LT1 to LT4 pump lash cap needed?

tom's2005gto · 12-16-2018, 01:08 PM

Upgrading to LT4 pump and injectors. Keeping stock cam for now. Does the lash cap need to be changed for the LT4 pump with stock cam?

oldman · 12-16-2018, 02:33 PM

nope, you need a lash cap when go to a bigger cam lobe, because there is no way to make the lobe "bigger" as it has to be inserted into the block. So the grinder takes off from the low side of the fuel lobe(s). Since now the the low side of the lobe (the base circle of the fuel lobe ) is smaller you need something to take up the slack.

tom's2005gto · 12-16-2018, 02:36 PM

Quote:

Originally Posted by oldman

nope, you need a lash cap when go to a bigger cam lobe, because there is no way to make the lobe "bigger" as it has to be inserted into the block. So the grinder takes off from the low side of the fuel lobe(s). Since now the the low side of the lobe (the base circle of the fuel lobe ) is smaller you need something to take up the slack.

Thank you sir

Brianw36 · 12-16-2018, 02:42 PM

If updating to lt4 high side pump and injectors, do you need a lash cap if the cam has been upgraded to a 38% fuel lobe?

Stefano · 12-17-2018, 08:05 PM

Yes, read what the "oldman" had to say.

oldman · 12-18-2018, 08:58 AM

and the "need" is you need to measure and file. Tossing any lash cap in even the slim LS7 cap (I think that is OEM for the exhaust valve), has a chance to hammer the pump off the block. So you best be reading every thread on lash cap. I did not buy any special cam base lobe seating tool/measure device. It was pretty easy putting the cam on the base circle and filing the cap for the clearance. Which is zero clearance with no gasket and no spring on the pump. Add gasket and bingo .015 ish to .020. I did a write up on my install. I ended up with a .020 lash cap wishing I started with the LS7 would have save a lot of filing... I think the cam grinder cap is .060 and the LS7 was .040. Once again be warned the cap has to be filed or pump fly though hood (just kidding), but it can be hammered off the block, which ain't fun.

Stefano · 12-18-2018, 12:49 PM

You can also use addition steel pump gaskets in order to get to the proper lash if needed, depending on the pump you are using.

oldman · 12-18-2018, 03:45 PM

Quote:

Originally Posted by Stefano

You can also use addition steel pump gaskets in order to get to the proper lash if needed, depending on the pump you are using.

yep, and if memory serves me if I ran no gasket and no shield, I would need no shim at all

Stefano · 12-18-2018, 05:07 PM

It also depends which lash cap you choose to use as the LS7 cap is different than the one from Comp cams.

8MM x 0.080" thickness - Comp Cams # 633-1
8MM x 0.060" thickness - GM part number: 12596509

oldman · 12-18-2018, 10:34 PM

, mine with gasket ended up at .020 with a Texas Speed 32 percent cam. I think that is 7.5mm or 1mm more than stock or .040.

laynlo15 · 12-20-2018, 01:33 PM

Just found out that my Livernois has a 35% fuel lobe. So it sounds like the LS7 would give me enough for my LT4 HPFP to correct the issue with the stroke on the pump. So hopefully I'm reading the stuff correctly and this is the right direction I'm heading.

Stefano · 12-20-2018, 06:25 PM

Measure twice, cut once

laynlo15 · 12-21-2018, 05:46 AM

So I still might have to grind or file the lash cap?

teesee150 · 07-09-2020, 06:29 PM

How much clearance is required?

I just dropped in a Lingenfelter HPFP. I had a gap of .010" with the pump bottomed out at the top of the cam lobe with the comp cams lash cash (0.080"). Instead of grinding .010" off, I just used the GM .060" lash cap and called it good. Am I missing out on any extra fuel by not grinding the Comp Cams cap down to say 0.070"?

12-16-2018, 01:08 PM	#1
tom's2005gto Drives: 2016 2SS A8 Convertible Join Date: Aug 2010 Location: Nashville, TN. Posts: 194	LT1 to LT4 pump lash cap needed? Upgrading to LT4 pump and injectors. Keeping stock cam for now. Does the lash cap need to be changed for the LT4 pump with stock cam?

12-16-2018, 02:33 PM	#2
oldman Drives: SS 6 speed of course Join Date: Jan 2016 Location: Hilo, HI Posts: 4,317	nope, you need a lash cap when go to a bigger cam lobe, because there is no way to make the lobe "bigger" as it has to be inserted into the block. So the grinder takes off from the low side of the fuel lobe(s). Since now the the low side of the lobe (the base circle of the fuel lobe ) is smaller you need something to take up the slack. __________________ Forged short block, large duration sub .600 lift Cam Motion cam, 7200 RPM fuel cut, Pray Ported Heads, 3.85 pulley D1X, stage II intercooler, DSX secondary low side, DSX E85 sensor, Lingenfelter big bore 2.0 pump, ported front cats, 60608 Borla, LT4 injectors, ZL1 1LE driveshaft and Katech ported TB, ported MSD intake, BTR valvetrain, ARP studs, ProFlow valves, PS4 tires.

