Hey friends,

I thought I was going crazy with a collapsed lifter, thankfully.. I’m not crazy. I’ve searched thoroughly, after reading the Big Mouth requires shimming of the rail so the injectors don’t bottom out hard, causing excess noise and poor injector performance.

My L98 does indeed have these exact symptoms after the install with AS&M runners and new valve guide seals.

Ive read multiple threads, however... none gave me specific guidance on what I should use and/or what TPiS provides in their instructions.


Any help would be fantastic.

I’m awaiting confirmation from another member on a Corvette forum but, 1/4” washer shims on the fuel rail towers should provide relief. I’ve noticed loud ticking and decreased performance, (ie running very rich) since the install.

Ive used a stethoscope in numerous locations, valvetrain sounds completely normal, the ticking protrudes mostly from the driver side injector banks.

I’ve been around quite awhile myself, and while most posts and research suggest it is normal for TPI engines to tick that loud... however, I do not agree. If you search enough, you will find quite a few with the same concern. TPiS included washer shims in the package and instructions, not sure why Edelbrock omitted them. I can assure you, it is obvious and loud.

Nevertheless, I’m tracking on it and it will be resolved.

Circa 2006:

https://www.corvetteforum.com/forums...gine-what.html


Another:

https://www.thirdgen.org/forums/tpi/...r-problem.html


The complaint is few and far between, but it does exist.

I agree with drew. Never heard of this problem before.

Injectors do make noise. Some brands are louder than others for whatever reason. Injector sitting in rails at different heights will not do anything for the noise. That just doesn’t make sense.

Second, as said previously, most aftermarket injectors are shorter by a tiny bit which would require you to double o ring the base OR grind down the fuel rail posts on the intake

my last install of a tpis base i had to do this. Did not shim up anything and with southbay injectors there was no excessive noise.

also had to cut down the posts on my stock tpi base to install bosch 36 lb injectors

The injectors are OEM, I cannot emphasize enough that I’m not making this up. The injectors are bottomed out at the intake base bungs (more or less) and I know for a fact after 12 years of playing with these cars that something is not right. I’ve driven myself crazy pulling valve covers and adjusting lash. I can go on and link others with the same symptoms with the same intake... but, I guess nobody would believe me heheh.

Update:

Shimmed the fuel rail with 2 standard washers a piece on the fuel rail towers.. no clearance issues with the plenum, obscenely loud ticking symptom is gone, just your standard injector ticking actuation is present, idle quality improved, as well as the rich exhaust fumes.

The injector bodies are not slammed down into the injector bungs like it was.

It threw me through a loop as well, I’ve built 3 TPI based engines, none of which had a Big Mouth intake base, so this has been a first for me as well. According to the TPIS instructions, step 7 in the included install instructions calls for the shims. (Vehicle dependent, injector dependent)

Im willing to bet, because of the thinner tolerances of the Big Mouth, and the fact injectors audibly acuate, the intake is prone to increased resonance of the dreaded “tick” that sounds like a Cold War era Russian beater car.

Id love for you to try and recreate it, and save someone heartache.. keep in mind, this is a ‘88 L98 with factory injectors, and the injector bodies were pretty dog gone deep in the bungs.

Nevertheless, it was abnormally audible, and it ran fairly sloppy considering this car is in fantastic condition. I’m glad I researched it, but it was NOT easy to find any information on it. Maybe 5 or 6 posts in the last 10-12 years with the TPiS Big Mouth and loud ticking.

Here is a shot during the valve seal job where those injectors are buried in fairly deep in the bungs.
After the adjustment, picture isnt great but.. the injectors bodies aren’t buried.

They actually are alittle on the high side, just because I really wanted to isolate the situation. I’ll probably tighten them down a smidge more. No leaks otherwise.

I can’t find the other post but, he said he scanned the original TPIS instructions, and sent it to the OP; annotating that step 7 calls for the usage of shims.

I would love an explanation how injectors height in the bung holes change fueling characteristics and idle quality

that just does not make any kind of sense

Im with you Orr, however research... no quantitive experience otherwise has said that having the injectors bottomed out severely causes the injectors to ride open, hindering the cycle. I’ll try and find that information, but.. with people moved on to LS, the tribal knowledge is hard to find.

My car in particular ran pretty dog like in open and even more so closed loop with the nasty click, wish I had some datalog to back it up.

https://www.corvetteforum.com/forums...size-pics.html

Found this, at least one instance anyway.

do you know why tho? The opening closing is voltage controlled and internal to the injecfor body. Being tight in rail should not change anything to the internals but i agree they shouldnt necessarily be too tight in there so you can easily move them to get clips on

Yeah Lethal, I was looking at pictures of my last two motors, and the injectors look like your picture... I think Turtle touched on it, they should be able to rotate freely, regardless of height. Given different intakes and injectors etc etc... the builder should just be cognizant of injector bind.

Im interested in the theory behind having injectors too tight causes a open condition which translates to performance issues...