I've recently switched over from TBI to a carb setup, it's an lo3 motor. It was bored .030 over and I have full exhaust , a 10inch converter that with my setup gives me a 2500 stall with. I have been looking at a few cams and was wondering what some of you think.

Crane cam Operating Range: 2000-6200 RPM
Duration Advertised: 278° Intake / 292° Exhaust
Duration @ .050'' Lift: 234° Intake / 244° Exhaust
Valve Lift w/1.5 Rockers: .498'' Intake / .500'' Exhaust
Lobe Separation Angle: 112°

Comp Cam Operating Range: 2000-6000 RPM
Duration Advertised: 280° Intake / 280° Exhaust
Duration @ .050'' Lift: 230° Intake / 230° Exhaust
Valve Lift w/1.5 Rockers: .480'' Intake / .480'' Exhaust
Lobe Separation Angle: 110°


Comp Cam Grind Number: 282 H06
Operating Range: 2400-6200 RPM
Duration Advertised: 282° Intake / 282° Exhaust
Duration @ .050'' Lift: 226° Intake / 226° Exhaust
Valve Lift w/1.5 Rockers: .470'' Intake / .470'' Exhaust
Lobe Separation Angle: 106°
Max Lift Angle: 101° ATDC Intake / 111° BTDC Exhaust
Open/Close @.050'' Cam Lift: Intake - 12° BTDC (opens) / 34° ABDC (closes)
Exhaust - 44° BBDC (opens) / 2° ATDC (closes)

 

All of those have more lift than stock TBI heads can handle or use.

 

I talked to the guy who built the engine and he told me that the heads could handle a maximum of a 500 lift, but he suggested that I don't go over 480. The cam that I have now has a lift of 450 but I want something that will extend my rpm range work with my converter and give me a rough idle.

 

Lift capability is one thing, flow capacity is another. TBI heads are designed to enhance low speed flow. They don't do well when you up the ante.

 

To my knowledge the TBI heads don't flow anymore than 480. Is it safe to say that if I stay under 480 I should be alright?

 

Not exactly, what he means is that the duration of those cams makes the engine make it's power at higher RPM ranges. TBI heads are optimized for below 4500RPM, those cams are more like 3000-6000RPM type of thing (throwing aside the marketing BS of "recommended RPM range").

Pick one with ~210-215 duration @.050. With a 305 that would be best with your TBI heads.

 

he switched over to carb from the tbi

 

Understood. That doesn't change the characteristics of the heads.

 

Ahh I see, so something with a lopey idle is kind of out of the question. What about this cam?

Comp Cam XE262H
Operating Range: 1300-5600 RPM
Duration Advertised: 262° Intake / 270° Exhaust
Duration @ .050'' Lift: 218° Intake / 224° Exhaust
Valve Lift w/1.5 Rockers: .462'' Intake / .469'' Exhaust
Lobe Separation Angle: 110°

 

That's a lot closer, make sure if you have a roller block you get the roller version of that cam. Some people will even say the 256 is a better choice for a street 305.

 

Hey, good call johnsonm, I totally missed that.
With an Lo3 block, find yourself a roller cam in that range. I'm thinging XR258HR. That would complement your LO3 nicely.

 

Alright, but is it absolutely necessary that I use a roller cam or can I use hydraulic flat tappet?

 

No, you could use a flat tappet, but you'd need to buy the cam, lifters, and pushrods.
And ----> WHY?

 

I wouldn't need to do all of that when getting a new roller cam?

 

NO you would not have to change all that stuff over, im prettys sure that the lo3 block is already a roller block, but if your gonna do a cam job than i suggest that you atleast replace or upgrade your lifters and springs to compliment your new cam, everything else should be just fine. i hope sonix and all agree.

 

Lifters you have will work, as long as they are in good order. Roll smoothly, move through bores easily, no obvious damage.

Roll pushrods along a piece of glass, no wobble? No need to replace. Keep all pushrods, rockers, and lifters in the same spot.

