I choose my cam before building the engine
1) choose horse power range I want
2)choose heads with enough flow to make that power
3)figure out what size engine and rpm is required and a good match for my application
4) figure out what compression ratio works best with fuel used and head material.
5) what combination best suits my car and application

If you are building a street engine for fun;
go with the biggest engine that fits the car and budget
race cars may have cube rules etc.

 

Well I asked, lol. If you put it that way, sure. You can build a 12:1 motor and run a 260 (advertised) cam if you had enough octane. But more specific, I was asking based on what a cam companies recommendation is, and whats considered the "norm".....shooting for a dynamic compression within a certain range.
Here's what I'm getting at.
If two cams have the same seat duration, say 280. One is 232 @ .050", one is 216 @ .050". Would the recommended compression be different or the same? 280 is 280 so the intake valve closes at the same point, assuming the same timing events.

Here's what really had me thinking.....the Edelbrock RPM cam (now a generic grind everyone sells on their budget line) for SBC is 234 @ .050" intake on a 112 lsa. Edelbrock says "on a 9.5 350 it makes xx horsepower". Of course the compression can be higher or lower within a range. One little thing though.......advertised duration is 308! Shouldn't it be a total turd then? Wouldn't recommended compression be minimum 11.5 or something?

 

advertised duration is relatively meaningless, so you may be best off not even reading it.

As for picking a cam- the cam should be chosen last according to what parts your engine is actually built with- BUT you should have a pretty close idea of what you want before you choose the rest.

Additionally edelbrock cams have ALWAYS been cheap reboxed cams that aren't anything special. As such I wouldn't recommend them unless you have one for free and just want to get it running.


I'll walk you through the basic thought process:

I'm starting with a 3200lb car with 3.73 gears, a 700r4, and 28" tires- a pretty typical street car. I'm wanting to build a 350ci sbc that is fuel injected and runs on 87 octane. We'll stick to gen 1 sbc's even though this screams for an LT1. We'll assume a factory hydraulic roller block and flat top 4VR pistons, and a 6,000 rpm redline.

I'm guessing my combo is going to peak around 5500rpm so I'll need around 220/230 112 is a pretty typical LSA so we'll start there.

Since I'm running 87 octane with 220 duration I'll need compression at about 9.5:1 for iron heads, or 10:1 with aluminum heads. Since aluminum heads are far easier to come by now we'll go that route. Assuming .020" piston to deck and a .020" head gasket and 6cc piston volume my compression comes out a little higher at 10.1:1- still workable with 87 octane with EFI in this combo.

So now I look for a head that suits a 5500 rpm peak with a 64cc chamber. Now is my first compromise (which affects cam timing), I like the assault racing heads, they're about the best head for the money and I try to never spend more than I have to. so I'll get my 64cc chamber but I end up with a runner that is 200cc's, about 15cc's larger than is needed. This will cause my cam timing to shrink slightly to maintain the same RPM peak- this is why some argue that a head that is slightly too big is actually just right. I'll also clean these head's ports up by hand prior to assembly, I won't get a flow test though but I know the exhaust will pick up significantly and I may get another 10-15cfm out of the intake. This will lead to a cam with less of a duration split than some typically see.

I will also be using 1 5/8" long tube headers with some good collectors, for this example lets say we're using the SUM-G9001, at $115 a set I can live with the price and they have the dimensions I'm after. I'm also going to pair this to a dual 3" exhaust with Thrush Welded mufflers and cutouts for the track- a good free flowing budget exhaust set up. This will allow me to keep that small duration split and also tighten up the LSA some if I want for peak midrange power

For the intake I will be using a stealth ram intake manifold because I'm smart enough to know better than to run a carb on the street. This will again push the power curve up slightly compared to an RPM or similar intake.

Ignition really doesn't affect cam choice but I'll go with an EDIS setup since its cheap and easy.

Rod length can affect it a little, but I'll stick with the stock rods since I'm trying to do this cheaply- 5.7".

the torque converter will be a cheap 2500 stall with lockup- it won't win any races but it'll work fine on the street.

So given all these parameters that came into play as I bought my parts how does this affect my original 220/230, after looking at how everything is affected in small increments I could get a power peak at 5500 with a cam around 218/222 on a 109 LSA or so, but I'm also wanting a hydraulic roller with at least .500" lift so lets see what I can find in the catalogs-

comp come pretty close with XR270HR-10, 218/224 on a 110LSA, with 1.6 rockers it has .495/.502" lift but I'll run 1.6 rockers giving me .528/.535" lift.

This combo should be good for around 450hp/450ftlb- maybe even more tq. It's also a great street engine with a lot of power down low, low maintenance, and runs on cheap gas. In a nova or similar car I wouldn't be surprised to see 25+ mpg out of this combo.

As you can see from this exercise, the cam specs did NOT change drastically from the final selection of parts but they did change some. Changing you cam choice by choosing it last did not cost you any additional money though and it will perform a little better. It's not going to be a drastic change but since it's free- you may as well choose it in the proper order.

BTW, this engine can be easily built for less than $2,500, and if you swap a dish piston for the flat top would make a great foundation for a turbo.

