327 or 377 for tube frame 1969 "Vintage Look" road race Vett

[bosco]

We are building a tube frame 69 Corvette for SCCA and HSR road racing. Chassis is done, body is being fitted. Body is lightweight with L88 flares with bolt on 'Vert top. Will look similar to the Owens Corning Corvette's.
Weight will be about 2500 # minus driver. Tranny is G Force T101 A into a Grand National Floater 9".
Tires will be the Hoosiers Trans Am 2 type bias ply 15x10x27

I have a nice 4.125 x 3.0 motor, actually about 326 ci, but I call it a 327 for obvious reasons.

It has the following:
* Dart Little M block 4.125
* early Brodix 23* heads with 2.08 intake and 1.60 valves. Heads were nicely hand ported many years ago.
* Matching Brodix intake
* High dollar 3.0 Callies Crank, Carillo 6.0 rods and JE pistons to make 11 to 1 compression
* 3 stage dry sump
* Roller cam...kinda mild
* Bo Laws 650 carb

This combo made 525 HP and about 420 torque

Motor has dyno time only...but has been sitting on the shelf for more than 4 years.

Would Like a bit more power and torque: Thinking a 3.48 crank to go with the Carillo's and a new set of pistons to make about 377 ci with a 7500 rev limit

HOPING for about 575 HP and close to 500 lbs ft torque

DOES THIS SOUND FEASIBLE AND IS IT WORTH THE EFFORT AND MONEY INVESTED?

Would love to have the extra power and especially the torque but concerned with the 10" wide tire as a limiting factor...may not be worth it.

What do you guys think ?

Thanks,

Bosco

[KnightEngines]

Why not turn up the wick on the existing short motor?

Can you run E85?

What I'd be doing is more comp, more cam, more carb.
You've got a nice short motor by the sounds of it, should be capable of 7500rpm no problem.

Heads may be the limiting factor - need more info on them, cross sections & flow figures, that'll let us know what is possible & what to suggest in the way of cam, carb etc to get some more out of it.

One advantage of a smaller cube engine in a light car is traction out the corners, won't tend to blow the tyres off so easy, can be easier to drive & less twitchy.

[user-612937456]

Why 3.48 why not 3.75 3.875 or even 4 inch the money is about the same horsepower is easy torque is even easier who cares about nostalgia there is not a nostalgic person out there to get warm and fuzzy about what he can't see inside your engine LOL with the right valve train components and cam you can make it easily screen 7500 RPM or like Knight says put some money into the valve train and turn it to 9500 rpm?

[pdq67]

How about considering an old 348" engine. BUT not a "W" engine, a SBC.....

4.125" b x 3.250" s = 348".

It will still rev and should have decent torque, imho.

And set up right, imho, a 3.25" stroked engine can go above 8,000 rpm and it isn't all that out of line with no more than a good solid flat tappet cam like an old Isky Z-30 or a more modern version of such.

Of course, the little 3.00" stroked engine can be made to rev almost to the moon if you really want to hear her sing!!

As always, jmho, and I dearly love the shorter stroked little motors!!

pdq67

[MadBill]

if you just change the stroke to 3.48", torque will increase by ~ 65 lb-ft. but HP only by 10-15. Add a not-too-on-the-edge roller matched to the head flow, CR, displacement, etc. and expect ~another 40+. 12.5:1 CR, and a 850 or bigger carb = 25 more and on down Racer Road...
A few points:
o TA2 cars are ~ 200# heavier than yours and run flat out for an hour with those tires.
o Having a car that "handles great on the straight" is always cheap performance.
o A 3.75" crank costs the same as a 3.48" and is a bolt-in with the right parts. More than that, not so much; the heads would be/become a huge restriction.
o At each corner exit, there will be a point where you can go W.O.T. with the 327". From there on to the next braking zone, the 377"/408" will be faster.
o Good torque is a boon for driveability and recovering from fumbles.
o Unless built to the hilt, a 408 will operate at perhaps 20% lower RPM than a 327, which is great for valve gear durability, the weakest point in most RR engines.

