Comp cams xe268h for 318
I have a question for the ones of you who say the summit (crane) or whatever it is grind is trash. And let me start by saying that I have great respect for you and acknowledge your experience and knowledge. But have you ever actually ran or drove a engine with the cam or you just saying its trash based on the numbers? Because I have read at least 10 or more reviews with ppl completely happy with it summits website has 3. One of them is a 4x4 360 he even commented on how great the low end torque was. So I'm curious have you had a bad experience with it or you just saying its trash based on the numbers on the paper? I get it the ramp like 74 is not ideal for cylinder pressure the 112 lobe separation doesn't help bottom end either but surely it cant be that bad cause summit still makes and sells these things after all these years. There is one video of a guy running it sounds pretty stout to me you can see the car squat at about 30mph and sounds like he is spinning. So like aj said less than 30mph its probably not gonna be set no 60ft records but I'm not racing this car it's a driver. So please let me know if you have any hands on experience with this(these) cam and again this is completely a respectful post.
Sorry for the long post to follow:
It is not this specific cam or engine, but the DCR that results from low static compression ratio and a too large cam predicts the result. I've run from a low of 5.7 DCR (lower than probably anyone here and for racing 6-7 THOUSANDS of rally stage miles, where you need a good broad torque band to be fast) to 8.3 DCR on the street and KNOW the difference from first hand experience. For the street driver application, all that has been said about low RPM torque needs is spot on. Your Summit cam is just plain and simply gonna put the DCR in the low 6's with consequent very poor low RPM torque.
Your setup is heading for what has been warned against over and over; you can find lots of threads about this in FABO, so it is not matter of guessing. See my above posts about my thoughts on why these are listed as 'OK' by some.... I truly don't think they know the difference, or they use the car for drag racing, not a street driver, and so don't really care about, or see, the situation in the same way. As for Summit reviews..... they'll filter out the bad ones LOL so IMHO it's quite unwise to rely on those.
IMHO these cams get sold mostly because they are cheap. Which is what took you there in the first place... perfectly understandable. I raced for over 10 years with a very limited budget, starting while still paying for my own college, and that,
PLUS not listening to good advice because I did not have a thorough grasp on DCR and how it predicted performance, took me to select a 300 advertised duration cam. (Yes, I thought top end HP was the end-all and be-all.) With a 7.6 SCR (like your 318), that ended up with the 5.7-ish DCR.
Result: engine would putter around 'OK' (like said in post #130) but was had no usable torque at all below 3700-3800 RPM. I am not fooling. Above that RPM, it took off, and I was saved somewhat by an engine that could rev to 8k and a 3.73 rear gear and smaller tires and a 2500 lb car.
But it would have been faster rally car with a 2-3 steps smaller cam; the 2-3 gear step really sucked on the hills where the engine would 'fall off the lower end of the torque curve on the upshift. Rally car use is a LOT more like spirited street driver use than drag racing use, so that situationo is MORE applicable than drag racing.
This was an Opel 1.9L CIH engine,
but it the same technology and operating principles as the SBC's and SBF's and SBM's. So don't believe it will be any different; it will not. You're gonna have good torque starting somewhere in the high 2k to low 3k range, going up to where the flow chokes or the valves float somewhere in the 5k range. Less than a 2:1 usable RPM range..... Your car's advantage over my Opel case is just in a better cubic inch versus weight ratio but with much poorer gear+tire ratio, it's guaranteed to struggle to get moving.
How much more real experience do you want? That's all I got.... (Well not all, but it relates the best to your situation. Someday I can describe how a 0.8 increase in static CR helps a turbo engine... from my actual experience.) Long term, it's up to you to decide if you will put your belief in blindly following unqualified subjective opinions, versus accepting the use of numbers to help you grasp where things will fall out. And please understand, I don't get hung up on difference in DCR of 0.1 or 0.2 points... but differences of 0.5 points or more will really show up in low RPM performance. Just like a change of 4 degrees in cam timing will really be felt in a street driver. (Yes, more actual experience in making that specific change.)
Starting with your 318's low SCR, you're only going to get so good, but it's discouraging to me to see it made worse. That's the reason I keep coming back to this and trying LOL.
