I have a 2500 stall and currently running a xe268 comp cam.

Just curious what yall are running without having vacuum issues.

Trying to figure out if I can get by with a XE274 comp cam without having to use a vacuum canister. Furthermore, trying to figure out if it's worth the increase in duration with a 1500-6000 rpm power band.

Bottom line keep the 268 or bump it up to the 274

 

Either one of those are very mild. I ran a 292 solid cam and it operated my vacuum stuff at 8 inches of vacuum with no problem. If your system is In good shape it will operate fine.

 

I ran a 248/254@.050 solid flat tappet cam in my 302ci '69 Z28. It made 7" of vacuum at idle and the power brakes worked just fine. The '69 L-88 had operational vacuum headlights and that thing had a 264/270@.050 camshaft.

 

That's good to know what size stall do you have in the car?

 

Better yet what size stall do you need to run a 292

 

any issues that yall can think of in bumping the cam up to a XE274?

 

You seen their dyno results? It will give you an idea what you can expect.
http://www.compcams.com/v002/Pages/389/XE274H-10.aspx

 

Thanks Reelav.....looks like the xe274 is the largest I can run with the stall converter that I have in the car.

 

How is the 268 doing with those ported heads? Good low end torque? If it's more than you need then the 274 may be a good move. Any though to a roller instead of a flat tappet? Cost for me all said and done was about $1000 to roller convert mine.
Those Xe's have a pretty steep ramp for a flat tappet and are more prone to wiping a lobe.

 

Reelav,

I just got the cam out last night and it was smaller than I thought it was, which would explain the idle and lack of lope. I believe that the old cam was a 250h or 256h.

The heads are going on next week so I still have the pre-89 vortec heads still on the car. I am taking it to the race/speed shop to have them installed. For the amount of money that I am spending on components I want to make sure everything goes in as it should. Its not that I cant do it I just dont feel like spending money on a stupid error on my behalf. Also, I would sleep easy knowing that someone with over 40 years of mechanic time is putting the parts on.

On the other hand I have really thought about converting to the roller lifters but I dont know if its worth the extra $250 to do so. Hydraulic Flat Tappet cams are not a bad cam from my experience but if I make it past the break in I should be good right!?

Everything should be in and complete in a week or two. However, the owner of the speed show highly recommends that I stick with the XE268 over the XE274. Not sure why that would matter as I have a stall in the car and the vacuum should be sufficient given the comments from others on the forum. It could be that this will be the best match for the heads that he is building.

 

I would go with the speed shop's recommendation. The 274 has quite a lot of overlap. 60* to be exact. The bigger the cam the less street friendly it becomes and more problematic to tune for street driving. The XE268 has 54* of overlap. Overlap is going to dictate your vacuum and to a large degree your idle quality.

As the heads get better at flowing air the need for greater duration to get the same level of performance decreases. So it could be the speed shop owner knows how well these heads are going to flow.
Getting past the break-in is the biggest hurdle for flat tappet but you still have the potential to have a wiped lobe down the road.
Part of the problem may be that since OEM's are not making flat tappet engines in massive quantities that the flat tappet cam suffers from lack of quality manufacturing that used to exist when it was used exclusively.
That combined with the XE's design in that it lifts the valve very rapidly with less rotation of the cam put the lobe under greater stress. The difference between the advertised duration and the duration at .050 is 44 on the XE274 and the XE268. If the difference in these two numbers is less than 50 then it is a steep lobe. This makes the flat tappet cam's job a lot harder and imposes pretty high side loads making a wiped lobe more likely.

My roller cam is a 270 advertised duration and a 219@.050. a difference of 51, and this is on a roller cam.
Do some searches on wiped lobes. See what the circumstances surrounding the wiped lobe were and the consequences afterwards.
If you have Vizards book "How to build max-performance Chevy small blocks on a budget" look up the cam overlap section in chapter 7 page 91, and see what he has to say about overlap selection governing cam choice.

 

REEVLER,

Brother your money!!!!

Thats some great information and advice that you have listed up there.

I have done some research on the Comp flat tappets and there have been some issues in the past couple of years. But the majority seem to be satisfied with what the one they have been putting in their cars. But you know how that goes these days.

I am also looking and the Lunati Bootlegger in the Hydraulic Flat Tappet, which is all new this year. They have put a ton of research into this cam so you would assume that it is a good product.

Also good points on the overlap I forgot to touch on that.

 

To sum this up in a nutshell, you really need to know what compression you are running. If you have the stock 76 350 engine with cast Pistons and the stock 76cc heads, you have horrible set up for a hot cam. Even a mild cam would be lazy at low rpm. Porting the heads help but you'll need to mill .040 or more to get the compression even close to where you need it and then you may run into sealing problems on the intake if milled too much. I'm not sure what pre 1989 vortex heads are exactly but if you are changing them out. Let us know. It would be much easier to advise on what cam would work.

 

That bootlegger cam has some interesting numbers. A long slow ramp on the exhaust (pretty big split advertised but not so much @.050) and a very short fast ramp on the intake. I wonder if that to get the rumpity sound at idle and still get performance in the midrange and retain some bottom end torque?
66.5* of overlap would make the idle pretty rumpity I would think.
I like the 108 LSA's as well for midrange power. They do present their own challenges at idle though. More overlap and smellier idle exhaust.

 

There are two sets of vortec heads pre 1989 and post 1989 which are the ones w the sawtooth pattern. I have the other ones. Compression is 9:3:1 with those heads. The calculator has me at 9:9:1 with the pro comp 64cc190 aluminum heads. Should be plenty to pick that cam up.

 

Maybe I will give the bootlegger a shot it does look pretty stout. Not many people have them so it would be nice to have a little different sound

 

What exactly are you looking for performance wise? Your 76 has what, a Th350 or 400 with 3.08 rear ratio?

 

The Bootlegger has a huge I/E split (12 degrees @.050). These cams are Lunati's answer to the Comp Thumpr series. Despite being targeted at folks looking for sound, I've heard they run good. I'd talk to your builder and discuss your specific head flow rates to see if a big split like that will work or not.

 

Reelav,

I have the original TH350 with the stock gears. The trans will be my next mission after I finish the engine. Anyways I am shooting for 425-450hp that is my optimal goal. I think with all the mods i should be in the ball park. I am also really considering going full roller a lot less headaches if i go that route. I just wont tell the wife. Shhhhhhhh.

 

good points i didnt realize that was their answer to the thumper.....they do have a 268 duration. Well now that i think of it thats in the voodoo line isint it.