hey guys I have a 77 l48 with a 600 quick fuel, dual plenum performer intake, headers and dual exhaust. I also installed a 2500 b&m stall I was wondering if I bought promaxx heads (185cc,64cc) and a comp cams xtream energy cam (.490 lift) and a MSD RTR system would this bump me up to the 400hp mark?? Thanks for your input!!
http://www.jegs.com/i/MSD-Ignition/121/8360/10002/-1
http://www.jegs.com/i/COMP-Cams/249/K12-246-3/10002/-1
http://www.jegs.com/i/ProMaxx-Perfor.../2168/10002/-1
Also would it be smart to go for a bigger intake runner? (225cc) link below
http://www.jegs.com/i/ProMaxx-Perfor.../2117/10002/-1

 

If you have a bunch of compression to go with it, like around 10:1. But more importantly is the DCR around 8.1 > 8.7.
See my profile.

 

So your saying the heads won’t get me to that compression ratio? If so how would I get there, new pistons? Also if I left the stock bottom end and did those upgrades what kinda hp would we be taking??

 

Oh yes, those heads will get you some decent CR with 64cc chambers, but only if your current pistons can support that chamber. By the way, those are the "angled plug" heads. (The straight plug are 2169) What CR do you have now? What pistons? Domed? Flat tops? Check out United Engine & Machine web site. Use the calculator on the left. Figure your pistons are .020 in the hole for that question. Try .040 for the gasket thickness question. Keep your SRC around 10:1 or less and D.C.R. 8.1 > 8.7 by playing around with different head gasket thickness.
For the cam you have chosen, I would stay with the smaller 185 runner for better street throttle response. More lift cam, bigger 225 runner.

Figure on using premium gas from here on out. H.P. estimate? Maybe 390-410.
And watch for those 2169s to go on sale in late Jan / early Feb like this yr. ($640 pr)

 

Currently my bottom end is stock so I believe that makes the CR 8.5:1. Are the stock pistons compatible with those heads or no? So if I choose a bigger cam then the bigger heads are a good idea? (More power) thanks again for all your help and the tip on the sale!

 

Keep in mind longer duration camshafts need lower rear gears.

 

They also need higher stall converters as well correct?

 

Correct. But you are close with the 2500 stall.
H-m-m-m-m. 8.5 CR. Not good. Tough to make any decent power with that. Smaller chamber heads will bump that CR up some. This is where you have to do your calculator work to find your true CR with 64 chambers, piston .025 in the hole, 0.040 gasket, etc.
Just guessing, you might be around 9.5:1. Your old heads are likely 76 chamber. But you have to crunch some numbers with those CR calculators or you are just throwing money away.

 

I’m going to spend some time and do some calculations tonight. I’ll get back to you guys when i come up with something!
Thanks again for the help highly appreciated ����

 

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I don’t know if anyone can see that or not but I tried to do some calculations last night and I’m not sure if I’m inputting the correct numbers? If someone can give me further details that would be awesome!!! With the 64 chambers 17cc dish pistons and them .020 in the hole compression is 8.9 is that a little low?? This is with the thinnest gasket I can find 0.028

 

there are .015" MLS gaskets available (stock on 90-91 L98). That is what I used for my ZQ3 rebuild. With 58cc L98 heads, stock 4 eyebrow ~6cc pistons and the .015" head gasket I am about 11:1

 

That's about right. Stock the L-48 is advertised as being 8.5:1 compression, but it actually measures at 8:1 (some even say 7.8:1). So with 64cc heads and a .015 shim head gasket you could get it up to 9:1, or a little bit over.


If pistons are in your budget, it might be worth it. If you could get something with a smaller dish you could dial in your quench distance and compression ratio just right. With aluminum heads you can easily run 10:1 compression and get a little more power.


If you're on a tight budget, I am running the stock bottom end (with those terrible dished pistons), .015 shim head gasket, 64cc Brodix heads, Lunati 268 cam. It runs strong and pulls hard! But I'm leaving a solid 20 horsepower on the table with my low compression ratio (little over 9:1) and flat tappet cam (if you can afford the extra cash for a retro roller cam, it would be worth it).


Personally, I don't think the stock bottom end at 9:1 compression with that small of a cam would make 400 hp, but it would depend on the dyno. Probably more like 350.

 

You guys are absolutely correct!
I did some more calculations and with a .020 gasket thickness I’m getting a CR of 9:1 and with .015 gasket thickness it’s 9.1:1 so very close.
unfortunately pistons aren’t in the budget right now as I don’t really want to get into tearing apart the bottom end, having that said in the future I will most likely bore it out and get forged internals.
Youre set up seems very close to what I’m looking to do (mobird) have you ever had yours on the dyno? What stall are you running? Are you happy with it or would you like a little more?
thanks again everyone!!

