Vacuum at max rpm question - EFI setup

[RSX302]

Understandably one would want little to no vacuum at max rpm for maximum horsepower.

My question is, if I have 1.78inhg (95kpa) at max rpm, what kind of hp am I leaving on the table and would it be worth going bigger on my intake setup. Start seeing vacuum at 4000rpm. 100kpa below 4k.

Dyno'd my new LS9 434 (4.155x4.0), AFR 245 head, Super Vic Single Plane, 1200cfm 4bbl TB.

635hp / 579tq

[andrewb70]

I am confused. How can you have more than 100kPa below 4000 rpm? What's your kPa at idle?

Andrew

[RSX302]

Hi Andrew

This is on a dyno at WOT. Where i'm located, atmosphere is 101.3kpa (14.7)

Theoretically with absolutely no intake/throttle body restrictions, I should see 101kpa throughout the rpm range at WOT.

[andrewb70]

Hi Andrew

This is on a dyno at WOT. Where i'm located, atmosphere is 101.3kpa (14.7)

Theoretically with absolutely no intake/throttle body restrictions, I should see 101kpa throughout the rpm range at WOT.

This makes sense now. My pure wild guess is that you might be giving up 10hp....this is purely a guess.

On the other hand, maybe even less. On my 5.3L with my bug catcher and dual 87mm TBs, I never hit above 95kPa when I am driving. This all of course depends on the DA at any given moment.

Andrew

[RSX302]

Twin 87mm TB's...damn

I was expecting around 650hp (565rwhp) with this engine as I've seen similar setups run 675hp. Although the compared engine has a FAST intake with a 102mm TB, open exhaust and no accessories.(on engine dyno)

10-15hp would make sense from my restricted TB to the FAST intake and 102mm TB. I'm thinking the open headers and no accessories is probably worth the other 25hp on the engine dyno.

Since I had the 1200cfm 4barrel throttle body, I figured that would be enough. After doing the math, (1.75" x 4) I find that it only comes to 77.7mm. dOh!!

Thats as big as a 4150 carb flange 4 barrel has unless I adapt something different (4500 flange or 102mm big bore)

I went with this set-up since I already had most everything from the turbo system I removed. Cost effective and saved 200lbs off the nose.

[71RS/SS396]

More air will help it, but I wouldn't go to a Fast 102, they choke big inch engines up top. I initially tried one on my 450" engine and it wouldn't pull past 6400 rpm, when I went to the Ozmo twin tb intake the engine picked up 50 hp and pulled to 7,800 rpm. I would try an adapter with a 4500 tb.

Fast 102



Ozmo twin tb intake, ignore the vacuum numbers it has a 5 stage dry sump that's pulling 15" on the crankcase.

[RSX302]

Holy smokes!! Ozmo is a serious piece of jewelry. That's an impressive hp gain you got and a ton of rpm!!

I was looking at getting a 4500tb with an adapter but then got a deal on a Holley 105mm.

Was doing the math on a 4150 flange and found the opening to be about 12.5-13sqin. The 105mm is 13.4sqin and 4500tb is 15.9sqin. I think to do the 4500tb justice I would need a 4500 manifold. Unfortunately the only one I found there for a cathedral port is Mast. Now hood clearance issues.

The 105mm Holley looked like it was made for the 4150 flange. Lol
Straight shot!

[71RS/SS396]

I think you might be surprised how well the 4500 will work even with the adapter. The problem with that Holley mounted like that is you have to put a turn in the intake directly above it which is going to disturb the airflow and it will also impact the the impulse waves. I experimented with several different air intake tubes when I had my engine on the dyno, I was stunned at how adverse the effect of the bends were to power. I had a tube with just one 45* bend in it and it knocked 25 horsepower out it so I ultimately put the filters directly on the tb's since it made the most power that way.

[andrewb70]

Holley makes a 4500 series 2000 cam throttle body that is fairly short. Maybe combine that with the Mast intake and see what the stack up height is...Mast also makes a ring that will mount over a 4" TB and allow the use of a regular air cleaner without doing an elbow.

Andrew

[RSX302]

Actually I'm going to try and use/modify my air cleaner setup to keep it looking old school.
Sorry for the sideways pictures, uploading from my iPhone.

[RSX302]

Cool, I'll check out the air cleaner adapter.

