I am having trouble figuring out my lift and duration for my setup. Can someone please help. I have: Comp Cams 270h Stock 1.6 rockers Stock valves 1.86 351 Windsor Heads I was told that my duration was 274 and the lift was .501. I am having trouble believing this because the Barry Grant website recommended a Race Demon carb based on the duration. Here is the link to get the cam specs http://www.compcams.com/Technical/Catalogs/106-03/HTML/68-75.asp What is the formula to determine these numbers. Thanks
What you want to look at is the duration @ .050" lift, advertised duration is almost a useless spec. So you've got 224 deg. w/ 110 deg. separation. Like they state in the description it's gonna idle rough, has a good bit of overlap. Most of the power will come in at the mid to upper rpm's. I don't think it would be too bad on the street if you have a decent intake, headers and some 3.50:1 or stiffer gears. You don't mention what size motor you have, are the heads ported, manual or auto trans, if auto what stall speed. You have to look at your whole package when choosing a cam. As far as what carb to get, it depends on what you want to use the car for.
I agree with bmcdaniel on everything but the idle, with a 110 lobe sept it shouldn't be to rough, this is no more then a good street cam. But like bmcdaniel said what motor are you running? With stock heads I wouldn't go much past a 650 carb if you do you may be pumping more fuel and air then your heads can flow. Bossmav
A point to know about cam specs from any company is that their based on gereral recomendations. If you don't have those extra areas covered, the cam may not do as well as the user expects. This cam in a stock motor will be guite rough in idle and poor in low end without the overall gearing and extra airflow for the upper ranges. This is often where the stock heads start to 'lay down' above about 4000 rpm just where the cam starts to have the 'capability' to make more power. This is due to airflow limitation and often the valve springs can't handle the more aggressive timing and lift unless the whole kit is installed. The end result is much less power than is possible. For general street use I would have picked a shorter cam but again it depends on what your putting it in (motor setup) and the use you want to favor. One can over cam or under cam for a specific use. It takes a knowledgable feel for what cam to select otherwise accept reccomendation from the cam co. based on your accurate discription of use.
Thanks for the recomendations. The block is a 302 bored +30, heads are ported, stock valves, springs, and rockers. Holley 600, MSD dist, Mallory Ign, TRW forged pistons, compression around 9.1:1. Full length headman 1 5/8 headers, C-4 tranny with 2500 stall. Currently running 3.00 gears. I dont feel like I am getting all the power I should be getting out of it. Needs more timing and the 4b doesnt seem to be opening early enough. Some things I plan to work on when it gets warmer. I plan on upgrading to AFR 185 heads, T5 tranny, 3.55 or 3.80 gears, new carb, and maybe a 100 - 200 shot of NOS. (depends on what the motor and I can handle) The car will mostly be for weekend street cruising with a few passes down the track per year.
said it before,car looks great, did you already get a new hood? I think it was you that said it came up while driving? I don't remember the scoop on the last picture I saw of your car
Nice color car- looks great, xrs. I just read your combination and it looks like you just need some tuning, and I agree that you are on the right track. First, you are right on about the 4 bbl. With the 302 engine - the comp 270 is probably only pulling about 9-10 inches of vacuum - so you definately have to lighten the secondary spring. The other carb component that is affected by lower vacuum signal is the power valve. You most likely need to lower it. Power valves are rated at the vacuum when they tip in - and you usually want to have it come in when you drop about 2 inches lower than idle. So you probably need about a 7 or 8. If it is an out of the box holley 600 the power valve may be partially open at idle with the lower vacuum - so you definately loose off idle response. I'm not sure what the MSD distributor has in it for advance springs, but since you have a 2500 stall converter, you should be able to dump all of your timing in by about the same rpm. If you are going back into the engine sometime - try milling about .030 -.040 off the heads. Although 9:1 compression isn't bad for that cam - 9.5: 1 would be better. Just my .02 worth. Best of luck. Cleaver 3.55 should be the icing on the cake.
YOu would be much better use the roaddemon 625 or 650 speed demonbased on your current specs. I run 10.4 to 1 comp E303 roller cam/ Roller Rockers(custom length pushrods) and use a 625cfm Road Demon. Even with stock jetting it revs like an on off switch. I use roush 200 heads milled to 61cc and KB pop up pistons. I also used a 2500stall but moving up to a 2800 to 3200 not sure yet. You are right on the edge with the ROad demon with the 224 duration at .500 lift. The Ecam and the Demon go to gether like bread and butter. If you were steping up another notch on the cam and afr heads 650 speed demon IMO.
Qicvick, I found a new hood the next weekend. I spray painted the hood to match the best I could and mounted the Comet GT scoop at the same time. I like it. I will have the car completely repainted sometime within the next year. The rattlecan job will have to do for now. I mounted the chin spoiler today. it makes the car look pretty cool.
