rtchaney

In an 87 305, carb, what affect, if any, would putting 1.6 ratio full rollers onto a stock camshaft provide? Wuld i need new springs and retainers? The cylinder heads was recently rebuilt and got slightly larger valves and new seals. They had a port job to match my felpro along with the exhaust ports being cleaned up. I was also wondering if i would need to replace my lifters if i got a larger cam. I ask because the individual who owned it before me had new ones, stock, put in. Thank you for any insight.

sixpackmtrspts

going with ratio rockers will give you more valve lift and more overlap. you may feel some differeance, but there will be a difference. you may have to elongate the pushrod holes int he head to run them though, you need a tool http://www.compperformancegroupstore...y_Code=PUSHROD

if you swap cams you will need to get new lifters as well, you cannont run used lifters on a new cam or vice versa, the cam will go flat typically.
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i just relized, you didnt specify whether it was a roller cam or flat tappet, the above statement only applies to a flat tappet cam, roller lifters and cams you can use old and new with no issues.

mnorton

In 1987 our cars got roller cams so the lifters are rollers too. You can re-use roller lifters with a cam swap, most of us do.

Going to a 1.6 rocker will open the valves a bit more, (use an online calculator to find the new lifts) but if you still have stock exhaust that won't gain you anything noticeable. With a full headers and back exhaust, maybe 5 to 7 HP gain over stock rockers.

I'm not sure if your car came with the "peanut" cam which has really low lifts and could use any kind of help. The 305 Autos all got it, but the 5-Speed TPI cars got the better cam. I'm not sure what came in the 5-Speed Carb cars....

Since the heads were recently rebuilt, you could probably use the stock springs with 1.6 rockers. But to get any good gains in power you will need to get a bigger cam, in that case you would also need new springs.

Do the full exhaust system first, with the 1.6 rockers. If you are going to do a cam swap, you need to pick the cam before buying the rockers so that you can calc the new lifts and not go too high as to exceed the capabilties of your heads. Coil bind when the valves are at full lift is the issue here. In many cases you would then want to have 1.5 rockers.

rtchaney

I'm runiing shorties to three inch collectors back to a 3" magnaflow cat, thats it. There is no back pressure; although there is a slight rumble in the drivers seat since that is about where the cat stops . That brings up another question. How much lift can you go stock? - Coil bind aside. If i get a new cam, i'm getting behives; I just don't want the valves to hit the pistons. I could see that causing a problem or two...

rtchaney

GM Stock Cams
.05" Dur 1.5:1 Lift 1.6:1 Lift Lobe Sep. Notes
202/207 .404/.415 .431/.443 114.5 87 350,305man
179/194 .350/.384 .373/.410 109deg 87 305 auto
207/213 .415/.430 .443/.459 117deg 88-89 350,305
202/207 .413/.428 .441/.457 114.5 90-92 350,305
- All of the above was pulled from the "Tech Article" and written by Paul Huryk.
What would be a good upgrade for a 305 with a shift point at 5000 or 5200? Lots of torque and streetable would require a lobe sep of 110-112, right?

dave-92gta

iTrader: (1)

sorry to but in.. im kind of after the same answer as you are rtchaney. i have a 92 l98, and i got everthting upgraded...intake and dual exhaust, no cat. i spend quite a bit of cash on this, and i want to get a new cam to get my car to about 450 hp... now since im broke, i would like to use my heads that i already have. i know tehre not nearly as good as aftermarket ones, but they will have to do. now much lift can i get without touching the pistons? i want to rebuild them and give them a nice port job etc. i decided on a cam i want but i dont know if it will fit. the cam is a comp cam

XFI" 268 Hydraulic Flat Tappet Camshaft
Chevy 262-400ci 1955-98
Lift: .520"/.515" w/1.6 Rockers
Duration: 268°/280°
RPM Range: 2000-6000
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oh.. also.. i would like the car to be able to reach 6000 rpm.. if i rebuild the top end of the heads i would be able to do this right? i think i will be able to becuase the heads arnt moving..but i jsut want to be sure before i spend 300 bucks on a cam

mnorton

It's hard to say where the valves would hit the stock pistons. That depends on a few things: The deck height, the head surface, the head gasket thickness not to mention the rockers and cam. The only way to really know is to measure, calc, and measure again. I've read that many have no stock piston clearence problems with lifts of .550. Personally I would stay below .525, most heads don't flow any better at higher lifts anyway.

mnorton

Dave 92 GTA - A 1992 engine is a roller, the cam that you listed is not a roller cam.