 

Never been on the dyno, however I have quite a bit of experience with performance cars and butt dyno says about 300 at the tire (so maybe 370 flywheel?).


I have a 4-speed, so no stall.


I'm a horsepower junkie, so I definitely want more horsepower! But we may have different goals. My ultimate plan is in the 500-600 hp range. For what it is now, it's a fun street motor. Has a nice lumpy cam sound, can roast the tires at will, and will run with most modern "sporty" cars (pulls slightly on my brother's 2006 GTO 6.0 with bolt ons which put down right at 400 hp at the wheels, however it weighs nearly 4,000 pounds).

 

The honest answer is no, you cannot get to 400 Gross HP, as it stands with that engine and those parts.

Starting backwards and working forwards, the stock L-48 in 77 had 180 Net HP with an advertised compression of 8.5:1 but more like 8.1-8.2:1. A seasoned engine at best would have around 8:1 compression, maybe less. Your dual exhaust and headers along with the intake is probably good for roughly 40 more HP (95% of that number is headers and exhaust, very little from the intake), giving you again roughly about 220 NET HP or close to the L-82 with slightly more torque and lower in the RPM range.

The ProMaxx heads are a moderately flowing cylinder head and with 64 CC chambers will get to you about 9:1 compression which is low compression trying to achieve 400 Gross HP (add .2 compression with .015 head gasket for a total of 9.2:1). The comp cams 230/236 duration, .490 lift, operating range of 1,800-6,200 will complement the better flowing heads but the cam will hurt bottom end somewhat. Your current L-48 cam is all about bottom end torque and is relatively low lift in today roller cam world. I think being optimistic you could add 50-60 Net HP to the 220 Net figure, bringing you to about 280 Net HP or about 335-340 Gross HP.

To get to 400 Gross HP you would need 10-10.5:1 compression along with great flowing heads like AFR's and others, along with a roller cam with .525-.550 lift, duration 225/230 or 230/235...400-450 Gross HP

 

Another thought. As somebody mentioned this is a seasoned motor with the compression dropping a bit with time and miles. Now you're going to put this thing up into an additional hundred horsepower. Which means you're going to be stepping on the gas harder than it ever has been before. Those Rings ain't going to live very long. Hopefully the bearings and the crankshaft do. I would really seriously consider going through that bottom end before you add 100 horsepower to this thing and start hammering it.

 

So what I’m gathering from everyone here is basically when I’m done I’ll be making anywhere in the 325-375hp range with a CR of 9:1. Also it’s a good idea to spend the extra money on the bottom end. Although guys on here have better speed parts than these on stock bottom ends and they are fine! (Not to mention guys with nitrous) I would go with a bigger cam but I’ve picked that one based on my stall specs and rear gears (355s I think) also what is a good set of roller rockers for my application? Thanks again!

 

Sounds like you about have it. I would recommend some 1.6 RRs to get a little more lift out of that cam (those heads do best in the .500-.600 lift range)

 

The 77 L-48 came with a 3.08 rear diff unless yours has been changed.

The 2500 stall is going to help quite a bit vs the stock stall.

With the stock dish pistons you will be limited on CR and that is probably a good thing as the stock piston top has no quench pad. Without the quench pad detonation is more likely due to lack of turbulence and transfer of heat from the piston to the head.

When I cc'd my heads on my 77 L-48 the combustion chambers were as large as 80 cc's. so much lower CR than 8.5:1 more like 7.6:1.

One other concern is ring seal. Adding compression to an engine with weak ring seal may create an oil burner.

A leak down test would be a good idea. 15% on a warm engine maybe a bit higher leakage would be the max you would want to see I would guess for a 9.0:1 CR with those existing rings.

The pistons themselves are just cast aluminum. good to about 350 HP if you want them to live very long.

An excellent idea to go through and change the rod and main bearings as part of the upgrade. May want to consider ARP main and rod bolts as well. Gonna have to use plasti-gauge to measure the clearances make sure they are in spec after new bearings are installed as well.

No matter what someone tells you do not go with a 225 intake runner. Keep it in the 180cc range.

Extreme energy flat tappet cams are a gamble. Much more likely to get a flat lobe. Then you gotta tear the whole engine down to clean it up.

If you got the $$ go roller. If not then I would stay away from the extreme energy cams.

Take a look at Iksy cams. I would get something on a 110 t0 108 lobe separation and an advertised duration of 260 to 270.