[CDMBill]

I am rebuilding a stroked big block which will now be a 580" 4.5 stroke by 4.530 bore with Lem and Charlies' fully ported TFS A heads, 10.4 to 1 compression. I want stay with the Comp Solid Street Roller lobes for as much durability as possible, the question is what size/duration? This engine has an old TFS single four manifold with a 1090 King demon and as much spacer as will fit under the cowl hood.

The standard SR292XR is 254/260, .698/705 (1.8 rockers) on 110, they have two larger lobes, 266/.716 and 272/.727 . This is a street driven 4000# 71 Mustang convertablewith a six speed and 4.11's.

What would you guys recommend: lobes, LSA, advanced/retarded?

 

[Lem Evans]

254*/260* too small for the size of your engine IMO . I like the 266*/272* deal .
Also , Comp will grind a 260*/266* unit . Maybe a 260*/272* would work .

 

[CDMBill]

bigger cam

Any thoughts on the LSA? and does there need to be that much split with the exhaust as good as it is on those heads? 72% based on an earlier post.

 

[kim]

Would like a little more compression, then you could move into some longer duration lobes. You have some monster heads on a monster displacement, but the rest of the intake is killing the combo. You could use another 1000cfm in carberation, and a tunnel ram and or sheet metal intake would really fill the bill.


Without the intake and carbs........ you have to crutch that intake charge. SO more duration to fill the engine,.... and the compression just isnt there to sacrafice the seal.

Your current combo is SCREAMING for about a 1200 cfm dominator....

Or as stated, if you go twins, the engine could really perform under a pair of 1000 CFM HP's.

 

[Lem Evans]

The pump gas/street thing clouds the issue . An engine like your's with compression and race only would look like 284*/300* with 113* or more LSA . These big engines seem to like a lot of exh lobe .
But the LSA etc will need to be diff for the pump gas...the amount of overlap effects the cyl pressure . It may be time to talk to the guru at Comp for a better overview .

 

[CDMBill]

Pump gas, low hood, reasonable longevity street rollers

It seems there are always compromises for this sort of deal. Yes I want all the power I can make, but even with a cowl hood I can only go so high which rules out the tall TFS single plane and a tunnel ram. As a "driver" I need some tractability, stable idle, decent part throttle operation at 2000-2500 rpm for highway use and no detonation with the always problematic California 91 pump gas.

I ran into occasional detonation issues in hot weather driving with a similar sized cam at 10.7:1 with the early style AL Cobar Jet heads on the prior 572 so I'm making the compression safer, plus it will see some nitrous on occasion. RPM range 3000-6500 is dictated by drivability, durability and keeping the bottom end in one piece.

So the remaining question is how far to push the cam specs within the existing set of constraints. I'm down to just a few choices and am looking for the best advice. Thanks guys.

 

[rmcomprandy]

Have ALMOST been there...

About a year and a half ago, I built a street driven combination similar to yours except it had "Blue Thunder Chevy Exhaust Port" heads on it.
CompCams has a .400" series lobe lift lobe, (316-7), which worked VERY well on the exhaust with the street roller lobe 304XSR on the intake lobe.
That cam was #4878/#4058-10 which is 266*/279*@.050" - .398"/.400" lobe lift on 110* seperation installed straight-up.

 

[jpierce55]

Try Ed Curtis at FTI cams. It sounds like a truly custom cam may be inline here.

 

[Guest]

Hey Bill, I really like your convertible. I have a 73' Mach 1 and a 72' Grande, so I'm partial to the big mustangs. Not to change the subject, but what's your source for a cowl hood - custom?

 

[Racer_Rick]

I am getting a custom roller for mine this month. This has got to be the friendliest, most knowledgable folks around. Give 'em a call!
http://www.mmeracing.com/

 

[92Prostreet]

580 SROKER

The pump gas/street thing clouds the issue . An engine like your's with compression and race only would look like 284*/300* with 113* or more LSA . These big engines seem to like a lot of exh lobe .
But the LSA etc will need to be diff for the pump gas...the amount of overlap effects the cyl pressure . It may be time to talk to the guru at Comp for a better overview .

For my Aheaded 572 Eric at Diamond hooked me up with 13.5 and suggested at least 112 LSA I'm looking at a crane 35-SR00012 272/[email protected] .640/.625 W/1.73 114LSA SPRING [email protected]/395
But with this amount of cr and the LSA Will I need to run at least 112 octane?
Or to bleed off some cr go to Comps 270/270 712/712 spring 230/600 ?Thanks for reading TOM

 

[CDMBill]

CR and cam shafts

To my unaided eye that compression will need better gas although it might live on 100 you may be looking at even better depending on conditions.

The springs on the Crane seem on the light side as well given the size of the valves in the A heads. There are far more knowledgable people on here than me however.

How you realy intend to use it makes all the difference, that and willingness to frequently check and replace parts.