mittens

So after many many searches and reading almost every build on LT1 or LT4 on here.

Back in the day people used LS7 caps on the fuel pumps, and then some lost them in motors. Then the Cam swaps came with fuel lobes with a smaller base circle and you used a lash cap, to make up the difference (cant make the lobe bigger because sliding it the bearing journals.)

When shopping for cams, some say "Lash cap required for fuel lobe" and others don't say **** about a lash cap just a fuel lobe.

Then I see Comp has like 5 different shapes of fueling lobes now..


So as we are at the end of 2017 what's the right answer do all cams still require a lash cap with the fuel lobe? or did the different shapes (basically causing an extra stroke on the pump/revolution) causing the fuel gains with out having to over stroke the pump? or what.

Higgs Boson

they have had all those lobes since the beginning, the only one you can use with the LTx HPFP is the 3 lobe.

as far as the lash cap, I am out on any application that needs one, even if it means less fuel.....fighting the DI system is just pointless, when you run out of DI capacity get a port injected auxiliary setup, IMO. don't even need meth anymore.

mittens

Ok so those lobes have been around before, good to know. what are they used for if not the LT stuff?

What causes the LT pumps to not allow the other lobes?

So Installing a Cam from BTR, with 38% lobe. its a triangle one, will it need a lash cap or not? LT1

robert miller

It will to be able to get the full amount of the 38% more fuel. But get up with FRYANT in here he has this part of this down good.

mittens

so how does it work with out the cap? is there some room to make the lobe a little bigger? so it can get the 38 with out a cap? or what

C7&7

This is all you need to know about lashcaps today. Courtesy of the Ant:

https://www.corvetteforum.com/forums...learances.html

mittens

I have read that thread many times. But again this is a direct question as some cams need it and some don't?

FYREANT

Did you see the part in my thread about pump pre-load? All cams that increase the fuel lobe output REQUIRE a lash cap. The thickness of the cap depends on the make and size of the lobe you have on your cam.

mittens

That’s what I read and how I understand it, but BTR saying you don’t need one???

FYREANT

Once you get to the point of installing the cam, follow my guide. It will definitively tell you if you need a lash cap or not through the measurement process. Im pretty certain you'll still need one but who knows for sure. No matter what they "tell you", ALWAYS measure your clearances in your build.

Ant

JHEBERT

I have posted this before, but...

The fuel lobe is already the OD of the bearing journal on the cam, so it can't be made bigger. The "larger" fuel lobes are ground on a .050 smaller base circle, so you would need a .050 (not .080) lash cap to get the extra fueling from the cam lobe. Not using a lash cap with the larger fuel lobe won't get you anymore fuel.

John

FYREANT

Correct. I believe the closest lash cap you can get to that is a 0.060". Which is the LS7 lash cap. Clearance measured correctly on mine.

mittens

there there is NO CAM made that has a fuel lobe that does not need a lash cap PERIOD.

correct?

I re-ask this because I just got off the phone with BTR and they say with a LT4 pump no lash cap to be used. and with the LT1 you do use a cap, this is with a 38% fuel lobe.

robert miller

That is what they told me also that is with the 38% cam that was the reason they did the cam like that. It would be good to have some one to do one of these cam with the lt4 pump & also inj to see. I know inj don't have nothing to do with that but if the pump I am sure the person also will do the inj also..

But then again I know Brian knows his stuff on heads and cams..

mittens

So after having a long talk with Comp, some need it, some don't period. There was a change at some point with GM and the newer LT1 pump can extend farther than the first ones. Thus Not needing a lash cap, because they still pre load the smaller base circle.

while if you have the older LT1 pump it cannot extend and pre load the smaller case circle.... and you need the .060/8mm lash cap to keep preload on the pump.

so as FYREANT stated you have to check every time. you want .030 of preload on the pump.

robert miller

You are not clear here on this, But to say if you have a early 2014 car but use the BTR cam that is 38% more fuel, Then IF you use the LT4 pump & inj you DONT have to use the lash cap.

But same cam BUT use the LT1 pump you do need the check for the preload.

mittens

The guy at Comp was not sure what the case was with the LT4 pump. He remembered the LT1 having the change and it causing them to be unsure and having to test fit/check.

he also stated it was not just a year break but sometimes newer ones would show up with the older shorter pump.

Again this is all from Comp , not my self.

FYREANT

Exactly why you should measure your setup personally!

mittens

SO my questions is now,.. If you have to use a lash cap... is this going to be a huge risk? all the horror stories of them falling into the motor, or something.

or was that only when installed wrong (on the pump instead of on the follower like it should be) or using one that kinda fit back in the day vs one MADE for that follower.

reliability wise, once set up with a lash cap, or with out is there a worry?

FYREANT

Its a combination. Either some installed it on the pump and not the lifter, or, as in the case of Higgs, his pump broke off the bolts and as a result of the pump coming loose the lash cap went MIA.

If the lash cap is installed properly, and measurements are taken to ensure you use the proper size, you won't have an issue.