4988S

[Riv]

Hi Everyone!  New here and thanks for letting me be part of the community.

I have a '69 Firebird that is a work in progress.  (I bought it in 2005, sold it in 2012, and bought it back again in 2018 after a long search)  The car was originally a 350 HO, but a previous owner replaced the engine with a strange combination of a '70 400 block and some #15 small valve heads.  He also swapped out the QJet for a Carter AFB that I've never really liked.  I don't know what the cam is, the mileage sucks, and it doesn't have the horsepower that I'd like.  I plan to use it as a driver, so something that's got some good streetability.

I'm replacing an Edelbrock intake with the original cast iron one and I just bought a QJet from a guy that had it rebuilt for use on his '68 Firebird.  I checked out the shop that did the rebuild and they seem reputable.  The rebuild looks thorough.  I gave it a cursory look and here's what I've found:

Primary Jets:  73
Primary Rods:  43
Secondary Rods:  BE

Everything else seems to be more or less in alignment with the second recipe in Cliff's book.

A couple questions:

I'm hoping that this setup will not be too much for the current configuration of the engine and that I can get better mileage and performance than the Carter.  Also, I'm planning on doing some work on the engine next spring/summer - I have a set of #48 heads that will be rebuilt for it and probably the 744 cam.  (I'm hoping that the pistons will allow for an engine that won't have too much compression)  I'm also planning to add some long branch manifolds.  I have a stock GM HEI installed.

Can anyone give me their thoughts on this setup?  Anything jump out that should be done differently?

Thanks everyone!

-Tim

[lightning boy]

What is the carb # that you purchased?

[Riv]

Sorry - I put it in the subject line but didn't clarify.

It's a 4988S, which I guess is a service replacement.

[Cliff Ruggles]

#48  heads are small chamber so make for some pretty high compression on a 400 build with flat top pistons.  Most will measure in the 68-72cc range, so plan accordingly.

The 744 cam is OK, but one of those cams that isn't now or ever has been very popular.  It's a spin-off of the older 066/067/068 cams where they wanted more duration but kept the low .406" lift.  It is rumored to required pretty hefty valve springs to be stable at higher RPM's. 

There are just a lot better choices out these days and I'd bypass that cam and use a modern version with more lift.....FWIW........Cliff

[Riv]

Thanks Cliff! 

When I sold the car in 2012 I neglected to give the buyer all the records and receipts from the PO and when I ran across them a year or so later I threw everything out.  I'm going by memory of what the previous owner told me he had done to the car, so I'm not really 10o% sure what's there are this point.  I don't know what the current cam is.  I was told that work had been done to the bottom end but I don't know if they're stock pistons or not.  (I may have to have dished pistons installed)  I recall that the current #15 heads are from '68 and he said at the time that he put these on for higher compression.  Looking at the specs online I'm seeing that the '68 heads are supposed to have pretty small chambers as well.  The #48s were what was original to the car so I'd kind of like to have them on there.  I'm trying to get the top end as close to stock as I can.  Since I'm sure the heads won't be replaced until at least late spring or summer, things could always change.

Any recommendations for a cam?  I'm looking for something that can be driven, but is a little more fun that what i does now.


And

[Cliff Ruggles]

#48's are excellent heads, but high compression in a 400 build so plan accordingly.

Even with that said with a little work all of the Pontiac "D" port heads are pretty equal in performance potential, even the smaller valve versions.

A few  years ago we tossed a set of small valve 1969 #46 heads on a 455 build as the CNC ported aluminum KRE heads we were waiting for weren't going to be ready for the Norwalk race in August.  The customer wanted to run his car in that race so we grabbed a set of #46 heads, added screw in studs, quickly ground the small valves and seats, and put good springs on them.

We topped off the very well prepared 455 with them, and tossed in a used Crower cam from a previous build from the parts room.

Right off the trailer his car went 11.80's and ran high 11's all weekend at that race.  We were expecting maybe mid-12's out of it.........Cliff

[Riv]

Thanks Cliff!  I probably won't get the heads on until the early part of next year.  First I want to see if we can figure out roughly what kind of pistons are in the engine.  Since it's running fine with the small chamber #15 heads it's possible that they're not stock.  Not sure yet.

Tim