Also you need to list the durations @ .050 as well.

rtchaney

That's a little more power than i'm planning on running, but the same thing to be achieved - good power on a stock cylinder head. I have heard that going to all roller aluminum rockers and chromoly pushrods will give a 350 anywhere between 25-45 hp... I know that friction kills but, that seems a little high. Any input apritiated.
p.s. - good luck on the 450, i only want 300.

mnorton

Whomever told you that 25-45 HP gains were possible lives in a different world than I do.

I'll say it again, much closer to 5 to 7 HP gains over stock rockers.

Supervisor42

Customer: Uh, yea, and I'd like the cam that makes 450 hp with stock heads to go with those 45 hp rockers.
Speaker: Will that be all for you today? Would you like a hot apple pie with that?
Customer: That's not going to be more than $6.12 is it? because that's all I have.
Speaker: Your total is $5.96 please drive around.

Office Depot commercial:
~That Was Easy!~

rtchaney

That would be a little too nice to fathom,

dave-92gta

iTrader: (1)

ok...yea im jsut looking at things... anywho..i need a roler cam eh... with the roler lifter... ahh got it.. thx so much...good info guys... anywho... i dunno about the logic behind this aftermarket heads dont flow better than stock at high rpm.. they have to.. slock l98 heads are 165cc, and aftermarkets are around 195-215.. or more.. depending on make and price.. like trick flow ehads are like 3gs said and done....but they are 250cc intake and 100cc exhaust.. that has to flow better then stock.... anywho....i dont know much.. and you could be right..it jsut does not make sence if you are.. anywho...Supervisor42.. are you telling me something with this?

Quote:
Originally Posted by mnorton
Whomever told you that 25-45 HP gains were possible lives in a different world than I do.

I'll say it again, much closer to 5 to 7 HP gains over stock rockers.

Customer: Uh, yea, and I'd like the cam that makes 450 hp with stock heads to go with those 45 hp rockers.
Speaker: Will that be all for you today? Would you like a hot apple pie with that?
Customer: That's not going to be more than $6.12 is it? because that's all I have.
Speaker: Your total is $5.96 please drive around.

if you are jsut tell me.. dont be mean... im jsut trying to elarn someting so i dont **** my car up.... if you think 450 hp is not aplauseable with a new cam and ported heads.. tell me im all ears. anywho... if there any way to machine your heads to take a bigger cam? for example.. if your heads can only take a .500 lift..is ther a way to make enough room for say a .550...jsut a question.. trying to learn somthing .

mnorton...what does this mean "Also you need to list the durations @ .050 as well." what is this.. i know what duration is.. but what does the .050 mean.. i see it everywhere!

anywho tell me if you guys like this idea..

new cam...over.500 and below .530
behive springs (comp cam)
new rockers 1.6
new seals....machined and ported heads
new lifters

with that setup.. willl i be able to reach 450 hp with a full dual exhaust..full intake upgrade with electricle, chip and injectors, fuel regulator and some lovin and mind power! give me some feedback.. im all ears.. jsut trying to elarn a bit before i blow some money on a flat tiped cam....haha.. thx again

dave-92gta

iTrader: (1)

also..for the record.. waht do these thigns mean??

Duration at 050 inch Lift
Lobe Separation (degrees)

mnorton

Duration at .050 means the duration that the lobe will hold the valve open when measured with the valve lifted to .050 (and greater) off the valve seat (barely cracked open). This is a very useful spec when shopping for an aftermarket cam. If you read some more you will learn that you can take the advertised duration and subtract the duration at .050 in order to determine the ramp rate of the cam lobe. Also a good thing to know when comparing cams.

Read the camshaft article on our homepage for more cam info.

Supervisor42

Here are the articles Mnorton is talking about.
Camshaft Article
SBC Camshafts – A primer
The biggest obstacle in making big power with a cam swap on your setup is the stock TPI setup.
The TPI makes gobs of torque at a low rpm. When the rpm rises above 4500 rpm the ram effect of the tuned pulses starts to work in the opposite direction. You hear a lot of people say that the TPI "falls on it's face" at 5000 rpm.
The problem with changing the cam on a TPI setup to one with a higher rpm range is that the cam will lose power in the lower rpm range (where the TPI really shines) and the TPI will still run out of breath on the top end.
In a nutshell: The cam swap will actually make the car slower.
This is a common mistake that is made because people will go overboard choosing a cam to swap into a stock TPI motor. The bigger a cam that is put under the TPI the more of a dog the engine will become.
Don't get me wrong, swapping the cam under the TPI and reprogramming the
PROM in the ECM will make more power. Browse here to read about that:
DIY PROM
Read up on the Holley Stealth Ram (HSR) and other alternatives to the TPI here:
Alternative Port EFI Intakes
These will make lots of horsepower without having the rpm limit of the TPI.
This will get you headed in the right direction.
Making big horsepower is not as simple as just changing the cam. That was the meaning behind my previous sarcastic post. Maybe this post will be more helpful.