[PackardV8]

Getting good advice. Where there is no displacement check/rule, always go bigger and turn it slower. The car will be faster, easier to drive and the engine will live much longer.

[bosco]

Thanks for the comments guys.

A little more info: The motor was originally built to be reliable, run for many hours between rebuilds, hence the lower compression, relatively mild cam and a desired self imposed rpm limit of about 7500. All done to preserve the motor and the wallet. The motor has good Comp roller rockers but not shaft rockers, another reason I didn't want to go past about 7500.

Note: I am retired firefighter, and at age 64 and 25 years road racing... I should quit, but I CAN'T! I also have a tube frame C6 Corvette that is getting a near 600 HP carbureted LS3 and a spec Miata to boot.

I thought the 377 might be a good compromise between power and torque while still preserving some of the sweetest sound on earth...a small block Chevy at full song.

Also, thought the 377 would be as big as I should go before blowing the lil ten inch tires off with torque. Been there and done that with a Lozano Bros 18 * 366 on my old ASA stock car with the same tire.

I want to stay with the Hoosier tire as they are only about 600 per set new. Will also be difficult to get anything much wider under the car with the current track.

[cjperformance]

Thanks for the comments guys.

A little more info: The motor was originally built to be reliable, run for many hours between rebuilds, hence the lower compression, relatively mild cam and a desired self imposed rpm limit of about 7500. All done to preserve the motor and the wallet. The motor has good Comp roller rockers but not shaft rockers, another reason I didn't want to go past about 7500.
.

This paragraph I just read in your last post is the reason I would be adding cubes. No need to turn it harder, get your grunt increase via 3.75 stroke, keep the comp and rpm within your wallet preserving limit ! Go thru the heads and see if you can gain a little here without spending too much, pay attention to all the usual port match detail , cam degree etc, a larger carb and get the most out of it.
There's no substitute for cubic inches!! If is too twitchy, use less throttle, or a tight vac sec carb!!

[KnightEngines]

One thing I have noticed over the years of building road race stuff - the fast guys running in restricted classes (head or intake restrictions) usually prefer smaller stroke engines - longer power curve up top so they can rev more past peak & keep it on song.
But it does take a good driver to see the best from a shorter stroke engine - it's easier to let it get off the boil & less forgiving to mistakes, but faster when the driver is good.
Longer stroke is more forgiving & a better option for closed public road tarmack rally type racing where the driver is often unfamiliar with the course.

[wyrmrider]

Nice Callies 3" crank and just needs a quick checkup and some lube to be good to go- where are you in your season- get out there and have some fun
get the parts together for a 4 1/8 x 3.75 motor for next year

[piston guy]

A 377 with a 7,000 rpm limit should go 50% longer between rebuilds and be a LOT more fun to drive and the 348 version. Your tube chassis will take all the power you give it. It will be faster off the corner for sure with the 377.

[66Vette]

This is a little different kind of racing, I autocross a Corvette with a 377. I did hem and haw over what size engine to build. I talked to many short track racers that said building a 434 was not the right direction for a car that needs to come off corners fast. Not sure I made the right choice and I would be curious to A-B compare it to a longer stroke engine. The 377 will easily overpower 315-35-17 Hoosier A6's in first or second gear. I'm now switching to a DOT200 tire class so traction issues will become even more pronounced.

The engine is a 4.125 x 3.5" stroke in a Bowtie block. AFR 195 competition heads, solid roller at around .6" lift, 240 duration. Super Vic, headers, Pro-Systems carb. Makes roughly 540 HP on the dyno. Rev limit set at 7800 RPM. And I drive it on the street, and to and from events......

[MadBill]

Terrific looking car, and great work getting so much tire inside the fenders!

Have you tried stiffer on the ARBs?

[hoffman900]

Bosco,

You should really determine what class you're building to. Is this a IMSA GT type build?

Jack Woehrle (HSR's Tech guy) has a forum here: http://www.vintageracerules.com Jack has and will pump cars for displacement.

If you don't know him, he's super friendly and will help you along.

