I can't aeem to find a clear, concise answer about this. I am retaining the stock TBI on my '89 RS, I just want to know what size of cam can the factory system be programmed to accommodate? I'm not looking at any extreme cams, just want to know what I need to be looking at. I'll be doing TBI mods, at least 61# injectors, clutch as well as rockers , springs, retainers, etc along with an as yet to be determined cam. engine is ready to go back together, just need a cam.
Cheers

'89 RS
5 spd
Out with the 305
In with a '98 Vortec 350

 

Check out Harris Tuning. There's a lot of info on his pages.

Harris Tuning - 350 TBI builds & details

From 250hp to 260hp the fuel pressure should be bumped up to 13-14psi on stock 350 truck injectors which will change their flow rating to 60lb/hr.

That's about the limit of a fresh stock TBI fuel pump as I understand it.


Here's a sample of his shelf cam choices for a 350 TBI.

LEVEL1 is stock cam which is 165/175 duration @ .050 and has a powerband of 0-3200 rpms.

Level 2 is going to be a duration of around 185/195 @ .050 and powerband will be 500-3800 rpms.

Level 3 is duration 195/205 @ .050 and powerband is 1000-4500 rpms. example for roller cam

Level 4 is 205/215 duration @ .050 and powerband will be 1300-4800 rpms. roller cam

Level 5 is 210/220 duration @ .050 and powerband is 1700-5200 rpms.

Level 6 is 215/225 duration @ .050 and powerband
is 2000-5500 rpms.

IIRC - TBIs ~ 475 cfm, but can be bored to flow ~650 cfm. Maybe support 345 hp in theory but you'll spend a fortune to make 345 hp with a TBI set up.

 

Thank you very much, this is the kind information I am looking for. I just want to make sure I get the right cam that can be tuned with the factory
TBI.

 

I use a stock L98 cam and it works good with a custom chip. I run 15lb fuel pressure and a bored 46mm TBI and bored intake to match as well.

 

Whatever cam you go with you will need to have it tuned. Either DIY with EBL or through an experienced TBI tuner. The car will be slower with an aftermarket cam and the stock tune. Tuning is as important and any of your listed mechanical upgrades.

 

Good, hopefully Harris (or other TBI guru) can help with cam selection and other details.

FWIW - TPIS - ZZ9 Cam might be a possibility too.

Easily see a 40hp gain on a stock LT1. With duration at 212/226, it gives you a slightly choppy idle, making it sound like you have a serious powerplant under the hood. This mid-range cam with .483"/.520" lift, has no loss of torque and works with you stock torque converter and is a good fit for a 305, but is an excellent choice for a 350 that is mildly built.

Use 1.6 rockers on the intake for more airflow potential. This part number ZZ9 has a step nose for use with a retainer plate on 87-94 SBC or LT1, and a cast iron distributor gear and is ground on a 112deg. lobe separation.

 

Stock cam is 194/203, .390/.410 lift on a 112 LSA in a 350 truck engine.
​​​​​​
As for cams, I have tuned a 232/240 on a 110 in a 10.5:1 383 using the later PCM in the 93-95 trucks. Honestly not all that hard to realtime tune with my AutoProm and TunerProRT with a wideband. I tuned for open loop idle.

I ran out of engine at 370 rwhp on my old 350. The single marine 2" TBi that was the same as the later 454 TBIs with the 30 psi regulator except 104 lb/hr from the high pressure 61s still had plenty of fuel left to give and then MAP was still close to atmospheric at 6,500 rpm.

 

Thanks gentlemen, you have confirmed what I needed to know, the cams I'm looking at will have no problems with a good tune. I just wanted to make sure I didn't want to get into a situation where the stock TBI couldn't be properly tuned with the cam I chose. That just makes for lots of extra time and money. I'll probably invest in the required hardware and software to program my own PROMS, but will definitely need to hook up with an experienced tuner until I get tuning basics under control.

Thanks again for all the advice and information, it's greatly appreciated and I'll update as the build progresses.

Cheers

 

That's what I'd have expected. Got a part number for this cam?

Got a part number for that cam?

It's WAY bigger than I'd expect for a "stock" TBI engine. But then, I saw a similar discussion on another forum, and didn't get a satisfying result.

 

This is the cam I've settled on for my build.

https://www.summitracing.com/parts/n...97395#overview

More a truck cam for low and mid torque, but that's where I do 95% of my driving, rarely, if ever wring the motor past 5K.

I meant to ask earlier, what are some of common, more user friendly software programs for tuning and chip burning? Thanks in advance.

Cheers,

 

I'm not familiar with burning TBI chips. Hopefully someone can advise.

Fwiw - Regarding cam choices, personally I found if the set up will spin higher making power - I will spin it higher and frequently, Camaro or Tundra pick up truck. Driving adapts to vehicle etc.

 

$61 mask use tunerpro rt to tune or dynamic efi ebl.

 

GM 929, Melling CCS2, Federal Mogul CS274, etc. Your ubber basic stock GM small block cam. Cam came in everything from a base 283, 307, 327, 350 and 400s.

Melling MTC1, Federal Mogul CS214R, etc 204/214 grind was the super common RV cam replacement for TBIs about 20 years ago. They would run on the stock chip, but ran better when properly tuned.

 

That is the GM TBI Marine cam and was recycled into the MPFI and later carb 305 and 350 marine engines before GM Performance Parts robbed the GM parts bin to use it in the Ramjet 350 and HT383. In the Ramjet 350 it once came with 1.6 rockers. It is done before 5,000 rpm with Vortec heads. Nice cam for a 305 in a truck that is used to tow, a little small for a 350.

 

Hey all, thanks for all the replies, greatly appreciated.

On another note, I will be keeping the stock TBI system, albeit with some modifications. I grabbed injectors, ESC and ECM/ECU out of a '93 1/2 ton. Question is, should I install all those parts in place of existing components and burn a new PROM? Or, should I just replace injectors, ESC then tune from there using the original ECM/ECU?

Thanks in advance.

 

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