elle88

On my L88 replica I have the early type 3885069 intake manifold -with 2 round and 1 elliptical bores.

I'm going to take the manifold off and modify the intake bores with a grinder to the late type 3885069 L88 type.


2 questions.

1) is this the correct replacement gasket ? port size and thickness correct?
http://store.summitracing.com/partde...9&autoview=sku

2)I have a 4.11 rear end. is it wise to go for an open plenum modification of the intake?
Sincerely I was thinking to stay anyway with a divided plenum ( after removing those odd bores on the intake) with a slight dent on the divider to have it midway between open and divided plenum.

I fear to have a too poor car behaviour at low rpm with an open plenum...

Shurshot

That gasket has a provision for a crossover (holes in the middle) that is usually blocked off by most performance minded owners.

Unless you are continually operating in a cold climate I would suggest you do the same.

Doug

elle88

never really cold here ( south Italy) so i would like to block off that holes.
please tell me more about them and how they work ( in fact I was asking myself which their purpose) and how to make their block

Aldo

Ironcross

A video may do more than words as to how they idle. And low end response is with a 60 foot time of 1.6 with a 4.56 gear The engine is a new stock 454 ci. LS7 with a port matched real L88 intake. This is the 454 engine scheduled to be used in the 1970 Vettes and was canceled. I can drive it anywhere as long as there is 100+ octane fuel in the tank....

The only issue is how to quiet it down for the street as it has Walker race mufflers and hope the cops are not in its vicinity at the same time........

http://s238.photobucket.com/albums/f...t=68RedLS7.flv

Bullshark

I put in an order for the LS7 1970 Vette back after I just graduated from college. Never got it.

TheSkunkWorks

The cross-over beneath the carb is meant to direct heat to the floor of the plenum(s) in order to lessen the effects of fuel drop out (of the AF mix) during cold operation. However, it does so by vaporization rather than atomization, and thus isn't something you want to introduce into a performance engine on purpose if you absolutely don't have to. FWIW, if your intake has one, I do NOT suggest grinding the divider away between the two plenums, or bottom end will likely suffer along with idle quality.

elle88

Thanks...

look at this video of the AIR L88. I think that with the open plenum intake , I should expect this type of low RPM behaviour : the car in the video has difficulties in getting onto the stage...but I think I can live with it.

http://it.youtube.com/watch?v=dDRxrBKYBr4

I think I'll leave some divider into the plenum : midway between open and divided and see what happens.

should I go for staggered jetting ? should I use the OEM staggered jetting?

I'm going to receive a package with a couple of Holley tuning kits, to tailor the carb-and the holley tuning book too.
please L88 -and similar- owners tell me more about your carb tuning , so I can go faster on mine.

the situation now is :
L88 cam , 4.11 rear end , divided plenum intake but going for semi-open, timing 18deg at 1000 , 38-40 at 3000rpm , 44xls plugs , 12.5:1 CR , 102 oct gas

850 DP with choke well removed , small holes in primary throttles , 31 discharge nozzles , 75-80 jets , 50cc acc pump at secondary, brown pump cams : at prim is at hole 2 , at sec is a hole 1

Capella

38-40 Degrees total advance is probably too much. Never seen the need for more than 38 on any engine dyno'ed, and then only an extreme situation on race gas.

Most likely you do not need more than 36 degrees total - probably less.

TheSkunkWorks

Before altering that plenum divider, keep in mind that it's much easier to remove more material than to replace it, and the only reason to consider doing so is if you're just not satisfied with top end after testing. Thing is, removing the divider in a 180* intake is a band-aid approach to not having utilized a proper single-plane intake in the first place and, besides, no one is going to know what the inside of your intake looks like, anyway. Yes, drastically altering the divider may well serve to further necessitate staggered jetting, which means an LM-1 will come in very handy.

Bottom line: if you remain true to testing and tuning the induction system for performance, you'll come out ahead.

elle88

my friend-mech has a pro exhaust analyzer. I imagine that's the same as the LM-1 wideband...

