I fired up the LT1 Intake Conversion project that I've been working on for the last few months... The subject is a 1991 Firebird that originally had a 305 TBI (and a tired one at that)... I repinned and adapted the wiring harness as outlined in anesthes' Repinning TBI to Speed Density TPI . The motor is a 355cid with Scat crank, I-beam rods, and KB flat-top hypereutectic pistons (zero decked).. Heads are stock L98 with better springs and cam is stock.. Compression is ~10:1 or a little higher (block is zero decked and heads were shaved a little)... Tuning is going well so far with the Ostrich (thanks Craig!). Couldn't imagine not having a realtime emulator now that I've got one.. And now for the pictures!!

I was really proud of how it came out...

 

Here's a front shot... One really cool thing about this conversion is how well the remote thermostat housing was able to be mounted... Since we've upgraded to the 125 amp alternator, the modified support brace made a perfect place to mount it... Worked out great..

 

Looks great . How well does it run?

 

Running good so far... Still taking it easy on the new motor.. Also, we need a different throttle cable, as the one we have now only allows ~75% throttle)... But, it definately has more power than the 305 TBI..

We need to get some different gears in it though, as it still has the 2.73's in the back... We're thinking a 3.42 drum out of a V6 car (will be cheap and available at u-wrench-it)...

 

Looks great, hopefully I'll be able to check it out sometime

 

Awesome!!! Yes 2.73's suck. I can't wait for some 3.42's as well. Do the V6's have LSD?

 

3.42 V6 gears will be one legger

 

The current 2.73's are on an open diff as well... So at least it will be a better ratio and a series 3 gear...

 

So that is a CS144 alternator? How did you modify the stock support strut? Did you shorten it or just bend it?

This is the first time I have seen pictures of someone actually using rear support on a 4th gen alternator. I just had to ask some questions.

BTW, your 355 looks great!

 

Yes, thats a CS-144... You modify the factory alternator support... The support is too long to fit at first (with the alt clocked that way); so from point A on the exh manifold to point B on the alternator is too long. You bend the brace in the middle (creating a point C midway between).. You continue to bend the brace until the imaginary triangle you have created with points A, B, and C makes the length from A to B (exh manifold to alternator via C) just right.. Then you have to bend the part where it bolts to the manifold slightly (so it will be at the proper angle once installed)..

I've got the same setup on my GTA as well, the brace is EASILY modified, plus it looks factory once you're finished...

Oh, and make sure you put the brace on there... It IS needed with the bigger alternator--I've had the extension piece (the piece that bolts in place of the small CS alternator to allow you to mount the big one) break and my alternator fall off to the side going down the highway before (on my old '88 bird)... So anyone who says the brace on the CS-144 alternator is unneeded has just been lucky..

 

Here's a pic I took of the same setup on my car (identical to my brother's but I don't have a remote thermostat )...

 

And one more for the curious:

 

Thirdgen88, thanks for the great pics of the alternator strut mod.

Did you have to do any grinding on the CS144 case to make the front support bracket (GM# 10118722 I think) work? I can not tell from you pics. Also, how much longer of a serpentine belt is required when doing the switch-over?

I am thinking of either buying an Iceberg CS133 this summer or going to a CS144.

Oh, I have one more question about the converted LT1 intake setup. Did you purchase that remote thermostat housing directly from John Millican?

 

Well, there are two types of the high output alternators... The ones we use come from the application for an '89 Chevrolet Caprice 5.7L police interceptor... Those are the 125 amp ones and don't require any grinding... Some of the bigger factory 140 amps are the ones that require grinding (but still mount up the same)...

As for the remote thermostat, yes, I purchased it through John... It is an offenhauser piece... Make sure to teflon tape the hell out of the fittings and don't forget to put thread sealant on the water outlet housing bolts as well...

As for the belt, we removed the smog pump so that changed things a bit.. A 985K6 is what is required with the HO alternator and the smog pump delete (without the fancy delete pulley)...

 

hey man looks really really good.. i was tossing back and forth the idea of the black intake as well but just thought i was gonna have to much black under the hood.... soo i went with red.... ohh btw on the drive ability tune from john,paper filter with stock duckting, and 87 pump gas and less than 1000 miles on the new motor i put down 277 hp and 303 lbs of torque at the wheels...

 

(To original poster) Using a stock L98 cam? Put a bigger cam in that thing and you'll really have some power!

I'm still in the process of the LT1 head and intake swap. Haven't worked on it in awhile as I've been spending all my money on suspension parts. I'm also going with 3.73 gears. Had 3.42s in my garage waiting to get installed but found a good deal on a parts car with a 3.73 rear in it I'm also going with a CC304 cam and SLP 1 3/4" headers. Basically doing everything possible that will make the best use of a 355 block when I get that in

 

I know a cam would be nice... However, money still needs to be spent on the rest of the car to really make the most of the combo thats there already.. The motor is still choking through L03 exhaust (even the L03 exhaust manifolds).. This summer will hopefully bring all new exhaust..

 

is there anywhere i could get just the spacerfor the distributor?
i think i saw one machined w ears for bolting it down, but cant remember where.

 

I asked John that one time (John Millican from lt1intakes.com) and he said he sells them for $20 I believe it was. Shoot him an email. Nice guy.

 

hey i am doing this for my new motor, and im wondering if either of you have pre-87 heads and what exactly has to be ground to get the bolts to start. the pics at lt1intake.com arent really clear.
also im thinking of countersinking the intake bolts to make up for the different angle on the mounting flange, what do yall ( yes im from texas) think?

 

We used '91 083 heads, so I don't know what clearancing will be needed... Its tight though on those center pairs, so I imagine some extra work is needed.