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iPd T cam slow off the line

adamdrives

Member
Joined
Aug 9, 2010
Location
San Jose
Hey guys, I put an ipd turbo cam in my 740 over the weekend and am a little puzzled by the results. Before install the car was very zippy from a stop. I had set WG preload to 10 ps, verified by calibrated gauge. With the cam installed, and ignition timing at 12*, the car is comically slow off the line--it feels gutless until 3k or so, when it takes off. It definitely pulls harder on the highway, but is very, very slow off the line, even with brake boosting. I've searched around and experiences seem to vary. I just watched a video of a stock, mbc and T cam equipped 940 spinning through 1st and netting a 6 second 0-60--that would be impossible in my car. Is it normal to lose much low end?

My plan is to make sure the harmonic balancer hasn't slipped and the timing marks are accurate, but it seems odd that power was okay before. I tried advancing the adjustable gear 2 and then 4 degrees, which made no noticeable difference. Valve clearances were all between .014-.018 when I installed the cam. Any ideas?
 
Sounds like your timing is off indeed. Easiest way to tell if it slipped is by checking base idle timing with a light. If it's not at 12 it is for sure slipped. You will lose some torque at the bottom end but the powerband should be nice and nearly stock smooth.

Also, FWIW, a good approximation for that cam is -4 degrees on a timing gear. That's where it lands when you set it to Enem's (original manufacturer) spec of 1mm of opening at TDC. This should result in more torque through the entire powerband (yes, even at low RPM).
 
I did check with a timing light and the timing is at 12 deg. I’ll make sure the balancer is in the correct position after work. When you say -4 degrees, do you mean btdc, meaning advanced? Thanks
 
No, 4 degrees retarded. The cam has too much advance built in.

Usually having the timing light illuminating the harmonic balancer on the wrong spot is the dead giveaway. You could also try erasing the ECU's fuel trims by disconnecting it for an hour and see where that gets you.
 
You sure about those numbers Harald? On my IPD cam, 1mm open required around 1* advanced. Taking into account the head height, I'm running 4* advanced, for an actual of 1* against the crank.

Yeah, it's not as torquey off the line as my VX was, and it doesn't bark on the 1-2 shift like the VX, but it also winds out a lot better, pulls better across the band, and doesn't hit a wall at 5k like the VX did.

OP, assuming LH2.2 car here, since you're talking advancing the timing. 12* should be fine, definitely check cam timing, make sure something didn't slip a tooth.
 
You sure about those numbers Harald? On my IPD cam, 1mm open required around 1* advanced. Taking into account the head height, I'm running 4* advanced, for an actual of 1* against the crank.

Weird. You sure it wasn't shaved a whole bunch? -4 has been it for a few heads.
 
Well, the balancer had a slipped, but that’s not the issue. Got a known good one on and it’s still a dog off the line. Gear set to 0, timing at 12* btdc. I’ll upload a 0-60 video for a sanity check, but I’m pretty sure it’s around 10 seconds.
 
Weird. You sure it wasn't shaved a whole bunch? -4 has been it for a few heads.


Yeah, actually did the proper setup on it in the 531, came in at -4 to run straight up, but I know how much that head had been shaved down, comes out to around 3* for that. I'll check the next one as well, when I setup the Ph1 in the SPM head for the next build.
 
if its an auto car, consider a converter change.

The car doesn't like to shift out of first until its warm, so that could be part of the issue, but it seems to shift and hold power fine once warm. Do you mean a straight swap? Or is there a converter that would be better matched.

edit: well, now im wondering if maybe the car loses first when hot. I just watched the 0-60 video I took this morning and it stays in "first" gear until around 45 mph. Anyone know how much mph it should have at the end of first? Looking around for gear ratios now.

edit2: no, looks like 1st should end up around 45mph or so with back of the envelope calculation. Sigh. How to get more low end?
 
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The car doesn't like to shift out of first until its warm, so that could be part of the issue, but it seems to shift and hold power fine once warm. Do you mean a straight swap? Or is there a converter that would be better matched.

edit: well, now im wondering if maybe the car loses first when hot. I just watched the 0-60 video I took this morning and it stays in "first" gear until around 45 mph. Anyone know how much mph it should have at the end of first? Looking around for gear ratios now.

edit2: no, looks like 1st should end up around 45mph or so with back of the envelope calculation. Sigh. How to get more low end?
You could run smaller diameter tires, which will change your effective gearing.
 
I will reset the ecu today and see if there is any change. If that doesn’t do anything I think I will put in the stock (T?) cam and see how it drives.
 
I'm with Harald, give that a shot.

With a 6800 limiter in mine, it'll hit around 40-45 in 1st, around 80-85 in 2nd. The stock converter isn't that poorly matched actually, depending on what turbo you've got. I did find mine responds a world better with an MBC to help boost ramp up faster, even if it's the same boost level as the WG.
 
Given the number of these threads of late (2 or 3, maybe 4) where there is a complaint of no low-end torque and a common denominator of a particular cam swap, perhaps we need to ask if there might be something wrong with the grind? I know that one thread in maintenance had issues prior to said cam swap, but who knows if the original concern was fixed and then the cam swap introduced new, similar symptoms?

This all just seems a strange coincidence to me.
 
Left the battery unhooked all day, reset cam gear to -4, if anything the car is slower off the line :/

Gonna find a cheap mbc and see if that “fixes” my issue. It definitely pulls hard once it’s going, maybe it’s just my expectations? We’ll see.
 
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