EFI cam in a carb motor? .... compromise?

[Caveman Tony]

Would the wider LSA of an EFI cam allow me to run more duration, but not lose low-end torque?

I'm debating what to put into the GM Goodwrench motor in my '56 this winter... right now, its "hecho en Mexico" bone-stock.

Edelbrock 600, dual-plane, headers. 200-4r, and 4.10s... Drives nice right now, but I'm wanting a bit choppier idle, and waaaay more mid-range power. Not much needed on the top-end, as the truck is just a cruiser for now.

I know its a bit handicapped by the 8.?-1 compression, but next year heads and thinner head gaskets are planned... not gonna do it all at once though.

Would love to go with a full-roller cam, but can't afford that expense.

Any thoughts?

[Caveman Tony]

This from TC on another thread... but addresses the exact topic. I definitely want better throttle response, so should I be looking at a cam with a tighter LSA? (i.e., less than 108?)


"....If his cam specs where close to what they run in ProStock he'd have to run a wide LSA because the durations are so big, but he's not running a cam with 290-300 duration at .050 or 1.000"+ lift, is he??...... So tightening up the LSA may bring him more power........especially if he's running something like 114 or 116........Put it this way the cam for my weepy old small block has 270/278 duration at .050 and has a 103 LSA.......

The reason I went with the 103 LSA is because it will create a shit load of cylinder pressure and cylinder pressure equates to horsepower........It also tightens up the powerband and increases mid-range torque at a small sacrifice to peak horsepower, but face it our motors spend more time down the curve than at peak Hp, so the added power you get down the curve with a tighter LSA should equate to better ET's(acceleration).........And another benefit will be that the engine will RPM faster(quicker) and have a way snappier throttle..........."

[TC]

This from TC on another thread... but addresses the exact topic. I definitely want better throttle response, so should I be looking at a cam with a tighter LSA? (i.e., less than 108?)


"....If his cam specs where close to what they run in ProStock he'd have to run a wide LSA because the durations are so big, but he's not running a cam with 290-300 duration at .050 or 1.000"+ lift, is he??...... So tightening up the LSA may bring him more power........especially if he's running something like 114 or 116........Put it this way the cam for my weepy old small block has 270/278 duration at .050 and has a 103 LSA.......

The reason I went with the 103 LSA is because it will create a shit load of cylinder pressure and cylinder pressure equates to horsepower........It also tightens up the powerband and increases mid-range torque at a small sacrifice to peak horsepower, but face it our motors spend more time down the curve than at peak Hp, so the added power you get down the curve with a tighter LSA should equate to better ET's(acceleration).........And another benefit will be that the engine will RPM faster(quicker) and have a way snappier throttle..........."

It all depends in what your trying to do, a tight LSA is not for everyone......It also depends on your Cam Specs, your not going to want to run a 106 LSA on a cam with 230 degrees of duration at .050, the cylinder pressure will be out of sight and detonation will surely happen......And let me say the 103 on my cam is not for everyone, all that the Crower Catalog says about it is "strong midrange and upper rpm torque, they don't even give a RPM range, just says dependent on Valve Train, though three different desktop dyno's all put the peak HP at about 625HP at 6300rpm.......This is where the 103 shines, by bringing in peak HP earlier in the RPM range....It will also narrow the power band, making it's power in a narrower rpm range, it's also why it's designated as a short track circle track cam along with being a drag race cam......The key to this cam is a stall converter and steep gears to keep the rpm's up and in it's power range......

And let me add, a tighter LSA will also have less idle Vacuum and a choppier idle......

[TC]

Would the wider LSA of an EFI cam allow me to run more duration, but not lose low-end torque?

I'm debating what to put into the GM Goodwrench motor in my '56 this winter... right now, its "hecho en Mexico" bone-stock.

Edelbrock 600, dual-plane, headers. 200-4r, and 4.10s... Drives nice right now, but I'm wanting a bit choppier idle, and waaaay more mid-range power. Not much needed on the top-end, as the truck is just a cruiser for now.

I know its a bit handicapped by the 8.?-1 compression, but next year heads and thinner head gaskets are planned... not gonna do it all at once though.

Would love to go with a full-roller cam, but can't afford that expense.

Any thoughts?

With 8:1 compression a tighter LSA will help raise cylinder pressure and you'll gain torque through the rpm range, though there might be a minor loss of HP at peak power........So basically tightening up the LSA can be a way to increase cylinder pressure on a motor without raising your static compression........For a daily driver and something that really isn't going to be raced I wouldn't go less than 108 especially on a cam that doesn't have a lot of lift or duration.......If you want to stay around a the stock lifts and durations I wouldn't go with anything less than 110.......

[Stich496]

my thoughts would be to do the heads first.. (vortecs) and be on the look out for a roller set up..
I'd do everything in my power to not run a flat tap cam.. the money you think you'll be saving will go out the window when you see the cost of the oil to let a flat tappet cam live.. 7-9+ a quart or 13 buck additive on top of the oil..
a trip to a big swap. hershey or carsles would yeild the roller retrofit kit used and not to much,

[CDMBill]

Umm, I think this is all mostly backwards. If you want to crutch the low compression for the moment a tight LSA cam isn't going to help as the higher overlap is what bleeds the cylinder pressure at the RPM ranges you'll be operating within. Intake air going out the exhuast.

The best bet is to build for where you are going to be eventually. I'd imagine there are folks on here who can point you to cost effective factory roller cam parts for your traditional SBC. I'd agree that you'll want to get to a nice hydraulic roller set-up if you can and used parts may be a very good way to go rather than new, cheap flat tappet stuff while keeping inside your budget constraints.

The typical EFI cam's wide lobe sep is there because it makes for a wide flat torque curve which is good for street motors. The newer factory stuff takes advantage of the good heads like to Vortec's so bear that in mind. Its a crusizer so the right cam will make a happy drving experience. I'd look at those Comp Thumper cams more top of the page if a bit of lope is desired.

Racier stuff has little to say for your situation. My new combination was intended to push the pump gas limits and it has with a 282/294 @ .050 spec at 113 lobe sep, .830 lift cam and 11.86:1 compression. It made silly power across a very wide RPM range. Yes it runs on pump gas and yes it can be street driven although cooling on the freeway drives was an issue at Drag Week this year so we failed that test. But these kinds of combinations and specs don't apply to your situation.

Buld carfully for the future knowing that you'll have some compromises in the mean time. The worst sin in my view is to spend money twice for the same component when you didn't have to.

[Barry Donovan]

efi cam works for carb motor.. as read in another forum (and agreed)
if the efi cams origin had a single plane or dual plane, might be a quirky problem down low.

Carbs tend to be tighter LSA..but run anything.

this subject had me on a four cylinder boxer.. the ever bouyant bouncy atmosphere..
I have a carb and large lobed EFI cams, but was afraid to use them together..

no problems at all, in fact it is the greatest unrunted full idle I have ever heard. Poor carb was treated like a runt for no reason.

you 8 cyl guys can do anything..I would not even second guess swapping things around.
go for it.