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Cam timing question
http://www.4g61t.org/forum/viewtopic.php?f=17&t=4804		 Page 1 of 8
Author:  socrateez [ Fri Aug 01, 2003 6:33 pm ]
Post subject:  Cam timing question
After getting tired of searcing through every post with the words timing, cam, adjusting, etc. etc. I decided to ask this question.
Has anyone tried to retard their cam on the 4g15? Dyno simulation show pretty dramatic improvement with a 5* retard. Whats the max before valves start hitting? I dont have a adjustable gear yet but was thinking of turning back a tooth. Any feedback?
Author:  Berserko [ Sat Aug 02, 2003 5:51 pm ]
Post subject: 
Never tried that might work I think you could have it out a tooth and have things ok but I bet you would have a ptretty lumpy idle...
Author:  Bill Spruill [ Sat Aug 02, 2003 6:52 pm ]
Post subject: 
:-? Don't know about the 4g15, but Jmauld calls for 1 tooth(5 degree) retard on the exhaust with the 4g63 exh. cam. Bill Spruill
Author:  Berserko [ Sat Aug 02, 2003 9:16 pm ]
Post subject: 
Yeah problem is this is only single cam in your simulation did you retard intake by 5 degrees also or only exhaust?
Author:  Bill Spruill [ Sat Aug 02, 2003 9:30 pm ]
Post subject: 
:oops: Showing my lack of smarts again. I only retarded the exhaust on installation. Should have it back from SDS install next week to try and eval. Any suggestions?
Author:  Berserko [ Sat Aug 02, 2003 9:46 pm ]
Post subject: 
No i wasn't knoing your suggestion bill i was suggesting to soc to see when he did his SW dyno simulation if he also back the intake timing up 5degrees because it may totally change the puzzle...
Author:  socrateez [ Sun Aug 03, 2003 8:48 am ]
Post subject: 
Yeah the sim is sohc. You have to change all the cam profiles. overlap, duration when all events open and close. Its more difficult to do for dohc.
Heres some info i discovered for all the 4g15 guys :D
One cam tooth equals 9* on the 4g15
Advancing one tooth boosts bottom end by a few horse but topend goes to crap big time. You lose over ten horse from about 3k on up.
Retarding one tooth (turning cam counter clockwise) yielded the best results. You sacrifice about three horse between 2k and 3k but then the hp and torque rise an additional 10 hp! the torque curve also shifts up the rpm range about 500rpm.
Ive only tested the results driving a few times so far. I'll have to do more driving but i noticed no more flat spot at 3k. Pulls harder at high rpm too.
This engine was a dog at low and high rpm, all the power in the mid range. Now there is more power all the way to redline. :D I believe this mod is worth the effort so far. One more note: I had to carve out the adjustment slots on the distributor to achieve the proper ignition timing. Other wise with the dist. cranked all the way, you'll get about 3* BTDC base timing. :( Runs crappy that way. I'm sitting at 8* BTDC now. After modifying the dist. i can get up to 12*.
I'll see if i can save the pics from the dyno sim so everyone can see the differences. Sorry so long
Author:  pumaproton [ Sun Aug 03, 2003 11:56 am ]
Post subject: 
Cool, this sounds worthwhile indeed! Is it worth making an adjustable pulley from a spare pulley? I don't really want it breaking thats all! And what about valve clearances? Have you pulled it all the way upto say 7k rpm?

I would really like to see the dyno prints!
Author:  Bill Spruill [ Sun Aug 03, 2003 1:45 pm ]
Post subject: 
Nice review Socrates, your nom de plume is well earned. :o There are other threads about retarding the exh. on a DOHC(w/o the distr.), but no one really explained what, where, or how we might expect a difference. Now I have an idea what to look for. :D Bill Spruill, oldest Colt
Author:  socrateez [ Sun Aug 03, 2003 4:42 pm ]
Post subject: 
I pulled rpm up to 7k with no problems. I wouldnt suggest retarding much more though. :) I know that RPW sells a cam gear for our cars. I dont know how much but they claim half the price of others. Basically, they mill a slotted section and tap the original cam gear and bolt the two together. Someone with access to a metal lathe could create these reasonably cheap.
Any tool makers out there?
Author:  colt-r-old [ Sun Aug 03, 2003 5:54 pm ]
Post subject: 
My girlfriend's dad is a tool and dye shop owner...
hes in the process of moving into a bigger shop... hes making a custom intake mani for free :D
I'll ask him if he can help me out... theres about 4 4g15 colts in the local yard, when hes settled in. i'm sure he can help me out
I'll ask him tonight as i'm going to her house tonight :twisted:
Author:  pumaproton [ Sun Aug 03, 2003 6:01 pm ]
Post subject: 
I looked about camshafts on the internet. Seems most people only retard or advance camshafts by 5 degrees, no more really. Each step on ours is 9 degrees as you say.

If I get a spare cam gear from a scrap yard tomorrow some plans could be drawn to be given to any decent machinist to make one. RPW ones are $130 USD according to AP Parts. Looks like they use the cam gear the opposite way around too. It's important to use bolts with a large built in washer to spread as much load.

Colt-r: I would be interestted in purchasing one if he can make them!
Author:  Bill Spruill [ Sun Aug 03, 2003 6:13 pm ]
Post subject: 
Quote:
Colt-r: I would be interestted in purchasing one if he can make them!
I'm interested, also, but would like a load of info. before committing. Also, it would have to be 4G61 specific, and how the design would improve over OEM. (I have been advised that 4G63's lose lower end when bolted onto 4G61's, even with a port match, as it creates a bulge in what should be a narrowing venturi, over longer runners.) Bill
Author:  pumaproton [ Sun Aug 03, 2003 6:17 pm ]
Post subject: 
I meant the adjustable cam gear actually :)
Author:  Bill Spruill [ Sun Aug 03, 2003 6:25 pm ]
Post subject: 
:oops: Oh me. I seem to have crossed threads again. I was really interested in the manifold Colt-r alluded to, vis. a vis., a camm gear. Sorry. :cry: Bill
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