BBC thoughts

General engine tech -- Drag Racing to Circle Track

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pdq67
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Re: BBC thoughts

Post by pdq67 » Sun Aug 13, 2017 12:32 am

prairiehotrodder wrote:How did we get on to the topic of building a smaller motor? Thats not happening.
Sorry, just food for thought is all. Back in the day, they used to spin these little class required size limited, short-stroked BBC engines up around 9 to10,000 rpm if not mistaken.

Need more compression, then hunt up a pair of old -206 heads and work them over.

They are large oval, 96.7 to 98 cc, bathtub, true closed chamber heads. I have a pair out in my garage! And they will breath just fine up to like 5,000/5,500 rpm or so! I bought them to play with a P/U 454" work-truck engine that is usually about 7.9 CR or so. I figure with the .020" thick steel shims, I could get it up to like 9.3 or so CR and not change the stock dished 454" pistons. Just a head change is all....

And there are the old, "smog", heads that are square-cut from the intake valve to the exhaust valve with the open chamber quench removed that are large oval that are down around 113 or so cc's. I read where they work a lot better than most would think because the exhaust valve quench is gone! BUT you have to CC these because they can vary a lot chamber volume-wise.... Like from 120 or so down to 112 cc's.... -818, -148, and -292 heads if not mistaken.

The late, great JL said that properly prepped large oval heads will support up to a mild 540 engine! And do dandy on the 496"/502" engines.

Years ago, JL did two mag. articles, One on the 496" and the other on the 502"! I want to say that the 496" engine got up to above 600hp with CC's great old 288AR solid street roller, but it's been years since I read both articles.

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Last edited by pdq67 on Sun Aug 13, 2017 12:58 am, edited 1 time in total.

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Re: BBC thoughts

Post by rmyauck » Sun Aug 13, 2017 12:50 am

Sorry my fault! Probably a better idea for road racing etc!

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Re: BBC thoughts

Post by Orr89rocz » Sun Aug 13, 2017 2:58 pm

prairiehotrodder wrote:looking for educated advice on the combo's i listed above.

It allready has 2.25" headers and they didn't help at all at my power level.
The convertor works better than what the tires will handle
The 4.10 gears are close as well.
Doesn't need more cam. allready tried 2 cams, same results.
Its easy to see that the CR is to low so i want to fix that. Don't really want to mill the heads because i wouldn't gain much there. Maybe 1/2 a point at most which would help but i would like to gain a full point.
Brian
Cam didnt work cuz the intake system is likely tapped out. Open head csa up along with intake and the power will be found.
Work on getting car to work at the track. No traction, no et. The suspension tuning needs taken care of and it will improve et.

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Re: BBC thoughts

Post by Newold1 » Sun Aug 13, 2017 7:59 pm

I'm going to go with my old keep it simple thoughts:

Go with your number 1. choice on your original post more compression and cubic inches can't hurt and when you've got the extra power and torque that will appear with that. Then you can fine tune the other needed aspects of the car and get yourself consistent high 9's. Be happy with that until your personality gets the better of you and you start yearning for mid 9's. JMHO

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Re: BBC thoughts

Post by prairiehotrodder » Sun Aug 13, 2017 11:03 pm

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
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Re: BBC thoughts

Post by statsystems » Sun Aug 13, 2017 11:08 pm

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


I wouldn't compromise on LSA just because you can't buy the cam off the shelf. The first thing I though was you were 3-4 degrees to wide on LSA without even doing the math.

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Re: BBC thoughts

Post by F-BIRD'88 » Sun Aug 13, 2017 11:15 pm

Why not just save rebuilding the motor and use that theory to get a DV cam
that makes the current motor in its current form make more power and torque.
If it is a valid way to spec a cam for better perf of the planned motor
it should also be a valid way to improve the current motor.

