first post, need cam help

[JesseByrd]

hello everyone. like a lot of others i am starting my first stroker and really my first engine build. I am trying to decide on what cam i should run and according to the formulas and math i learned in class the comp cams 68-239-4 seems like its ideal for the specks I'm planning on running

first off i want to say that this will not be a dd or even see the pavement very much so i don't really care about mpg and other common concerns when running a cam like the 239...soooo on to my specs (basicaly the mod poor mans)

89 renix block
4.2l crank
4.0 rods
ic944 pistons
.0 deck clearance
9.6:1 scr but i would kinda like to see a bit more but not sure on how or if i would just see detonation issues

i have a 7120 head that i will fit with LS1 2.0/1.55 valves and springs
i also will be porting the head with the use of a flowbench so it should flow quite well

as for the running gear it will be planted in a 88 Cherokee w/ 35s and when i get a d44 or something for the rear i will re-geared from 3.55s to 4.88s,trans is aw4 that i would like to do the tcm delete/ manual shift mod

plan on sticking with the factory renix comp for now

like i said i would like to run the comp 68-239-4 and maybe advance it a few degrees.

and finally what the heck im actually asking

1 is anyone running a similar setup?
2 how bad will the idle be ( could i delete iac and manually control idle...would that help)
3 how much will advancing the cam bring down the rpm range
4 any other words of wisdom



hope i posted this in the right section, i don't intend for this to be a build thread but i tried to list the buld of the specks so i can get more accurate responses. a lot of what i have read about this cam on here is asking how it will do in daily driven rig and I'm just not concerned about that so its been hard to find accurate information...really hope im not

thanks

[6TIME]

First off i want to say that this will not be a dd or even see the pavement very much so i don't really care about mpg and other common concerns when running a cam like the 239...soooo on to my specs (basicaly the mod poor mans)

What type of use will this motor see? Will you nee low rev torque for crawling or rpms for mud?

like i said i would like to run the comp 68-239-4 and maybe advance it a few degrees.

and finally what the heck im actually asking

1 is anyone running a similar setup?
2 how bad will the idle be ( could i delete iac and manually control idle...would that help)
3 how much will advancing the cam bring down the rpm range
4 any other words of wisdom

The idle will be dependent on how well the MAP sensor jives with your vacuum signal with the 239-4. You might have to do some tuning/tweaking to get it to run right. I would guess that with the 111* lobe sep. and duration figures on that cam it'll have a slightly choppy idle regardless. If you are already planning on advancing the cam, why not just get a milder grind like the 235-4 and run it straight up?

[JesseByrd]

first off thank you for reply

as far as use i gess i kinda want both (i know that doesnt help much haha) but i figgured with the lower gears and relativly small tire compared to (40s or something) i may beable to get some use out of the higher rpm power

i like the lift of the 239 at almost .500 it would fit right in to the 4:1 ratio for valve size..acording the math if i want to run a 2in valve i "need" .500 lift but i guess the 235 is a good option iirc they have about the same overlap

so basically it sounds like with a map adj. i should be able to get it running fairly well. i dont think a choppy idle will bother me at all, as long as it will idle

how would top end suffer with a map adj. seems like it may onlt think im at 90% load at WOT

[6TIME]

I wouldn't get yourself stuck on engine math formulas so much... There's a lot more that affects what the "ideal" lift is for any given motor/application than calculations.. Bore size, port efficiency, and valve spacing are things that you have to consider when trying the "bigger is better" idea with valves. Increasing the intake valve size to over 1.95" will not get you much without extensive porting and matching the chambers to the bore. With a 2.0" inlet valve, bore shrouding will affect the total flow around the valve.... your calculations probably have no way account for this?.. A smaller valve in this application creates more uniform flow around the valve that increases efficiency. When picking cams.... being a bit conservative is always better than too much. A 231-4 cam will rev happily to 5k in a stroker and produce gobs of low rev torque as well. Are you planning on running this thing at 4-6k all the time?

[JesseByrd]

i completely understand that there is more to it than the math, that's why i am asking about it here. i plan on doing a fairly extensive port job to the head. i am actually in collage right now for "high performance" and plan on on making this my career and am hoping to continue schooling at the school at the school of automotive machinists. i know that there is still a ton i need to learn and most of what I'm going off of is what i have been learning here. basically I'm not just trying to build a good motor for my jeep but something a little on the radical side. sadly i have a fairly limited budget right now but if i can build a stout motor now i can back it up with a custom header and a mega squirt to really make it scream....maybe I'm just being foolish and wanting too much for the $$$ i can put into it.

basically right now im "stuck" on the math because its all i really know right now

that being said i don't mean to sound ungrateful for your advice because i really do appreciate it

[jsawduste]

With the 4.88`s/35`s I might suggest the Hesco 274/480 224 @ .050 with 113 LSA

I ran this cam advanced 4 degrees with 37`s and 5.13`s/NV4500 for several years. Now running 5.38`s and think I found the sweet spot.

the 113 LSA helps to pull 16 inches at idle which keeps the MAP happy.

Having said that.......With the conversion to OBD2 that is happening now and tuning of the ECM I suspect the engine will be able to run a bit more cam with proper tuning.

Off topic but I`ll throw my 2 cents in.......Thought hard about the MS systems. For the most part liked what I saw. Only real caveat was if the ECM fails your done. With OBD2 you can swap in a readily available ECM from most any local source and get yourself home. MS is saying the latest to be yet released versions have a limp modes. Not al sure what that means but I would not want to miles from civilization to find out.

[JesseByrd]

@jsawduste

thanks for your input, had not thought about that aspect of the ms, though most of the places i wheel back home aren't that far out there (although i dought i will be staying in that location after i'm out of school) also having a little trouble finding that cam you mentioned. hesco doesn't seem to give the specks on the cams they have, do you recall the lift on that cam?

if i had 2 cents for every time some one gave me their 2 cents i would be doing a 401 swap instead

[jsawduste]

480

http://www.contentedits.com/img.asp?id=4651

[JesseByrd]

yah i guess you kinda said what the lift was