Low Dyno number
03-21-2018, 08:03 PM
#1
Low Dyno number
I have a 2015 z06. With Haltech intake. Mamo ported tb. Corsa axle back exhaust. I’m running 91 octane non ethanol gas. I did a Dyno run and pulled 530 on the first pull. Then 330 on second pull right after 1st. Waited till car cooled. No check engine light or codes. Did another pull and made 530. Did second pull right after first and made 460 hp. Could I be having heat soak after just 2 pulls on a Dyno? I’m thinking about adding weapon x heat exchanger and expansion tank. Any advise? Thanks.
03-21-2018, 08:48 PM
#2
Le Mans Master
I have a 2015 z06. With Haltech intake. Mamo ported tb. Corsa axle back exhaust. I’m running 91 octane non ethanol gas. I did a Dyno run and pulled 530 on the first pull. Then 330 on second pull right after 1st. Waited till car cooled. No check engine light or codes. Did another pull and made 530. Did second pull right after first and made 460 hp. Could I be having heat soak after just 2 pulls on a Dyno? I’m thinking about adding weapon x heat exchanger and expansion tank. Any advise? Thanks.
From whAt I hear these cars pull timing big time when hot and with high intake temps. Maybe this can be tuned out of them. That might explain your huge discrepancy on the repeated dyno runs plus the 91 octane. They really need 93 octane. These cars should make 550 to 580 rwhp on 93 octane.
Last edited by Mr. Gizmo; 03-21-2018 at 08:53 PM.
03-22-2018, 11:44 AM
#5
Race Director
03-23-2018, 12:03 AM
#8
Race Director
03-23-2018, 02:19 AM
#9
The LT4 really does need 93 octane.
03-23-2018, 10:43 AM
#10
03-23-2018, 11:41 AM
#11
Race Director
Direct injection engines have a cylinder pressure of approximately 300 psi at idle to over 1000 psi. You can figure why with a fuel pressure of 500 psi a motor couldn't run. Fuel would theoretically be pushed backwards into the injectors.
03-23-2018, 12:05 PM
#12
Former Vendor
Make sure you used a dynojet or the numbers are meaningless. But it's not uncommon to have large power drops on the factory tuning as IAT temps go up.
03-23-2018, 12:16 PM
#13
Le Mans Master
Does the Chevrolet DFI system ever actually inject fuel after the spark has been initiated? I haven't read up on their injection strategy, I don't know, but assume they continue to add fuel after the spark event. If so, then the pump is working against combustion pressures too.
03-23-2018, 04:00 PM
#14
Race Director
Member Since: Jul 2007
Location: Texas Hill Country
Posts: 10,763
Received 2,379 Likes
on
1,238 Posts
Does the Chevrolet DFI system ever actually inject fuel after the spark has been initiated? I haven't read up on their injection strategy, I don't know, but assume they continue to add fuel after the spark event. If so, then the pump is working against combustion pressures too.
if you sprayed DI any time after the spark event you would be just pushing fuel out of the exhaust. a port injection system can begin injecting again as soon as the intake valve closes and this is one of the reasons it is so easy to run out of fuel with DI, the injection window is very small....100 degrees instead of 600.
03-24-2018, 11:58 AM
#15
Le Mans Master
if you sprayed DI any time after the spark event you would be just pushing fuel out of the exhaust. a port injection system can begin injecting again as soon as the intake valve closes and this is one of the reasons it is so easy to run out of fuel with DI, the injection window is very small....100 degrees instead of 600.
If I can read your mind a moment it sounds like you object to fuel added after the spark as wasted, but it will burn. The flame kernel (or whatever its called) burns like a little campfire in the bowl of the GDI piston and then they can add fuel like a hillbilly adding starter fluid to an already-running BBQ. Whether they do in the LT motors I don't know.
There's a long time during compression, and then initially after spark, before pressures rise during the first phases of combustion where they could easily be adding fuel.
But I'll see what I can find on their DFI setup, what I know comes from Lexus!
Last edited by davepl; 03-24-2018 at 12:02 PM.
03-25-2018, 09:47 AM
#16
Race Director
Member Since: Jul 2007
Location: Texas Hill Country
Posts: 10,763
Received 2,379 Likes
on
1,238 Posts
I don't get why you'd say that. Exhaust valve isn't open anywear near peak combustion pressures - it doesn't pop open after spark.
If I can read your mind a moment it sounds like you object to fuel added after the spark as wasted, but it will burn. The flame kernel (or whatever its called) burns like a little campfire in the bowl of the GDI piston and then they can add fuel like a hillbilly adding starter fluid to an already-running BBQ. Whether they do in the LT motors I don't know.
There's a long time during compression, and then initially after spark, before pressures rise during the first phases of combustion where they could easily be adding fuel.
But I'll see what I can find on their DFI setup, what I know comes from Lexus!
If I can read your mind a moment it sounds like you object to fuel added after the spark as wasted, but it will burn. The flame kernel (or whatever its called) burns like a little campfire in the bowl of the GDI piston and then they can add fuel like a hillbilly adding starter fluid to an already-running BBQ. Whether they do in the LT motors I don't know.
There's a long time during compression, and then initially after spark, before pressures rise during the first phases of combustion where they could easily be adding fuel.
But I'll see what I can find on their DFI setup, what I know comes from Lexus!
If you are just asking about split pulse or dual pulse, I don't really know why GM doesn't employ this (except during starting) but they don't use a DOHC setup or a lot of other modern tech either, I guess they just don't think it's needed....but to me their V8 DI fueling strategy is just handicapped PI fueling, almost an experiment until the ZR1 is out with dual fueling.
