LT1 350 370 Hp...vs ZZ4, and others..

[Jack]

Stan:
Sounds as though you may've DE-stroked a 400 ... used a 350 crank w/ground rod journals to 2.0" for 5.7" long 327 rods. It's also quite possible the 350 crank's rod journals were offset ground to make a 3-9/16" 350 stroker crank ... still less than 400 stroke. A thirty over 400 block (4.155") X offset ground steel 350 crank (3.5625) makes about 386" ... in years past piston choices for this combo were limited. Such a combo would make most power in upper ranges at expense of low end tq. It's my understanding this stroke is still used in circle track racing in some regions ... but not in mine.

Thirty over 400 block (4.155") X steel 327 crank (3.25") makes about 352" ... this is the basic combo used in chevy cup, busch, truck motors. This is a "DE-stroked 400." Noted for very Hi-rpm HP ... at the expense of low-end TQ (grunt)

Thirty over 400 block (4.155") X steel 350 crank (3.48") makes about 377" ... popular combo at many dirt circle tracks. This is also a "DE-stroked 400." Noted for higher-rpm HP ... but only fair low-end TQ (grunt).

In addition to hand-built motors ... we're using ZZ4 & Fastburn & L31 Iron Vortec headed GMPP crate circle track motors. Both 350 block X 350 crank = 350". We're using them only on local short asphalt circle tracks at hi-rpm.

We operate these within a much higher rpm band than what a street car operates in ... how well they work from 1K-3K means little to us. With track rules offering a weight break for crate motors, they're competitive with hand-built motors & generally cheaper overall.

Our local circle track rules do not permit hand-built motors w/ L98 or fastburn or L31 vortec heads ... only allowed if they're on a GMPP crate motor that came with 'em. Hand-built motors must use a GM production Iron head w/ no less than 70cc chamber (no vortec L31 iron). No AFR, Brodix, Dart, EB or other non-GM aftermarket permitted by our local asphalt circle track rules.

The local drag & rod guys prefer the AFR aluminum heads because they flow so well ... they're remarkably better-flowing in the valve lift ranges seen in typical street rod cams. A statistical analysis of the various heads' flow rates from 0.2"-0.6" lift clearly shows AFR's advantage ... at both individual lifts or grouped ranges ... and bears out local preference. Although they cost more, I may use AFR for a 406 street vette motor I'm assembling.

IMHO, there's a clear path to exceptional low end torque/grunt ... more stroke ... a 350 block w/ 400 stroke (3.75") or 400 block w/ 400 stroke (3.75"). Nowadays, reasonably-priced good steel cranks are available off-the-shelf in virtually any bearing size & stroke desired. Same goes for rod lengths & pistons' pin placements. Same goes for crate motors ... stroker or not.
JACK:gap

 

[Stan's Customs]

Helo Jack...

Well I'm not sure what we did except that it was a stroker. Of course a stroked 350 is still a stroker ....perhaps not what commonly is refered to today (383) but another variant. I do remember that the pistons were expensive because ther wern't many mfgs. who had them. So maybe the 3.5625 offset grind you mentioned is was what we did...that's been almost 30 years ago ...I just can't remember. I do remember that the low end torque with the heads and cam we chose was dissappointing even with some prop manipulation. Boats with a lot of low end torque will blow out at the prop...so I was working on less torque on the bottom (engine wise) with a deeper pitch prop...and then hopefully make up the difference on the other end with more high end RPM horsepower, for speed. The end, hopefully, was to come out strong and still have a top end on a fairly heavy runabout. Like I said it didn't work to suit me...even though it was worlds better than a stock marine hi-perf engine.

Back to the early 70's LT1 350...strokers aside. I won't run a stroker just to be different if nothing else....besides a C1 can't get enough tire under it to worry about maximum hp. If iI went old school instead of the new retro build, I'm thinking that the LT1 350 might not be that far away from the performance of the ZZ4. Just for comparison's sake what say 'ye to that?

The ZZ4 heads are an older chamber design with 1.94 valves...where the LT1 head is a small chamber 2.02 valve head. Compression on the LT1 is 11 to 1...the ZZ4 is 10 to 1. Chances are that I would mill the LT1 pistons to 10 to 1... so that would be the same...