izcain

IMO I dont think you will make your 450 mark with anything other then full aftermarket heads and changing compression. Are your looking for 450 Flywheel HP or to the ground? Going to the larger cam is going to help you out but at some point your stock heads are going to wheeze out of breath (even with porting and polishing) the port work will help flow a little better but their still going to have limitations.

dave-92gta

iTrader: (1)

ok.. way helpfull.. thx you guys, yea i said goal of 450 at the flywheel...just a number i thought i would set a goal to. i want something that is more powerfull then the average street car, and modified car where i live. most cars are around 300-400 where here, so i thought maybe 450 would put the edge iin my favour. i also didnt want to go crazy hp because its really expensive, and i want to be able to keep my tip setup and AC even if it cost me a bit of hp. its jsut a personal choice. so your saying to go with more of a low end cam. i found a cam on summit that reaches rpm max at about 5500, and starts at 1500 or so.. if i remeber better. its got a lift of .525 in and .525 exhaust. this would work better? i wanted to avoid this becuase it means really bad gas milage at the low end. like from what i herd a cam does not suck gas back really bad untill its in it rpm range where it starts to make power. if you drive your car nice under the cam range it does not burn gas like crazy..this is waht i herd.. if you know anything about that you should tell me.. more helpfull advice. i will read those articles thx again. this is waht i wanted..you guys taught me more in this thread then like 5 of my threads combined thx again...jsut learning

mnorton

dave 92 gta-
The cam that you have mentioned sounds like it has the right RPM range and valve lifts, but what LSA is it? In order to work well with a TPI it needs to be 112 to 114. Also I suspect that cam is a single pattern cam...? Most folks use dual pattern cams in these engines. Dual pattern cam have the exhaust valve open longer than the intake valve, and typically the lift is higher on the exhaust too. The idea is to help balance the exhaust flow so that it more closely matches the intake flow. The reson being that the exhast valve is much smaller than the intake valve.

Also, really if you want to get good advice on these boards, you need to be very specific about your facts and issues. In this case list all of the cam specs when asking about a particular cam. Not just the RPM range and lifts.

dave-92gta

iTrader: (1)

mnorton: take a look at the cam...
http://store.summitracing.com/partde...5&autoview=sku

i know it ahs a lobe seperation of 110, and from the thread before, the intake and the exhaust are the same lift. i looked into summit racing and you can make your own cams. custom ones. thats pretty cool. from what you guys told me, this is what im going to try. il just tell comp cams to make the lift at about .520 intake and .535 exhaust.. if i did that the rpm range might change a bit, but i cn live with that. i want this because the rpm range is right for the car.. as you guys told me... any good?

mnorton

dave 92gta-
Is your engine a TPI, Carb, Other? Is it computer controlled? Are you going to use it as a daily driver or just as a strip car? What intake is on it? What injectors? AFPR? What heads are on it, what valves, have they been ported, what do you think they flow? etc.....

I'm sure you are a fast learner, but maybe take a breather... two days ago you were looking at buying a flat tappet cam for a roller engine. Now you want to specify a custom grind... There are lots of great cams to choose from, I suppose they were all custom at one point in time, but they are proven to work well now.

dave-92gta

iTrader: (1)

its a tip. upgraded runners to slps. plenum, runners and intake have all been ported and polished to flow better together. it is computer controled, and im going to be getting it chipped after i get the cam done. injectors are stock for now but il be putting a set of svt for injectors in there. 24 lbs/hr. bbk 58mm intake and AFPR. exhuast is a true tual with x pipe, not cats. stock heads period.. nothing done. once i get the cam il be putting a stall TC in there, just have not decided yet due to no cam. tranny is built up with an aftermarket temp sensor and tranny cooler(putting on as we speak) 3.23 rear gears. dunno if im going to be changing those yet. i also did a bunch of routine stuff, fuel filter, plugs, wires, cap roter, coil. keepin the ac.

so all i got left is the ehads and cam. and well after all this i dont really got much cash left. so this is why i ask all this about heads. and heads are really the only thing i dont know on my car.... for now...more lessons from you and il be set haha. i think i know what im going to do. till i get some cash for a set of tf victor jr. il jsut send them out to get ported and polished with new 1.6 rockers, be hives from comp. if they work well, il jsut keep them. im looking for anywhere from 400-450 hp at the flywheel and if i dont get it, thats not the end of the world, jsut a goal. im going to talk to comp about the cam.. they are the overal experts... i jsut wanted to have some background before i go in there and look like a fool. see what they can do for me when it comes to custom. its the same price so its good to jsut ask