3400 upper end work opinions

[prophiseer]

Hey y'all, planning on doing the upper end on my 3400 here soon; installing a 3500 UIM, 65mm TB, porting and matching the UIM and LIM; porting and matching the heads with the LIM, etc. Had a coupla of questions though;

the heads I'm porting are the p/n24507577 casting, and I've got 2 extra sets of heads (just in case); planning on doing some work to the intake ports, prob open up the top of the runner some, work on the short side radius a bit; doing some smoothing with the intake and exhaust ports; prob work on the combustion chambers some; I'm thinking 4 angle valve seats, also. Anyone know of spots on the heads that can be tricky to work on, if the casting is thin or otherwise? Any suggestions or opinions?

As far as the valve work, I'm thinking of going with the LS1 springs or something similar, but was wondering if anyone has had any problems with these springs while still running a stock cam? I'm also going to be upgrading the pushrods and valves (prob chrome moly or something similar), but will be keeping the rockers and lifters stock (don't feel there's a need without changing the cam). I don't think I'll run into any problems with this setup, anyone feel otherwise?

Just looking for some extra opinions or thoughts before I start whipping out the credit cards

[onefastV6]

Why not just go with the complete 3500 top end setup?
I don't know how good your porting skills are, but I can tell you that you are going to have a hard time beating the flow of stock 3500 heads.

Put Ls1 springs on the 3500 heads, the 3500 valve are already pretty good, the store on this site sells the TB's and adapter for the plenum.

I would bet money that you would have less in the 3500 top end and have more power than a ported 3400 top end.

[95SleeperAcheiva]

complete 3500 upper end used $600. car-part.com

[CNCguy]

Complete 3500 with 12K on Ebay... $450

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=250003408521&ih=015&sspagename=STRK%3AMEWA%3AIT

[95SleeperAcheiva]

Complete 3500 with 12K on Ebay... $450
http://cgi.ebay.com/ebaymotors/ws/eB...RK%3AMEWA%3AIT

show up.

Of course I checked on that motor...

Those were the same guys that sold me my 3400 with 9k for $325.
I asked "why so cheap" they said they were getting rid of old stock. 2004 is old stock? maybe this 3500 is old stock too huh?

[prophiseer]

Only reason I'm not looking into buying new heads is cause I've currently got 3 total sets of '99 3400 heads (incuding the set currently sitting in my car), but . . .

. . . the 3500 heads already flow that much more better stock? If so, that's prob a better starting point (less work I'd have to do).


Alright then, 3500 LIM compared to a 3400 LIM . . . same or different with similar bolt boses?

[SappySE107]

The 3500 heads don't flow that much more than stock at .500 lift. 214 vs 219 cfm. Its the low lift values that are better. The 3500 lower has to be used cause the ports sit higher on the 3500. Same mounting though.

[prophiseer]

that motor for $450 is kinda tempting, although I hate paying shipping costs; I'm thinkin about it, though; buying the motor, doing some work to the upper end and swapping it onto the 3400 block currently in my car . . . prob build up that 3500 block in the in-between, too . . . and maybe sell my extra gen3 3100 long block and gen3 3400 short block (aren't us mechanics pack-rats? ).

Well, in that case if I go that route . . . what valve springs would you recommend on the 3500 heads while still running a stock 3400 cam? I don't think she needs to be way too stiff - I just want to tighten up some of that stock valve float at high RPM, and although I'm planning on stronger pushrods no matter what, I get that squirelly feeling that the lighter 3500 valves couldn't stand too much stiffer a spring, or has anyone proven otherwise?

[onefastV6]

I am running LS6 springs on the 3500 heads and haven't had any problems yet.

[prophiseer]

blarghh!!! Money is too tight right now to go the 3500 route, so I'm stuck working the 3400 upper end, no prob, I guess . . . unless anyone is willing to swap a '00 3100 long block w/ a blown head gasket for a comparable 3500 long block

So, quick question about the LS1 valve springs . . . what are they rated open and closed compared to the stock 3400 springs? Also, do the LS1 springs require shimming on the early 3400 heads (heads were cast in '9? Just trying to get my ducks straight before I order parts.

[torq455]

LS1 springs are a great for a stock upgrade. they are rated
1.7" 106#
1.3" 177#
Coil Bind 1.290

for comparison:Stock 3100/3400 Spring
1.7" 78#
1.3" 157#
Coil Bind 1.230

[prophiseer]

Thanks.

BTW, which GM p/n should I use for the LS1 springs?

p/n12589774

or

p/n12553696


or is there some other p/n I need to use with ordering?

[SappySE107]

Im not sure on the part number but those coil binds aren't true coil bind. They are about as far as you should go but lorenzo has ran the LS6 springs to under 1.2" without coil bind. Its damn close but not quite.

[prophiseer]

so, just looking at the numbers involved . . . I don't foresee any issues with just swapping the LS1 springs in place of the stockers; numbers are close but it appears all will be good. Granted I'll have to measure everything out once I'm done with the heads, just to be sure for myself . . .

Oh, and if anyone can tell me the correct part number for the LS1 springs that'd be great . . . talked with Teh Dealer yesterday and they're not sure; their computers list both p/n, but offer no specifics for the applications (left vs right, intake vs exhaust, cheap vs expensive, etc)

[prophiseer]

Sorry fer floating this thread so damn much!

Called the dealer this morning andwas able to figure the right spring p/n and ordered the LS1 springs and shims from GM today, paid $26 for 15 springs and $25 for the seats(shims). Spring p/n 12589774, if anyone needs it. Supposedly the same part number for the LS6, also.

Anyways, back in the shop today . . . I was able to grab the valve spring specs for both the 3400 and a LS1 off the shop computer:

3400
installed height: 1.700"
load closed: 75lb@1.700"
load open 230lb@1.260"

LS1
installed height: 1.800"
load closed: 76lb.@1.800"
load open: 220lb@1.320"

So I figure the LS1's installed at 1.7" should be ~86lb and open at 1.26" ~245lb. I plan on test fitting a spring before I send the heads to be decked, so I'll try and dig out the equipment to measure them out. Sorry, but I couldn't find the exact specs on this site right off the back.