I'm stilll thinking the LT1 is somewhere in between the ZZ4 and the Fast Burn 385...give or take. I can build it some cheaper , but that's not an issue really.

I guess it boils down to a comparison between the two heads...('70 LT1 and ZZ4 )since we know the fast burn heads flow more with less bottom end. Do you think the LT1 or the ZZ4 heads would have the most bottom end all other things being the same (cam etc)....

Regards ...Stan

 

[Jack]

Stan:
I think you'll find ZZ4 has a bit more low end grunt than Lt1. Solid flat tappet Lt1 can outrev a roller (ZZ4) anyday.

I'd pick the aluminum ZZ4/L98 58cc heads over the iron Lt1. Look around ... you should be able to find a good usable L98 pair for around $400-$600. Of course you can use whatever lifter you want as long as you use right spring.

Note their smaller 58cc chambers MIGHT pose an interference issue with domes (ZZ4 motors have flattops, L98 didn't have domes either). Also, L98/ZZ4 heads have a slight angle to the plugs ... not quite as much as most angle plug heads ... but not straight either.

If you can get past any possible interferance issue ... I've little doubt you can build a screamin' 350 w/ZZ4/L98 heads & right cam. I'd pick the cam & springs AFTER I've settled on rear gear, heads, pistons, block deck height & resulting CR.
JACK:gap

 

[wallyknoch]

LT1`s

The LT1 1970 model is probably the best iron small block 350 Chevy ever produced. Good heads, cam, pistons, and a special pink rod no longer available except at horrible prices. If you dont believe me, try and get one. Truly one *****en engine, all it needs is fuel.

 

[Stan's Customs]

OK Jack...

Does that mean that you also think that the 1970 LT1 350 is somewhere between the ZZ4 and teh Fast Burn 385....I also agree that the ZZ4 probably has a little more low end than the LT1....

I think that the LT1 has more top end Horse Power than the ZZ4 ..but not as much as the Fast Burn 385...

If that is correct then looks like the LT1 would be somewhere in the middle...at least that is my thinking.

Seems like the more things change, the more they remain the same...


In that case this very low mileage dead stock LT1 350 would be a very cool choice for a nostalgia 1961 non stock Corvette, and run strong ...at least for a small block....

The LT1 does have domed pistons I believe (11:1 compression...so I might mill them a little).

Like Wally said ...LT1's are very hard to find....unlike the afore mentioned. This one is a new factory crate engine that was not uncrated...until a couple of years ago , run briefly for a couple of thousand miles. The car was sold "less engine" and now the engine is sitting on an engine stand . Practically a virgin factory motor. Thats why I'm looking at it for this special project.....

For my generation there would be some cool factor in a having a "real" LT1 350...now if it runs comparable to these other two well.....the fastest doesn't always win...just the first one there.

I'm just wondering which engine would be "most appreciated" by knowledgeable car enthusiast.......considering the personality of the car being built....

Votes anyone ???

 

[wallyknoch]

If this is a true 1970 LT1 engine with very few miles and available, buy it as it cannot be replaced. Forged 11-1 pistons, 4 bolt mains, 202 heads with screw in studs, teriffic manifold, solid lifter engine and extremely rare rods worth about $800.00 bucks a set. Put a 4.11 or a 4.56 gear behind it and your friends had better tape their doors shut, because they will be extremely mad at you for blowing them off. The best small block made. It dosn`t get much better than that. There`s one in the 62 below under it`s FI unit since 1970 with a 4.56. :L

 

[Lucy64]

I had a 70 Z/28 with the LT1 350 and that was one very nice running smallblock. I did have a 68 Z/28 with the 302 that in my opinion was the best small block ever built. But the LT1 comes in a close second.

 

[Stan's Customs]

Hi Wally...

It is indeed low miles and a true LT1...The manifold is not GM but a Edelbrock Performer . I don't know if it came with one as a crate replacdement motor or not. I suspect it came as a long block engine ..no intake.


Stan..

Did you say you had a LT1 in your '62? Real LT1...?