antman89iroc

I've got my new build tuned out pretty well. Runs great but has a strange condition. See my sig for more but basically it's a 414CID motor with HSR intake, 210 AFR heads and a Comp 236/242 cam cut on 112LSA running on a MAF system.

The motor doesn't like very light throttle. In the 1500-1800 RPM range and 60-70LV8 load range it has what I would call a surge. It seems the rpm fluctuates back and forth. Since I have a manual trans it seems to kind of magnify the condition. This occurs when I'm trying to hold a steady low speed such as in traffic. It goes away with more throttle (higher load) and is most noticable in the lower gears but it is present in OD on the highway too.

I have tried more/less timing and changing the timing curve in the lower load ranges. It was lessened by pulling the timing back as the load goes down (LV8 <80) Adding fuel doesn't seem to help much except for making sure it's not too lean.

Anyone experiance this condition? I presume it is what people mean by the term "cam surge" but I have not experiance it before and it doesn't seem to be too much cam for the engine size.

gta324

I almost have the same combo but I cant recall I have any surge. DO you run closed loop?


( havent been driving it for a while now...)

antman89iroc

Right now I am having the best success in open loop. I eventually want to get back to closed loop but that is when the condition is the worst. BTW right now I have been able to reduce it a lot. I have added what seems to me to be a BUNCH of timing. This combo seems to like a lot at low rpm/Lv8's. I have ~40' @ 1600, ~42 @ 1800 and 45 @ 2000+ from 112LV8 and lower. Also running much richer ~14.5 according to wide band.

This motor/trans/rear combo is under very low load/throttle during 40-50MPH cruise conditions. At 50MPH I'm running about 1700RPM in 5th gear. Lv8 in the 50-60's and very low throttle so account for some drive line slack and you can see how this gets magnified. Very touchy. I think the cam/intake are at the bottom of their ranges also. It just seems difficult to get everything perfect at such a low demand point.

formula_novice

iTrader: (1)

Not sure if you've already done this but I would start with some basics before I spent too much time dialing in the tune.

Check your vacuum with a gauge. IMO, I don't think your cam is too big but you could have a vacuum leak somewhere else.

In my experience, a failing fuel injector(s) can also cause a surging issue. Ohm them and see if their electrically ok... if they're failing mechanically, you'll have to replace them or have them rebuilt.

Since you're checking things, I would also check the fuel pressure from the pump.

Just my 2 cents.

Hope this helps!

abray1

I had a surge problem once and I had to clean my idle air motor and its passage and also change the TPS.

dabomb6608

iTrader: (3)

I have pretty much the same symptoms with my setup (see sig) it is VERY annoying and can be easily heard with my exhaust. It will just about jerk your neck off from surging so bad. What are you meaning when you say Lv8 or whatever? Is that your Kpa cell? Im tuning with EBL and Tunerpro so the wording might be different.

Orr89RocZ

iTrader: (20)

I think you are on the right track with timing increase in those real low lv8 areas. Thats very load load and surprised you are seeing that on that setup

Also can simulate locked timing by making all rpm/lv8's in that problem area the same value.

Also note that hsr has some minor air distribution issues which can add to the surge problem. May want to try a large swing in air fuel both rich and lean to see if it cleans up. My guess is a slightly lean spot

92RSZ

iTrader: (6)

You've got reversion. The same thing happens with my car at low rpms. It's a 420 small block with a miniram, zzx cam, and t56. Open loop and timing helps but I'm not sure it can be completely eliminated. Definitely could be an air distribution issue too. I run it at 13.5-14.0 afr and it seems to buck a lot less than at stoich

antman89iroc

Well when I said timing and fuel don't help I wasn;t going far enough. Lots of timing (~40*) and AFR in the 12.5-13.5 range helped a lot. Pretty darn smooth now. I was way to lean at 14.5-15 so a little more or less was still not enough. Thanks for all the help.