If so I'm going to check my carb and possibly rejet it with the analyzer help.
I suppose that I should check the A/F ratio at steady throttle operation at 2000 , 2500 and 3000rpm. is that right?

I'll check also the manifold vacuum at idle (and immediately off idle) to find the most suitable idle A/F mix and power valve

Any more advise about? just waiting to receive some Holley tuning parts and then I'll do the job.

Ahh...what about the power valve at secondary? same value as primary? block off? I don't know what's inside now : I suppose a pair 4.5 hg

Shurshot

Do not use a power valve in the secondary........ there needs to be a block and a gasket installed where the PV thread hole is located.

If you have a PV in your secondary then it needs to be removed and the jets stepped up .......... anywhere from 4-10 sizes depending on the individual car.

Doug

63mako

The early L88 intake is very valuable. I would sell that and buy the later style before I ruined the rare piece.

elle88

OK Doug , no PV at secondary , as I imagined...but how to check the correct jetting at secondary with an exhaust analizer. Should I steady run the engine at 4000 rpm? that's really a mess...

63mako. the intake I have is not so valuable at the end. already checked on Ebay. it's not the L88 type, but the L72 65 or 66 , I don't have the details handy now...can't remember correctly. If I was in the USA , it would be much easier to swap , buy , sell parts...

a couple of recent pics of my car and engine

I want to add soon the racing stripes like in the last pic- just a test with cartons

TheSkunkWorks

elle88, please excuse the sidebar, but can't help observing that your ride heights appear conspicuously higher than L88 specs and especially L88/F41 specs.

OK, back to the intake thingy...

Shurshot

Hmmm nice car

If I can ever afford another old one the 69 BB would be one I would be looking for. That being said SW has said it right....... your ride height is noticeably high in comparison to the rubber. Did it have taller tires at one time?

Personally I like my cars low and I see your tire tread looks good so IF (it is your car and your preference) you want to take up some of the gap IMO I would shoot for lowering your suspension a little.

Regarding secondary jetting, they are a WOT thing so unless you can change plugs on a warmed up motor and then right away go for a 1/4 mile blast and shut if off to read the plugs, I would suggest a measured distance and highest speed attained to determine what jet to use.

Either a dragstrip or maybe easier get one of those Beltronic G2 GPS performance meters........ forget the $250 or so list price as they can be found online for about sixty or so (US). Then you can do it wherever you feel comfortable about going fast and whatever jet gets you the highest speed in a given distance at WOT is giving you the most power so it is really not to hard to figure out.

Doug

chevymans 77

Doug why do you recomend removing the PV from the secondaries?

Neal

Shurshot

Hi Neal

IMO if you are doing strictly drag racing on drag days with sedate daily driving in between those days, IMO PV's in the secondary are OK (actually an advantage for mpg on the street days)

However the design of a PV cannot compete with WOT and then backing off some such as takes place in either road racing or spirited street driving. Consequently its slow reaction will result in a lean condition when the motor is demanding full fuel.

That condition is asking for serious trouble and can push a high performance motor on the edge to going outside of the edge of the envelope of what works and what "does not"........ "does not" is translated as "detonation" that without being corrected will in time destroy a motor. Especially so when a PCV system that adds oil into the combustion chamber (as the standard factory system does) that already has a hot spot is added into the equation.

Doug

elle88

the car's ride height looks higher because :
tires are 245/60/15
the chassis mounts are the rubber type ( not solid) and like new( not compressed). I love the ride with them
front springs were replaced 4 years ago and are not f41
the rear spring is a 79 f41 ( took out from my 79 L82) but I adjusted the rear ride height to align with front.
It's OK like this because I already have the headers sometimes touching the floor.
I attach another pic
advises are welcome

Power valve

I'm not actually Drag Racing the car , at least not in the way you US guys mean. I'm closer to the road racing use of the car. I have some nice free roads here and a kind of "personal drag strip" where to do any carb tuning.
Gas mileage is somewhat an issue...I already have 4-5 mpg and I can't go worse. so if I can get both performance and a slightly better MPG in road racing and spirited fast driving , probably better to keep the PV. or not?
what about the oem L88 carb . does it had the PV at secondary or not?