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505 BBC Cam vs Compression ratio

General engine tech -- Drag Racing to Circle Track

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505bbjason
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505 BBC Cam vs Compression ratio

Post by 505bbjason » Mon Jun 29, 2020 12:20 am

I currently have a 505 BBC with the following:
13:1 CR
Dart Pro1 325's
Intake Valve: 2.300 Exhaust Valve: 1.900
Lift Int. Exh
.100 85.2 71.9
.200 153.1 120.0
.300 218.0 172.5
.400 286.2 215.9
.500 338.7 247.8
.600 386.7 296.4
.700 388.1 309.6

Cam is as follows
Numbers are based on a 1.7 rocker ratio (the engine has a 1.8 intake rocker on it)
Int. Exh.
Lift .707 .707
Adv. 294 302
.050 265 273

110 lobe sep.
106 Int cent.
.016 lash

@ .050 lift
IVO: 26.5 BTDC
ICL: 58.5 ABDC
EVO: 70.5 BBDC
ECL: 22.5 ATDC

I am putting together a pro touring car, and happened to have this engine laying around. What I'd like to do is see what I can do to make it pump gas friendly while spending as little as possible on it (switching to an LS down the line). If I were to knock the CR down to 10.5:1 or 11:1, would it make it a total dog, or am I going to need to do a cam change as well? It will be going in front of a close ratio T56 and a 3.70 rear gear FWIW. I'm not necessarily trying to optimize this combo, but just trying to make it something I can have fun with until I go to an LS.

F-BIRD'88
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Re: 505 BBC Cam vs Compression ratio

Post by F-BIRD'88 » Mon Jun 29, 2020 12:42 am

Yes lower the compression ratio to 10:1.

This will require a piston swap.
No it won't be a dog..

Wat ch the max spark timing when on pump gas
Don't give it more than it needs .

505bbjason
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Re: 505 BBC Cam vs Compression ratio

Post by 505bbjason » Mon Jun 29, 2020 12:52 am

What would you recommend for a starting point on timing? 32* total and slowly add more while checking plugs?

F-BIRD'88
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Re: 505 BBC Cam vs Compression ratio

Post by F-BIRD'88 » Mon Jun 29, 2020 1:33 am

BBC's generally like 38 deg . ( Stock like conbustion chambers )But on unleaded premimum pump gas the combustion can be a bit faster.. So if 35-36 deg is all it needs, thats all it needs.
The important thing on the street is to not over time it.
if with aggressive compression ratio.

My427stang
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Re: 505 BBC Cam vs Compression ratio

Post by My427stang » Mon Jun 29, 2020 9:08 am

I agree, I also think that's a lot of lift, over time you may lose some spring pressure, especially with added rocker (maybe not, I stay under .650 on street motors, so not a lot of experience way up there) Going back to a 1.7 rocker may be a little easier on parts if you have the spring pressure, although you could likely live to buy it back with a little more seat pressure. However, the combo at 10.5:1 should be a monster and run on pump premium with that cam, assuming the tune is good.

Depending on the piston and chamber design, if you have some quench pad and a tight quench distance, even with a relatively large bore and chamber, I'd set it to 35 total and test from there.

Be sure that you run a good oiled pin lifter though, street use on a solid roller is different than ripping down the strip. Oil helps incredibly, but back in the early 2000s, I was rebuilding a run of non-oiled pin Rat motors from other builders (and converting to flat tappet or less common then, hyd roller) It wasn't the builder's fault, people would ask for solid lifter Rat's and then cruise around with loose lash and hammer parts. At the time, Comp would recommend a max of 75 1/4 mile passes before a lifter swap/rebuild. If you didn't a lifter would come apart and take anything oily with it. 351Cs, and small blocks didn't seem to fight it, but the Rats seemed to hammer the lifters to pieces. This was before oiled pins became standard
70 Mustang, 489 FE, TKO-600, Massflo SEFI, 4.11s
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Orr89rocz
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Re: 505 BBC Cam vs Compression ratio

Post by Orr89rocz » Mon Jun 29, 2020 12:11 pm

I have a similar cam in my 10:1 555 with ported pro 1 345’s

It was built for turbo and on a 114 lsa. Still not a dog by any means. Lots of torque down low and probably would be alot better with a tighter lsa and earlier intake centerline.

My chambers were welded and cnc’d so they are 109 cc but liked 34 deg timing for max power

I run high 30’s at cruise rpms and around 30 at idle. Efi car so i control all that

10-11:1 should work. I dont think it be a dog at all.

505bbjason
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Re: 505 BBC Cam vs Compression ratio

Post by 505bbjason » Mon Jun 29, 2020 1:46 pm

Thanks guys, I’ll have to do some digging to see what springs are in it. I know the lifters are Crower HIPPO, so they should be adequate. Currently the cam is installed straight up. Thoughts on advancing or retarding any?

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