.75 stroke, the cam is a TK series comp grind
266-273 @.050
189-191 @ 200
295-306 total
775-757 lift
53.5 overlap

My machinist agreed to back the cam up from 104 c/l to 107 because of the cubic inch increase and stroke increase.

comp cams says this cam in 410 inch motor should run well from 4500-7500 all day long

the TK series is one of their most aggresive lobe profiles from what I understand

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Postby KRYPTINITE RACE ENGINES » Mon Mar 24, 2008 7:31 am

[quote]On the 410 sprint car engines we run 264/272@.050" on a 108-LSA all the time. 15:1 on Alcohol with mechanical fuel injection. Why would this be any different?

What lift and where are you intalling this cam,looking for a 410 cam now.
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Postby mmmitch588 » Mon Mar 24, 2008 8:48 am

"xenginebuilder"In my experience, that tight a plug gap does not get enough spark exposure to the mixture for reliable ignition, no matter what the box. If your ignition can't fire across a gap of .035" -.040" at w.o.t., you need to upgrade to whatever different ignition that will. When you start throwing around a lot of spark energy, your plug wires need to be really good, and completely free of dirt and oil, or you end up trying to ignite the outside of the engine...

We run magnetos with that plug gap.Open up the gap & if you get a misfire ,then you aint got enough spark to handle your cylinder pressure
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Postby Hendrens Racing Engines » Mon Mar 24, 2008 9:25 am

I agree with Ron,try shortening up your ex duration.we did several years of alky cam testing on the dyno and found long ex duration blows all the torque out the ex. we run cranking cyl pressures of 300 lbs + in 15.0/ 16.0 -1 SB2.2 circle track engines all the time so I don't see how it would be a problem in a drag race application.in our tests top end power didn't suffer with shorter ex but we saw gains of more than 50 lbs torque @ 4000 rpm. the MSD 7AL with .045 plug gap never had a problem firing the mixture,in fact we run 6AL in the circle track cars with no firing problems. Bill
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cam duration and lift

Postby seefour » Mon Mar 24, 2008 4:50 pm

lift is .775 intake .757 ex lift lash .018-.020 , running lash at .016-.018 hot
duration at .050 266-273
295-306 total duration
108 sep
104 c/l intake 112 ex , but installed 107/109

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Postby mmmitch588 » Mon Mar 24, 2008 6:33 pm

We had a cam sent from Reher Morrison for our injected alcohol 580 ci BBC.Sounds like they gave us the wrong grind. 288° 304°@ .050".We were happy with the results.Nearly 2 seasons & the same springs still going.
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back on subject

Postby seefour » Sat Aug 23, 2008 7:47 pm

well Im back on this subject.
#1 the cylinder heads require only 24-25 timing
#2 methanol burns slower than gas
#3 I have high cylinder pressure
#4 the difference in MJ's between 7AL2 and MSD-8 115-120 vs 325-345
#5 crankshaft rotation msd7al2 is 20 degrees the 10 is 20-30 degrees and I dont know what the -8 is

would my motor bennifit from a hotter spark for longer rotaion given the cylinder pressure and timing requirements?


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Re: back on subject

Postby Ron C. » Sat Aug 23, 2008 8:54 pm

seefour wrote:well Im back on this subject.
#1 the cylinder heads require only 24-25 timing

**Most likely that's an ignition capability problem with the high cylinder pressure.

#2 methanol burns slower than gas

**So it needs more ignition lead time.

#3 I have high cylinder pressure

**Improper camshft and advanced way to much.

#4 the difference in MJ's between 7AL2 and MSD-8 115-120 vs 325-345

**And the MSD 10 Plus puts out 700mj's

#5 crankshaft rotation msd7al2 is 20 degrees the 10 is 20-30 degrees and I dont know what the -8 is

**That feature only works up to about 2800 rpm then the additional degrees of spark stops. Coil recharge time is not sufficient above 3000 rpm.

would my motor bennifit from a hotter spark for longer rotaion given the cylinder pressure and timing requirements?

**Alcohol always benefits from a hotter spark, it's oxygenated....so if you can fire it you can add additional fuel for additional power...within reason. Not so for gasoline.

Mike S


Your killing your performance capabilities, your trying to run a sprint car engine in a drag racing condition. Drag strips don't have corners to drive out of. It's wide open throttle conditions...period.

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Postby aussie mouse » Sun Aug 24, 2008 10:32 am

seefour,

Seems like you are stressing over lots of issues here.

I dyno lots of Alcohol engines for both Drag Race and Sprintcar customers

An MSD 7AL-2 will do what you need without any problem, have lots of customers running them on injected Drag Race set up's similar to yours.
Plug gap on Alcohol with MSD is best at around 0.032 to 0.035.

Nearly every engine I have tested with CHI 3V heads has ended up with the ignition timing between 25 to 28 degrees, so you are in the range here.

I have backed to backed a MSD 7AL-2 with MSD 10 and MSD 7 digtal units and on many serious N/A engines are yet to see any power gains once the timimg is optimsed for each unit. But make sure you have good battery voltage have seen this cause issues.
However if you were drowing the engine with a wet sogging A/F mix you could have ignition issues with nearly any ignition.

You may have some power to be gained on in the fuel system by going to 33 nozzles, on a similar combo 434 CHI Drag Race Cleveland we sawthe power go up around 40 hp everywere changing from 35 to 33 nozzles, mainly due to higher system pressure and the resulting much better fuel atomization.
However this not something you should be atempting on a chassis dyno, it sounds like you should spend some quality time on a good engine dyno, were things can be observed much better
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Postby seefour » Sun Aug 24, 2008 1:52 pm

what injection unit were you using on 434 chi motor? enderle or rons?
what pump and return?

I have rons billet 0 1/2 vain 78 return 33 nozzles already


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Postby fearitself » Wed Jul 15, 2009 9:00 pm

One thing no one offered to tell you the msd 7 they are right about the msd 10 is one bad daddy, but you best run two good batteries to power it at the track. or go with a magneto and run .019" on your plug gap anyway. Not to say i am smarter, just a fast learner and driver
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Postby Piranha » Thu Jul 16, 2009 8:50 am

Off the top of my head, the cam looks alot like the isky I had in a n/a 406 sbc, but I don't have detailed specs on it, and at much higher RPM's (7700 stall to 9000 shift). Granted this was a bigger bore, shorter stroke. No one mentioned promag 12's which is what everyone I run with uses, and anywhere from a .025-.040 gap. I run .035.

What does your pump flow? Without that # nozzle and pill sizes dont tell us much.
On a quick tour of the web I saw someone saying their Ron's 0 1/2 flowed 4.85 @ 4000.
If that is similar to your pump with 35 nozzles, 78 main, and no highspeed I would think the motor has too much alky in it.

That puts you at roughly 2.62 gpm at 7000, and probably 71ish lbs pressure.
That's more than the JF or comp B/ND's run in the mid-high 9000's even up to 10K.


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