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Discussion Starter · #1 · (Edited)
Hello everyone,

I need some help with cam selection for 1975 SBC 355, stock heads (ported and polished), Edelbrock 2701 Performer EPS intake, Edelbrock Thunder Series AVS 650 carb with vacuum secondaries, block hugger shorty headers (unknown brand), 8.5 to 1 compression ratio (as per previous owner). The engine is in a 1984 Fiero with 4 speed manual trans and final drive ratio of 4.11. 16" wheels with 225/50/16 tires on the rear. The headers dump into a Y pipe then a single magnaflow muffler (I can't really upgrade the exhaust system much due to lack of space). Current cam specs are unknown. Engine seems to run out of breath at around 5000 rpm which comes quickly with a 4 speed trans and 4.11 gears.

I also have a five speed Getrag trans that may be a future upgrade for the car. This is a street car, no drag racing. But I would like more torque and improved throttle response. Reasonable fuel economy would be good as car has only an eight gallon fuel tank, but fuel economy is not the overriding concern.

What would you recommend for a camshaft? Engine has to come out for a cam change (have to drop entire rear cradle with engine, trans, rear suspension, etc.), so nothing too radical that would have the possibility of wearing out quickly.

Thanks.

Wade
 

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You have a fairly light car, and with that gear ratio, 4 speed, and tires you will always have plenty of RPM. However, the stock heads will limit the flow and the power you can produce. I would probably use a cam with a duration in the range of 220-230 @ .050, with a moderate lift (.50 max?), but I prefer to keep decent vacuum and idle quality. Something along the lines of the comp cams XE268H, or even the XE274H may be what you want.

Bruce
 

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Because you asked for more RPM I would look in this area
110951-08 NA 275 285 221 231 .470 .470 108 104 Hyd. Hyd. 1
1800-5800 Good idle, Strong Street performance. Needs 4 barrel, headers & lower gears.
the 5 speed will make up the mileage issue,though dont expect to have high mileage and higher RPM and more power.To make more power you need to burn more fuel
 

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Discussion Starter · #5 ·
Thanks for the replies.

Sounds like I need to save up for a set of heads (since the engine will have to come out to put in the cam; also need to remove the engine to replace the heads as it is too tight to get to the front head with the engine in the car sideways). Any thoughts on the best heads (Patriot, Dart, Edelbrock E-Street, Jegs aluminum 180 cc intake port 64 cc chamber)? I figure I might as well go aluminum for the weight savings and better performance. And does this change your cam recommendations. I was hoping to do just the cam, but if the heads are going to be the bottle neck and I have the engine out, I might as well (spend another $1500). I am assuming I need new rockers, push rods, intake manifold gasket, head gaskets, and head bolts?
 

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How much more power do you want? Heads are a great way to make power,,,I use dart heads on my engine.AFR heads are really good out of the box.
remember,more power means using more fuel.
 

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Discussion Starter · #7 · (Edited)
How much more power do you want? Heads are a great way to make power,,,I use dart heads on my engine.AFR heads are really good out of the box.
remember,more power means using more fuel.
325 - 350 hp, 350 375 lb ft torque would be great. And I am thinking that the AFR heads would use up my entire budget before I got to rockers, push rods, gaskets, head bolts, etc. This car is a toy that I would like to get working good, but I will not recoup any investment in high dollar improvements, so I would like to go with good, but not the best parts. If one of the $900 set of heads will make a big improvement, I would prefer to go with them versus AFR for max performance and significantly more money.
 

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If you are removing the engine anyways,consider a quick freshen of the engine? For 350 hp use a set of modified GM vortec heads and a small cam like mentioned above.No need for expensive aluminum heads.This will also give you a chance to see exactly what is inside the engine.
also check to see if the engine was balanced
 

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Pulling the heads would be the best idea. You can see what type pistons you have also. If they are the stock D-cup pistons you might want to use a set of Vortec heads. They have a smaller chamber that will boost your compression ratio. Then you can use a higher duration camshaft. This Howards camshaft would be good to use after you get better heads. Howards Cams 112581-10 - Howards Cams Hydraulic Flat Tappet Camshafts - Overview - SummitRacing.com COMP Cams 12-238-2 - COMP Cams Xtreme Energy Camshafts - Overview - SummitRacing.com COMP Cams 12-246-3 - COMP Cams Xtreme Energy Camshafts - Overview - SummitRacing.com All the cams above should put you in the 350+ hp and 400 lbs of torque range.
 

