BBC thoughts

General engine tech -- Drag Racing to Circle Track

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F-BIRD'88
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Re: BBC thoughts

Postby F-BIRD'88 » Mon Aug 14, 2017 5:10 pm

Question: If both the Lunati and the Straub cams ran the same and the lunati cam is showing wear,, why would you sell the Straub cam?
i am missing the logic here...

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Re: BBC thoughts

Postby GARY C » Mon Aug 14, 2017 5:14 pm

prairiehotrodder wrote:
GARY C wrote:
prairiehotrodder wrote:Yes plan #1 seems most logical and affordable. Now i've started thinking about cams again. As i stated in my other post, I sold my Straub cam and this Lunati is on its 3rd engine and is in roughish shape. Plus i don't feel its optimal. Its was just local and cheap so i tried it. I've been studying my David Vizard book and this is the cam i come up with according to his theory loosely scienced out by me for 555 cubes at 11 CR with a 2.3 intake valve.

ERSON E129894 302 / 306 274/278 @ .050 .740/.740 108 LSA

Chris Straub told me that my AFR 335 CNC heads require less difference in duration between the intake and exhaust than other heads so thats the reasoning for that. DV's book would put me at around a 104 - 105 LSA but thats impossible to find without going custom. I used 93 for overlap based on DV's graph and 106 for LSA to do the math to come up with 302 / 306 duration and used 4 for the difference to do the calculation to figure the duration. The overlap graph wants me to have 12.5 + CR but thats not happening either. I used 555 cubes and 7250 rpm to arrive at the 93 overlap. after all the math the Erson cam above seems to come closest to what should work. I'm sure everybody will have a different idea on this but i'm willing to hear everyone's idea. I've been wrong before.
Brian

If I read that correctly, after studying DV's book you misused his info to choose a cam that you your self admits is wrong for your application?

The cam does not make your engine a 7250 RPM engine... It is designed for an engine that is properly built for 7250 rpm...(Compression, head and intake size!) It is not a matter of will it turn the rpm but is it making power at that rpm?


I used the formula 's in DV's book which got me in the ball park plus what i've learned from the 2 cams i've allready run, plus what i've learned from talking to Chris to come up with the Erson cam above. For a real DV cam recomend i would need to pay $100 and all my flow numbers put into his program. Since i'm just in the 'kicking around idea stage" i don't feel like paying the $100 and thought i'd take a stab at it myself. I haven't bought anything yet and i'm not sure i am willing to fork out money unless i know cam specs ahead of time. I allready had an incident that took 2 months off my life over a secret cam. Many pro cam grinders are fully willing to tell you up front what cam i should buy.

I am not saying you should run a Vizard cam, I am just saying if your going to use his method you will be better off doing it as he intended.

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Re: BBC thoughts

Postby prairiehotrodder » Mon Aug 14, 2017 5:22 pm

F-BIRD'88 wrote:Question: If both the Lunati and the Straub cams ran the same and the lunati cam is showing wear,, why would you sell the Straub cam?
i am missing the logic here...


The Lunati cam is in now, it had a little better MPH. Got good money for the Straub cam and i want to move forward. I would happily buy another Straub cam but not the same one. If not now, one day i will up the CR and the cubes a little and then i WILL want a new cam. If my motor comes apart the Lunati cam Will be on racing junk. I have bought 2 cams and lifters from Chris and have been happy with it all. But i just want to keep going faster and setting new goals for myself.
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Re: BBC thoughts

Postby RevTheory » Mon Aug 14, 2017 5:23 pm

This is the correct chart. Is this the one you used?

BBC Overlap Chart.png
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Re: BBC thoughts

Postby prairiehotrodder » Mon Aug 14, 2017 5:33 pm

yes thats the chart however my book doesn't have that paragraphs underneath. I came up with 93 by using 555 cubes at around 7250 rpm. As the paragraph says its not dead on and other factors come into play such as CR and low lift flow. You tell me what DV would suggest for my current motor.

2.3 intake valve
540 cubes
9.9 CR
AFR 335 CNC heads (all flow numbers are on their website)
car crosses the line at around 7200 rpm.
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Re: BBC thoughts

Postby cstraub » Mon Aug 14, 2017 5:49 pm

4.350 Bore
4" Stroke
6.535 Rod
9.8 to 1 compression
Ported Brodix Oval ports
.903" Hyd roller
Straub Custom Hyd roller cam 260/258 .050" Duration
Engine was designed to run on pump gas. Customer is in Winnipeg.
At 475CID making 680HP, that is 1.43HP per cube at 9.8 to 1. At 540CID x 1.43HP per cube the correct engine combo should make 772HP. That should put any 3500 car deep in the 9's.
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Re: BBC thoughts

Postby GARY C » Mon Aug 14, 2017 5:57 pm

prairiehotrodder wrote:yes thats the chart however my book doesn't have that paragraphs underneath. I came up with 93 by using 555 cubes at around 7250 rpm. As the paragraph says its not dead on and other factors come into play such as CR and low lift flow. You tell me what DV would suggest for my current motor.

