BBC thoughts

General engine tech -- Drag Racing to Circle Track

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statsystems
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Re: BBC thoughts

Post by statsystems »

MadBill wrote:Given that the G forces are 90° to 'normal' for a sideways drag carb, do they use circle track-type cutaway floats?

They should have slanted floats but most guys don't use them and it causes issues.
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Re: BBC thoughts

Post by prairiehotrodder »

Here is the update on my last race of the year. I made 2 changes to my car
1 - advanced cam from 108 to 103 ICL
2 - installed electric water pump / electric fan

Air today was no better than any other day.

first pass of the day was 9.972 at 135.61 which was my best pass ever barely and i had the exhaust on.

it was a street legal event and traction went away as street cars with radials began to dirty the track. Made a few 10.1 passes with terrible 60' times.

then they re-prepped the track and i had dropped my exhaust (about 50 pounds) and i went 9.964 at 136.62 which is my new best ever. All my 60' times today were terrible and if i could have had a better 60 i could have done much better. Overall i had hoped for more improvement but i'm happy that i made two 9 second passes and my motor and car treated me good this season.

I have 3 major things that will happen for next season:
-the tunnel ram with two 750's
- the erson cam
- change tires from 28 x 10.5 to 29.5 x 10.5

Brian
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cjperformance
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Re: BBC thoughts

Post by cjperformance »

Good results so far, nice work.
What is your exhaust setup? Looking at mph results on v off it seems line its working quite well.
Craig.
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Re: BBC thoughts

Post by F-BIRD'88 »

Very nice......
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Re: BBC thoughts

Post by Bob M »

prairiehotrodder wrote: Sun Oct 01, 2017 12:25 am Here is the update on my last race of the year. I made 2 changes to my car
1 - advanced cam from 108 to 103 ICL
2 - installed electric water pump / electric fan

Air today was no better than any other day.

first pass of the day was 9.972 at 135.61 which was my best pass ever barely and i had the exhaust on.

it was a street legal event and traction went away as street cars with radials began to dirty the track. Made a few 10.1 passes with terrible 60' times.

then they re-prepped the track and i had dropped my exhaust (about 50 pounds) and i went 9.964 at 136.62 which is my new best ever. All my 60' times today were terrible and if i could have had a better 60 i could have done much better. Overall i had hoped for more improvement but i'm happy that i made two 9 second passes and my motor and car treated me good this season.

I have 3 major things that will happen for next season:
-the tunnel ram with two 750's
- the erson cam
- change tires from 28 x 10.5 to 29.5 x 10.5

Brian
Have you considered a drag radial tire? I found better all around times switching from a 28 x 10.5 slick to a 275/60 DR. Not to mention a much better "feel" down the track then the bias ply slick.
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Re: BBC thoughts

Post by prairiehotrodder »

i've considered drag radials but i;m scared to take the risk and buy a set and find they won't work. My car is always on the edge of traction as it is. My track surface is easily polluted by radial tire cars dragging up sand and rocks and ripping up the rubber. I'm not saying they won't work but i may leave that idea for another time. I've been thinking about my combo lately and i know i've made some mistakes. I never should have put in a glide but now that i have it i don't think i'll change it. I need to do things to my motor to make torque. That will make my car faster with the glide. I think the Erson cam i bought and the tunnel ram will both help in that department. Its crazy how certain things virtually did nothing.
the crank trigger
the lemons headers
the lunati cam
moving the cam around.
mini tubbing my car
the exhaust on or off

all of these things did next to nothing. Maybe just shifting the torque and hp rpm range around a bit. I'm real curious to see what the t-ram will do.
Brian
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Re: BBC thoughts

Post by F-BIRD'88 »

One thing I noticed that might want to llok at is the big outlaw style tall cowl induction hood scoop.

