I am currently swapping the 305 TPI in my 89 Trans-Am. I have already purchased the following:

• Magnum-F 6-Speed Transmission (2.66/1.78/1.30/1.00/.80/.63 Ratios).
• T56 conversion kit for LSX engines (Hawks Stage 1 Clutch Kit w/steel flywheel and RAM Billet Steel Flywheel).
• Hawks rear end 8.8 (3.73 gear ratio, True Trac 33 spline)
• Strengthen chasis with SFCs, front and rear sway bar, LCA, Panhard bar, Torque Arm, etc)
• Upgraded suspensions, struts and springs
• Upgraded to Wilwood 4p 12" rotors front and rear

Engine: Initially, my Auto shop recommended to go with 5.3L engine block(was throwing the block and 243 head in for free ) and have machined to 5.7 and ported 243 heads with 2" valves. But its been 8 months and the machine shop still hasn't got to it yet. So now looking looking for different options:

• Hawk's has 2012 Cadillac LSA supercharged 20k miles engine (probably 550HP ). Hawks recommended LSA instead of LT1 and LT4s)
• Hawk's ESS 6.2L LT4 Supercharged engine 625HP (Hawks recommended that this wont be an easy swap)
• A buddy of mine has 383 Stroker 525RWHP with 2K miles:
  • Dart head motor with complete roller assembly. Cam , Rockers, titanium valves, H beam 6" Titanium Rods, ultra lite crank, balanced and blue printed.
  • Performer Ported intake with S&S carb

I am trying to decide between LSA and 383 stroker and wanted this groups opinion on this build. LSA might give better mpg than the 383, but hopping to get 10-12 mpg on 383. I am not motor guy, so reaching out to this forum for their opinion. Looking to make this a street card, probably wont see track. Probably need to change out Hawks Stage 1 Clutch kit, not sure about the flywheel (will talk to them about it)

 

I'm running a 405 hp/405 tq 350, carbureted, in front of a T-5 with 3.27 gears in the rear and I'm getting somewhere between 15-20 mpg. Choose whatever you like best, either can get you good mpg (especially with the 6-speed). I will say in the cars & coffees I've been too it seems that everyone and their brother has an LS swap, to the point that old school small blocks actually get more attention, if that's your thing.

 

Who's doing the swap? You or a 3rd party? The 383 would probably be the easiest swap with the least amount of money spent. On the other hand, if you need reliable and easier to drive, the LSA will probably be the big winner.

 

I agree with aliceempire. The LSA swap is the better end product by far, but not easy to do. Need to really access whether its something you can take on, if you were planning to do it yourself. If you were planning to have it done, whatever shop you choose needs to be experienced in these swaps.

The 383 is much more straightforward, especially with a carb. Only issue I see with the 383 is that you said you have the LSX conversion for the T56, which will not work with an SBC. You'll need the kit for an SBC or LT1.

 

@RedLeader289, Thanks for reply. 3.73 gears might give me around 10-12mpg then. Did you have enough clearance under the hood. I have stock hood

 

Not even close, have to run a 2” cowl hood haha

 

My Auto shop is doing the build and they said that the 383 would be bolt in since it is new. For the LSA they suggested to rebuild it since it is 2012 motor and that would be additional cost + the motor cost from Hawk for 15K

 

Yes, my Auto shop suggested i reached out to Hawks and see if i can exchange it back for and SBC kit with at least Stage 2 Clutch kit

 

That 383 doesn’t sound very street friendly

 

I don't see why they would suggest a rebuild on a 20K mile motor. That motor is barely broken in with a lot of life still in it. Age doesn't matter as far as wear parts, only things like gaskets, injectors, etc. But, 12 years still isn't that long. That motor should be good to go just the way it is. Based on that comment from this auto shop, I would find a new shop.

 

why?, can you please elaborate more on this. Is there something i should be aware of?

 

titanium valves usually means pretty aggressive cam setup for high rpm, the light weight is needed. Usually not ideal choice of valve and seat for street driving but its been done. Titanium rods seems odd, and I would have expected them to be I beam if titanium, not sure if there are H beam titaniums out there. Usually another indicator lighter weight but strong rotator needed for high rpm. To make a real 525 hp at the tire in a 383 sbc means high compression and a lot of rpm. Its gonna have a rough idle with a cam that big. Probably solid roller meaning a little more maintenance on valvetrain and lifter life, depending on type of lifter it is and how much spring is in the head.

honestly need way more information on it to know for sure. Some of the lingo you use sounds like a race motor some of it sounds like typical car cruise guy talk…aka port polish intak, balanced and blue print

 

525rwhp is around 600 flywheel horsepower and that kind of power level from an old school small block Chevy, even stroked to a 383 is going to be pretty much a race motor, won’t idle well, won’t make any power at low rpm and will be generally just temperamental. I would also question the claim of 525rwhp without a dyno sheet to back it up. Easy to claim, not so easy to do.