New springs should be a yes. To keep the warranty offered by the cam company use only the springs they recommend. If you are el cheapo, and a gambling man, you can use some knock off pioneer or melling 100# springs, for like $25, but comp cams entry level, stock replacements are only like $60.

 

excellent, that's just what I wanted to hear. Thanks to everyone for the input, now back to the hunt.

 

LT1 take-out cams are pretty popular for LO3's. Similar to the XE258HR, roller lifter, etc. You can find them for decently low prices on eBay.

The nice thing about roller lifter cams is they don't tend to wear out unless really abused (like no oil changes). Ditto with the lifters - I'm using high-mileage factory roller lifters in my 350.

 

does anyone know of a roller cam that will give me a nice noticeable, while not going over a 500 lift.

 

Again, you don't want a noticeable idle. In order to get a "rumpy" idle, it needs duration, and or a low LSA. High duration will make power at higher RPM's, and unfortunately work exactly the opposite of your cylinder heads. So you'll have bad low end due to the cam, and bad low end due to the heads. But it'll sound cool, aside from being outrun by cavaliers.
Just get a loud exhaust, that'll make anything (V8 that is) sound good.

 

im not quite sure what your looking for here? you want a good cam that will make horseopower all the way through the band, have a lumpy idle to sound "cool", all for a good price and easy installation?

 

Something like the Comp XR252HR is about as big as you're going to be able to get and stay under .480 lift. It's too small to have any noticeable idle.

 

Ok since the bumpy idle is out of the question, the cam that I have in there now is 203/450 even on duration and lift. I had the company that built my motor upgrade the cam, and that was the biggest one they offered with the tbi. It's from a cam company called delta cams that was actually down the street from the company that built my motor. Is this cam good enough for my setup or could I benefit from something else? I also have a set of lt1 heads, but I don't think they'll work. Is there anything that I can do to make them work, i do know someone that welds aluminum.

 

Look up how to swap on LT1 heads. It's basically plugging up the coolant ports and rerouting them with external hoses, IIRC.
Those are leaps and bounds better than what you have, and would allow you to use a respectable cam.

With the current heads on there, it's barely worth the cash to upgrade to an LT1 cam, or comps 252HR, over your 203/.450" cam.

 

I know I'm going to get flamed for this, but if I were you, I'd hold off and save money for a 350 or something. You could get a 350 in your car for 1000 bucks I bet.

 

Its what i'm doin... just rebulding a 350 to replace my LG4...

 

Going to a 350 sounds nice, but the only problem there is that I just bought this motor which only has 8500 miles on it. I do have an lt1 block the heads and a 400 crank, but the block has been sitting for a while outdoors at my brother in laws house. It's something that I could do on the side I guess, but that's just bringing me back into the computer area which I was trying to get away from in the first place.

 

You can put a carb on an LT1.

 

Oh, is it difficult to do that?

 

Its the same as putting a carb on anything else.

 

can I use the same intake that I'm using now? It's an edelbrock performer intake 2104 87-95 non egr.

 

You'd need an intake for LT1 heads.

 

OK, I don't know why I didn't use my own common sense to figure that one out. Heh

 

What if I added a set of 1.6 roller rockers, how much if at all would that affect lift or duration?

 

You'll get 7% more lift, no real change in "advertised" duration, but a very slight increase in duration @ .050".

 

Ok great because I can get my hands on a set of those for hopefully nothiong. I just want to thank you all for the information you've given to me, it's helped me a great deal with some decision making that I needed to do. Those Lt1 heads that I have are cast iron not aluminum, is that harder to weld?

 

The problem with making an LT1 carbed is that you can only find one intake for it. and the intake sucks. if you were to have a performance engine your better off buying an intake for a 350 just not an LT1 (the ports on the heads and intake have to match tho) and making your own holes to mount it to the block and fill the orriginal holes. I did a little research since i was planning on turning an LT1 to a carbed set up. there is a plug in the block that you can remove to install a distributor