While I have my intake off to replace leaky gasket was wondering if blocking the heat crossover would have any performance benefit. I don't really drive the car in the winter, so cold start throttle icing I've heard about shouldn't be an issue. Next what would be the easiest way to do it? Don't want to remove heads. Heard you can drive plugs into head, like small freeze plugs. Don't want to risk any engine damage from something falling into head so I rather not drill and tap for a pipe plug. My engine is stock as far as I know internally with the addition of a Poston intake, TA 1-5/8 headers and a rebuilt quadrajet from Quadraet Power. Thanks for your advice and opinions. Steve
Maybe if you running a 160 thermostat with it . you won't see much with at as ambient temps go up . might be better off figuring if you may benefit from the sp3 intake. Might have more benefit blocking crossover if you had a boosted engine.
Did you ever look at a stock factory intake that has been on an engine? Guess where the paint get burned off. Right where the exhaust crossover is. The exhaust x-over helps the intake/carb heat up faster for quicker choke release and to keep the carb from icing over in cold weather. It won't make a difference on how fast the car starts, just how fast it warms up to smoother running. Exhaust is a couple hundred degrees hotter than a 190* thermostat so it pretty much doesn't matter what the ambient temp is outside, the exhaust will always be way hotter. There will be a performance enhancement from blocking the crossover. It only makes sense. Can't say how much but something. Every little bit helps. You can use the correct sized freeze plugs to block it off. Something like 3/4" or so will do the job. If you can get a pipe plug to fit and a tap that would be good too. If you have a choke on the intake or you plan on driving it in the winter you probably want to drill a single 1/4" hole in the plug closest to where the choke would be. That will allow some intake heating by the exhaust. I haven't heard much good about the Poston intake so I'd really recommend a stock intake or maybe a TA Stage 1 dual plane. Without an upgraded cam mentioned which would allow the engine to make power at a higher rpm than the stock cam I wouldn't recommend a SP3 single plane intake especially with no gears or converter to help make up for the low end torque loss.
Thanks for you input, car currently has 160*Stat. Carb converted to electric choke. Have 3.73 gears and a 4 speed. As far as I know cam is stock, I just replaced the nylon cam gear so I feel my assumption is correct. I mean who would put in a performance cam with a nylon gear? I guess I'll block the crossover and see what happens, can't hurt. As for the SP3 , that's part of the plan, but the plan is on hold till my son is finished with college. Glad to see the attention the 350 is getting.
We are running a 180* thermostat in my sons car, along with a SP-3 intake. (Exhaust cross-over blocked off) Running a manual choke on the 750 Holley. Only drives the car in the summer, so don't have to worry about to much trouble. I mean really...in the summer....it's warm outside all day, and he has learnt to let vehicles run for a few minutes before driving away in the mornings.
Whatever you do, if you block it off, do not try to use the material the valley pan is made of, I tried that years ago, and it smoked the metal piece I had made, the exhaust just fried it.
Thanks for sharing that experience Mark . I used the intake pan to cover crossover. Looks like I will be yanking intake back off.
How well does the freeze plug need to be staked in to keep it from popping out from the exhaust pressure? Or is there a better idea of doing this.
X2 At one time you could get a 455 factory intake gasket with the rectangular crossover blocked off. I tried one and at some point after I installed it I removed the intake and the metal was very distressed from the heat. It didn't blow through but I'm sure sooner than later it would have. Freeze plugs got installed in the passage ways after that. When you see that you can really understand why you want to keep that heat away from the carb at least from a performance perspective.
I think I'm going to use pipe plugs. I'll just stuff a small piece of a rag in the hole, then put little grease in the hole and on the tap to collect the shavings and also be sure valves are closed. Tape closed the adjacent intake ports and crossover to the valley pan so no metal goes where it doesn't belong. An ounce of prevention equals a pound of cure I was always told.
That's a pretty big tap to try to keep straight or turn while in the vehicle! I'm assuming the engine is still in? You'll be amazed at how tough it is to turn it using hand tools once you are in the full taper part of the tap. You'll be about 1.5" in depth or more with a tap that big. I'd also put some serious thought into making sure the tap starts straight, they aren't fun to get out when they break. I'd definitely do that with the heads off the vehicle and secured down well. I wouldn't worry about exhaust pressure pushing the plug. If you have even 2 psi back pressure in the exhaust you might want to think about improvements to your exhaust system. A cooling system has 15+ psi. When I've added sealer to the inside of castings after welding they are subject to 35-50psi or more. Cup plugs should hold just fine. Save the tap for when you are doing that crazy hp build up.
Here it comes, the 'devil's advocate' response... Believe it or not, the engine runs much more efficiently with a 195* thermostat and the crossover left in tact. The exhaust crossover does more than simply hasten the warm-up time frame and allows your choke to operate properly, it reduces exhaust emissions by permitting the EGR valve to operate, which will in turn allow the engine to run cooler under cruising conditions (assuming of course you leave it in tact). The EGR will also give 2-4 more MPG. The fuel charge moves through the intake runners so fast the heat of the intake really doesn't have much time to warm it up at full throttle, with or without the EGR (which disengages at full throttle). A warmer running engine also affords the benefits of your oil lasting longer because it steams away the moisture condensation better, along with the pistons and cylinders wearing less over time, vs a cooler running iron block. The only real downside is the intake paint, which if it isn't very high temp paint, can burn away from the crossover section on the intake. A thick insulating gasket(s) and/or a phenolic spacer interfaced between the intake and the Quadrajet will keep the carb cooler and have better performance. Gary
If you intend on keeping your vehicle 100% factory original and well maintained, the above is very true! Once you start hot rodding your engines, these carefully engineered factory systems become problematic as the entire machine is now "unsorted". Everything is about managing trade-offs. When you are raising cylinder pressure, the need for more built in octane tolerance becomes more important. Keep in mind that inlet air temp becomes a major part of that equation, and that big hot chunk of iron presents some risks to the overall package. At the extreme end of tuning things, I haven't seen the EGR automatically add any mileage. (Talking about when cammed up and header'ed, etc.) The engine doesn't care what methods you employ to affect combustion, it only shows you the results.
i think you would be better off to take the heads off do the mild porting and have the plugs installed at the machine shop or on your Bench at home...but I personally would not take the risk of installing pipe plugs in my heads on a stock engine installed in a vehicle. The performance gain is not worth the risks
My previous girlfriend said that I recked my car when I rodded it up. She didn't last very long. :grin:
My soon to be ex said the same thing, lol. As if 8 liter engines lasting 250k miles exceeding 500hp and delivering 28-30 mpg's is a BAD move! Glad to see her go :laugh:
And even if you don't, it's 100% true. The main thing that becomes 'unsorted' is the erratic idle and lowered intake vacuum signal, which won't operate the power brakes very well, much less an EGR...true statement. Indeed. They make higher octane pump gas, available at most refueling stations around the country. For an all-out racing application, I would say this is the case, but only in part. The main impact that big hot chunk of iron presents is no weight savings. There have been countless posts regarding the efficiency of the factory Buick 350 iron intake and how difficult it is to make one better, when considering stock-moderate combinations (not just 100% factory stuff). EGR's aren't typically suitable for cars that primarily see full throttle usage at the drag strip, obviously. Surely you're not saying you've used an EGR with a hot rough idle cam and headers in order to make this claim? If so, see above comment regarding low vacuum and vacuum controlled devices. Thank you for reiterating my points. Gary