2.3 intake valve
540 cubes
9.9 CR
AFR 335 CNC heads (all flow numbers are on their website)
car crosses the line at around 7200 rpm.

Then shouldn't you be looking for peak power at about 6700 rpm?

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Re: BBC thoughts

Postby GARY C » Mon Aug 14, 2017 5:58 pm

RevTheory wrote:This is the correct chart. Is this the one you used?

BBC Overlap Chart.png

Is this the updated chart that did not get put in the book?

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Re: BBC thoughts

Postby RevTheory » Mon Aug 14, 2017 6:02 pm

prairiehotrodder wrote:yes thats the chart however my book doesn't have that paragraphs underneath. I came up with 93 by using 555 cubes at around 7250 rpm. As the paragraph says its not dead on and other factors come into play such as CR and low lift flow. You tell me what DV would suggest for my current motor.

2.3 intake valve
540 cubes
9.9 CR
AFR 335 CNC heads (all flow numbers are on their website)
car crosses the line at around 7200 rpm.


Just checking because there was a "whoopsie" on the chart when his book first came out.

Off the top of my head? 268/274 at .050, 106 LSA (ish- give or take a few on duration and hopefully that's enough to start nosing over at the stripe) but I wouldn't run that on 9.9:1 compression. I'd either cam down to match the existing compression or up it to make the combo right at 7,000+ rpm. But you know what they say about opinions...

Again, that's just right off the top of my head. Sniper Jr. and a 4500 too.
Last edited by RevTheory on Mon Aug 14, 2017 6:16 pm, edited 1 time in total.

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Re: BBC thoughts

Postby MadBill » Mon Aug 14, 2017 6:09 pm

Beyond DV's chart is of course his complete COS cam program..
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: BBC thoughts

Postby F-BIRD'88 » Mon Aug 14, 2017 6:18 pm

Look up the Difference in the weather data currently right now at Saskatoon,,, Memphis and Winnipeg BIG different note the uncorrected Barometer pressures and temperature.

Memphis and Winnipeg is going to dyno and track test run very similar

Saskatoon is NOT. It is a lot different. (especially today) And it is going to be a lot less power today
and at least some LESS power every day than the other locations.
This may be why you seem to be able to get away with a higher cr than me....
My air is always better air most of the time and it is hotter here to most of the time.

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Re: BBC thoughts

Postby F-BIRD'88 » Mon Aug 14, 2017 6:33 pm

I came up with 93 by using 555 cubes at around 7250 rpm

The car crosses at 7200

You are using the chart wrong.

you have to run the car higher than the Peak HP rpm point a the end of the 1/4..
A LOT higher if when the trans is a glide and the car is heavy.

So you'd need to gear it to trap at about 7800rpm.
you are not so tame the overlap
You also don't have 14:1cr so again tame the overlap and or advance the cam.

But of you are going to trap at 7200 rpm then pick the cam overlap for about 6600rpm
THEN ALSO correct for the lower compression ratio (and or advance the cam)

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Re: BBC thoughts

Postby F-BIRD'88 » Mon Aug 14, 2017 6:54 pm

If you ultimatly want to end up with a fast car the STraub cam was worth more in your hand
So you can test and compare car performance or even dyno performance
with it to compare against any new cam Straub or different to see if the new cam is
ACTUALLY better.. You have 2 good BASE LINE CAMS
They both run good.

You can by another cam "the perfect cam" or.... 10 more cams
You will NEVER actually know if that new "better" cam is actually better
on the dyno and or in the car where it actually counts
UNLESS and UNTIL you Test and compare it to ANOTHER cam.
You should have kept that cam whether working with the current motor
or a different 555 BBC w 11.5:1cr
That was a bad choice if you want to end up with a fast car.

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Re: BBC thoughts

Postby prairiehotrodder » Tue Aug 15, 2017 9:30 pm

Electric water pump, electric fan are now on the car and the cam is in at 103 ICL from 108. Good September air is coming soon.
Looked at a couple tunnel rams today. The Weiand and the Edelbrock Victor are my main 2 choices. The Eddy looks to have shorter, straighter ports while the Weiand is taller more curved. The Weiand is also cheaper.
Brian
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Re: BBC thoughts

Postby statsystems » Tue Aug 15, 2017 9:40 pm

prairiehotrodder wrote:Electric water pump, electric fan are now on the car and the cam is in at 103 ICL from 108. Good September air is coming soon.
Looked at a couple tunnel rams today. The Weiand and the Edelbrock Victor are my main 2 choices. The Eddy looks to have shorter, straighter ports while the Weiand is taller more curved. The Weiand is also cheaper.
Brian



You do realize a TR takes a different cam than a single 4 right?


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