[RSX302]

But before I finalize a direction, I need to get out and tune. I'll also run it back over to the dyno and see if this is how it will stay. I'll report back with the numbers. Might be the moment Tim says "See, I told you so" Lol

I'm hearing airflow on the AFR LSX245 heads supports up to 700hp, so I figure if I can get anything close to that, I'll be happy.

[71RS/SS396]

Do a dyno pull with and without the air filter and with the hood closed. I would be curious to see the results.

[RSX302]

Do a dyno pull with and without the air filter and with the hood closed. I would be curious to see the results.

Will do..

Update...

I did a quick drive around without filter. Drove very nice. Low rpm throttle/tip-in had more resolution than the Accel 4bbl TB. I purchased the Holley 105mm with the low rpm taper. I was pleasantly surprised how well it worked.

On to the power run data log...

As soon as I opened up in 3rd gear getting on the freeway, my knock sensors immediately kicked in and retarded timing. Never had this issue with the smaller TB.

Drove around a little more then tried again. This time starting in 2nd gear. Pulled hard in 2nd to 6500 without timing retard. Shifted to 3rd, then boom, knock sensor timing retard again.

Brought it home to investigate data log files. Sure enough, 10deg timing retard on knock.

Pulled spark plugs and they looked hot but no sign of detonation. I found out that I screwed up and put the wrong heat range in. dOh..had NGK TR5's..I change to TR7's.

Fuel had a splash of VP110 in the tank. I figure mix is 95oct. Should be fine for my setup but I will put 5gals of 100oct in and try again.

I'm thinking this is a positive sign of power!!
The good data I recorded in 2nd gear shows 6500rpm, 24deg timing, 12.8:1A/F, 275lbs/hr fuel. (685ish hp) Fuel flow with the smaller TB was 255lbs/hr.(635hp)

Now that it started raining in Calif, I'll need to wait to test again. Looks promising.

BTW, I have the Holley HP FI system

[garvir]

you mentioned using a paper filter, that will cost you around 5 hp... a guy from K&N spotted my paper filter (14"x3") on my small block and claimed it was costing me 10 hp or more. because it was more restictive than the K&N.

[chpr1972]

RSX302, you are running a knock sensor on your motor. I have a Holly HP_EFI and was told I could not run a knock sensor because of different harmonics than stock. BBC 489 10:1 230/ 236 510/ 520 Comp cam with early closed chambered heads and a tunnel ram with 2 4bbl TPI. Is it possible for an amateur?

[RSX302]

I apologize for taking so long. I have everything complete and I'm happy with the result. I used the Spectre air intake (aka K&N..lol)

[RSX302]

RSX302, you are running a knock sensor on your motor. I have a Holly HP_EFI and was told I could not run a knock sensor because of different harmonics than stock. BBC 489 10:1 230/ 236 510/ 520 Comp cam with early closed chambered heads and a tunnel ram with 2 4bbl TPI. Is it possible for an amateur?

Funny that you mention knock sensors.

Yes, I'm running them and it's driving me nuts!!

I can get them to work, then they kick in out of the blue. Kill'n me!!

Before I installed the bigger throttle body, never an issue.

I've tried 114oct fuel and still kicked in. Has to be false knock.

Perfectly fine in 2nd gear with no knock retard, pulls hard. As soon as I shift, instant knock retard. I'm still tuning and getting everything dialed, but it's hard to do when the knock sensors are so intermittent. Tip in fuel data log is good. Set at 12.7:1 af at WOT.

If I slow roll the throttle in 3rd, I can avoid knock retard.

I thought I would start changing the freq and sensitivity to see if that helps. I've tried 5.5khz @ 50 sensitivity and 9.5khz @ 35 sensitivity. Knock hits 100 instantly. This weekend I was going to try bouncing around to see what affects, if any.

If all else fails, I will turn them off. Plugs look clean with absolutely no sign of detonation.

[RSX302]

Knock sensor parameter set to 5.5khz @ 10 sensitivity. Knock level data log recorded between 10-50. Seems that this may work.

Now time to schedule a dyno session.

[RSX302]

Results are in!!!

Throttle body was good for ~20hp

No noticeable difference in power with and without hood and air cleaner.

Accel DFI 1200cfm TB (27deg timing, 95-96kpa)
552rwhp
504rwtq

Holley 105mm TB (29deg timing, 98-99kpa)
573rwhp
518rwtq