I took on a side job to add power to a 1968 427/390 HP 4 speed Vette.

The owner is disappointed in the lack luster performance of his "stock" Vette. He doesn't want headers or valves that he has to adjust. He doesn't want a hood change because of tall manifold. His idea is a cam change, intake, and carb. The car is actually beautiful. Somebody did an excellent paint job on it.

I'm going to talk to him about H-roller and H-flat options and work out a prices.

He had the motor rebuilt 12 years ago and bumped the compression to 10.5 and he said he might have 10,000 miles on it. So he wants to leave the heads on it. Just new cam, springs if needed, intake, and carb.

So you BBC guys please tell me what is the best low rise dual plane and some thoughts on your cams please.

 

what is the carb pad height of the current intake ? can a air pan be used ?that would give you more room for a taller intake .my air pan rest on top of the radiator support .the incoming air temps drop when the car is moving .do the hydraulic roller cam .

 

A roller cam would produce the biggest bang for the buck without loosing any streetablity
If chosen correctly

 

I would say your best bang for the dollar would be a gear swap to a 3:70 or 4:11.

 

Your intake options are pretty much limited to the torker II or possibly the old Holley street dominator. The stock manifold is at least aluminum.

Hydraulic roller is really the way to go on this thing, and Id leave pretty much everything else the way it was. For simplicity, Im tempted to say throw in a ZZ502 hydraulic roller and use the thrust plate and Gen VI timing set up, but I think that may be a little radical for those cubes.

Im sure there is a hydraulic roller better suited to this set up, but if it were me, that would be the only modification I would make at all.

 

I had a 454 fairly stock making 500hp, nothing special. Fit under the stock hood on my 76. Ran low 12's in 1/4mile. Fast enough to beat most new factory cars at the track.

Here's the general details:
9:1 CR
GM Intake (I have it on the shelf I can get the number off it when I get home if you want to know it)
Holley 850
Side Pipes with baffles
Reeds Solid Roller Cam 284 Duration 624 Lift with 1.7 rocker arms
990 heads (totally stock)

I know its a solid roller cam specs but maybe you can get a hydraulic roller cam that will have similar flow or whatever it is you do with a cam to make the swap from solid to hydraulic and keep the power close to the same.

Roger

 

the motor already has an open element K&N with the filter top. So it could go to a dropped base with even a shorter filter than the existing 3 inch.

I'm going to measure clearance and do some figuring on how tall of a dual plane I can get away with. It is actually a 431 ci because of a .030 over bore and his receipts for the rebuild show TRW forged pistons.

It has a full dual exhaust and kind of louder mufflers.

Changing gearing is not in the works or budget. I just did a rough calc on the gearing and it must be 3.36.

 

When I first got my L36 I swapped out stock exhaust for Hedman headers - the inlet for Torker 11 and carb for 750 DP with the 4 speed and 3.08. Given that Torker inlet is supposed to be poor by my reckoning a cam change to something mild would have been in order (I stuck with stock cam). Set up gave improved mid range response only (although in fairness stock cam was probably past its best)

 

If it was up to me it would get some full length headers and 3 inch exhaust with an x pipe But the owner doesn't want to deal with headers.

I need to fugure out what the stock cam specs are and proceed to maybe an additional 10 degrees @.050 and if the lobe center of a stock cam is 114 maybe get down to 110. Tonight I'm going to measure the lift

 

What heads are on it now? I've not built a big block yet, but recently bought one and am in the research stages. It seems as some of the stock BBC heads are good and respond well to porting. To bad he's not open to a set of afr or brodex oval ports.

 

George, as you know, any other improvement will be amplified by headers and headers alone really help a decent big block. Any idea why he objects to them? If it's leaking gaskets, they've made big improvements in materials in recent years and that should be no problem.

IMO the stock intake, as limited as it is, is better than the Torker II overall. What he'd pick up in the way of top end power would likely be offset by a stumble coming off of idle. For that reason the Edelbrock techs themselves didn't recommend the Torker II when I was considering it. A swap to the L88 hood would open up some great choices but it doesn't sound like that's an option.

