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Old 08-25-2008, 04:49 PM   #1
slim396
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Default which cam for 468 bbc

Which cam for a 468 bbc . The car weighs 2900lbs with driver , has 990 gm heads (ported) victor jr intake , 4:11 gears , stalls at about 5600 , turbo 400, 13:1 comp on alcohol rons toilet, and has a current 60' of 1.45 . The car currently runs 10.25 @ 4000' @ 129.5 mph .

The cam I am currently running is a 50225 lun solid roller .722 in/.722ex and duration is 280 in/284 ex at .050 110 lobe sep .

I am hoping to get into the high 9s is it possible with a cam change or can anyone see a bottleneck with anything else . I know the heads are not the best but I am hoping to hold off till I buy a bigger mill .

thanks ,

Slim
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Old 08-25-2008, 08:58 PM   #2
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If it were mine, I'd change the rear gear. Either 4.56 or 4.88.
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Old 08-25-2008, 09:25 PM   #3
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I built a 468 for my brother that runs on gas with a 850 Holley and the same basic stuff you mention. It made just over 700 HP and it will run 9.90s in a 3100 lb combo with a P/G and brake using a 4.88 gear and 32 inch tires. I used a .680 lift roller in it and it has an old scorpion intake which is weak. If I ported the heads and used a better intake it would make about 750 HP. If the info you provided is accurate being on alcohol it should be running 9.90s now. I agree with horndog the gear needs to go. I gave my brother a old TRW flat tappet 460 engine when he got the car and it ran 10.30s with a 5.13 gear in it but he hated turning the old motor so hard. JMO, RM
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Old 08-25-2008, 09:36 PM   #4
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DO a compression ck, does it make more than 165 ????? probably NOT use a 502A8LUN and grab ur ars that 722 deal the middle of the three is what i use in a 540 dragster running 5500-7500 @2000 lbsmakes no torque but good upper hp and after u find three tenths start working on the converter if it still hooks,,,
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Old 08-25-2008, 09:40 PM   #5
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DO a compression ck, does it make more than 165 ????? probably NOT use a 502A8LUN and grab ur ars that 722 deal the middle of the three is what i use in a 540 dragster running 5500-7500 @2000 lbsmakes no torque but good upper hp and after u find three tenths start working on the converter if it still hooks,,,
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Old 08-25-2008, 11:44 PM   #6
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Does the turbo 400 rob that much power . I am using 32 " tires so gear is probaly an issue . My egts are reading 1090 - 1150 and am using a 35 nozzle with a 104 pill
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Old 08-26-2008, 09:09 AM   #7
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Quote:
Originally Posted by slim396 View Post
Does the turbo 400 rob that much power . I am using 32 " tires so gear is probaly an issue . My egts are reading 1090 - 1150 and am using a 35 nozzle with a 104 pill


If you want to compare a 400 turbo to a glide, then the answer is yes - a 400 consumes more crankshaft power than a glide.

Knowing now that you are running 32" tire, you really should think about changing the gear.

As far as your EGT's they are right where they need to be.

Being that you run in altitude, you need to spin the engine faster to make power...... as long as the bottom end is up to snuff. If you spin it faster, you may need to add just a taste more fuel to keep the EGT's in the range you have now.
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Old 08-26-2008, 11:24 AM   #8
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X 2 on the gear change to a 4.56 or 4.88.

How hard are you turning it?

What do you go through the traps at (RPM wise)? General rule of thumb is near the shift point or slightly higher.
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Old 08-26-2008, 05:34 PM   #9
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I launch the car at 5000 , shift at 6500 and go through the traps at 6000 . The crank is a crossdrilled gm forged and was told only run it to 7000 . i can get a set of 4.56 or should i look harder for a 4.88 . I have to buy a different cam as this one is toasted so any thoughts comp cams tech advised me to go to a 277/278 , 742/744 at 112 lsa special grind and wont have it in time for next race .

Thanks

mark
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Old 08-27-2008, 08:51 AM   #10
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Quote:
Originally Posted by slim396 View Post
I launch the car at 5000 , shift at 6500 and go through the traps at 6000 . The crank is a crossdrilled gm forged and was told only run it to 7000 . i can get a set of 4.56 or should i look harder for a 4.88 . I have to buy a different cam as this one is toasted so any thoughts comp cams tech advised me to go to a 277/278 , 742/744 at 112 lsa special grind and wont have it in time for next race .

Thanks

mark

A GM steel crank to only 7000 ??? Why ?
My bb cast cranks seen 7500 with a top shelf balancer and good balance job.

If your crank is sound, it will spin beyond 7000 and live.
What are your pistons, rods and rod bolts (size) ? Then the next area to look at is the valvetrain. It needs good springs, rocker arms, pushrods, and spot on rocker geometery to live at higher rpms. Are you running a stud girdle ? If not, recommend one.