12-16-2018, 02:42 PM	#4
Brianw36 SNSTRSS Drives: 2016 Camaro 2SS A8 Join Date: May 2016 Location: North Florida Posts: 583 View My Garage	If updating to lt4 high side pump and injectors, do you need a lash cap if the cam has been upgraded to a 38% fuel lobe? __________________ 2016 Black Camaro 2SS A8 NP

12-18-2018, 08:58 AM	#6
oldman Drives: SS 6 speed of course Join Date: Jan 2016 Location: Hilo, HI Posts: 4,317	and the "need" is you need to measure and file. Tossing any lash cap in even the slim LS7 cap (I think that is OEM for the exhaust valve), has a chance to hammer the pump off the block. So you best be reading every thread on lash cap. I did not buy any special cam base lobe seating tool/measure device. It was pretty easy putting the cam on the base circle and filing the cap for the clearance. Which is zero clearance with no gasket and no spring on the pump. Add gasket and bingo .015 ish to .020. I did a write up on my install. I ended up with a .020 lash cap wishing I started with the LS7 would have save a lot of filing... I think the cam grinder cap is .060 and the LS7 was .040. Once again be warned the cap has to be filed or pump fly though hood (just kidding), but it can be hammered off the block, which ain't fun. __________________ Forged short block, large duration sub .600 lift Cam Motion cam, 7200 RPM fuel cut, Pray Ported Heads, 3.85 pulley D1X, stage II intercooler, DSX secondary low side, DSX E85 sensor, Lingenfelter big bore 2.0 pump, ported front cats, 60608 Borla, LT4 injectors, ZL1 1LE driveshaft and Katech ported TB, ported MSD intake, BTR valvetrain, ARP studs, ProFlow valves, PS4 tires.

12-18-2018, 10:34 PM	#10
oldman Drives: SS 6 speed of course Join Date: Jan 2016 Location: Hilo, HI Posts: 4,317	, mine with gasket ended up at .020 with a Texas Speed 32 percent cam. I think that is 7.5mm or 1mm more than stock or .040. __________________ Forged short block, large duration sub .600 lift Cam Motion cam, 7200 RPM fuel cut, Pray Ported Heads, 3.85 pulley D1X, stage II intercooler, DSX secondary low side, DSX E85 sensor, Lingenfelter big bore 2.0 pump, ported front cats, 60608 Borla, LT4 injectors, ZL1 1LE driveshaft and Katech ported TB, ported MSD intake, BTR valvetrain, ARP studs, ProFlow valves, PS4 tires. Last edited by oldman; 12-20-2018 at 03:37 PM.

12-17-2018, 08:05 PM	#5
Stefano Drives: 6th Gen NicKey Camaro & others. Join Date: Nov 2015 Location: Loves Park, Illinois Posts: 492	Yes, read what the "oldman" had to say.

12-18-2018, 12:49 PM	#7
Stefano Drives: 6th Gen NicKey Camaro & others. Join Date: Nov 2015 Location: Loves Park, Illinois Posts: 492	You can also use addition steel pump gaskets in order to get to the proper lash if needed, depending on the pump you are using.

12-18-2018, 05:07 PM	#9
Stefano Drives: 6th Gen NicKey Camaro & others. Join Date: Nov 2015 Location: Loves Park, Illinois Posts: 492	It also depends which lash cap you choose to use as the LS7 cap is different than the one from Comp cams. 8MM x 0.080" thickness - Comp Cams # 633-1 8MM x 0.060" thickness - GM part number: 12596509

12-20-2018, 01:33 PM	#11
laynlo15 Drives: 2022 Lt1 A10 Join Date: Nov 2015 Location: clark, mo Posts: 8,860	Just found out that my Livernois has a 35% fuel lobe. So it sounds like the LS7 would give me enough for my LT4 HPFP to correct the issue with the stroke on the pump. So hopefully I'm reading the stuff correctly and this is the right direction I'm heading. __________________ 2022 Lt1 6.2 A10, Maggie 2300, THPSI Port Inj/10 rib, Rotofab, E, Nickey, SCOL, Griptech, RC Bandits, Hoosiers/MT 9.80@142.96 1.44 60ft, 6.34@112 707/669 RWHP/TRQ. 16SS Maggie 2650 9.41@147 1.35 60ft, 5.99@119. 16 C7 A8 10.90@128 Bolt on stuff

12-20-2018, 06:25 PM	#12
Stefano Drives: 6th Gen NicKey Camaro & others. Join Date: Nov 2015 Location: Loves Park, Illinois Posts: 492	Measure twice, cut once

12-21-2018, 05:46 AM	#13
laynlo15 Drives: 2022 Lt1 A10 Join Date: Nov 2015 Location: clark, mo Posts: 8,860	So I still might have to grind or file the lash cap? __________________ 2022 Lt1 6.2 A10, Maggie 2300, THPSI Port Inj/10 rib, Rotofab, E, Nickey, SCOL, Griptech, RC Bandits, Hoosiers/MT 9.80@142.96 1.44 60ft, 6.34@112 707/669 RWHP/TRQ. 16SS Maggie 2650 9.41@147 1.35 60ft, 5.99@119. 16 C7 A8 10.90@128 Bolt on stuff

07-09-2020, 06:29 PM	#14
teesee150 Drives: Camaro Join Date: Mar 2016 Location: Michigan Posts: 107	How much clearance is required? I just dropped in a Lingenfelter HPFP. I had a gap of .010" with the pump bottomed out at the top of the cam lobe with the comp cams lash cash (0.080"). Instead of grinding .010" off, I just used the GM .060" lash cap and called it good. Am I missing out on any extra fuel by not grinding the Comp Cams cap down to say 0.070"?

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