If your customer is on a budget and heads with bigger valves are out of the question, a decent cam and a good tune seem to be what you have to work with. I know you like roller cams, and for good reason, so there you go. Do keep in mind that there isn't a lot of valve/piston clearance with the closed chamber heads. I can recommend some specs on a hydraulic flat tappet that had me running low 12's if you're interested, but that was after the stock heads were set up with the larger valves. FYI, the stock cam is very mild.

This spring I picked up a good bit of throttle response by going more aggressive with my ignition curve. However that was in conjunction with putting in a new MSD distributor, so part of the gains could have been due to replacing the worn out stocker.

Good luck. Too bad about those headers though.

 

If I had the same charge, I'd just go with a HR cam that complements the stock intake and exhaust and leave the rest stock. You're not going to find an aftermarket intake manifold that fits under the stock BB hood that is a noticeable improvement over the stock intake. There's nothing to gain from changing carburetors either.

It is strictly a street-driver and has a fairly decent 3.36 gear with a four-speed so a HR that peaks at around 5,500rpm would seem to be a very good fit. The money he'd be saving by not replacing the carb and intake would allow you to move him up to the HR and not affect the bottom line.

 

Les & Jerry, Thanks for the input. It has an Accel hei with an external coil. So I will be figuring out it's advance curve.

I don't have problems with header gaskets or bolts backing out. He is trying to go cheap, But i might say that I'm not comfortable with leaving the heads on. Because of valve clearance and we really don't know for sure what the compression ratio really is other than someones word that it is 10.5. I don't want to get a detonation prone cam.

It is kind of boring to drive campared to my 434 ci small block

 

There's a part of me that wonders how a 431 could be "lackluster" ;-)

Has he had a decent dyno tune by a good shop or have you gone over to ensure everything's working right? It would suck to find out that the only issue was a misadjusted throttle linkage...

 

Have you ever driven the 390 hp 427's? It is like something chevy put in family station wagons in 1968. years ago they would show up at the Vette Magic all Corvette drag races and they were in the slowest classes high 12 seconds to 13 something.

This thing has a smooth 600 rpm idle and quiet. The tail pipes look small maybe even just 2 inch.

 

Soooooooo soft that with the worn stock shifter you would select 3rd instead of 1st when pulling away and ask your self the question "why bother to re-select 1st, its all the same" - once I had installed the MSD the thing actually would lug down, and pull away with no stress from 700 rpm in 4th gear!

 

I have - not a screamer but gobs of torque...which is usually what folks complain about. And to be fair...mid 12s for a 60's car isn't really shameful for it's time.

Just thought I'd ask - but it sounds like it's in good tune and everything is working perfectly

 

I really hate when people is "trying to go cheap"..
If they want to save their money, well dont mess with the engine at all then.

Leaving the heds on sounds imo like a bad idea..
Pull the heads and verify they are in good condition, check the valve guides and do at least a nice valve seat job.

Intake manifold.. The never ending question..
I have the LS6 manifold and a Holley800 4150 carb on my 454 and it fits under the hood.
I have a hyd roller and the max power of 470hp is at 5500rpm.
The engine pulls strong from 2700rpm and i shift at 5500rpm, no use to rev any higher.

A better intake i think would be a tri-jet setup but then the budget propably gets blown..

 

I agree 100%.Even 25 years ago they claimed headers were worth 75 hp on a stock ls6.If you do a compression check that should help verify
the actual compression ratio.I would also reccomend posting the head
casting numbers so you'll know if the heads are open or closed chamber.This sounds like a good time to contact Chris Straub.

 

Sounds like Straubs out of budget and it will be a HFT cam used intake type thing?
With that gear hard to go wrong with an Isky 270 mega or something like that.

I dont help with cheap/budget no more you know how it goes. They wont be happy, youre the jerk and they will spend the money twice anyway. Just cant tell em anything.