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Discussion Starter · #11 ·

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AP, you don't think the 200cc runners are going to be an issue???

It is going to take a big cam to make use of that. A big cam is not going to like that 8.5:1 CR.
 

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I too think it is likely your heads that are limiting you and not really your cam.

here is a set of heads I would recomend:
EngineQuest, Performance Chev SB Vortec Heads, 170/64cc, Pr.-Competition Products

RHS used to make a great vortec style head but they have discontinued the model :smash:

the EQ heads that I posted accept the early intake bolt pattern and use perimeter bolt valve covers (so pretty much you can use the same intake and valve covers you have now) I'm not sure if they require self-aligning rockers or not but they can had for around 80-110.00 a set. to go with this I would recomend going with a roller cam since you mention that it is so difficult to get the motor out that you would rather not have to do it again anytime soon. the flat tappet cams have a tendency to wipe out with todays oils if not properly taken care of.

either way here is a hyd roller cam I would recomend:
Howards Cams 113215-10 - Howards Cams Retrofit Hydraulic Roller Camshafts - Overview - SummitRacing.com
Howards, Street Retro-Fit Hyd. Roller Lifters, Chev SB-Competition Products

here is a decent flat tappet cam and lifters
Isky Racing Cams 201264-27112 - Isky Hydraulic Flat Tappet Camshafts - Overview - SummitRacing.com
Howards Cams 91111 - Howards Cams Performance Hydraulic Lifters - Overview - SummitRacing.com
 

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Everything that's being said here is "what if". The what if question is.....What is the true static compression ratio of this motor. Until you know that for sure, you have no idea how to proceed. If the SCR truly is only 8.5:1, then the MAXIMUM cam I'd use in the motor would be 210 to 212 degrees duration @0.050" tappet lift. And even using a cam that small, when compared to the 8.5:1 SCR, will result in a weak DCR (dynamic compression ratio). If you want to rev the motor higher, as you have indicated it runs out of breath too early for you, then you will need more SCR in order to support more cam to support more rpm's. That's the bottom line.
 

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AP, you don't think the 200cc runners are going to be an issue???

It is going to take a big cam to make use of that. A big cam is not going to like that 8.5:1 CR.
Big runners are not as detrimental as people think. I have no idea where that came from other than people just wanted to feel better about having stock tiny ports. It won't need a big cam either, the one I listed would match the combo just fine and its fairly mild.
 

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Big runners are not as detrimental as people think. I have no idea where that came from other than people just wanted to feel better about having stock tiny ports. It won't need a big cam either, the one I listed would match the combo just fine and its fairly mild.
Same reason you don't put a 850CFM carb on a 283.

Larger runners reduce intake charge velocity and thus require more RPM's to increase that velocity. Of course you need a larger cam to get get up there and take advantage of that. All this maybe fine at the track, but the OP said, "This is a street car, no drag racing." No one likes a soggy bottom end.
 

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Discussion Starter · #19 ·
Wow. Lots of great information and suggestions. My first post on this forum and I have received some great responses. Thank you all.

And yes, I knew the question of the actual CR measurements was going to come up. I guess I could pull the intake manifold and the rear most head off to see what I have inside the motor. It is pretty much impossible to get the front head off with the engine in the car. Remember the engine goes across the rear of the car. I also not sure that I have the knowledge to do all the measurements around the CR either.

I agree with the thoughts that the heads may be the bottle neck. It may be that I remove the engine over the winter and tear it apart. Then I can determine what to do with heads and cam both. I am assuming that I would get some increase in compression with the right set of heads.

It is always a challenge when you buy a car modded by someone else and all I have to go on is their word for what is in the engine.

I was thinking $300 for parts for a cam, now that is looking more like $800 if I went with a roller. Yikes.

Lots to think about. I will get this car working correctly - it will be a fun little machine with 350 hp.

I think the first thing I will do is a compression test. It has to be done at some point I guess. Will a compression test give any hints as to CR?

I have just got the car on the road and have not driven it a lot yet. I was thinking it would have more low end torque, especially with the 4.11 gears and the four speed trans.
 
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