stringbean

I'm currently in the process of deciding what parts to use to build my 305 in my 91 rs. I'm going for a good lower rpm motor with good torque and decent hp numbers. My goals are 250 hp and 325 torque at the crank and would like to meet this goal at or below 5000 rpm. I would also like this engine to have a rough idle not so much that it causes issues with vacuum but enough for a good sound. The current parts list are as follows.

Edlebrock performer intake
Edlebrock performer 600 cfm carb
Ported l03 heads (I know there not the greatest for performance so please don't tell me)
Hooker competition headers
Full Exhaust
Comp Cams High energy 268h cam

My question is will this cam work well with my other parts and do what I want if to do. If not what other options are out there I am open to any suggestions as long as in the end i meet my goal. Thanks

InfernalVortex

iTrader: (4)

The idle/performance you want does not match the lumpy idle you also want. That said I think the cam choice is a good compromise.

I think the xe262 might be a better cam than the 268H. What heads do you have? The TBI 187 heads or the TPI 081 heads? The 187 heads have relatively good exhaust flow and probably would work better with a 268h. The 081 heads would probably work better with the xe262.

I think you'll get a lumpier idle than you expect and the powerband will go a little higher than you want, but I think it'll still be a decent street car.

I would consider an RPM or RPM air gap intake manifold, though. That some quick easy power over the regular performer which is pretty much a stock replacement. Hood clearance may be a concern but worst case scenario you can run a slightly shorter open element filter. The Performer RPM is by no means a high rise intake, it's just taller than the regular Performer.

FueledSoul

iTrader: (18)

So im just going to assume that you have a hydraulic roller block in your 1991 RS and you said l03 heads... So unless you or someone else swap in a different non-roller motor... The High energy 268h cam is for hydraulic flat tappet unless you want to run hydraulic flat tappet's in a roller block but why? The flat tappet is old technology. In roller set up the components last longer and you can make more power due to the lifters having rollers you can have a more aggressive ramp profile... Anyway id recommend a roller cam for your roller block if that is indeed what you have now... look into a XR264HR... but now another problem arises the heads, l03 heads can only support about 0.450" or 0.460" of lift im not sure how much more you can run with beehives springs but anything over 0.460" you are going to risk pulling studs but you can pin them by drilling them and pinning them to keep them from pulling out or do screw in studs... Also the 1.84 valves ant going to cut it if your looking for a good cam the factory 305 heads are going to hold you back A LOT... But if you are planing to do all this work to the heads then i would really look into 1.94 valves and a 3 or 5 angle valve job and maybe a back cut, this alone would yield better flow even over porting...

five7kid

iTrader: (14)

Swirlport heads are actually pretty good for low-RPM torque. But, the 268H is not.

And, not only are the heads not capable of supporting over .450" lift without modification, the intakes also don't flow any better after .450" lift (even with "porting"). But, the exhaust ports do flow pretty well without "help".

This cam should meet all your needs, assuming you are starting with a roller-ready block: http://www.summitracing.com/parts/CCA-08-300-8/ . As stated, rough idle and low-RPM power are not compatible. You could special order a cam with less LSA to roughen the idle a bit, but that would also raise the powerband. Just pick a good muffler to get the appropriate sound (the LG4 in my Berlinetta II had a great sound with factory exhaust manifolds & Y-pipe, cat, and a Flowmaster 80 series muffler).

Oh, assume new valve springs. Might as well do retainers while you're at it and eliminate the heavy exhaust valve rotators.

A "regular" Performer would be better for low-RPM torque and power than a Performer RPM.

Oh, I'm not sure I'd convert to carb to achieve your goals. TBI should be more than capable.

stringbean

So what kind of power curve could I expect if I did choose the 268H cam vs another cam more suited for lower rpm. Also will the cam work with my heads or will the higher rpm cam be "fighting" with the low rpm l03 heads. As far as machine work on the heads I work in a tool and die shop so machine work is no big deal. In the end I want a good engine to make a decent street machine and have at least some what of a rough idle. I do not care to have a slightly higher rpm engine as long as it performs the way I want.

InfernalVortex

iTrader: (4)

I think something like the 268H or an xe262 would be a nice setup for you if you didn't want a lower RPM range. If you dont mind spinning it to 6000 RPM they'd be pretty good. It's just a choice you'll have to make.

However... do you have a roller block? If you have a roller block there are FAR better options out there than the xe262 or 268H. Dont even bother with flat tappets, go roller. It's more than worth it.

If you want to learn the hassle of tuning a TBI, stay with it. It can support the power you want - look into the EBL system. If you want the hassle of converting to a carb and driving a carbureted car in this day and age, then do that. Just do what you prefer.