 

Meaning this in the friendliest way.....I'm not building anythng right now. I'm asking specifically what specs of a cam determine "acceptable" compression. Normally I'd try and shoot for the higher end of recommended compression. I know whats considered the "norm" for various cam sizes, but see some things that are contradicting sometimes.

 

your DCR calculators are going to give you a generic number.steeper ramps)ie,roller cams) shut the door faster the actual dcr may be slightly higher than a flat tappet hydraulic cam.the 308º advertised duration will be a turd compared to any roller cam with similar .050º figures.The 308º advertised cam if hydraulic will even be a turd compared to a similar solid cam.
whats cool(mostly to squids) about the 308º hydro flat tappet cam is it sounds like a race car with a 1,000 plus rpm idle.
The next guy over that has a moderate lope solid roller does not sound nearly as evil but likely makes a lot more power with a cleaner idle and wider use able rpm range
I know I got off your questions track a little,just want to make it clear that a big,flat tappet hydraulic will be a turd,period,when compared to anything else.

 

This is similar to swapping 1.5 rockers for 1.6 rockers. The seat to seat timing doesn't change, but the @.050 does. I saw a test a while back where they dyno'd the difference on a 383, and the 1.6's actually reduced horsepower.

 

I hears ya. For the record, i wouldn't run an RPM cam unless it was given to me and I was doing an El Cheapo motor. And 308 is ALOT for 9.5 compression. What I was getting at is if someone wants to run, say, a 280 cam and only 8.5:1 compression, all people would say is, "don't do it, it'll fall on it's face, it needs minimum 9.5 to even run decent", etc.
Yet the Performer cam, which is only 204 @ .050" is 282 seat duration, an 8.5 CR is considered more acceptable. Oh well it's apparent nothing is set in stone.

 

Yeah true, Silver Surfer. What we were getting at is.....if a cam has 280 seat duration, whether @ .050" it's 242, 230, or 210.....compression can't really happen til the valve is seated. And its always said, "larger cams bleed off more cylinder pressure, mainly due to a later intake closing point".

Ok.....so, if a cam has, say, 270 seat, 230 @ .050", it (theoretically) should require less compression than a cam that's 280 seat, 204 @ .050". It would seem anyway.

And yes, other specs of the motor are a factor too. That's all, just pondering stuff.

 

the advertised numbers are not seat numbers. disregard them.

 

Ok thanks, AP72 (and everyone). This was just a question about cam theory.

 

Ok, now that's what I'm thinking! Cause if that were the case, the compression vs cam scenario I described would hold true. It does to a point, but not 100%. Otherwise the old 30-30 cam would need 14:1. LMAO!:thumbup:

 

Ok, now that's what I'm thinking! Cause if that were the case, the compression vs cam scenario I described would hold true. It does to a point, but not 100%. Otherwise the old 30-30 cam would need 14:1. LMAO!:thumbup:

. Actually, the 30/30 cam would prolly be much stronger at 14:1 ... like 450 HP instead of the stock 375 HP @ 11:1... with better than stock heads, of course...

. Of course, the duration at .030"/.030" lash is more like 240/240 instead of the raw 254/254...

 

OK,Richard Im baiting you into this thread,,,
the valve does not have to be seated for compression to start,,,,,

 

This could be a very long and draw out thread... :mwink:

 

https://www.youtube.com/watch?v=gIxKiaN8e5w&hd=1

https://www.youtube.com/watch?v=_StYoDufuEQ&list=UUrV8PVtn6UpZ0pMLa5edVwg&hd=1

first cam 292 hydraulic from comp
second cam(mine),.256º intake duration)solid roller comp

 

https://www.youtube.com/watch?v=gIxKiaN8e5w&hd=1

https://www.youtube.com/watch?v=_StYoDufuEQ&list=UUrV8PVtn6UpZ0pMLa5edVwg&hd=1

first cam 292 hydraulic from comp
second cam(mine),.256º intake duration)solid roller comp

They're in different environments so the sound is different, but they both have a nice rump to them!

 

Just considering duration and lift isn't really taking in the whole picture of how a cam does or doesn't respond with a particular compression ratio in an engine. LSA will have a big affect on how a cam works, and a wider LSA will make cams with identical lift and duration work much better than a close LSA works.

 

works better how?



maybe elaborate on this theory?
low ICLs and tight LSAs work very well in some situations where wide LSAs do not

 

What I was trying to say is that you can't just consider lift and duration when deciding what works. Some cam grinds work well with a 107 LSA, while others work better with a 112 LSA. Not meaning a 107 LSA is better or worse; just that cam lift and duration are not the only things to consider.

 

By the way the eddy rpm cam does work real well
When you install it in a real motor and give it the other stuff it needs
Carb heads gears converter.
Friend here runs this in a 355 street 78 camaro.
3500 stall- 4.56 gears. 10.5:1 ported camel backs hurricane, 750 demon Runs solid mid low 12's.
Sounds great too. It hauls. 400++ hp simple reliable build
It works fine.

