We need something like this here i think. Being a total noob to building an engine, it would be nice to have something written up to help noobs like me.
Anyone willing?
Just a little excerpt example:
Consider the camshaft. On the one hand, it's a simple thing, a stick with bumps on it. It sits above the crankshaft, linked to it by a timing chain, and spins at half the crankshaft's speed. The camshaft's rotary motion is converted, through a lifter, pushrod, and rocker arm, to linear motion. Voila, the valves open and the engine operates. If only it were that easy. The configuration of those bumps--more accurately referred to as lobes--defines the performance personality of an internal-combustion engine. By determining when an engine's valves will be open, and how long they will stay open, the camshaft determines how much power an engine will make. It also dictates where this power will be made throughout the engine's rpm range. And that's just for starters. The camshaft is often called the brains of the engine, and that brain determines what kind of powerplant you will have.
If it feels right, then STROKE it!
You're lucky that hundred shot of CAPS LOCK didn't blow the welds on the forum!!
It would also be nice to have a list of cams that would be more for crawlers, street rigs, and racers. Ones that work best with the fuel injection and ones that work better for carbs. I am building a rock crawler and one of the most important things you can have is the ability to let out the clutch, don't touch the gas, and be able to idle your way up very steep inclines, and over rocks. Because of this I'm going to stick with the 87-95 cam. I could go with the newer stock cam but it has less lift. Since I am adding many breathing mods to the motor I think its a good idea to stick with the higher lift stock cam with more lift. Plus I'd rather spend 60$ on a stock cam and reuse all the old parts then spend atleast 130$ for an aftermarket cam plus atleast 150$ for valve springs with retainers, locks, and all that other stuff that goes with switching cams.
Thanks Flash .. unfortunately my mind is in 15000 directions today, so ill have to read it a few times and see if i understand better. If not then ill get back to you. For the most part though i do understand.
If it feels right, then STROKE it!
You're lucky that hundred shot of CAPS LOCK didn't blow the welds on the forum!!
I've read in old stroker buildups the desire to use the stock HO cam as it builds more hp - which it does, but at higher RPM. Closely associated to that cam is the fact that the EGR was eliminated - because the cam had so much more overlap it actually allowed dilution/reversion into the combustion chamber! This is a normal fact of high overlap cams and certainly makes more horsepower - but it does so by moving it out of the lower rpms. Ergo, less power off idle and under 1500 rpm.
As a point to the story, the "Renix" cam is supposed to have better specs for power down low, producing more power under 3000 rpm because of the optimized pattern. It just happens to be less able to manipulate emissions without bandaids like an EGR. It's not necessarily a "dirty" cam.
However, add another .5 liter of displacement, and this becomes moot - stroker motors commonly "feel" less peaky on a higher overlap cam because the larger displacement uses so much more of the air flow. It takes a further increase in lift and duration to push the peak values up the RPM scale, or conversely, the "bigger" cam has less negative effect down low. This is incremental, meaning a cam spec'd for a 4.0 as borderline in providing better low end torque may fill the 4.5 perfectly.
That's where a much closer look at the stroker is required. Just like MPFI, you can't use the same size injector, so let's continue that line of thought and not use the same "size" cam. You may be going too small for the motor and not taking full advantage of the increase.
IIRC RENIX and OBDI used the same cam, so it wasn't the cam that forced EGR on the RENIX system. It my have been how AMC engineers dealt with emissions, but since OBDI doesn't have EGR, the cam didn't the bandaid, the system did.
I'm not clever enough to have a clever signature. I'll just steal yours.
'98 XJ 2-door, '94 YJ.
Ok, i have had a chance to read this better, and this is what i would like to see if possible: By the way, i do understand what you wrote flash... its pretty easy to understand... however i probably never remember/retain it.. so i will need to refer to this over and over again.