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Re: BBC thoughts

Post by statsystems » Sun Aug 13, 2017 11:37 pm

F-BIRD'88 wrote:Why not just save rebuilding the motor and use that theory to get a DV cam
that makes the current motor in its current form make more power and torque.
If it is a valid way to spec a cam for better perf of the planned motor
it should also be a valid way to improve the current motor.

Agreed.

Run the numbers for the combo you have and and post them if you don't mind. And then post up,the numbers of the two other cams you used.

That would be interesting.

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Re: BBC thoughts

Post by prairiehotrodder » Sun Aug 13, 2017 11:55 pm

F-BIRD'88 wrote:Why not just save rebuilding the motor and use that theory to get a DV cam
that makes the current motor in its current form make more power and torque.
If it is a valid way to spec a cam for better perf of the planned motor
it should also be a valid way to improve the current motor.

The Straub cam was a great cam but no matter what cam i feel the motor needs a point of compression. Then the optimum cam will work better and make more power. It has to. The motor is 3 seasons old and could use a freshening anyways.





[/quote]I wouldn't compromise on LSA just because you can't buy the cam off the shelf. The first thing I though was you were 3-4 degrees to wide on LSA without even doing the math.[/quote]

The Straub cam was on a 108 and i think Chris knows what he is doing. I'm thinking a DV cam would be 106 but i could be wrong. Many builders would go 110 or 112. Hard to know what theories to believe. After seeing the difference on paper between the 2 cams i allready ran then seeing the performance difference (both ran exactly 9.992 ET) i think the 108 would be fine. Also considering that 11-1 CR is at the upper end of the LSA selection formula by DV.
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Re: BBC thoughts

Post by MadBill » Mon Aug 14, 2017 12:00 am

statsystems 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


I wouldn't compromise on LSA just because you can't buy the cam off the shelf. The first thing I though was you were 3-4 degrees to wide on LSA without even doing the math.
2X. Ask yourself how much money you have in your car then look at the added % of that total for a custom cam. Regardless of what combo you choose, it's false economy to throw a lot of expensive parts together but settle for a cam that could easily be off 30-40 HP from a well-researched ideal.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: BBC thoughts

Post by statsystems » Mon Aug 14, 2017 12:05 am

MadBill wrote:
statsystems 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


I wouldn't compromise on LSA just because you can't buy the cam off the shelf. The first thing I though was you were 3-4 degrees to wide on LSA without even doing the math.
2X. Ask yourself how much money you have in your car then look at the added % of that total for a custom cam. Regardless of what combo you choose, it's false economy to throw a lot of expensive parts together but settle for a cam that could easily be off 30-40 HP from a well-researched ideal.

MB just threw down some good old fashioned common cents.



















See what I did there????

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Re: BBC thoughts

Post by Orr89rocz » Mon Aug 14, 2017 8:17 am

That erson cam would work well imo. Like to see tad more lift tho

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Re: BBC thoughts

Post by Newold1 » Mon Aug 14, 2017 10:28 am

You answered your own question about why taking the engine down is answered. "Freshening". If you need to do this type of work then that is the time to add the compression and cubic inches to the engine THAT CAN ONLY HELP! Matching a new camshaft design and profile to the resulting build is the best time to undertake that change also. Obviously a lot of attention should be given to picking the ideal cam and that will help yield the best results.
Bottom line, Idea number 1. is the best answer in my humble opinion. Don't get caught up in trying to do to many things at once,that only generally leads to being unable to identify what changes worked and what changes did not.

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Re: BBC thoughts

Post by RevTheory » Mon Aug 14, 2017 10:45 am

I totally agree with getting your compression up and who doesn't want more cubes?

Personally, I'd get all of that done and then hit up Vizard's COS-Cams for a grind. http://www.twperformanceparts.com/index ... ct_id=5532

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Re: BBC thoughts

Post by Orr89rocz » Mon Aug 14, 2017 11:02 am

With same heads and intake tho? All cubes is gonna do is make the intake system act smaller and its already on the low side. It will make more lower rpm power and torque but the thing already has trouble working at the track with the current power.

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