That level of power is much easier to achieve on an LS based platform and will be more drivable and less temperamental.

 

hmm..
They explained it this way on why they were leaning towards 383. That on the 383, everything is known in what is installed in the engine with paperwork and the machine shop paperwork with high quality parts. This engine should not give me any issues. With LSA, although it is stock and there are a few unknowns on how is it was driven and if there is any damage to the engine since it is totaled car. However, Hawks has a video of that engine running..

 

if they got a detailed build sheet with parts used, more details on heads and valvetrain, post it up

 

This is true that you don’t know how it was driven or maintained. However, it was running and driving before the car was hit, so no reason to believe it has any serious issues. Sure, there could be damage do to the collision, but that would be external engine damage which could easily be inspected before installing. There wouldn’t be internal engine damage from the accident. If it runs good based on Hawks video, I would install it as is.

 

I've never seen anybody say, "I hope to get 10 mpg"

That 383 sounds rowdy and very high maintenance. That's the way high strung, naturally aspirated engines are. Unless its been a life long dream of yours to have that particular engine.... I'd skip it.

 

I agree that would go a long way in us helping to determine "streetability".Just as a point of reference, back in 1990, I built a dyno certified 614 FWHP @ 6,400, flat-top 406 with heads flowing 320cfm at cam lift (.645 net solid roller) and 250/260-ish duration. It ran great on 92-octane pump gas and idled fairly smoothly at 1200 rpm. The thing had violent, instantaneous throttle response with a self-modified and tuned 850 annual discharge carb. It pulled great off the 3200 stall speed converter. Vacuum was low at 9”, but it had one good emergency stop in it. Situations where it required repeated heavy braking, not so good, but I never had a problem with braking in normal every day driving. I never had it on a chassis dyno, but based on the ETs and MPH, it was making between 480 and 490 RWHP through a TH400 and Ford 9”.

There aren’t a lot of heads even today that flow as good as those heads and the extra cubes (compared to a 383) helped torque output at a lower RPM and kept peak HP at a reasonable RPM. A 383 making similar power, especially if “lesser” heads, will typically mean either, or a combination of, higher compression (harder to run on pump gas), a larger cam (higher idle speed, higher shift points, and less lower RPM torque and at a higher peak TQ RPM), and less vacuum (worse repeated braking). So, a 383 making similar HP is highly likely going to be less streetable than my old 406, but that definition means different things to different people. So, while others and I might not think a 600 FWHP 383 (more HP required for 525 RWHP if through an automatic) would be streetable, it might be fine for someone else.

 

That's spot on. Everybody has a different tolerance for suffering. My friend can tolerate far worse driving manners than I will. And he doesn't even wince when something major blows up. I can't take that, it would literally ruin the hobby for me.

 

I have a 406 SBC dart block dart heads, built by Nyes racing engines in February 2020. I have 140+ passes on it, more than that in burnouts, many dozens of autocross runs, and this is a street car with NO trailer. Just today, I drove it to the track, made eleven passes, and drove it home. 700r4 built with 12 bolt rear. Holley sniper efi. Nitrous gets it into the 10.60s and 10.70s and on motor it goes 11.55-11.60. I think years ago i calculated around 11-13 mpg. Its not a high rpm screamer, but it does what i hoped it could do and looks the way I wanted my engine bay to look so it works for me.

 

Havent read the comments but SBC's with about 475hp+ with a 4" bore starts to get kinda aggressive. 510-525hp is about as much as they tolerate before becoming wilder than what a typical street car owner would like. They spit, shake and dont draw a lot of vacuum. Theyre fun tho! This all boils down to how much you want to spend. If you have the money, do the LS if you want a 500rwhp street car. If you just want a fun car that can be driven on the street, get the SBC. The ol small block will still have you all over the road on a street tire.

 

It’s worth mentioning, not knowing the OP’s experience with past vehicles, that HP numbers have gotten rather ridiculous in the past decade and even 300hp in a thirdgen platform is plenty fun and more than enough for a street car/cruiser.

Maybe try to find some similar built options and ask for a ride along or something.