I know the 268H is an older grind, but it's only 218/218 @.050. My 262 is 218/224 @ .050, and it's a newer grind with more aggressive ramps, but my 350 makes torque from 1250 RPMs and up, and Im running an RPM intake.



A 305 will be a lot more torque-challenged, but those aren't exactly huge cams you've chosen. I'd say they were perfect but you said you want a low RPM motor. I think an xe256 might be a pretty good cam for you if you're going flat tappet, should have a nice lowish powerband.

stringbean

Ok well out the window with the idea of the non-roller cam and the idea of keeping this engine a low rpm motor. I'm going to go with a roller cam and settle for a slightly higher rpm cam to get the effect that I'm looking for. So now my current thought for a cam is a xr270hr. Its power range is from around 1500-5500 rpm. So would this cam be a better choice for my build and work with all my other parts to give decent power and do closer to what i am wanting?

InfernalVortex

iTrader: (4)

Those powerband figures are for 350s, 305s will go a little higher.

With a roller you can make more power with less cam. Also your TBI heads flow a LOT better through the exhaust than the average SBC head. Terrible intake flow, but decent exhaust flow. This cam might be pretty good for you:

http://www.summitracing.com/parts/CCA-08-420-8/

I wish I knew more about the factory grinds, there's gotta be some good stuff in that 210-220 duration range for you.

I dont think the xr270 is a bad choice, may be a tad large for your 305, but it wont be extreme. But I wonder if a single pattern cam might be better for you.

stringbean

These type of questions are the ones I need to consider before buying my cam I don't want to be one of these people that just buy a random cam because its big and think it will make more power, I want to make a educated decision. If there's anyone out there that cam help it would be greatly appreciated.

stringbean

Ok so I talked to a guy at comp cams today and he recomended to me a cam its not on there web sight but heres the specs 224/230@ .050 502/510 and 110 lsa. Does this sound about like something that would suit my needs? thanks.

bluers91

A cam that big is going to push the peak rpms up > 6k rpms. I am going to run an isky roller 209/217 but with vortec heads because I got it cheap. Consider something like the Comp xr264hr or xr258hr. The lower rpm tq will be better with less duration.

86LG4Bird

iTrader: (1)

Speaking of factory grinds: GM ZZ3/ZZ4 cam - 208/221/112. I've picked up two of them, takeouts from the ZZ3 and ZZ4 crate motors for under $75.
Unless your exhaust is factory quiet, you'll hear a rough idle for sure in a 305. At 650 rpm in my 350, you definitely know it's not a stock cam.
Peak power will be 5500-5800 in a 305 with Performer intake and headers, I'd conservatively estimate 275 crank hp with those heads.

bluers91

Right, that zz4 is a great affordable option too.

stringbean

Ok so the cam that he recommended would take me up into the 6000 rpm range to make peak power. Where would I expect to see peak power at with the xr264 and xr270 cams? Also how fast can a safely spin the stock bottom end in my lo3. I really don't care to spin it that fast as long as it is not going to kill it to fast btw the motors got 88k on it rite now.

stringbean

Ok so today i was at a good friends house and he gave me a holley 750 carb with vacuum secondary's. If I get this carb jetted correctly would it run ok on my engine or is it just going to be way to much?

NagleMac

iTrader: (1)

I'm in the same position as you, I'm thinking just an f-body lt1 cam, they are just under the amount the heads can take and they aren't a high rpm can like most aftermarket ones are, I can get one from an impala for $50 but it's smaller than the f-body one

86LG4Bird

iTrader: (1)

The B-body (ImpalaSS) cam doesn't give up much at all to the F-body cam, despite its shorter valve events. It has a 111.5 LSA as opposed to the F-cam's 116 or so. Identical overlap. It has more low end up to about 3000 rpm than the f-cam, and peaks about 400 rpm sooner. I made 309 rwhp with it in my Impala (LT1 engine).
I believe GM rated them at 15 hp difference (275 vs 260); however, most of that difference is due to the more restrictive factory intake and exhaust on the B-cars.

NagleMac

iTrader: (1)

I know, and for $50 you really can't beat that

HUSSAIN

good luck

five7kid

iTrader: (14)

stringbean, I'm afraid this thread got past me.

I don't see where you're doing something other than LO3 heads. None of the cams that have been discussed will work well with them.

A 750 VS on a 305 will run, but you probably won't be very happy with the way it drives.

Oh, a ZZ4 cam with Performer intake with LO3 heads on a 305 will NOT make peak power at 5500-5800 RPMs. The parts mix is just all wrong.

86LG4Bird

iTrader: (1)

Good catch. Thank you; I forgot about his heads.