LT1 Mix and Match

[zgeezer]

I have two salvage LT1s: one is 5.7/ aluminum heads and eight (yeah, I said eight) spun rod bearings. The crank is trash; the block is good. The other is a 4.7 (265ci) with an excellent crank and rods. Boy, are they ever looong. Can I simply run the 4.7 crank and rods with the 350 pistons for about 327 ci. Are there balance problems? The local machine shop tells me that no LT1 rod can be resized or re-balanced because there is no "boss" on either end to allow metal to be removed in balancing. Is there any merit to this or should I be shopping for a new machinist? Finally, if I can't use the 4.7 crank and rods, who sells a 383 or so stroker for LT1s. How are LT1 stroker kits balanced: internally, externally? Finally, I have a chevy roller cam shaft purloined out of an early 345hp (zz3, I think) crate engine. The one with aluminum heads that was sold as a smog legal exchange for middle '80s Camaros. It appears that this piece with minor adjustments to the snout and pin would fit in an LT1. Is this a workable cam swap or should I just bite the bullet and go after market. I really would like to use stuff still hanging off my garage rafters.

 

gw

[Guest Anonymous]

Z Gee.This sounds like a Grumpy Vette or Mike C or Tim 240 Z ? If you dropped a 283 crank with the same size journals in a standard 4 inch bore 350 or 327 you would have a 302.Why bother when you could most likely change the crank and have a 350 or a 383. Would the 265 rods and crank be compatiable with the 350 main journals and pistons? With all the 383 stroker cranks out there.. there has to be one for a LT1 with either internal or external balancing plus a one or two piece rear main seal. The Z will not take a 400 SBC 8 inch harmonic balancer wothout hitting the steering rack but smaller diameter balancers are available. Maybe someonelse may answer your questions more specifically

[Guest Anonymous]

GW,

In theory, it is possible to do the swaps you suggested, the real question you should be asking is: does it make sense from a cost perspective? The answer is NO! You can't drop your 4.7L crank/rods into the 5.7L without modifications, which means custom machine shop time, which means $$$. Same idea with the cam you have, you'd have to make mods for it to work in the LT1, and even if you did get it to work, the performance would be terrible, that cam is not designed to work with the LT1 intake/heads. Don't try it. As a general rule, Gen I and Gen II SBC motors share nothing in common, so parts can't be mixed and matched.

 

About the rods: For all LT1 and newer engines, GM now uses 'PM' or Powdered Metal rods. Unlike standard rods, PM rods are made by compressing powdered metal into a single piece rod blank, (the metal equivalent of particle-board), they are then "cracked' at the big end to separate the cap from the rod. In my opinion, PM rods are very reliable up to 425 hp and 6700 rpm, but many machinists don't trust them, and don't like working with them. The manufacturing process for PM rods makes them very close in weight (unlike standard forgings), so balancing is generally not an issue for a competent shop.

 

So to answer your question: Go with an after-market rotating assembly that comes pre-balanced (internal), you'll save money and aggravation in the long run.

 

http://www.strokerkits.com offers a 383 LT1 stroker kit that has everything you'll need at a GREAT price: $1250 The kit includes a new cast crank, high quality forged rods with ARP bolts and quality forged floating pistons, as well as rings and bearings.

 

So your choice is: Spend a lot of money and time trying to get your used parts to work together, and end up with a soggy 306ci motor, or spare your self the aggravation and spend $1250 to get the guaranteed power of an all new 383.

 

If you're budget is really tight, I suggest you go to the local pick-n-pull. I just bought an entire iron-headed LT-1 long block out of a '94 Caprice taxi cab for $230. Most people think of F-bodies (Camero/Firebird) when they think of LT-1's, but remember, the iron-headed version was installed in thousands of 4-door full-sized chevy luxo-barges, that served as taxis, police cars, and personal transports. With iron heads, the LT-1 was rated at 260 hp. Buy the long block for $200-250, have the heads ported/3-angled for $250, and add a performance cam, and you easily get a 350 hp long-block LT1 for under $800. Not a bad deal if you already have the wiring harness, ecu, and intake.

 

Hope this helps

Cyrus

[Mike C]

You will need to get a custom set of pistons, but if memory serves, the "little" LT1 crank is a 3" stroke. You can get a set of SCAT rods brand new for $219 and with bushied 6" rods for $269. A set of flat top 3" stroke pistons will eat you up, however at around $500 (which seems like a smokin' deal compared to 6 L6 forged pistons at $900!) Coupled with the 350 LT1 block standard bore would give you a 302. GM did this in a 30th anniversary 67 Z/28 they built back in 1997. Torque Vendors gives you some good advice. I like the idea of the high winding 302 vs. the 383 torque. While making less overall power, a 7000+ rpm is an awesome experience. Add your aluminum heads and an aftermarket LT1 camshaft. If you are using all of the FI parts for the little motor, you need to investigate and find out if the intake is the same or has smaller ports. You will have to increase the injector size as well, but the stock 350 injectors should work well in a high winding 300" motor.

[Ray]

This swap has been done.. the longer rods in the 265 motor are to compensate for the shorter stroke of the motor. The piston if I remember correctly has the same pin height in the 265 motor as the 350. Take a look at the motor chevy built for their late model show 302 camaro's. they did one with the 265 long rods, crank and stock 350 pistons and the lt4 heads which is esentially what you are doing.. If you have a good machine shop who can get the rods off the pistons in the 5.7 motor without messing them up you should be able to peice the two together and make a 302 with very little money. Also the motors that chevy built used the GM HOT roller and made 425hr on 302cid so there is a lot of potential in the combination. Especially if you are putting it in a Z as their will be less low end torque and the car should be easier to launch at the strip..... Good luck If you have someone with a Chevy High Performance subscripion they shoud have the article it was done in 1997 just before they went to the LS~1....You can always call the magizine I am sure they keep back issues on file and will fax or email you the aritice....

[zgeezer]

As allways, thanks for the replies. I've researched the magazine article, reviewed the stroker site and will be working on either a 302ci or 383 ci. Common sense and wretched excess dictate a 383, but, then, show me a gearhead with common sense. Along that line, it appears that early intake manifolds, including the Edelbrock Performer require only minor drilling of additional bolt holes to bolt to the LT1 heads. The benefit to this is the ability to run an LT1 with a rear mounted distributer and any older Gen 1 intake manifolds. I haven't checked the older 270 hp dual quad intake, but it may end up bolted on to my LT1 and run "dry". Hey, maybe I can run a dummy h20 hose from the manifold to the radiator and tell all sorts of stories to the rice for lunch bunch.

 

gw