The GM factory ones 2" ish tall on a stock flat hood work. They do create a high pressure cool air pick up point at the base of the wind shield. But the real tall outlaw cowl hood tends to let the air go right over the roof of the car and creates a low(er) than ambient pressure at the base of the wind shield ( relative )
and or the air comes thru the radiator (heated air). The result is like a negative supercharger where the engine is recieving air that is at a less relative pressure than the ambient air is and much less pressure than
say a ram air or forward hood scoop or true functional cowl 'induction"

This can be solved by a sealed carb pan with air duct that picks up the air in front of the radiator, all under the cowl hood.
Looks the same but functions a lot different.
Another path is a forward facing hood scoop ( also best of sealed to the carbs with a carb pan)

This can be the limiting factor ( "the cork") that will limit or stop other engine upgrades ( cams, headers etc) to not show a performance gain.
this may not be the only factor that is limiting further car performance gains but it is a area that needs addressing. Another is the Chin spoiler that goes under the radiator support. If it is missing a lot of air gets trapped under the car at high speed, creating excessive body air drag. The faster you go the worse it gets
when the critical front chin spoiler is missing.

Whats going on with the 1/8th mile time slip data compared to the 1/4 mile time slip data?
Can show you what if and where and how the car is performing as it goes down the track.

With the glide and now planed taller new tires you may want to swap the rear gears too.
The higher you rev up the motor with the tunnel ram and long duration cam the better if with a glide.

You could evaluate that by just doing 1/8th mile test drag passes or limited 1000 FooT passes with steeper gears
to see if the car likes it especialy with the tunnel ram. ET MPH
Then decide based on that for running the whole 1/4mile trap while buzzing the motor higher thru the traps with steep(er) gears.
It will either react to the change or it won't. The more gear, (mechanical leverage) the better the weight transfer on launch to get all the cars weight on the (limited size) back tires for traction.....Especially with a Power glide.

The taller diameter tries you have planed tend as a rule to "grow" a bit more than a short diameter drag tire does at higher speeds
thru the traps acting a bit like a "overdrive" in effect and allowing more agressive gearing.
This is how you make a heavy(er) weight, power glide car with small tires work.
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Re: BBC thoughts

Post by F-BIRD'88 »

Does your 'Glide have a trans brake or are you "footbraking it" ?
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Re: BBC thoughts

Post by prairiehotrodder »

it has a trans brake, i have the chin spoiler and a 4" cowl hood. I will run without a hood untill untill i decide if i am gonna commit to the tunnel ram. Then i will likely just cut a hole in it. I'm sure you are right about the gears. The car would likely work good with 4.30 or maybe even 4.56 with those taller tires. After i get a few passes in next summer i will consider it.


My 60' on saturday was 1.467 1/8 was 6.369 at 109.3 and 1/4 was 9.972 at 135.61 on my first pass with exhaust
later run was 1.481 6.375 at 109.73 and 9.964 at 136.62 without exhaust.

Also i was playing around with the timing and i think i finally noticed that with the cam at 103 the motor finally didn't need 40 degrees of advance.

Brian
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Re: BBC thoughts

Post by F-BIRD'88 »

It is too bad you could have not gotten more passes that day. Would have been interesting
to try looser valve lash to see if it liked a "smaller cam"

Every Big Block chev I have ever played with.... mine and others over the years have all wanted 38° BTDC
ignition time. Excessive hungry for spark timing @WOT tells me something is slowing down the combustion burn time
on 1 or more cylinders.. EG: Exhaust reversion EGR effect, lean or rich running cylinders (1 or more)...something like that. slow burning racing fuel..... Head gasket water leak.....
Carb air flow disturbance....

When you run the tunnel ram with no hood using a (forward facing) areo scoop on the carbs is a good idea.
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Re: BBC thoughts

Post by cjperformance »

prairiehotrodder wrote: Wed Oct 04, 2017 12:22 pm it has a trans brake, i have the chin spoiler and a 4" cowl hood. I will run without a hood untill untill i decide if i am gonna commit to the tunnel ram. Then i will likely just cut a hole in it. I'm sure you are right about the gears. The car would likely work good with 4.30 or maybe even 4.56 with those taller tires. After i get a few passes in next summer i will consider it.


My 60' on saturday was 1.467 1/8 was 6.369 at 109.3 and 1/4 was 9.972 at 135.61 on my first pass with exhaust
later run was 1.481 6.375 at 109.73 and 9.964 at 136.62 without exhaust.

