[scratch the itch]

Now I am really convinced I know nothing about this stuff.....but I am hooked.
My 67 Gto convertable was rebuilt frame off in 05 and Engine 400 4sp was rebuilt I thought by Jasper. I never really was happy with the off the line power of the car. A buddy had his 442 rebuilt by a guy here locally and I was real impressed by the power of his car so I took mine in for an opinion.

I found out that the pistons were missed sized and cast and not what had been specified and the engine really had not been rebuilt. the folks at Jasper(performance division)immediatley sent some more pistons and really have been cooperative.My compression was 7.5 to 1 and the thing was burning and leaking oil like crazy.

Ok so I am in so deep on this thing so I went ahead and bit the bullet on another rebuild. WOW here is what we did.

M21 trans
The engine was already 60 over
New TRW 10.5 to one Flat top 4 eyebrow pistons
New Lunati Cam 507-510 240-246@ 50 HYDRAULIC FLAT TAPPET
New Timing chain
True Roller set 4 degree advance
Lunati roller rockers 1.5 competition 7/16 studs
New Clevite tempered race bearings
crank polished 10 under
rebuilt 800 CFM QJET OUT OF A 1970 GTO 400
CENTERFORCE 11.5 clutch
Ported and polished 670 heads w/ 86cc chamber and 40/1000 head gasket and 18/1000 in hole making compession 10.7 to 1
Super 40 flow masters
Car already had 2.5" Dougs headers

Lots more power but still slow off the line. I dont race, but really, I can't even bark the tires. So its back in the shop and this is what I need opinions on.

It has a 3.23 gear now. I was going to a 3.55 but my guy wants me to go to a 3.73 because of the m21. I dont race but want around town power. I dont want any one embarassing me at stop lights etc. I drive on the interstate rarely. Opinions please.

[i82much]

Something is *DEFINITELY* not right. My 65 had 3.23 rear with a 4 speed, granted a wide ratio, but it would smoke the tires all the way through 3rd gear and that was with a 350 chevy (since replaced w/505 IA2, relax, stop throwing rotten vegetables at me).

that said, your cam is probably too big for a close ratio w/3.23.

Is the engine running right? I mean it has good vacuum, not missing, etc.? Seems like it would be tough to get the timing curve right with that compression on pump gas with iron heads.

Smarter folks than me will chime in, but those are some thoughts.

Oh and one more thing. If it were me, I'd keep the 3.23 and get a wide ratio over keeping the close ratio and swapping gears.

[scratch the itch]

engine runs and sounds great. Better now on 93 octane than before the most recent rebuild It is weird.

[i82much]

You're saying you rev this baby up to 4 grand and come off the clutch hard in first gear, floor it, and you don't start smoking the tires?

[scratch the itch]

nope

[Z Code 400]

Your camshaft and M-21 need a 3.90:1 axle ratio to operate at optimum efficiency.

Also...you could have some troubles with the Q-Jet, so I would suggest picking up Cliff Ruggles book on the Quadra-Jet. There is a lot of tuning information in there that you can do yourself.

What is your idle vacuum readings??? What is your initial timing??? How much total advance??? Are you using vacuum advance??? If so, how many degrees of vacuum advance do you have and are you running manifold or ported vacuum to the advance???

More information would be helpful to accurately diagnose what is going on with your car...Robert

[i82much]

dude it almost sounds like you have an aluminum flywheel. but that can't be right.

[screamingchief]

Something is *DEFINITELY* not right.

That's for sure,,,sounds like a chevy guy is building this pontiac...

New Lunati 10.5 to one Flat top pistons.

Lunati pistons,,,had no idea they made pistons for pontiacs???

Ported and polished 670 heads w/ 88cc chamber and 40/1000 head gasket making compession 10.7 to 1

I'm real interested to find out how ya'll got 88cc's from those 670's???

Not to mention 88cc's and flat top pistons wont yeild anywhere near a 10.7:1 compression ratio...

Even at zero deck that would yeild like 9.18:1 CR.

And consider most pistons are down in the hole .020" on uncut decks,so it could be as low as 8.84:1 if that is the case.

Maybe you meant to say the 670's are 78 cc's???

That gets you 9.65:1 @ .020" in the hole with a flat top,or 10.0:1 at zero deck with most flat tops.

Then there is the cam,as already mentioned,it's awfully big for a "street" 400 4 speed with 3.23 rear gears,will be real soft at low RPMs,a cam like that will need 4.10's or such for good results.

The closest lunati cam to those specs is the #307A5LUN here is it's description:
New Street/Strip Pontiac All V–8 (1955–1981) Hydraulic; Rough idle. Good cam for Pro street or bracket racing applications. Needs 4200–4500 RPM stall converter, headers, 11:1 compression ratio and 4.56 gearing. Works well with big 4 bbl carburetor

So you see what were talking about,not the best combination of cam,compression,and gears.

Should have came here and asked for some recommendations to take to your builder,would have gotten some good combos to duplicate aand I'm sure the results would have been better.

[Z Code 400]

I see a LOT of Q-Jets here that have inmproperly adjusted secondary air valves. One 455 was so bad it would literally kill the engine when you snapped the throttle open.

Scratchy...How many Q-Jets have you worked with??? Are you comfortable checking some of these things yourself??? We can supply you with all the technical information that you need...Robert 10851man@gmail.com

[Z Code 400]

Right you are Screamingchief....could be very low static compression with a lot of camshaft...Robert

[screamingchief]

Better now on 93 octane than before the most recent rebuild It is weird.

