Ok guys. I have a 1973 Corvette with a stock LS4 engine, TH400 trans and a 3.08 rear axle. I just picked up a 502 short block that needs to be bored .030 over (so it'll be 509) and I have a Super T10 with a cast iron case and midplate (2.43 first gear so it splits the difference between a Muncie close and wide ratio). I'm cool with going up with the rear gears as well depending on what advice I get from everyone here. Heads are ported Edelbrock 100cc chamber "roval" ports, intake is an aluminum 1969 Q jet "pancake" intake (I also have a 1971 LS6 "pancake" intake I could use if a switch to a Holley carb becomes necessary, along with an 870CFM Street Avenger vacuum secondary Holley carb). Porting/valve job picked up about 10% all through the lift range on the intake side, exhaust shows most improvement up to .200 lift. Cam will be Crane Blueprint LS6 with 1.8 SS roller rockers. Will use either 1 7/8" or 2" headers with an X pipe Pypes exhaust system. As stated, rear gear is up in the air. I'll run compression as high as needed to stay compatible with pump premium (93 octane 10% ethanol here in the northeast) and make this thing thump. I also have a 4.250 stroke Eagle crank, but it's a 2 piece seal style so I'd need an adapter to run it in this one piece seal Gen V 502 block. Car has factory A/C, PS, PB, PW, map light, etc...so it's no lightweight racer for sure. I'm NOT looking to build a race car, I just want a fun driving, thumping BBC Vette with creature comforts. Car will also run offset trailing arms for bigger tires, and (eventually) a Global West suspension system. Looking for thoughts/advice from any/all BBC gurus on here...thanks in advance !!!

EDIT : Exhaust shows improvement up to .300 lift

 

Wow...112 views and not a single opinion ?

 

I have a recommendation - if you really want A/C, while you have the motor out, install a Vintage Air system. But, I live in the northeast too and I removed all the A/C stuff including the evaporator, and I've never missed it. I assume you have a C6. Drive that on hot days. I have a C5 and that's what I do.

 

Wonder why they went light on the exh porting

that pancake intake....id put if off to the side and put something on that will let it work to its potential;if you need to mod or get a bigger hood so be it Sounds like fun anyway.

Edit: def change out the 3.08 it will be happy cruising with a little rpm anyway and pull the way its supposed to

 

No way I'm loosing the factory AC, I can't afford to spend for Vintage Air, and it gets hot enough up here in July-August that I'd miss AC if I didn't have it...

The Q Jet pancake intake has been ported to the hilt, I know it's no Air Gap (or even close), but it allows the factory hood and air cleaner to be used along with the cool cowl induction set up. I've read that the stock pancake intake will support 500-550 HP without mods (probably with a more radical cam and compression than I'm planning though).

Thanks for the replies guys...please keep them coming.

 

I won't read a huge paragraph, IMHO you should break it down to make it easier to read. I never got past the third line. Here's how I would post it

"Ok guys. I have a 1973 Corvette with a stock LS4 engine, TH400 trans and a 3.08 rear axle. I just picked up a 502 short block that needs to be bored .030 over (so it'll be 509) and I have a Super T10 with a cast iron case and midplate (2.43 first gear so it splits the difference between a Muncie close and wide ratio).

I'm cool with going up with the rear gears as well depending on what advice I get from everyone here. Heads are ported Edelbrock 100cc chamber "roval" ports, intake is an aluminum 1969 Q jet "pancake" intake (I also have a 1971 LS6 "pancake" intake I could use if a switch to a Holley carb becomes necessary, along with an 870CFM Street Avenger vacuum secondary Holley carb).

Porting/valve job picked up about 10% all through the lift range on the intake side, exhaust shows most improvement up to .200 lift. Cam will be Crane Blueprint LS6 with 1.8 SS roller rockers. Will use either 1 7/8" or 2" headers with an X pipe Pypes exhaust system.

As stated, rear gear is up in the air. I'll run compression as high as needed to stay compatible with pump premium (93 octane 10% ethanol here in the northeast) and make this thing thump. I also have a 4.250 stroke Eagle crank, but it's a 2 piece seal style so I'd need an adapter to run it in this one piece seal Gen V 502 block.

Car has factory A/C, PS, PB, PW, map light, etc...so it's no lightweight racer for sure. I'm NOT looking to build a race car, I just want a fun driving, thumping BBC Vette with creature comforts. Car will also run offset trailing arms for bigger tires, and (eventually) a Global West suspension system. Looking for thoughts/advice from any/all BBC gurus on here...thanks in advance"

 

I'd say your on the right track. I went with the LS6 and gave up the top end. For a street cars at 500TQ at the wheels it's a nice driver.

I also used the Edelbrocks but mine started at 110 so I has them milled.

For the rear I'm at 3.36. More would be nicer but going down the freeway with a really balanced setup 85-90 MPH doesn't feel like it's going to blow apart like it did before.