Also i was playing around with the timing and i think i finally noticed that with the cam at 103 the motor finally didn't need 40 degrees of advance.

Brian
You may have missed but back a bit i was wondering about your exhaust combo, what are you using for an exhaust system?
Also do you know air conditions/DA from run to run?
Craig.
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Re: BBC thoughts

Post by prairiehotrodder »

exhaust is lemons 2.25" into 4" headers with 4" exhaust pipe into 4" magnaflow race mufflers and no tail pipes. I think the only thing that helps when i take the exhaust off is losing the 50 pounds. I do not know the air conditions from run to run.
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Re: BBC thoughts

Post by cjperformance »

prairiehotrodder wrote: Wed Oct 04, 2017 6:15 pm exhaust is lemons 2.25" into 4" headers with 4" exhaust pipe into 4" magnaflow race mufflers and no tail pipes. I think the only thing that helps when i take the exhaust off is losing the 50 pounds. I do not know the air conditions from run to run.
60' & 1/8th was faster with exhaust , just lost 1mph at the 1/4 stripe. Thats very good, would be great to know air conditions!
Craig.
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Re: BBC thoughts

Post by prairiehotrodder »

this is what happens when you work at night in my shop with the door open. Muskrat. Caught him in my shop the next morning. Released him into the wild.
Picture 363.jpg
Back on topic. I pulled the old Lunati cam out of my motor and am preparing to install the new Erson cam

http://www.pbm-erson.com/Catalog/Erson/ ... ERSE129894

The card calls for it to be installed at 108 ICL. Since the LSA is also 108 does that mean it is at 0 advance or retard ? Does that seem like a good place to start?

Brian
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Re: BBC thoughts

Post by F-BIRD'88 »

Yes when the LSA is 108 and the ICL is 108 the cam is "straight up" 0 degrees advanced...

Many racing cams are made like this and it is up to you the end user to find the best installed cam phasing.
It is not intended to be optimum. It is up to you to find optimum....

With the low compression ratio I'd advance that cam. Your last cam test drag test session showed this.
Advancing the (big) cam improved top end power (higher MPH) therfore overall power was better with the cam advanced...
Not unexpected (to me)

That long duration cam really want 14:1cr.. Advance it.....generously,,, if VTP clearance allows.
Start testing it (generously) advanced. Move it , test it.

You could do simple very short WOT stations stall tests with the trans brake to see which cam position give the highest observed trans flash stall rpm. Keep the stall tests short.
Allow plenty of time and air flow to cool the transmission and allow the trans fluid to recover
( air bubbles and temp) between stall tests.. Find a average. Find the best average stall test of a group of tests ( short time duration stationary stall tests should not hurt the trans)

Essentially you are using the trans as a load dyno.

A digital laser mechanics tach is better as it has much better rpm resolution than your tach unless it has digital readout or a USB port. If your spark box has a USB port or tach output it is usefull for this too.

You could also consider getting (build your own) a stationary test stall transmission where the trans output shaft is physically locked and using another test torque converter say with a disabled stator so it does not multiply torque at stall. It just acts like a high stall fluid coupling as opposed to being a "torque converter".
This allows you to test the motor under a controlled load, at home.
A crude dyno. Could use any GM trans for this. Got a spare GM transmission kicking around?

This can help you dial in the cam position and lash and dial in the carbs at home, under load.
before hitting the track next spring.
A th350 or th400 or even a th700r4 could be modded for this.
(make the trans be locked in high gear only and physically lock the high gear planetary or out put shaft)
A GM 8" to 10" torque converter could be modded for this.
(Disable the stator so it just spins)
if you do build this stationary stall test transmission be sure to build a full trans shield for it too.
Just in case it does come unglued.
This test trans could save you a TON of TIME and MONEY in getting the new combo dialed in
compared to multiple trips to the track or multiple dyno sessions.
You can even make money testing other peoples race cars with this test stall transmission/fluid coupling combo.

Got another glide transmission kicking around? or any other GM auto trans?
junk yard?
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