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I need opinions please. I'm putting together a budget motor to get me back racing while I save and gather parts for my good motor. I've narrowed it down to 2 options. Both will be built with stock blocks, "781" open chamber oval port heads, forged pistons, 5140 I beams, and cast crank. The first choice is a 12.3:1 468 or a 10:1 496.

I'm thinking the drop in compression will negate any gains made by the extra cubic inches. The price difference between the two is mute (like $200 more for the 496). The only other factor is I do have a set of worked over "702" closed chamber ovals that would bump the 496 up a little over 12:1, but the small chambers are pinch off the exhaust side so really don't see them as an option.

What are your thoughts. Again this isn't my main motor, just something to get me by and keep as a spare. Thanks
 

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^^x2^^
 

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Long Live The King
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More cubes and better airflow over compression any day.

G
 

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The 702 heads and the 496cui. The exhaust will get out. maybe cam it a little different. CUBIC INCHES are more important.
 

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Discussion Starter #6
The 702 heads and the 496cui. The exhaust will get out. maybe cam it a little different. CUBIC INCHES are more important.
Forgive my ignorance here I'm just getting back into racing after about a 10yr break. I've always had small blocks before, this is my first BBC build. That being said- My first thoughts were just that, 496 with the closed chamber heads yeilding 12+:1. Was talking to some local BBC guys and they all told me I'd be f'n up with the 702's. They said the small chambers shroud the exhaust valve. Now granted I doubt none of these guys can even spell flowbench musch less evere seen one or a dyno for that matter. These are guys I used to walk all over with 100 less cubic inches back in the day. That's why I posted here I'm hoping some of you can shed a little light on which way to go.:confused:

I'd like to make around 500hp with this one. My local track is at 3622' so that should put me in the lower half of the 11's in a 3600# car.

Thanks to anyone willing to help
 

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T/S 368E
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Just went through this with a couple of pretty smart builders.
The head will flow what it flows, so throwing a few more inches at it doesn't make it flow more air.
In my case I was going to add 25", thinking the bigger bore would help unshroud the valve.
In my case they convinced me to just save the meat in case of a boo boo and get a custom piston with more compression.

I actually proved this years ago, but thought it was my lack of tuning skills back then.
I ran 9.31 with a 468" on nuts only, next year stroked it to 557" and ran 9.32 same heads and more inches didn't do jack.

Good luck.

.
 

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Long Live The King
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I ran 9.31 with a 468" on nuts only, next year stroked it to 557" and ran 9.32 same heads and more inches didn't do jack.

Good luck.

.


You ran the same heads with 90 more inches....did you run the same cam too?

He is adding 30 cubes.....

G
 

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Just went through this with a couple of pretty smart builders.
The head will flow what it flows, so throwing a few more inches at it doesn't make it flow more air.
In my case I was going to add 25", thinking the bigger bore would help unshroud the valve.
In my case they convinced me to just save the meat in case of a boo boo and get a custom piston with more compression.

I actually proved this years ago, but thought it was my lack of tuning skills back then.
I ran 9.31 with a 468" on nuts only, next year stroked it to 557" and ran 9.32 same heads and more inches didn't do jack.

Good luck.

.
If you don't mind telling, what Comp, weight of the car & heads did you use to rip out a 9.31 ET on just motor. Thanks
 

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T/S 368E
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The second part was just my experience, as a novice racer.
My point was 2 builders I trust and know a thing or 2, said if you are going to spend the money, add compression and save the meat.
I know a huge difference is not what he's doing, but I was going to add 25" and they both agreed 100%, all I would do was change the HP per inch.
So I am not max boring my block this winter, I'm going to have it honed and order the smallest piston I can, with plenty of wall left if ever needed.


My 468" was in a 3000 lb 10" tire 2nd gen. Ladderbar, double strange, BB-2's (for sale) single 1050, 5500 Coan, and not that great of a 60'.
I was actually out 60' by many many slower cars, but I just couldn't get it to what most other same set up guys were??
The key was those heads were kick ass on smaller engines. They were done by EPD, and he got it right for that combination.

.
 

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Long Live The King
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My 468" was in a 3000 lb 10" tire 2nd gen. Ladderbar, double strange, BB-2's (for sale) single 1050, 5500 Coan, and not that great of a 60'.
I was actually out 60' by many many slower cars, but I just couldn't get it to what most other same set up guys were??
The key was those heads were kick ass on smaller engines. They were done by EPD, and he got it right for that combination.

.

I'm guessing you changed the cam and gearing to work with the added 90 cu/in ?

G
 

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T/S 368E
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The cam was destroyed in the BOOM, but with a new converter, the rpms were the exact same, so no gear change needed.
I know the new cam was more aggressive, but like I said, it really didn't like more size.
People were shocked and thought I was lying it was a 468", and then disappointed when the 557" ran the same.
I did abort a lot of runs with the big motor and ended up with a glide, and that helped a bunch.

.
 

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Long Live The King
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The cam was destroyed in the BOOM, but with a new converter, the rpms were the exact same, so no gear change needed.
I know the new cam was more aggressive, but like I said, it really didn't like more size.
People were shocked and thought I was lying it was a 468", and then disappointed when the 557" ran the same.
I did abort a lot of runs with the big motor and ended up with a glide, and that helped a bunch.

.
Curious, were you running the same carb with both engines?

G
 

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496 and dont look back in your case.
Compression would be the second way to go or do both as youll have to buy pistons anyway.
 

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Well, since we're talking about a deflagrate* reaction here, what's not to like with both compression and volume, to a point. Sounds like a win-win situation to me. :p

*Everyone that messes with race engines should take a look.
 

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Long Live The King
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The cam was destroyed in the BOOM, but with a new converter, the rpms were the exact same, so no gear change needed.
I know the new cam was more aggressive, but like I said, it really didn't like more size.
People were shocked and thought I was lying it was a 468", and then disappointed when the 557" ran the same.
I did abort a lot of runs with the big motor and ended up with a glide, and that helped a bunch.

.

Curious, were you running the same carb with both engines?

G
Just checking ????

G
 

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T/S 368E
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The 468" used a #8896, 1050, the 557" didn't like it and it needed a 1150 to run right.
Trust me I tried to figure out why it made about the same HP, but those heads just loved being on smaller motors.
I put them on a 477" and the thing ran 8.50 in a 3200 lb car with a 150 plate. Whatever EPD did, they did it right!!

.
 

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The 468" used a #8896, 1050, the 557" didn't like it and it needed a 1150 to run right.
Trust me I tried to figure out why it made about the same HP, but those heads just loved being on smaller motors.
I put them on a 477" and the thing ran 8.50 in a 3200 lb car with a 150 plate. Whatever EPD did, they did it right!!

.
That makes perfect sense to me.... if they are sized correctly for a set combination of cubes and RPM... adding cubes will lower the RPM and most likely the thrust output. Realize that today most BBC heads like MORE cubes rather than less.

Did the larger motor like less gear?
 
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