Now I understand why your car ETs what it does. With the gearing it has now and your current cam specs, it is not seeing any rpm: at shift point or thru the traps. Your current cam and the new Comp cam both have pretty big @.050 numbers so the engine needs to rpm to get into the powerband. Since you are running at 4000', the wider LSA of the Comp cam should help fill the cylinders. It also, moves the powerband up higher in the rpms. So the engine needs to turn more than what you are currently doing.

When you buy your new cam, be sure to get a new set of valve springs for it then too. You don't have to stay with Comp on the springs - FYI.

What caused the current cam to take a dump ?
If the lifters are scarred or the rollers don't turn freely or have too much slop in them, time for a new set or if they are rebuildable, get them rebuilt.

As for gearing, run the 4.88s if you stay with the 32" tall tire.

Hope this helps.

Jim
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Old 08-27-2008, 11:01 AM   #11
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I have run a GM forged crank for as long as 7 yrs turning the motor to 7 grand. That was using 7/16 bolt GM dot rods which are heavy but I used real light pistons and pins in it. RM
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Old 08-27-2008, 12:19 PM   #12
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My rods are Crower Billett Steel series . I just put new manley nextex springs in . I can not remember the size but I thought they were 280 lbs , 0.800" . So Horndog what size cam do you recommend , I will get a set of 4.88 gears and turn that engine harder . My other problem was airflow into the toilet . I was running a fiberglass frontend with no cutouts and no scoop . The throttle body was only 3/4 " from the hood . I have now installed a velocity stack to see if engine will breathe easier . I also am running crane gold rockers 1.7 and will be installing a set of crower lifters. That is what ruined my cam I piled up a lifter .

Thanks ,

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Old 08-27-2008, 03:34 PM   #13
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Originally Posted by slim396 View Post
My rods are Crower Billett Steel series . I just put new manley nextex springs in . I can not remember the size but I thought they were 280 lbs , 0.800" . So Horndog what size cam do you recommend , I will get a set of 4.88 gears and turn that engine harder . My other problem was airflow into the toilet . I was running a fiberglass frontend with no cutouts and no scoop . The throttle body was only 3/4 " from the hood . I have now installed a velocity stack to see if engine will breathe easier . I also am running crane gold rockers 1.7 and will be installing a set of crower lifters. That is what ruined my cam I piled up a lifter .

Thanks ,

slim


-) Rods are good.

-) Cam - go with the one Comp spec'd for you. It looks pretty good.

-) Double check the valve springs. They need to match up with the cam and RPM. That 280 # would be seat pressure NOT open pressure.

-) Rockers good. If you are going to buy new roller lifters, look into the severe duty Crower units with the HIPPO option. These lifters are machined to feed pressurized oil to the roller axle and bearings. BB's are hard on the valvetrain and money spent on premium lifters is a good investment. Also, make sure you are NOT RUNNING oil restrictors in the block.

-) Don't forget the stud girdle.

-) I'd ditch the velocity stack and run either a 2" or 4" cowl hood or put a forward-facing hood scoop on it. Fab up an air box either way you go. 3/4" is too small. It is starving for air. If this is a one piece front end, which sounds like it might be, run it with and without the velocity stack to see how it performs until you decide which scoop you want. It will be able to pull air from the hole you have in it now.


Good luck !

Jim

ps
you can pm if you have any more questions.
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Old 08-28-2008, 06:32 PM   #14
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Quote:
Originally Posted by slim396 View Post
Which cam for a 468 bbc . The car weighs 2900lbs with driver , has 990 gm heads (ported) victor jr intake , 4:11 gears , stalls at about 5600 , turbo 400, 13:1 comp on alcohol rons toilet, and has a current 60' of 1.45 . The car currently runs 10.25 @ 4000' @ 129.5 mph .

The cam I am currently running is a 50225 lun solid roller .722 in/.722ex and duration is 280 in/284 ex at .050 110 lobe sep .

I am hoping to get into the high 9s is it possible with a cam change or can anyone see a bottleneck with anything else . I know the heads are not the best but I am hoping to hold off till I buy a bigger mill .

thanks ,

Slim
sorry to hijack, but i have a setup similar to this but i have a glide and a 29.5 tire. what gear ratio should i use? mainly 1/8 mile racing but would like to be able to run the 1/4. thanks for any help.
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Old 08-28-2008, 06:47 PM   #15
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sorry to hijack, but i have a setup similar to this but i have a glide and a 29.5 tire. what gear ratio should i use? mainly 1/8 mile racing but would like to be able to run the 1/4. thanks for any help.
Try this,
http://wallaceracing.com/calcrgr.php
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