The Edelbrock Performer series cams seem to all be built to be very streetable, and most appear they would work well even with stock conveters in automatics.
Here's the specs on their 3 cam choices for flat tappet:
265-400 V8 (1957-86) 2102 204° / 214° .420" / .442" 112° 107° 14"
305-350 V8 T.B.I. & LG-4 3702 194° / 214° .398" / .442" 112° 107° 16"
400 V8 2103 214° / 214° .442" / .442" 112° 107° 15"

 

Right-on BuzzLOL. A friend has a 327 with the 30-30 cam (its a legit 365hp motor) and he says it just doesn't pull as strong as all the hype about it. Am suggesting he set the lash a little tighter. Maybe that's when they DO run strong. But 240 is still a pretty big duration. Maybe his is off a tooth, lol.

 

. Yeah, could be lots of problems... engine rebuilt with dished pistons, too small air cleaner, or air cleaner lid too close to top of carb., wrong iron exhaust manifolds, poor carb. tune, poor flowing exhaust system, heads swapped, not the cam he thinks is in it, poorly matched rear gear, PowerGlide tranny, secondaries not opening, choke not fully opening... it's only a 327, don't expect it to pull like a 454"...

 

It is the build you are making. If you are adding compression that is adding power.

If you can't get the cylinder fill will the stroke, a supecharger will keep the velocity , and force feed the sucker.

Things that you drive around, cruise nice at .450 " lift with an operating ceiling of 5500 rpm. If you are racing you you want the 280 style cams, the 280-282 point is where things really wake up, and things under 3500rpm fall off.

 

Back when the solid lifter Duntov 30-30 was THE cam to use, I built a '55 Chevy gasser with a '67 283 in it. A stock bore and stroke 283, with 11:1 pistons, a pair of highly ported and polished 1.94/1.60 camel hump heads, factory dual quad intake with real Carter AFB's, and the Duntov 30-30 cam. It was a dual purpose car for street/strip, and a real runner that grabbed 7,000 rpm's pretty quickly. The late Dick Ott did all the machine and head work for me back then, and although Dick was a Mopar guru, he could make any engine sing! The '55 was a consistent low 13 second car, which might not sound all that fast today, but back then it was. The little 283 surprised a lot of SS396 Chevelles and Camaros, not too mention other big block powered muscle cars. Always wanted to make it into the 12's back then, but the 4 speed held me back, and I didn't want an automatic.

 

Back when the solid lifter Duntov 30-30 was THE cam to use, I built a '55 Chevy gasser with a '67 283 in it. ! The '55 was a consistent low 13 second car, which might not sound all that fast today, but back then it was. The little 283 surprised a lot of SS396 Chevelles and Camaros

. Yeah, stock 283" records were like 14.5 seconds... in well sorted out cars...

 

He checked the carb and even tried another.

 

13 seconds, in a road driven car , is very fast.

10 seconds in your hobby race/drag car is slow. Quit being a puss, and do it.

The laws of physics didn't change since then. People became dumber. They are no longer aware of what's going on around them. So it takes more to impress them. It is an unfortunate character flaw in the 20 somethings. 30 somethings, 40 somethings too.

 

Yep, same can be applied to music, movies and stuff. The average new car today is quicker than decades ago. Raised the bar for what makes a fast hotrod.....high 11s are the new low 13s. Tires on the average production car were skinnier back then too.

 

Yes, you get excited when your 17 second 72 cutlass convertible now does 13's cause you swapped the heads, cam , and gears.

I do not have interest in making my driven cars go 10's. What a waste of money.

Is that you Turretto? You found Letty? Hobbs is commin.

 

I can agree that its unnecessary, but a waste of money... well that depends. I mean all hotrodding is a waste of money, and sometimes 10's aren't as expensive as you'd think. Also, while its rare to use 1/4 mile performance on the street, having a car that can launch you at a stop light can be an enjoyable thing.

I don't build for 10's but I do respect the guys that do. Especially the ones that do it on a shoestring budget with their own hands in their little 2 car garages.

 

13's really isn't slow...just drive slower stuff most of the time and it feels quick again, lol.
Along with the easy power today comes idiots who don't know how to drive them. I recently saw a video of several late Stangs leaving a car show , and a good bit of them wiping out, a couple wrecking....all from the same show. Not saying nobody lost it back then, but 5 cars from the same show? Inexperienced drivers who aren't used to some power.

 

Inexperience is part of it, but stupidity is a larger part of it! There's a time and place for that stuff, and it sure isn't anywhere near a bunch of expensive cars that guys have given blood, sweat, and tears to build.

 

want a 10 second car,just go buy the new Dodge super charged 6.2 liter,sure shames GM's Corvette

 

Very true....build what one likes and don't worry about the next guy digging it.

Ok so that about wraps up this thread.

Next week we'll start with, "how much power are coated piston crowns worth", and finish with, "if someone doesn't currently have wheels, can they drive a riding mower as long as it has that farm equipment triangle thing on it".

:welcome:Good night everybody.

 

Very true....build what one likes and don't worry about the next guy digging it. ... "if someone doesn't currently have wheels, can they drive a riding mower as long as it has that farm equipment triangle thing on it".

. LOL! I think that safety triangled riding mower/golf cart/Amish buggy is what's left after you lose your driver's license...