Im definetly a hands on learner, and reading something just usually doesnt do it for me.. What i would like to see is this:
Pick 2-4 (2 is fine if its to much work) of the best / most commonly used cams for building our strokers and provide their specs. Then explain the differences of each cam's specs. Like for example (using rediculous numbers just for examples sake) one cam has 200* of duration. The other has 240*. The cam with 200* of seperation will do: (pros and cons go here) the cam with 240* will do this: (pros and cons and maybe even why its better then the 200* cam go here). This i think will help newbs like me understand common specs for this application better.
Does that all make since?
If it feels right, then STROKE it!
You're lucky that hundred shot of CAPS LOCK didn't blow the welds on the forum!!
Muad'Dib wrote:Ok, i have had a chance to read this better, and this is what i would like to see if possible: By the way, i do understand what you wrote flash... its pretty easy to understand... however i probably never remember/retain it.. so i will need to refer to this over and over again.
Im definetly a hands on learner, and reading something just usually doesnt do it for me.. What i would like to see is this:
Pick 2-4 (2 is fine if its to much work) of the best / most commonly used cams for building our strokers and provide their specs. Then explain the differences of each cam's specs. Like for example (using rediculous numbers just for examples sake) one cam has 200* of duration. The other has 240*. The cam with 200* of seperation will do: (pros and cons go here) the cam with 240* will do this: (pros and cons and maybe even why its better then the 200* cam go here). This i think will help newbs like me understand common specs for this application better.
Does that all make since?
Sounds good. I will try and throw my hand at it tonight, and see what i come up with................If they have fixed the tower that supply my internet conection at home
Flash.
89 XJ with 300,000 on the original eng
"I've also never completed a motor, yet. My mouth (fingers) is also writing checks my ass can't cash."
oletshot wrote:IIRC RENIX and OBDI used the same cam, so it wasn't the cam that forced EGR on the RENIX system. It my have been how AMC engineers dealt with emissions, but since OBDI doesn't have EGR, the cam didn't the bandaid, the system did.
I thought that the only difference between the early HO and late HO was the cam advanced by 4* on the later on
Dug up my cam spec's for all three cams......renix had a .405" lift, early HO, .424......Late HO .408/.414
Do's any body have cam spec's for the two Ho cams???????? I don't believe my early HO cam spec's are right
Flash
89 XJ with 300,000 on the original eng
"I've also never completed a motor, yet. My mouth (fingers) is also writing checks my ass can't cash."
Dr. Dyno
10-29-2003, 15:32
It's a popular myth that the cam was changed during the changeover from non-HO to HO engine but it is, in fact, exactly the same for all the '87-'95 4.0 models. The FSM definitely got the duration and lift specs wrong. The correct duration is 197* @ 0.050" (equivalent to 253* advertised) for both intake and exhaust, the valve lift is 0.424" (cam lobe lift 0.265"), LSA is 112*and ICA is 120*.
The cam specs changed in '96 with the introduction of OBD II. It became a dual pattern cam with an advertised duration of 253/259* (the longer exhaust duration was to compensate for the smaller exhaust ports in the newer head). Lift is 0.408"/0.415", LSA 107*and ICA 114*. The upshot was that the torque and HP peaks were reduced to lower rpm.
The torque peak of the '91-'95 HO engine is much lower than the 3950rpm that DC claimed according to real world dyno tests. It comes in at about 3200-3500rpm.
im willing to take dino's word for it unless he would like to chime in with some new info.
Last edited by Shark on March 27th, 2008, 9:28 pm, edited 1 time in total.
All that i have learned about cam profiles was done by reading lots of cam manufacturers suggestions, like the link above......and all of them may be more accurate then mine..........But hopefully mine is a little bit easier the grasp.
NOTE: the cam spec, Desk top Dyno's, was run with a 258 rods.....Missed that detail above
Flash
89 XJ with 300,000 on the original eng
"I've also never completed a motor, yet. My mouth (fingers) is also writing checks my ass can't cash."
I ended up actually just splitting out the important information into a new thread in the FAQ section. Im closing this thread so that further discussion will take tplace in the proper FAQ thread.
Thanks again!
If it feels right, then STROKE it!
You're lucky that hundred shot of CAPS LOCK didn't blow the welds on the forum!!