Not weird,expected,with the big a$$ cam and lower than assumed compression your cylinder pressure and DCR are probably in the toilet now!

Hate to be the bearer of bad news,but somebody needs to steer folks in the right direction.

Do a compression test and get back to us with the results.

Bret.

[i82much]

Jasper opened up the chamber to 88 cc? Or did you mean 68 cc?

[scratch the itch]

Like I said, I am a novice at this , all my info is coming from the guy that built the engine. I really do think the engine is much much stronger post rebuild. Starts well,not rich or lean ,no smoke. no ping

[scratch the itch]

no Jasper is not doing the work now. Iwas told 88cc by the local guy who had it machined at a local shop.

[toddmoll]

Your 88cc chambers might be total cc's including valve reliefs, piston dish and gasket area.

Even a poor mismatch of parts with a 4 speed and your gears should have little problem turning the tires.

Has your distributor been checked? Check to see if the advance is working properly.

Another thing to check are the secondaries, after the engine is fully warmed up shut it off and have someone mash the throttle into the carpet while you look down the carb (with the secondary air door pushed open with your finger) at the secondaries to see if they open all the way. This is where you might find your problem, I have come across many Q-Jets with secondary problems, for several different reasons.

Todd.

[screamingchief]

Your 88cc chambers might be total cc's including valve reliefs, piston dish and gasket area.

That's entirely possible,and would make a bunch more sense here,if that is indeed the case here,by using appx. 9.4cc for a "standard" .039"ct x 4.3" bore fel-pro headgasket,along with -6.6cc valve reliefs in a "standard" TRW/FM "flat top" forging,add them two and you get 16cc's volume,added to a 670's "nominal" 72cc chamber gets one to 88ccs total chamber volume.

That's the problem with these boards,lots of details get lost/confused in the translation process between there and here.

Still,on an uncut deck with the pistons .020" "in the hole" as most of those pistons are,the compression ratio comes in at appx. 10.18:1,if it were indeed zero decked that would get the CR much closer to the stated 10.7:1 as I come up with 10.65:1 when the zero deck is used to compute this.

Still,that cam would work a little better with a tad more compression,and a lot more gear for optimum results,RPM range listed for cams like that is 4200-6500,so it obviously will be "soft" down low.

Also note that lunati recommends it be installed at 104 ICL,so you might even wanna try it at 102 ICL to see if it feels a little better.

A wider LSA cam would have been better suited if going with a "big hydraulic" cam like this.

Also feel this would be a good candidate for a set of rhoads lifters IMO too.

I myself would have just used a "healthy" solid cam.

And it will definitely need some seriously skilled tuning for decent results,as well as a stout fuel system to feed the Q-jet an adequate supply of fuel.

Bret.

[GTOGreg]

Others have made some very good recommendations for you to follow. If you can deal with a little more valve train noise, the Rhoads lifters would be the quickest way to bail you out of your situation a little bit, along with a lower gear (M21's came with at least a 3.90 I believe). You need to optimize all your stuff to work in the same RPM range or you will have a bunch of high priced parts competing against each other and you have nothing to show for it. You should be able to shred your tires with that motor.

With all that said, those 670's can't be 88 cc's. I had Dave @ SD do his chamber mod on mine and they ended up netting like 79-80 cc's. I went on to deck the block to .005 and my static comp was very close to 9.5:1. I think 88 cc's is your total chamber area if you are running a std valve relief, TRW-style piston.

[scratch the itch]

Ok got off the phone with the mechanic

Here is one problem
May have a M20. He is checking the numbers now. He thinks it is the wide ratio which would be m20?
Questioned him a bit on chamber size, compression and pistons here are the answers

400 + .060
18/1000 in the hole
40/1000 head gasket
actual measure at the machine shop was 86cc

He is getting the stock # on the cam but said it is a 2300 to 6500 lunati cam
with a 4 degree advance making it 1900 to 6500. Timing had to be reduced to 32%.

Pistons are actually TRW (not Lunati) forged aluminum flat top 4 eyebrow pistons. Pontiac steel rods

Thats all I know now.

If it is an M20 Is a 3.73 OK?

[Z Code 400]

M-20 has a 2.52:1 first gear. That would be a better gearbox, but difficult to identify with the tranny in the car, unless it is the original unit. That would be a good choice with a 3.73:1 axle.

With a .060" over 400 (4.181" bore) the piston 0.018" below the deck, a 0.041" head gasket and 86cc combustion chambers, your static compression ratio would be 8.95:1.

Since you mention the camshaft was 4° advanced, we have to assume that it was actually degreed and not just 'guesstimated.' In most cases, when the customer comes to me with a low or no power complaint, I have found a multi-keyway timing gear incorrectly installed.

I would suggest degreeing the camshaft to verify its position, but this is not an easy task in an assembled engine.

If the camshaft position is correct, I would also second the motion for Rhoads Lifters...Robert

[Z Code 400]

Scratchy,

By the way, my above suggestions reflect the least amount of labor to make the car driveable. Honestly, the right way to fix this would be with a different camshaft altogether.

I designed a custom hydraulic flat tappet that runs very well in a 406 (0.030" over 400) and a 413 (0.060" over 400) with a 4 speed. Specs with 1.52 rockers are .466"/.466" - 220°/226° @ .050" on a 111.5° LSA.

I have several of my customs grinds on the road currently and references are available.

I personally don't use off-the-shelf camshafts, but there are a lot of decent camshafts out there and with just under 9.00:1 compression, a more appropriately sized camshaft would be the best (but not the easiest) route to go.

Let me know if you need anything...Robert 10851man@gmail.com