 

OP if youre going to keep the intake have you considered an aggressive extrude hone to get where the grinder cant maybe even play with a spacer/drop base if it will fit?
It will love the little extra plenum volume
just a thought

 

Certainly the 509 will fly.....but if you're not opposed to doing the adapter, another 40 or so inches should be worth nearly 60 HP and similar torque. Having A/C etc will like the cubes and help keep the rear gears sane.

I'd do a search on AJROTHM here on the forum. He's got a sweet 496" C-3 with iron oval ports, A/C PS PB T-400 and 3.36's that runs mid 10's all day long. Great combo of low rpm torque.

I think cam and intake are the big items. If you're locked on the intake....I'd use the LS-6 rectangular port to gain some volume. Then I'd do some serious cam thinking to accomodate a somewhat choked intake side...but a decent exhaust side.

JIM

JIM

 

I'd run a Performer RPM.... This member fit it under the stock 77 hood no problem.

https://www.corvetteforum.com/forums...post1582079091

If you have a 73 or later with a BBC there's really no reason not to run a good intake. Now is 68-72 guys is a different story.
Will

 

Sorry guys, been tied up a bit with life, but I'm back and ready to talk about this some more. Here are my needs.

1 Engine must function with factory AC and reasonable rear gearing with a flat tappet (solid) cam. I'm not a Hyd roller fan and I don't want the costs of a solid roller setup

2 Q jet aluminum intake (heavily ported) is my preference because it retains the stock hood AND the factory cold air induction setup for a factory look.

3 This is NOT a race car, it's a driver (daily in good weather)if needed.

4 Car will run the aluminum intake and heads as mentioned previously, as well as an Edelbrock aluminum water pump so handling is more like a small block car

To 427Hotrod : Jim, I'm fine with the rear seal adapter, but I don't like the 6.385 rods I'd have to run with oil ring support rails in a street car (maybe 3500 miles a year, could be more but not more than 5000) that won't be torn down every winter. What is your experience with this ? Also, I'm VERY familiar with AJROTHM'S car, it's a BEAST ! But I don't want a TH400 and a 10" converter, I want to run my Super T10, and Allan's car runs a hyd roller, it also runs a very tall L88 hood which I don't want. I know I'm limiting performance potential quite a bit with these choices, but that's the way I want it. Taking the late, great John Lingenfelter's theory that a balanced street engine running street compatible compression and components should make 1.1 HP for every cubic inch, that puts the 509 at 559.9 HP and the 540 at 594. Can a Q jet carb pass enough fuel for almost 600 HP in a street car ? Remember the GEN V 502 block has to run an electric fuel pump anyway, so I won't be using some weak, stock block mounted mechanical pump...

Thanks again guys !!!

EDIT: I should mention that I have a spare '73 hood (got it for $100 on CL) that I would be willing to cut to raise the center section "power bulge/cold air induction" that would allow a Performer RPM Q jet or a Performer RPM with a Holley (but I have to admit I'm ignorant about putting a Holley on a car with factory AC with the idle compensator solenoid) IF I can do the work myself at a reasonable cost (I've never worked with fiberglass before), because I got quotes from 2 different shops in my area of $1000.00 to do that work and get the hood back into primer only, no paint. IMO that's way too much money.

 

The 6.385" rod isn't an issue. My 540/555 has been running many years. Yes it's been torn down a few times, but only to change the combination for more power. I've used SRP pistons first time (same as in 502's stock), Mahle's with thinner rings and now it has Diamonds for the turbo application. Never had an oil usage issue. Look at the pics below....it's with the SRP's that I ran for 12 years or so. There's no carbon between the ring grooves from any ring issues.Tops of pistons are dry and exhaust ports are dry. I ran this with .0055 clearances...much larger than you would because I spin it 7500+ RPM..and it was still dry.

The oil ring is supported by a steel rail when the pin extends into the oil groove. That little area isn't going to change the world one way or the other on oil control. Oil issues are caused by poor honing/cylinder wall preparation. For what you're doing I'd run tight piston to wall clearances. I prefer forged pistons and a set made from 4032 material will allow clearances to be set very close.

The induction will limit things...but it will still be a heck of a lot of fun.









JIM

 

Jim, Thank you. I was planning SRP pistons in 4032 alloy anyway, was a toss up between 509 or 540, I think you settled that for me !!!

Can you give a solid flat tappet cam recomendation ? I'd appreciate it.

Also, can you run a Holley with factory AC ? How do you set up the idle compensation solenoid ?

 

Does anyone have a cam/rear gear recomendation for this car ? Flat tappet solid lifter please. Decided to go 540 and will be using Super T-10 trans, 2.43 first gear.

 

Sorry late to the party here. So we're doing a 540 with 10'ish compression? Edelbrock ovals with some port work? Got any flow numbers you can post?That would help a lot.

And the LS-6 intake and Holley or an oval port one with a Q-jet?