The 10" wide tire can easily handle the power. The SVRA Group 6 (vintage SCCA B-Production and A-Production) cars are putting a lot more power than you through 7" wide tires. The suspensions are a lot more stock than what you should be using with a tube-frame set-up. It comes down to the driver and how good you are at setting it up too, ymmv.

Note: the 310ci BP Fords are pushing 595bhp+ with iron heads and a low rise intake, and have a fat powerband. They also redline about 700rpm beyond what your redline is. They're not cheap engines. Bill_C on here is involved with Cobra Automotive.

From Bill-C

dont think that it is fair to my customers to just give away all of the info and "secrets" that they paid dearly for, but I guess it would be ok to give a few general trends. I believe it is important to match the engine specs to the customers budget, the class that they are running, the skill level of the driver, the skill level of the mechanic, how much maintenance they are willing to put up with, and lastly, are they racing to win, or just have fun. Under ideal circumstances, 625 hp and 430 tq is "possible". To run at the front of the pack in the vintage road race world you're gonna need the highest compression ratio you are capable of tuning (at least 13-1), an agressive solid roller that has the best compromise of torque off the corner @ 5000 rpm and top end horsepower @ 8500 rpm. The heads need to have the highest velocity you can achieve and still flow 320 + cfm @ .750 lift. We're on our 5th revision to our head cnc program for the rhs castings for the sb fords and 3rd for the dart sb chevys. (I'm assuming you want to run B /P in svra with a vette). The performer rpm intake will need a huge ammount of work. You also have to make sure the valvetrain is very stable. The f@#$ing drivers ALWAYS come in from the track with tach tell-tales pinned.I'm told that a jerico trans will down shift from 4th to 1st gear @ 160 mph NO PROBLEM. Oil pans have been a worse problem than expected also.

In-car from CA's house car: https://www.youtube.com/watch?v=fB-1rEntau0 ... all purring along through an Elston built exhaust system.

[F-BIRD'88]

use a 3.75" stroke crank.. Drop the compression ratio by .5 cr. 10:1 to 10.5:1cr
Use a racing single plane intake to tame low rpm torque. and make big top power with the 406 cubes Dyno it and install the cam more "straight up" phasing as opposed to advanced, to tame the torque curve and move it up in the rpm range . It may well then need and want a longer duration cam both to feed the 406 cubes to get more horsepower AND tame the low rpm torque to keep the tires glued. Get a MUCH bigger carb for the 406.
850-950
Or get 2 carbs for it.

You may want to play with a few cams and or cam lash/phasing with on track testing to get the power curve right.

Use a wider than optimum LSA cam with plenty of intake and exhaust duration in the 406 (wider LSA than what would create the most torque) This will modify the engine torque curve, shifting the big power up higher.
You will need a different bigger duration cam in the 406 to hit your goal of 575Hp anyway through those same heads.
(you won't need to rev it higher,the 406 will naturally peak sooner.)
The cam you got now will probably not work well. Its probably way to short duration.

Get a new cam designed for endurance-road race purpose.

Add ballast weight to the back of the car over the rear tires.
you can dial up-down the engine power with carb linkage adjustment and throttle pedal linkage GEOMETRY

Longer less aggressive throttle pedal linkage GEOMETRY allows MUCH BETTER engine power CONTROL.
and ignition timing control in various gears as required. (limit the spark advance in the low gears)
(Accel makes a cool electronic programmable multi switchable retard box just for this.)(it works with all the popular CD spark boxes) Accel #49355
Then you won't come up SHORT on POWER when the bite is good.
Cause you can dial it back in as required.

if you are going to bother to change the crank, change it to a 3.75" stroke.

What Brodix cylinder heads? You need to look at intake porting. The 406 will want bigger intake port volume. ( it needs to eat)
You can really play with the engine torque curve on these heads with the intake port. Especially on the intake port floor.
Both to get to your 575hp power goal and tame torque. I bet there is "room to grow" there in those heads.
You can and SHOULD look at the intake ports and the intake manifold ports to get what you want (575hp)
Easy to tame the torque too. That little carb is CHOKING IT .
This car would be very cool with dual quads on 406CID. A very effective way to get very PROGRESSIVE throttle control.
and 575hp.