I was considering building a 402ci or 408 ci TPI motor to replace the mostly stock LT1 longblock in my '86. To eliminate confusion, my motor is an LT1 with an Accel TPI intake base with the LT1 bolt pattern (bought it that way) and the engine is stock except for the cam, intake, springs and timing chain.

I wanted to do something a little different, upgrade, and at the same time, maximize torque. I was thinking of getting the LT1 heads ported, upgrade the valves, swap to 30# SVO's, keep the 54mm throttle body (it's ported), and have the intake extrude honed.

I was also considering swapping a turbo header on the driver's side since I have TONS of room... but I really dont like that idea of a turbo feeding off of one side only, and a motor like thise should make awesome torque as it is.

My '86 is going to be my DD again, so I wont be going large on the cam at all. Right now I sport a 220/230/114... kind of large for a 350 'TPI' but would work fine with a 383. I am also considering a 396 instead for a better r/s ratio as an alternative to a 402/408.

 

cant go wrong with the 383

 

well as far as i know.. most of the guys say that normal tpi cant feed an engine that big.. u need something along the lines of a stealth ram or wut u have

 

well, yeah you cant go wrong with a 383... but more cubes rules and this wouldnt be for making power, it would be for maximizing low end andf midrange torque. If it were for power, I would get an engine with a bigger bore... I have a 434 and a large bore late model bowtie sitting in storage right now. a 402 is 'square' so it would be far from optimal for power production in theory, but it seems to work for LS1's. My understanding is the problem with an engine with a stroke equal to or larger than the bore size is flow required by the heads, shrouding problems, etc that create a condition where the engine peaks early because the heads dont flow enough... but LS1's also have superior flowing heads. Might be the reason the LS1's can pull it off. I just decided to say fawk it and I'm building a 427 LS1 for my Vette with L92 heads so there are no shrouding or flow problems

Anyway it is just for maximizing low end torque. With an aftermarket TPI intake, good heads, and some porting, they could support a TPI engine of 402 cubes IMO... as long as HP wasnt one of the things you were after. Engine would gain a ton of HP by swapping intakes... but loose a ton of torque. So pick your poison.

The 402 doesnt cost anything more than the 383 if you build it forged. I found several vendors who sell a $550 4340 forged internal balance 1 pc RMS 4" stroke sbc crank...typical price even for a 3.75 stroke.

I guess a 396 TPI would be right in the middle, and I never see those either... but I like thinking out of the box. I figure if I'm going for torque, go all the way But I wouldnt build anything bigger than a 383 without EH porting the intake at least

 

it seems as though no one thinks like we do man. i think that would be a great combo, since it seems like keeping the bore around 4 inches doesnt make the motor require as much airflow as opposed to a 4.125/4.155 bore. the powerband should be similar to a 383 but with more torque i would think.

 

Longer stroke makes it harder to fit a big cam in there... rod to cam clearance is once issue. I never seen anyone take a LT1 block past 3.875 inches of stroke but if you can take a 350 block to 4", then I dont see why an LT1 cant either.

I'd go for it. BUT to get the most out of it, i'd have the base opened up to better match a good set of heads. Since RPM range is low, dont need as much head. 190-200 cc is all you need. Abit better rod to stroke ratio would be nice, but since RPMS are gonna be low and your not boosting/spraying it, who cares what the piston compression height is as long as the oil rings seal. Keep a larger chambered head tho for compression....since with short pistons you wont have room to make a dish, so chamber volume needs to increase to keep this thing streetable with pump gas. 4" stroke is looking at 11.7 to 1 compression with a typical 5cc relief flattop and 64cc chamber head. 10.4 to 1 with 75cc heads, so somewhere in between is where you want to be.

cam i'd go up in the mid 230's deg on the intake. Cubes will eat that up. Run good lift for the heads and it will make loads of power.