Seriously, for a motor like this I'd use a hyd roller all day long...and I'm a solid cam sort of guy. Here's why....by going up on cubes we're going to pick up TQ but we're going to tax the heads/intake even more than the 502/509 combo. It's going to want to run out of steam earlier. So the advantage of a solid cam for the ability to rev won't really be used. I did some testing a few years ago with a 555" using Dart 335's and several intakes. I used a pretty nasty solid flat tappet with 276*@.050 and near .700 lift with 1.8 rockers. Against a Hyd roller with 254*@.050 and similar lift, the HP at peak was nearly identical 760 HP (6400 or so)....but the Hyd roller was up probably 40 lb ft in the lower RPM ranges. Now that's a pretty healthy HR...and it was happy to 6800 RPM or so. The solid flat tappet eventually made 820HP with a Dominator and Super Vic intake and some more RPM.

We're wanting nice manners and driveability..so the combo is likely to peak around 6000-6200 RPM or so. A HR cam will be down in the 240-245* range probably and it will be pretty thumpy but easily driven with the 4 speed.

For a solid flat tappet...it's going to take low 250's@.050 to get similar peaks...but low speed won't be as nice.

See if you can find the flow numbers on the heads and we can narrow it down a lot closer.

In the meantime, this series of articles does a lot of testing that will demonstrate general direction and what does what.

http://www.hotrod.com/how-to/engine/...-chevy-engine/

http://www.hotrod.com/how-to/engine/...vy-parts-test/

There's another one in between these two but I can't seem to find it. Might search Hot Rods site

JIM

 

Hey Jim, thanks for responding. I would prefer the Q jet, it's been massaged by SMI for 850ish total flow. Intake has had front to back dividers removed and lots of blending at bottom of carb pad bores, and it's been port matched back into the runner as far in as possible (to the point where the runner taper is larger than the port match), this wasn't easy (think hole saw and TIG welding), and a slot .500" wide and .500" deep milled between the carb secondaries so the engine draws from both sides of the secondaries, but stays torquey down low on primaries.

Head flow numbers .200 138 149 119 122
.300 193 218 145 153
.400 233 278 168 170
.500 272 306 189 187
.600 299 331 202 201
.700 318 347 210 216
.800 327 359 230 226
INTAKE EXHAUST

My concern with the Q jet is fuel flow, not air flow...

I'd run compression up to 11 or 11.5:1 IF it'll run on pump premium.

I'll say this again just in case...I have a spare 73 hood that I'd cut up and raise the center power bulge/cold air induction system on IF I can get some help on the fiberglass work (too expensive to pay someone to do it) so I could run a Performer RPM Q jet or a Performer RPM Holley flange, and I have a brand new in the box Holley Street Avenger electric choke 870 cfm carb...what say you ?

Not in the budget for a roller of any kind, so it's either a solid or hyd flat tappet I'm afraid...

Thanks

EDIT : Sorry about the flow chart, It lays out fine when I type it out, then gets all messed up when I post it...the stock #s are to the left in each column.

 

I think you're right...the Q-jet bowl capacity will be a challenge...but there's gazzillions of 10 sec and even some 9 sec doorslammers running with them. Might need a larger needle seat etc.

Got any pics of all that intake work? Sounds pretty cool? Did they flow test it too? Just curious what it might do to headflow.

The heads are moving decent air...valve sizes 2.19/1.88? I wouldn't think they would have had to open runners too big to get those numbers....but we're not looking for crazy RPM anyway.

That's about a 62% I/E ratio on those heads...so it's going to take a big split to make it do what's needed. Let me do some cyphering and see what I can come up with. If it's definitely going to be a flat tappet, then I'd go with a solid just in case the RPM got away from me...these big engines WILL rev faster than you think they will. I'm leery to go into the more aggressive lobes for a motor like this. I don't think you're wanting to live on the edge that close. Any chance of going up to .904" lifters?

What if we saved $$$ and reused the crank and rods and made it a 509....would that get us into HR territory? A 509 with a HR will do as well or better than a 540 with a flat tappet considering the heads and intake. Just thinking it all through....


JIM

 

Already have the crank, need pistons either way, so I'm only spending for rods and seal adapter at that point.

No pics of intake, I did the work...haven't had it tested yet. The Bridgeport mill makes this stuff not as time consuming.

 

My '72 454 was as fast on the street as I ever wanted in a naturally-aspirated Vette. Torker single-plane, Holley 650 DP, headers and a high-torque, non-loping cam. Everything else was stock. It could pull the front wheels off the ground with the TH400 and 3.70 rear. Was only bested by two cars - both Chevys - during five years of intense street racing. So... my advice is don't get carried away. With that many cubic inches, you don't need fancy parts, just the right combination.

 

I have a hard time believing that you could "pull the front wheels off the ground"...a '72 is low compression, you put a Torker single plane on it (killing low end torque), choked it with a 650 Holley (the stock Q jet was 750...), and an "RV" type torque cam...mismatched combo IMHO