Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
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I just bought brand new MSD 22lbs injectors last year and now i've decided to upgrade the motor and I'd like to know if I'll be ok. I got TF Heads a 218/224 495/502 112 cam and a highflow tpi unit. Msd said the injectors will support 50 PSI and 400 HP. Do I have to upgrade to the 24's. I just paid an arm and a leg for the 22lbs.
For 400 HP, you would need 25# injectors @ 42 psi. However this is at 100% duty cycle. You should never exceed 80% duty cycle, which means you will need around 30# @ 42 psi.
22# injectors @ 42 psi = 24# @ 50 psi. The key is at what psi are the MSD's getting their rated flow.
Which TFS heads? 23* ? Your new combo sounds a lot like my current setup..... Anyways, the short answer is no, 22 lb injectors will not support that kind of power with that combo. I know because my 22lbs @ 51psi were not keeping up on the high end and were causing some serious lean conditions at part throttle and idle applications. So I bought some 30lb SVOs and am running them @ 43psi with pretty good results..... Unfortunately my EEPROM burning facilities have failed me at the present so I still have some issues with my setup...... Even without a solid EEPROM to work with the injectors, my car runs much smoother.....
Good Luck....
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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam My GTA
<font face="Verdana, Arial" size="2">Originally posted by 92zeddar: well how come I seen in a super chevy magazine where stock 305 fuel injector 19# made 400 horse??
</font>
For how long before they toast it?
The calc for determining fuel injectors required are:
HP = Inj Flow x 2 x.8 (duty cycle) x # cyls
or
Inj Flow = HP / (2 x .8 (DC) x # cyls)
Obviously if you want to run at a Duty Cycle higher than 80%, you can run smaller injectors. But you are asking for problems.
To determine the "new flow equivalent for a given PSI, the formula is:
New Flow = (New PSI/Old PSI)^.5 x Old Flow.
But remember that raising fuel pressue only equates to the higher flow at low vacuum (ie. WOT). The effects of raising fuel pressue via an AFPR has minimal effect at idle due to the vacuum affecting the Fuel Pressure Regulator.
<font face="Verdana, Arial" size="2">Originally posted by Glenn91L98GTA: But remember that raising fuel pressue only equates to the higher flow at low vacuum (ie. WOT). The effects of raising fuel pressue via an AFPR has minimal effect at idle due to the vacuum affecting the Fuel Pressure Regulator.</font>
Exactly. Thinking that way about how much maximum power an injector will support will lead to some serious driveability issues, like Glenn says....... I know - I had them...........
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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam My GTA
