adis

I just accepted an overseas posting and am scheduled to depart in September, at which point I'll have to put the Cutlass in storage for 3-5 years. I was thinking of trying to squeeze in one last project this winter to enjoy one last summer of driving before packing everything up. The project will have to be be fairly simple and inexpensive as I don't want to spend my last cruising summer wrenching instead of driving. Car is a 72 supreme vert cruiser, stock 350 (7a heads) with a few bolt-on upgrades (mildly up-jetted stock q-jet, 7111 intake, and shorty headers to 2.5 exhaust.) I am sitting on a set of 7 heads and a set of Comp Cams roller rockers. I was thinking of modding the 7's to fit BBO valves, with valve job and appropriate (mild) bowl work, and possible mild milling of the head for a slight bump in compression, then fitting back on with the roller rockers and remaining stock valve train. Would appreciate any opinions as to the utility of this mod, particularly as it won't be in conjunction with a new cam. My decision will be based on whether or not it would 1. give me one last chance to wrench on the car, 2. whether the mod will noticeably enhance performance (measured by seat of pants), and 3. it won't cost more than $300-500.

If it turns out to be a worth doing, a few questions:

- what size valves (2.00/1.625 or 2.07/1.68)? the reason I ask is because when I get back, I may or may not keep the SBO, possibly swapping for a BBO (with possibly aftermarket aluminum heads) in which case perhaps I could reuse the valves.

- what type of valve job and bowl work, keeping in mind budget? (any recommended shops in Balto/DC area?)

- Compression? I'd like to continue to be able to use 87 octane gas and don't really want to have to mill the intake, but would be willing to think about increasing compression up to a level where I could still use 93 octane pump gas if the price/timing worked out. If I keep the SBO when I get back, it will probably be stroked and use smaller dish pistons in the 9-9.5:1 range.

- any other considerations? Thanks in advance - mark

jmos4

Hi,

Not sure swapping heads will do much for compression as I believe 7 and 7a both have the same size combustion chambers unless you are having them milled down.

Someone with more knowledge should be able to better advise you about your upgrades

Regards,

Fun71

Yep, the 7 and 7a heads have the same size combustion chambers, so if you don't mill them then no change in compression ratio. I don't know if installing larger valves will give any performance increase with the puny factory camshaft. Seems like a lot of work that wold benefit a larger cam, but with the factory one I wouldn't bother. Just drive the car and enjoy it as-is.

If you really want a final project, swap the rear gears as that will give the most bang-for-the-buck performance increase. Been there, done that and can testify to the results.

adis

Thanks for the replies guys. That's sort of what I figured. I'm just thinking about not having a garage for 3-5 years and was looking for a reason to get in one last project.

I don't want to change the gears because I have a 200R4 that will go in eventually and I think the stock 3.23 gears will be a good match for that based on wanting to keep the car a cruiser.

Fun71

Both my 70 and 71 had 2.56:1 rear gears from the factory and they cruised very nicely on the highway at around 2200 RPM. With a TH200-4R and its 0.67:1 overdrive you can get the same effective final ratio using a 3.90:1 rear gear. Using a 3.23:1 gear with the OD trans gives a final drive ratio of 2.16:1 which may be too low, or at least way lower than needed. My engines really seemed to like running in the mid-2000 RPM range.

jmcghee

BillK is a registered member. He is owner operator of Advanced Automotive Machine in Waldorf MD. He has excellent reviews.

adis

jmcghee - thanks for the info, ill keep AAM in mind.

Kenneth - admittedly I'm pretty ignorant about it all, but using online calculators: 3.23 gears with 0.67 OD on 26" tires nominally get me 80 mph @ 2237 rpm, 140 mph @ 3915, and it gets me to 50 mph in first gear (2.74:1) under 6000 rpm - all pretty squarely in my goals. Granted, there will be limiting factors, but that satisfies my caveman understanding. However, i will try to learn more about gearing to see if i should be thinking about shorter gears as you suggest. Thanks

Fun71

Look at what the calculator shows for 60 to 70 MPH as I doubt you will be doing 80 to 140 very often.

My cars with a TH350 and 2.56:1 rear gears would do 50 in first gear. Really sucked for performance and general around town driving. At one point I swapped in a 3.55:1 rearend and around town driving was much, much nicer as the throttle response was much crisper and I got the same MPG since the trans shifted through the gears easier and got into 3rd quicker. What I REALLY liked was it shifted out of 1st at around 30 MPH under WOT.

FYI, over the years I swapped from the 2.56 rear to a 3.08 rear, then from the 3.08 rear to a 3.55 rear, and each time it felt as if I had an engine with more horsepower. Better rear gears are by far the best and easiest performance upgrade, way better than what you would see with the head mods you mentioned. And if you are going with an OD trans, don't be afraid of lower gears. I drove my car for years (like 25) with short 14" rear tires and low gears, turning 3000+ RPM on the highway, and it was never an issue.

adis

Kenneth, thanks - you've made up my mind. I'm going to do the 200r4 as my final project. Ive been sitting on that thing for 5 years, don't know why I havent done it already (timing I guess). That way, I can start putting together data based on my driving habits to help me decide what rear end and engine I ultimately need. Also, it gets rid of 150 lbs of dead weight that I'd otherwise need to put in storage. All I need is to decide to what level I should build it. I'm leaning toward 300hp/400tq at the wheels as a goal - which should cover either a stroked high(er) compression small block, or a mild big block. I go back and forth, and fuel costs will likely be the deciding factor. Regardless I think if I build the trans to handle 300/400 it should be appropriate for my 80/140/13.x goals. Thoughts?

Fun71

I say build it stout as you can afford (we all have budgetary limits). Overbuilding is better than underbuilding.