Don Terrill’s Speed-Talk

Does anyone know what the designations mean? I assume LT1 is the corvette, L83 is 5.3L Truck and L86 are larger valves and 6.2L Truck and Camaro, but I do not know for sure.
Does the Gen 5 have the same deck height as the Gen 4? Does anyone have detailed drawings or prints of the Gen 5? I'm interested in the fuel pump mounting and location.

Sooooooooo, I cut up a L83 gen 5 head. Sorry for the cell phone pics, more to follow.

The shapes of the ports are incredibly good, IMO. I haven't measured anything yet, cross section seems small and since these are 5.3L heads it would seem to keep the air speed high. It does seem to have plenty of "meat" to make it a serious head for ~800 hp NA level. To me this design seems to be a small SB2 on crack, so, pretty good.

I don't know when I will get time to really play with these. I am curious if others have any information to share. From what I can gather so far, the L83 and L86 are the same casting with different valve sizes to clear different bores. I do not know this as a fact, just what I have been able to glean on the interweb.

Looks like a logical progression in 2 valve performance to me. I do wish the castings were thicker.

The casting is thinner than I hoped. It still looks like it can be ~400 @.600" with a 2.200 valve. I guess we'll see

L83 has a 248cc intake and 107cc exhaust 57/58 combustion chamber. That's from LPE. Can't find the L86 port volumes but supposedly they are about 50cfm better than the L83 head... I feel like the L86 was 26x cc volume in some literature I read.

I think its very impressive to see how far GM has come with cylinder head design and manufacture since 1999 when they first started manufacturing the early LS1 ! Notice how tall they had to get to really get those ports straightened out. It looks as though these heads with some additional work will provide the basis of some serious power N/A. It looks as though the limiting factor will be valve size and CSA as yes there is not a lot of material in that port area.
I would suspect the really tricky area of any rework will be the combustion chamber as with the DI and with the special swirl and charge distribution required any wrong move (guesses) here will have some possible serious disruptions and negative results. I understand that GM spent thousands of hours of finite analysis and CFD getting these heads to perform (emissions, economy, longevity, etc.) and get the final product where they needed and wanted.
Obviously most outside that industry do not have the money and resources to redesign these heads for maximum power so I suspect a lot of trial and error will have to take place before big power improvements can be made successfully.

I know some builders like Katech early on where adding an additional efi injector upstream to get over the issues of modified DI injector availability and achieving some reasonable results and I think CP and Diamond have come up with some new piston iterations that work with the heads and the DI system.

Imagine the possibilities if GM had just gone to a 4.500" bore spacing on this new engine originally! Amazing sometimes to think that a .400" longer engine is so important in today's car world.

If most here could see the pressure cast processes GM uses to speed cast these heads they would be wowed with the process!

Thanks for the cut ups and the pictures they are very informative and enlightening! Hope you got the heads on the cheap!

Newold1 wrote: Thanks for the cut ups and the pictures they are very informative and enlightening! Hope you got the heads on the cheap!

I am always about the cheap, as in free Also turns out they have the same layout for the 10 head bolts as a std LS, the small top bolts are now gone, they didn't do anything anyway and GM agrees, hehe. Thinking I will plug the DI and put them on a 430 cu in LS and fab up an intake manifold. That's IF I can get them to ~430 cfm @ .700, I think there is enough material for that

I'm still curious if there is a deck height change with the newer LT vs LS 9.240"

tt 383 wrote:L83 has a 248cc intake and 107cc exhaust 57/58 combustion chamber. That's from LPE. Can't find the L86 port volumes but supposedly they are about 50cfm better than the L83 head... I feel like the L86 was 26x cc volume in some literature I read.

According to a post on their forum from Tim@Lingenfelter,

L86 LT1 General Motors Cylinder Head Runner Volumes and Chamber Volumes

The factory L86 LT1 cylinder heads runner volumes and chamber sizes are as follows.

Stock L86 LT1 cylinder heads -

297 CC intake runner volume / 107 cc exhaust , 56.5 cc chambers

Lingenfelter CNC ported L86 LT1 cylinder heads -

308 CC intake runner volume / 110 cc exhaust . 61 cc chambers before surfacing.

With a camshaft change you would require better valve springs.

We offer the following camshafts for the LT1 engine & the related spring kits are included on the item pages

http://www.lingenfelter.com/mm5/merc...gory_Code=C606

I would suggest checking the pushrod length during assembly. In most cases the stock pushrods can be reused (LT1)

And the LT1/L86's flow somewhere around 320/210 estimating from a quick glance at the graphs

http://www.lingenfelter.com/forum_linge ... -flow-data

That's pretty poor flow out of those port and valve sizes. Cutaway's look nice. Gm is obviously going for something besides coefficient of discharge.

Thanks for clearing that up. I do remember thinking they were big ports especially since they don't carry fuel... what's up with that?
Edit: their is also a Holley "efi" hi-ram intake and 2 carb top adapter so the idea has already started to trickle through.

interesting idea to be 'different' by trying these on a gen IV/III

Deck is the same 9.240, but I guess deck ht wouldn't matter, if you are going to have to fab custom intake.
but my opinion on a 430 gen III/ IV shortblock, you would need:
reconfigure the valve reliefs on pistons
custom cam core

and most likely you would still get out gunned by a well sorted LS7 head

I think these Gen5 stuff will end up being a good Daily Driver / not real high performance use...keep the DI and the cam phasing features that come with the Gen5 and you have a really versatile DD type engine

A_VAS wrote:interesting idea to be 'different' by trying these on a gen IV/III

Deck is the same 9.240, but I guess deck ht wouldn't matter, if you are going to have to fab custom intake.
but my opinion on a 430 gen III/ IV shortblock, you would need:
reconfigure the valve reliefs on pistons
custom cam core

and most likely you would still get out gunned by a well sorted LS7 head

I think these Gen5 stuff will end up being a good Daily Driver / not real high performance use...keep the DI and the cam phasing features that come with the Gen5 and you have a really versatile DD type engine

Hi A-VAS and tt 383
Thanks for the reply, Have you physically verified that the deck is the same 9.240"? I didn't know about the Holley intakes so this could get fairly easy

Here's the .pdf of the Holley manifold and options on tops...single 102 front feed, dual 4150 and dual 4500.

Lol no I have not verified anything like that, but I don't believe the general architecture changed merely addons to support the fuel/afm etc... I am just a hobbyist that reads and researches a lot. I enjoy the technical side of this as much as the hardcore racing side of it. Especially some1 doing something like what your intending. I think their is something to the fact Lingenfelter doesn't remove much, but flow is increased so much, if in fact their numbers are legit. Please keep us informed as you move forward it's always appreciated.