Has anyone went from a sbc to a bbc and slowed down? I have!

Old 06-09-2008, 08:40 PM
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I972Nova
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Default Has anyone went from a sbc to a bbc and slowed down? I have!

I went from a 500 Horse SBC to a 700 Horse BBC and slowed from 5.8's to 5.9's.

I am wondering what experiences anyone has had with this, I think the converter is my problem. It was built for my 535 Horse 406. It stalled 5400 behind it. Now it stalls 6200 behind my 468.

I thought it would work, now I am thinking it is way too loose!...

Any thoughts or advice would be greatly appreciated...

My 468 is a 12:1 motor with a .722 Roller and World Merlin III 320cc heads that have 2.300 and 1.880 valves. It has a 1050 Dominator with 38 degrees of timing.

My car is about 1950 pounds with the bbc and me in it... It has 4.86 gears (set up for 1/8 Mile) It only sixty footed 1.30 with the BBC and it had a 1.23 with the 406.

Thanks,
Josh
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Old 06-10-2008, 01:59 AM
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cepx111
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The torque your making now with the big block will make that converter stall much higher and seem alot loosier than behind your smallblock, or you might have just broke something in it.
I'd pull the trans pan and look for metal which would be a good indication that something let go in the converter.
I would have a new one built especially for that motor rather then trying to tweak your old one.
Also dont forget to figure in the weight difference between your sbc and the bbc which effects things like weight transfer, center of gravity etc. Maybe a chassis adjustment is all that's needed?

JMO
Goodluck, Charles
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Old 06-10-2008, 06:40 AM
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3dracing
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I have a 477 in a 1950# dragster and it runs 5.30's in the 1/8th. I'd say converter should fix it. I have it for sale in the classifieds if you know anyone interested.

Steve
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Old 06-10-2008, 08:49 AM
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OneBadGMC
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Default Re: Has anyone went from a sbc to a bbc and slowed down? I h

Originally Posted by DragsterJosh
Any thoughts or advice would be greatly appreciated...
Sure... Easy advice.

1. Call your current converter manufacturer, tell them your new combo, give them the serial from your current converter, and ask them if they can adjust it.

2. If they can't adjust it, post said SBC combination on RJ and put the converter for sale. Then get a new converter from your favorite converter manufacturer.

A converter is a hydraulic coupling that is made specifically for a given combination. Change the combination and the fluid coupling no longer responds as intended.
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Old 06-10-2008, 09:44 AM
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john858
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converter. and onebadgmc said it so well 8)
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Old 06-10-2008, 02:43 PM
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topcat572
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The 4.86 to me is a bit much. With a 4.00 stroke and that gear Your starting line ratio is killing You. For 1/8 mile with Your weight I think 4.30s would be the most I would put. Ran a 468 in a 2150 lb. roadster with 4.11 and ran a lot better than that, and this was a 1/4 mile car. I also had a 5800 converter, You may not be that far off. Good luck.
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Old 06-10-2008, 06:14 PM
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hammertime
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Default Re: Has anyone went from a sbc to a bbc and slowed down? I h

Originally Posted by DragsterJosh
I went from a 500 Horse SBC to a 700 Horse BBC and slowed from 5.8's to 5.9's.

I am wondering what experiences anyone has had with this, I think the converter is my problem. It was built for my 535 Horse 406. It stalled 5400 behind it. Now it stalls 6200 behind my 468.

I thought it would work, now I am thinking it is way too loose!...

Any thoughts or advice would be greatly appreciated...

My 468 is a 12:1 motor with a .722 Roller and World Merlin III 320cc heads that have 2.300 and 1.880 valves. It has a 1050 Dominator with 38 degrees of timing.

My car is about 1950 pounds with the bbc and me in it... It has 4.86 gears (set up for 1/8 Mile) It only sixty footed 1.30 with the BBC and it had a 1.23 with the 406.

Thanks,
Josh
Converter needs to be adjusted 5800 stall max, you need some help getting going with a 468, 6200 stall would be good for 540+ ci in a dragster. What did launch and shift at ? Your compression is hurting your HP #'s I'd bet its in the mid 600HP range not 700 also after seeing the #'s. A converter makes and breaks what a car runs for sure. 60ft is slow you need to get up and going. A little help it should be easily faster then the 406.
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Old 06-10-2008, 07:16 PM
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I972Nova
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I only shift at 6600 and was leaving on the converter at 6200.

Thank you all for your advice, I have a friend who has a group 1 TCI converter we are going to try in it, it stalled right at 5000 behind his 468 and I think with shifting at 6600 that should be a good start.

I can live with around 650 or so. Thats not bad for a poor ol truck driver ...lol...

I pulled the pan and everything looks great in there, A new filter and fluid never hurts though.

It is a hard tail car so no rear suspension to play around with, The car works great as far as planting the tires and going it just feels like my motorhome taking off after the initial hit.

The 4.86 gears were on the winter change list, but with the Aerospace rearend I have to buy the hi dollar gearset, so they got put on the back burner. If it would be consistent and run in the 5.40 - 5.50 range I would be very happy with that.

It hits great then gets lazy, I had 1.135 in my delay box and had a .006 first round. I was thinking converter myself so thank you all for confirming it... I am going to a 3 day race at Dragway42 with the TCI converter and i will let y'all know how it does up there...

Thank you ALL again,
Josh
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Old 06-10-2008, 07:38 PM
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hammertime
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Originally Posted by DragsterJosh
I only shift at 6600 and was leaving on the converter at 6200.

Thank you all for your advice, I have a friend who has a group 1 TCI converter we are going to try in it, it stalled right at 5000 behind his 468 and I think with shifting at 6600 that should be a good start.

I can live with around 650 or so. Thats not bad for a poor ol truck driver ...lol...

I pulled the pan and everything looks great in there, A new filter and fluid never hurts though.

It is a hard tail car so no rear suspension to play around with, The car works great as far as planting the tires and going it just feels like my motorhome taking off after the initial hit.

The 4.86 gears were on the winter change list, but with the Aerospace rearend I have to buy the hi dollar gearset, so they got put on the back burner. If it would be consistent and run in the 5.40 - 5.50 range I would be very happy with that.

It hits great then gets lazy, I had 1.135 in my delay box and had a .006 first round. I was thinking converter myself so thank you all for confirming it... I am going to a 3 day race at Dragway42 with the TCI converter and i will let y'all know how it does up there...

Thank you ALL again,
Josh
Leave off a chip not the converter the motor doesnt have (i'll say) enough "ass" to get it going leaving on the converter. I think you can make the 486 gear work, see it done all the time around here. Launch it at 4400 shift it at 6600. I hope the converter stalls atleast 5500 with your motor.
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Old 06-10-2008, 07:38 PM
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topcat572
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Default BBC

Just found my SLR chart, You good on that, My bad. ops:
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