Question for cam gurus

[AA Performance]

Posted on another site as well but trying to find out how much cam I need to get 1000HP + on a BBC pump gas pro street engine. It will be solid roller, 4.60 by 4.75 stroke running Brodix SR20 heads, tunnel ram intake with 2 x 4500 cards, static comp around 12:1. Would like to achieve the goals with a max RPM around 7000. Cam I have discused with a cam company is around 278 / 294 @ .050" with .475" / .460" lobes with a 1.70 or 1.75 rocker on a 114° LS. Was told due to the TR intake to run more exh duration. Why???. I have also seen that GM new 1004 hp 632ci runs 270 / 287 HR with 780 / 782 lift with EFI. Both cams are close. I haven't run that much split except on heavy nitrous use. Whats the reason?

[Tom68]

Posted on another site as well but trying to find out how much cam I need to get 1000HP + on a BBC pump gas pro street engine. It will be solid roller, 4.60 by 4.75 stroke running Brodix SR20 heads, tunnel ram intake with 2 x 4500 cards, static comp around 12:1. Would like to achieve the goals with a max RPM around 7000. Cam I have discused with a cam company is around 278 / 294 @ .050" with .475" / .460" lobes with a 1.70 or 1.75 rocker on a 114° LS. Was told due to the TR intake to run more exh duration. Why???. I have also seen that GM new 1004 hp 632ci runs 270 / 287 HR with 780 / 782 lift with EFI. Both cams are close. I haven't run that much split except on heavy nitrous use. Whats the reason?

Definitely not a cam guru, the split does two things, 1 get's your idle speed down a little by decreasing overlap, 2 later inlet closing for high rpm power peak, which you don't need. Will either be set with several degrees of advance or the lobe center should be tightened up, not a recommendation but 109 degrees would be what I'd have expected to see recommended. Again only layman observations from me at this end of the field.

[PRH]

Seems like it should be 1000hp to me.

I don’t think it would need that much split if you’re targeting 7000rpm though.

[AA Performance]

I asked the cam company if timing events would be different with the tunnel ram intake compared to a single 4bbl and this is what he came up with, the extra duration on the exhaust. I dont know the reason behind it but if you look at what GM has with there new 632 EFI crate engine making 1004 HP with there symetrical port heads, its a HR cam which ends up to be very similar to this SR cam in all aspects, just dont know what LS it is ground on.

[CamKing]

I would recommend a 273/283@.050", .500"/.485" Lobe Lift, 115 LSA

The reason for the longer exhaust durations, is that with an over-square 2-valve engine, you don't have enough exhaust valve area, so you need to add duration to evacuate the cylinder.

[PRH]

I would recommend a 273/283@.050", .500"/.485" Lobe Lift, 115 LSA

The reason for the longer exhaust durations, is that with an over-square 2-valve engine, you don't have enough exhaust valve area, so you need to add duration to evacuate the cylinder.

Over square?

4.60 by 4.75 stroke

[BOOT]

Over square?

https://en.wikipedia.org/wiki/Stroke_ratio

[PRH]

Uh yeh....... I know what over square is.

A 4.60 bore x 4.75 stroke is under square.

[CamKing]

Uh yeh....... I know what over square is.

A 4.60 bore x 4.75 stroke is under square.

I can never keep that straight.
the longer the stroke gets for a given bore size, the more undersized the valves are for the CID.
With that 4.75" stroke you need a lot of exhaust duration for that undersized exhaust valve to evacuate the cylinder.

[PRH]

I figured that’s what you meant....... I just wanted to point it out and give you the chance to respond instead of leaving out there on the interwebs for eternity.

[CamKing]

I figured that’s what you meant....... I just wanted to point it out and give you the chance to respond instead of leaving out there on the interwebs for eternity.

Oh, it wouldn't be the first mistake I've made. Not even the first today.

[bob460]

This one peak's at 6400rpm on pump gas and 10.75 comp!!

https://www.shafiroff.com/chevy-pump-ga ... d-sr20.php

[F-BIRD'88]

Another reason for the longer exhaust duration is with a tunnel ram you want to rev it up and rev it out the back door. (thru the traps) Extends the top end power.
Follow Cam King. . You won't go wrong.

[KnightEngines]

I would recommend a 273/283@.050", .500"/.485" Lobe Lift, 115 LSA

The reason for the longer exhaust durations, is that with an over-square 2-valve engine, you don't have enough exhaust valve area, so you need to add duration to evacuate the cylinder.

Yeah, this is pretty close to what I'd use, I'm a bit of a pig tho, I may add another 2-4 deg.

The one you had listed has too much extra ex duration.

[AA Performance]

I would recommend a 273/283@.050", .500"/.485" Lobe Lift, 115 LSA

The reason for the longer exhaust durations, is that with an over-square 2-valve engine, you don't have enough exhaust valve area, so you need to add duration to evacuate the cylinder.

Yeah, this is pretty close to what I'd use, I'm a bit of a pig tho, I may add another 2-4 deg.

The one you had listed has too much extra ex duration.

So you guys think 10° extra on exh is fine? Why has GM on there 632 1004HP EFI pump gas deal HR cam running somethging very similar to what I have shown? Only thing is it doesn't mention LS. They are running a single plain intake with a throttle body designed to run your 93 octane.
CamKing, how aggresive are your lobes and how much spring would they need with steel valves?