Took the new combo (Lloyd's big valve heads, XE 224/230) to the track last night for the first time. Really hot and humid.

Best run of the night was a 12.96@104.96. That was the first run of the day at about 7PM. 1.84 60ft, 8.2 1/8th.

Shift points were way off. And I still have a whole lot of work to do in that area, but what threw me off was the MAP readings at WOT.

I saw 98-99 MAP at WOT until about 5400. At that point it would begin to drop...97..96...it wasn't consistent, in some frames it would be back up to 98 but I saw as low as 92kPa once and 94kPa several times. I am running a 52mm ported stock TB now. The MAF is also 100% stock too. I am going on the assumption the TB is the restriction and with the MAP reading dropping that much (quite a bit of vacuum as compared to nominal) that there is a good bit of power left to be had. FYI The MAP read 100kPa with the engine off and key on.

I found a thread in LT1 Tech where Injuneer says if you see more than 1" hg in vacuum then you need to make a change in the intake tract. 1" hg equals 3.31 kPa. Ideal is 99-100kPa (atmospheric pressure), so seeing 92-94 is a significant amount of vacuum, over 2" of mercury at some points.

I am assuming that this condition would only get worse in cooler air because the engine would make more power and the airflow demands would increase. I have a feeling I'm definitely going to need some more fuel pressure once the engine has all the air it needs. I am running the SVO 24lb injectors and saw a peak pulsewidth of 18.29, which is very marginal at 6100 rpm or so.

Just looking for some Advanced Tech opinion/analysis on this situation.

 

Looks like you know how to hook that car up.

My vote goes for heads and/or tuning.

 

Heads? I just installed a set ported by Lloyd incl. the 2.00/1.96 valves.

I was tuning all night (LT1 edit). The 02s were averaging .880-.900

FYI..that 60ft is not very impressive when I reveal that it was on a set of ET streets with 18psi in them. However they usually cost me about 1 mph in trap speed due to the taller diameter.

 

Your maifold vacuum is kinda like the sum-total of all the restrictions in front of the manifold. TB, piping, MAF, more piping, air filter, air filter housing (if any). Everything adds it's own little restriction to the mix. Like an elephant being eaten by lots of ants. No single part determines the total restriction.

 

Interesting post!

Going through my datamaster file reveals the same thing. I hit 99kpa @ 4250rpms, then it slowly drops down to 91.5kpa @ 6375rpms.

I am running a larger filter on the CAI, a 51mm TB, and a Z06 MAF. Shouldn't be any restrictions - I wouldn't think.

How do you increase MAP readings with tuning?

Ryan

 

I see the same readings with my set up. I am running a volant LS1 airbox, ported MAF, Fernco coupler, 58 mm TB and a LT1 intake which was gasket matched for the TB and heads. I see as low as 94 KPA above 5K RPM. I am out of ideas of what is causing the restriction.

 

I've read every thread I could find with the Search function on this issue.

We hear all the time that for most engines a 52mm tb flows enough theoretically and that the 58 is too much although since velocity through the manifold is not important in an EFI setup it won't hurt you. I was hopeful going into this new combo that the 52mm tb would be plenty or that at most it would be costing me 5hp. I am frankly suprised at the readings I'm getting and judging by the trap speed and inferring from the MAP readings I'm probably off 30+hp.

I went ahead and bought a BBK 58mm TB. I'm going back to the track on Tuesday to quantify the results. Also picked up a set of the plastic maf ends, figured I'd try them out. I will compensate for their tendency to lean out the mixture with LT1 edit by either adjusting injector constant or modding the MAF table (I'd rather not touch the MAF table though).

I'll let you know what comes of it.

 

Good luck at the track Chris! I'm really hoping you find 5mph with that TB .

Keep us posted.
Ryan

 

the higher vacumm at WOT in the hgher RPM's is normal, the engine is requireing more air due to the higher demand from the higher RPMS, in the lower RPM's it has abdundabce of air due to plenum volume and it is a lower RPM .

 

Well I have some mixed results to report.

Not very scientific I'm afraid. I put the new 58mm TB in yesterday. This morning I scanned a WOT pull and saw basically the same readings...MAP got as low as 92kPa at 6200 rpm.

Next I pulled the air filter and ram-air lid and tried again. This seems to be the magic bullet. MAP still dropped, but no lower than 97kPa, and at some points I saw 101kPa for the first time with this combo. MAF g/s increased greatly to a peak of 285 at 6100 rpm and there was a spike of 293 at 5600rpm but the sampling rate on my scanning software is too slow for me to see if that was indeed a spike or not.

I have a set of plastic maf ends to try next...the MAF may now be the final restriction although I doubt it is significant. Problem is I do not want to run an un-screened MAF w/o an air filter.

I can cut the "grates" from the ram air lid and that may help flow some, and I can clean the K&N, but results may show that both need to be removed for the best flow.

Sorry I didn't try pulling the lid/filter FIRST before spending money. I dont' regret the TB because so far I am pleased with it, no adverse drivability issues, and because I am on a mission to eliminate any pumping losses in the intake tract. But it is unfortunate that I cannot quantify the effects of just the lid/filter. (I could put the 52mm TB back on but I'm too lazy )

 

Chris: I doubt the MAF ends will help. I am running a Z06 MAF already. However, there is a pretty big difference between the two:

http://images.cardomain.com/member_i...79_34_full.jpg


BTW, did the car FEEL any different with the 101kpa reading?
Ryan

 

I couldn't tell much of a difference to be honest with you. It felt like it got to the shift a little faster but I think when you start getting into big power cars the gains get harder to quantify with the ol' butt-o-meter.

 

Could it be that you need more timing in the upper RPM range? If it's combusting too early you might not be getting enough cylinder pressure to keep the engine pumping in as much as it could.

Just a thought...

 

There's the rest of the equation. It's the same reason carburated cars usually gain 10-30 hp with a 1-2" spacer. It's all about plenum volume when your pulling that much air through the system at high RPM.

SC-

 

Here's some more logging results from today:

Here's the comparison.


Parameter--Before(52mm tb)--58mmtb--58mmtb and no air filter/lid

LowestMAP----91------------------92---------------95

Peak MAF g/s--261----------------267-------------287

Peak Inj
PulseW -------18.29--------------18.8-----------20.96!!!

It appears the TB did help, but it wasn't until the filter was removed that the TB could do its job. My guess is that if I ran the the 52mm tb with the air filter out that it would show lower numbers than the 58mm w/o air filter did.

Chris Renner